Microsoft Word C040239e doc Reference number ISO 21438 1 2007(E) © ISO 2007 INTERNATIONAL STANDARD ISO 21438 1 First edition 2007 12 15 Workplace atmospheres — Determination of inorganic acids by ion[.]
General definitions
A chemical agent refers to any chemical element or compound, whether in its natural state or produced through various work activities This includes substances that are used, released, or disposed of as waste, regardless of whether they were intentionally created or marketed.
〈general definition〉 space around the worker's face from where he or she takes his or her breath
A hemisphere, typically defined with a radius of 0.3 meters, extends in front of the human face It is centered at the midpoint of a line connecting the ears, with its base forming a plane through this line, the top of the head, and the larynx.
NOTE 1 The definition is not applicable when respiratory protective equipment is used
NOTE 2 Adapted from EN 1540:1998 [1] , definition 3.8
3.1.4 exposure (by inhalation) situation in which a chemical agent is present in air which is inhaled by a person
3.1.5 measuring procedure procedure for sampling and analysing one or more chemical agents in the air and including storage and transportation of the sample
3.1.6 operating time period during which a sampling pump can be operated at specified flow rate and back pressure without recharging or replacing the battery
TWA concentration concentration of a chemical agent in the atmosphere, averaged over the reference period
3.1.8 limit value reference figure for concentration of a chemical agent in air
NOTE An example is the Threshold Limit Value® (TLV) for a given substance in workplace air (see Reference [3])
3.1.9 reference period specified period of time stated for the limit value of a specific chemical agent
NOTE Examples of limit values for different reference periods are short-term and long-term exposure limits (see Reference [3])
3.1.10 workplace defined area or areas in which the work activities are carried out
Particle size fraction definitions
3.2.1 inhalable convention target specification for sampling instruments when the inhalable fraction is the fraction of interest
3.2.2 inhalable fraction mass fraction of total airborne particles which is inhaled through the nose and mouth
NOTE The inhalable fraction depends on the speed and direction of air movement, on breathing rate and other factors
3.2.3 total airborne particles all particles surrounded by air in a given volume of air
NOTE Because all measuring instruments are size selective to some extent, it is often impossible to measure the total airborne particle concentration
Sampling definitions
3.3.1 personal sampler device attached to a person that samples air in the breathing zone
3.3.2 personal sampling process of sampling carried out using a personal sampler
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3.3.3 sampling instrument sampler a device for collecting airborne particles
NOTE This definition is formulated for the purposes of this part of ISO 21438
EXAMPLES Instruments used to collect airborne particles include sampling heads, filter holders, filter cassettes, etc
3.3.4 static sampling area sampling process of air sampling carried out in a particular location
Analytical definitions
3.4.1 blank solution solution prepared by taking a reagent blank, laboratory blank or field blank through the same procedure used for sample dissolution
3.4.2 calibration blank solution calibration solution prepared without the addition of any working standard solution
NOTE The concentration of sulfate and phosphate in the calibration blank solution is taken to be zero
3.4.3 calibration solution solution prepared by dilution of the working standard solution, containing sulfate and phosphate at concentrations that are suitable for use in calibration of the analytical instrument
3.4.4 extraction solution solvent or solution used to solubilise the analyte(s) of interest
A field blank filter undergoes the same handling procedure as a sample, but it is not used for actual sampling Instead, it is loaded into a sampler, transported to the sampling site, and then returned to the laboratory for analysis.
3.4.6 laboratory blank unused filter, taken from the same batch used for sampling, that does not leave the laboratory
3.4.7 linear dynamic range range of concentrations over which the calibration curve for sulfate or phosphate is linear
NOTE The linear dynamic range extends from the detection limit to the onset of calibration curvature
3.4.8 reagent blank all reagents used in sample dissolution, in the same quantities used for preparation of laboratory blank, field blank, and sample solutions
3.4.9 sample dissolution process of obtaining a solution containing sulfate and phosphate from a sample, which might or might not involve complete dissolution of the sample
3.4.10 sample preparation all operations carried out on a sample, after transportation and storage, to prepare it for analysis, including transformation of the sample into a measurable state, where necessary
3.4.11 sample solution solution prepared from a sample by the process of sample dissolution
NOTE A sample solution might need to be subjected to further operations, e.g dilution, in order to produce a test solution that is ready for analysis
3.4.12 stock standard solution solution, used for preparation of the calibration solutions, containing sulfate and/or phosphate at a certified concentration that is traceable to national standards
3.4.13 test solution blank solution or sample solution that has been subjected to all operations required to bring it into a state in which it is ready for analysis, e.g dilution
The blank test solution serves as the reference solution, while the sample test solution is the analyzed sample solution, provided that neither solution undergoes any additional operations prior to analysis.
A working standard solution is created by diluting stock standard solutions to achieve sulfate and phosphate concentrations that are more appropriate for preparing calibration solutions than those found in the original stock solutions.
Statistical terms
3.5.1 analytical recovery ratio of the mass of analyte measured when a sample is analysed to the known mass of analyte in that sample, expressed as a percentage
3.5.2 bias consistent deviation of the results of a measurement process from the true value of the air quality characteristic itself
3.5.3 coverage factor k numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded uncertainty
NOTE A coverage factor, k , is typically in the range 2 to 3
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Combined standard uncertainty (\$u_c\$) refers to the standard uncertainty of a measurement result derived from multiple other quantities It is calculated as the positive square root of the sum of terms, where these terms represent the variances or covariances of the contributing quantities The weighting of these terms is based on how the measurement result is affected by variations in the respective quantities.
Expanded uncertainty refers to a quantity that defines an interval around a measurement result, which is expected to include a significant portion of the distribution of values that can be reasonably associated with the measurand.
3.5.6 precision closeness of agreement of results obtained by applying the method several times under prescribed conditions
3.5.7 true value value which characterises a quantity perfectly defined in the conditions which exist when that quantity is considered
NOTE The true value of a quantity is a theoretical concept and, in general, cannot be known exactly
3.5.8 uncertainty (of measurement) parameter associated with the result of a measurement that characterises the dispersion of the values that could reasonably be attributed to the measurand
NOTE 1 The parameter may be, for example, a standard deviation (or a given multiple of it), or the width of a confidence interval
Measurement uncertainty consists of various components, which can be assessed through statistical analysis of measurement results, characterized by standard deviations Additionally, other components are evaluated using assumed probability distributions derived from experience or additional information According to ISO Guide 98:1995, these evaluations are classified as Type A and Type B, respectively.
NOTE 3 Adapted from ISO Guide 99:1996 [5] , definition 3.9
4.1 A known volume of air is drawn through a filter to collect acid mist The filter is mounted in a sampler designed to collect the inhalable fraction of airborne particles (see 7.1.1)
4.2 The collected sample is then treated with water (6.1) or eluent (see 10.1.1), without heating, to extract sulfuric and phosphoric acids
Aliquots of the sample solution undergo ion chromatography to effectively separate extracted sulfate and/or phosphate from other anions After this separation process, the anions are quantified using a conductivity detector.
Analytical results are derived by graphing the measured conductivity against concentration levels These results are essential for evaluating occupational exposure to sulfuric acid, phosphoric acid, and diphosphorus pentoxide in the air.
The measuring procedure shall comply with any relevant international, European or national standard which specifies performance requirements for procedures for measuring chemical agents in workplace air (e.g EN 482 [6] )
Use only reagents of recognised analytical grade and only water as specified in 6.1 It is advisable to check the blank values of all chemicals before use
NOTE Sulfates and phosphates are found ubiquitously in the environment and the presence of sulfates and phosphates in reagents can lead to high blank values
6.1 Water, from a purification system that delivers ultrapure water having a resistivity greater than
6.2 Reagents for chemically suppressed ion chromatography
The sodium carbonate/sodium hydrogencarbonate eluent provided is suitable for analyzing phosphate and sulfate through chemically suppressed ion chromatography For specific column types, refer to the manufacturer's literature for detailed information on the appropriate eluent composition.
6.2.1 Sodium carbonate (Na 2 CO 3 ), anhydrous, mass fraction >99,9 %
6.2.2 Sodium hydrogencarbonate (NaHCO 3 ), mass fraction >99,5 %
6.2.3 Sodium carbonate/sodium hydrogencarbonate extraction and eluent stock solution, containing
0,27 mol l −1 Na 2 CO 3 and 0,03 mol l −1 NaHCO 3
Dissolve 2.86 g of sodium carbonate and 0.25 g of sodium hydrogencarbonate in 25 ml of water, then swirl to mix Transfer the solution to a 100 ml volumetric flask, dilute to the mark with water, stopper, and mix thoroughly.
6.2.4 Sodium carbonate/sodium hydrogencarbonate extraction and eluent solution, 0,002 7 mol l −1
Na 2 CO 3 and 0,000 3 mol l −1 NaHCO 3
Transfer 10 ml of sodium carbonate/sodium hydrogencarbonate stock solution (6.2.3) to a 1 l one-mark volumetric flask (7.2.2.1), dilute to the mark with water (6.1), stopper and mix thoroughly
6.2.5 Cartridge for eluent generation, suitable for use with the eluent generation system (7.2.6.2), if used 6.3 Reagents for electronically suppressed ion chromatography
Phthalic acid and borate/gluconate solutions are examples of eluents utilized in the analysis of phosphate and sulfate through electronically suppressed ion chromatography For specific column types, it is essential to consult the manufacturer's literature for detailed information on the appropriate eluent composition.
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6.3.4 Lithium hydroxide monohydrate (LiOHãH 2 O), mass fraction >99,5 %
6.3.5 Boric acid (H 3 BO 4 ), mass fraction >99,8 %
6.3.6 D -Gluconic acid (C 6 H 12 O 7 ) solution, mass fraction approximately 50 % of D -gluconic acid in water (6.1)
6.3.8 Phthalic acid extraction and eluent stock solution, 0,1 mol l −1 phthalic acid in a 9+1 volume ratio mixture of acetonitrile and methanol
Dissolve 1,66 g of phthalic acid (6.3.1) in a 9+1 volume ratio mixture of acetonitrile (6.3.2) and methanol
(6.3.3), in a suitable 1 l vessel and mix thoroughly
Dissolve 4,2 g of lithium hydroxide monohydrate (6.3.4) in water (6.1) Quantitatively transfer the solution into a 100 ml one-mark volumetric flask (7.2.2.1), dilute to the mark with water (6.1), stopper and mix thoroughly
6.3.10 Phthalic acid extraction and eluent solution, e.g 0,005 mol l −1 phthalic acid, pH 4,9
To prepare a phthalic acid solution, transfer 50 ml of the solution to a 1-liter volumetric flask, add about 900 ml of water, adjust the pH to 4.9 using lithium hydroxide solution, and then dilute to the mark with water.
6.3.11 Borate/gluconate extraction and eluent stock solution
Dissolve 17 g of boric acid (6.3.5), 4,8 g of lithium hydroxide monohydrate (6.3.4), 8,8 ml of D-gluconic acid
(6.3.6) and 62,5 ml of glycerol (6.3.7) in water (6.1) Quantitatively transfer the solution into a 500 ml one-mark volumetric flask (7.2.2.1), dilute to the mark with water (6.1), stopper and mix thoroughly
6.3.12 Borate/gluconate extraction and eluent solution
Transfer 15 ml of borate/gluconate stock solution (6.3.11) and 120 ml of acetonitrile (6.3.2) to a 1 l one-mark volumetric flask and dilute to the mark with water (6.1), stopper and mix thoroughly
6.4 Sulfate and phosphate standard solutions
Use a commercial standard solution with a certified sulfate concentration, e.g 1 000 mg l −1 of sulfate, traceable to national standards Observe the manufacturer's expiry date or recommended shelf-life
Use a commercial standard solution with a certified phosphate concentration, e.g 1 000 mg l −1 of phosphate, traceable to national standards Observe the manufacturer's expiry date or recommended shelf-life
6.4.3 Sulfate and phosphate working standard solution, 200 mg l −1 of sulfate and phosphate
To prepare a fresh solution monthly, accurately pipette 4 ml of the sulfate stock standard solution and 4 ml of the phosphate stock standard solution into a 20 ml volumetric flask Dilute to the mark with water, stopper the flask, and mix thoroughly.
Sampling equipment
7.1.1 Samplers, designed to collect the inhalable fraction of airborne particles, complying with EN 13205
The operating instructions supplied by the manufacturer should be consulted to find out whether particulate matter deposited on the internal surfaces of the sampler forms part of the sample
NOTE 1 In general, personal samplers for collection of the inhalable fraction of airborne particles do not exhibit the same size-selective characteristics if used for static sampling
Some inhalable samplers are specifically designed to collect only the inhalable fraction of airborne particles on a filter, disregarding any particulate matter that settles on the internal surfaces In contrast, other samplers allow airborne particles that pass through the entry orifice(s) to conform to the inhalable convention, meaning that any particulate matter deposited internally is included in the sample These second-type samplers typically feature a removable internal filter cassette or cartridge for easy recovery of the collected material.
Reference [7] provides examples of inhalable samplers that could meet the EN 13205 requirements, highlighting those available on the market until 2004 along with published performance reports.
Filters with a diameter appropriate for the samplers must achieve a collection efficiency of 99.5% for particles with a diffusion diameter of 0.3 µm, as specified in ISO 7708:1995, section 2.2 Additionally, these filters should be made from materials that are compatible with the methods used for sample preparation and analysis.
Sulfuric acid and phosphoric acid are potent acids that can dehydrate and react with various organic and polymeric materials, leading to the degradation of filter materials Therefore, selecting the appropriate filter for sample collection is crucial, ensuring it is made from non-reactive materials Additionally, certain filters, such as glass fiber filters, may contain metals like barium that can react with these acids to form insoluble salts Suitable filter types must be carefully considered to avoid these issues.
⎯ polyvinyl chloride (PVC) membrane filters, of pore size 5 àm or less;
⎯ polytetrafluoroethylene (PTFE) membrane filters, of pore size 5 àm or less; and
Sulfates and phosphates are commonly present in the environment, and their occurrence in filter materials can result in elevated blank values Consequently, it is crucial to verify the blank values for every batch of filters utilized.
7.1.3 Sampling pumps, with an adjustable flow rate, capable of maintaining the selected flow rate (see
9.1.1.2) to within ±5 % of the nominal value throughout the sampling period (see 9.1.2)
For personal sampling, the pumps shall be capable of being worn by the worker without impeding normal work activity
The pump should have, as a minimum, the following features:
⎯ an automatic control that keeps the volumetric flow rate constant in the case of a changing back pressure;
The system features either a malfunction indicator that signals a reduction or interruption in air flow after sampling is completed, or an automatic cut-out that halts the pump if the flow rate decreases or is interrupted.
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The flow rate adjustment mechanism is designed to be operated only with specific tools, such as a screwdriver, or requires specialized knowledge, such as software operation This ensures that unintentional changes to the flow rate cannot occur during use, enhancing safety and reliability.
An integral timer is a highly desirable additional feature
A flow-stabilised pump may be required to maintain the flow rate within the specified limits
According to EN 1232 and EN 12919 standards, pump performance must ensure that flow rate pulsation remains below 10% Additionally, the flow rate should not vary more than ±5% from the nominal value under increasing back pressure Within ambient temperatures of 5 °C to 40 °C, the flow rate must also stay within ±5% of the value measured at 20 °C The pumps should operate for a minimum of 2 hours, ideally 8 hours, while maintaining a flow rate deviation of no more than ±5% from the initial value throughout the operating period.
When using a sampling pump, it is crucial to adhere to the conditions outlined in EN 1232 and EN 12919 If operating outside these specified parameters, necessary measures must be implemented to maintain performance standards For example, in sub-zero temperatures, it may be essential to keep the pump warm to ensure optimal functionality.
7.1.4 Flowmeter, portable, with an accuracy that is sufficient to enable the volumetric flow rate
(see 9.1.1.2) to be measured to within ±5 %
The flowmeter calibration must be verified using a primary standard that is traceable to national accuracy standards Additionally, if applicable, it is important to document the atmospheric temperature and pressure during the calibration process.
It is advisable that the flowmeter used is capable of measuring the volumetric flow rate to within ±2 % or better
7.1.5.1 Flexible tubing, of a diameter suitable for making a leakproof connection from the samplers
7.1.5.2 Belts or harnesses, to which the sampling pumps can conveniently be fixed for personal sampling (except where the sampling pumps are small enough to fit in workers' pockets)
7.1.5.3 Tweezers, manufactured from or tipped with PTFE, for loading and unloading filters into samplers
7.1.5.4 Filter transport cassettes, or similar, if required (see 9.5.1), in which to transport samples to the laboratory
A thermometer with a range of 0 °C to 50 °C, marked in divisions of 1 °C or less, is necessary for measuring atmospheric temperature as needed (refer to section 9.1.3) For applications involving temperatures below freezing, the thermometer must be capable of measuring the appropriate lower temperature range.
7.1.5.6 Barometer, suitable for measurement of atmospheric pressure, if required (see 9.1.3)
Laboratory apparatus
Usual laboratory apparatus, and in particular the following Disposable plastic labware is generally preferable to glassware
Sulfates and phosphates are commonly present in the environment, which can result in elevated levels of contamination Therefore, it is crucial to ensure that all disposable plastic labware is inspected for sulfate and phosphate contamination, and that all reusable laboratory equipment is thoroughly cleaned prior to use.
7.2.1 Disposable gloves, impermeable, to avoid the possibility of contamination from the hands and to protect them from contact with toxic and corrosive substances PVC gloves are suitable
7.2.2 Glassware, made of borosilicate glass 3.3, complying with the requirements of ISO 3585, cleaned before use with water (6.1)
Alternatively, the glassware may be cleaned with a suitable laboratory detergent using a laboratory washing machine and afterwards rinsed thoroughly with water (6.1)
7.2.2.1 One-mark volumetric flasks, of capacities between 10 ml and 1 l, complying with the requirements of ISO 1042
7.2.2.2 One-mark pipettes, complying with the requirements of ISO 648
7.2.3.1 One-mark volumetric flasks, of capacities between 10 ml and 1 l
7.2.3.2 Screw-cap polyethylene vessels, of capacity 10 ml
7.2.3.4 Graduated centrifuge tubes, with caps, of capacity 15 ml
7.2.3.5 Filter funnels, of polypropylene, of a size suitable for use in transferring washings from the internal surfaces of the sampler (see 7.1.1) into a tube
7.2.3.6 Disposable filters, of PTFE, of pore size 0,45 àm, for use in ion chromatography
7.2.3.7 Disposable syringes, of capacity 2 ml or 5 ml, with 60 mm × 0,6 mm needles
7.2.3.8 Autosampler vials, of capacity 1,5 ml to 2 ml
Piston-operated volumetric instruments with capacities ranging from 50 µl to 10 ml, which meet the standards of ISO 8655-1 and are tested according to ISO 8655-6, serve as reliable tools for preparing standard and calibration solutions Additionally, pipettors that comply with ISO 8655-2 offer an effective alternative to one-mark pipettes for sample dilution.
7.2.5 Ultrasonic bath, preferably with a timer, suitable for use in the ultrasonic extraction method for sulfuric acid or phosphoric acid (see 10.1.2.1.1)
The ion chromatograph, detailed in sections 7.2.6.1 to 7.2.6.10, is designed with components and tubing that should ideally be made from inert materials, such as polyetheretherketone (PEEK), to minimize interaction with the sample solution or eluent.
7.2.6.1 Pump, capable of delivering a constant flow within the range 0,1 ml min −1 to 5 ml min −1 at a pressure of 15 MPa to 150 MPa
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7.2.6.2 Eluent generation system, for producing an eluent suitable for use with the selected separator column (see 7.2.6.5), as an alternative to use of a manually prepared eluent (see e.g Reference [10])
7.2.6.3 Sample injection system, comprising a low dead-volume, non-metallic valve fitted with a sample loop having a volume of up to 500 àl, for injecting the sample solution into the eluent stream
7.2.6.4 Guard column, placed before the separator column (7.2.6.5) to protect it from fouling by particles or strongly adsorbed organic constituents of the sample solution
7.2.6.5.1 Separator column for chemically suppressed ion chromatography, packed with high capacity pellicular anion exchange resin, suitable for resolving sulfates and phosphates from other inorganic anions
7.2.6.5.2 Separator column for electronically suppressed ion chromatography, packed with silica or organic polymers, suitable for resolving sulfates and phosphates from other inorganic anions
7.2.6.6 Suppressor module for chemically suppressed ion chromatography, suitable for use with the separator column (7.2.6.5.1)
7.2.6.7 Conductivity detector, flow through, low volume, with a non-metallic flow path
NOTE A conductivity detector can be used with both chemically and electronically suppressed ion chromatography
7.2.6.8 UV-vis detector, flow through, low volume
NOTE A UV-vis detector can be used with electronically suppressed ion chromatography for inverse UV detection
A compatible recorder, integrator, or computer is essential for capturing detector output over time, enabling the measurement of peak height or area It is advisable to utilize an automated system for this process.
7.2.6.10 Eluent reservoir, comprising of a container suitable for storing eluent or water (6.1) used for eluent generation (see 7.2.6.2)
General
ISO 21438 addresses the collection of personal and static (area) samples For developing an effective assessment strategy and general measurement guidance, refer to relevant international, European, or national standards such as EN 482, EN 689, and ASTM E 1370.
Personal sampling
Personal sampling is essential for accurately determining workers' exposure to sulfuric acid and phosphoric acid, as the concentrations of these acids in the breathing zone may differ from the background levels present in the workplace.
Static sampling
Monitoring the background levels of sulfuric acid and phosphoric acid in the workplace is essential for assessing ventilation efficiency and identifying the location and intensity of emission sources.
Selection of measurement conditions and measurement pattern
Sampling must be conducted to minimize disruption to workers and their regular job performance, ensuring that the samples collected accurately represent typical working conditions and align with the chosen analytical method.
8.4.1.2 The pattern of sampling shall take into consideration practical issues, such as the nature of the measurement task and the frequency and duration of particular work activities
8.4.2 Screening measurements of variation of concentration in time and/or space
Screening measurements of concentration variations over time and space are essential for understanding the distribution patterns of chemical agents These measurements help identify areas and times of increased exposure, guiding the duration and frequency of sampling for compliance with limit values Additionally, they enable the identification of emission sources and allow for the assessment of the effectiveness of ventilation and other technical measures.
8.4.3 Screening measurements of time-weighted average concentration and worst case measurements
Screening measurements of time-weighted average concentration provide preliminary insights into exposure levels, helping to identify potential exposure issues and assess their severity These measurements are also useful for determining whether exposure levels are significantly below or above established limit values, as referenced in EN 482 [6].
Screening measurements of time-weighted average concentration are conducted in the early phases of a survey to evaluate the effectiveness of control measures Sampling is performed during representative work episodes to gather clear data on exposure levels and patterns, or worst-case measurements may be taken.
NOTE Screening measurements of time-weighted average concentration made to clearly identify work episodes during which highest exposure occurs are typically referred to as “worst case measurements” (see EN 689:1995 [11] , 5.2.3.2)
8.4.4 Measurements near an emission source
Measurements taken close to an emission source can reveal its location and intensity When combined with additional data, these measurements can help determine whether a suspected source significantly contributes to exposure (refer to EN 482 [6]).
8.4.5 Measurements for comparison with limit values and periodic measurements
8.4.5.1 Measurements for comparison with limit values
Measurements for comparison with limit values are conducted to ensure accurate and reliable data regarding the time-weighted average concentration of specific chemical agents in the air that may be inhaled.
8.4.5.1.2 For making measurements for comparison with a short-term exposure limit, the sampling time shall be as close as possible to the reference period, which is typically 15 min
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To ensure accurate comparisons with long-term exposure limits, it is essential to collect samples throughout the entire working period or during several representative work episodes, as outlined in section 9.1.2.1 regarding minimum sampling time.
For accurate long-term exposure estimates, it is ideal to collect consecutive samples throughout the entire working period; however, this approach may not always be feasible due to potential filter overload.
Periodic measurements are performed to determine whether exposure conditions have changed since measurements for comparison with limit values were made, or whether control measures remain effective (see EN 482 [6] )
Preliminary considerations
9.1.1 Selection and use of samplers
Select samplers that are specifically designed to capture the relevant fraction of airborne particles, as outlined in ISO 7708, ensuring they align with the particle size fraction for which the exposure limits for the relevant acid(s) are applicable.
If possible, the samplers selected should be manufactured from conducting material, since samplers manufactured in non-conducting material have electrostatic properties that can influence representative sampling
When selecting samplers with an internal filter cassette or cartridge that requires rinsing during sample preparation, it is essential that the cassette is made from a material that is resistant to acid reactions.
9.1.1.2 Use the samplers at their design flow rate and in accordance with the instructions provided by the manufacturer See CEN/TR 15230 [7] for further guidance
Select an appropriate sampling period for the measurement task, ensuring it is sufficiently long to determine sulfuric or phosphoric acid with acceptable uncertainty at levels significant for industrial hygiene For instance, calculate the minimum sampling time, \( t_{\text{min}} \), in minutes, needed to collect an amount above the lower limit of the analytical method's working range when sulfuric or phosphoric acid is present in the atmosphere at a concentration of 0.1 times its limit value, using Equation (1).
The lower limit of the analytical range, denoted as \$m_{lower}\$ in micrograms, is defined by the equation \$m_{lower} = \min(0.1, q_V \cdot \rho_{LV})\$, where \$q_V\$ represents the design flow rate in litres per minute of the sampler, and \$\rho_{LV}\$ is the limit value measured in milligrams per cubic metre.
9.1.2.2 When high concentrations of airborne particles are anticipated, select a sampling period that is not so long as to risk overloading the filter with particulate matter
9.1.3.1 Effect of temperature and pressure on flow rate measurements
Refer to the manufacturer's instructions to assess if the volumetric flow rate of the flowmeter is influenced by temperature and pressure Evaluate whether the difference between the atmospheric conditions during calibration and sampling is significant enough to warrant a correction, particularly if the potential error exceeds ±5% If a correction is needed, ensure to measure and document the atmospheric temperature and pressure during the flowmeter calibration, as well as at the beginning and end of the sampling period.
NOTE An example of temperature and pressure correction for the indicated volumetric flow rate is given in Clause A.1 for a constant pressure drop, variable area flowmeter
Evaluate the need to adjust the concentration of sulfuric or phosphoric acid in air to reference conditions as outlined in ISO 8756 If adjustments are required, document the atmospheric temperature and pressure at both the beginning and end of the sampling period, and apply the correction using the equation provided in Clause A.2.
NOTE The concentration of sulfuric acid or phosphoric acid in air is generally stated for actual environmental conditions (temperature, pressure) at the workplace
To reduce the risk of damage or contamination, filters should only be handled in a clean environment with minimal concentrations of sulfuric and phosphoric acids in the air, using PTFE tweezers for safety.
Sulfuric acid is extensively utilized in various industrial applications, including the extraction of rock phosphates, metal processing, electroplating, and as a component in lead batteries Workplaces may also contain other sulfur compounds such as sulfur dioxide and sulfur trioxide Similarly, phosphoric acid plays a crucial role in industries for producing phosphate fertilizers, porcelain cements, and flame retardants, with additional phosphorus compounds like metaphosphates often present It is essential to consider potential interferences before starting sampling procedures.
When comparing results to limit values for sulfuric acid and/or phosphoric acid, it is essential to account for the presence of sulfates or phosphates in the test atmosphere This can be achieved by collecting and analyzing a sample from the emission source, such as the pickling bath solution, to accurately determine the free acid content.
When comparing separate limit values for phosphoric acid and diphosphorus pentoxide, it is not feasible to differentiate between the two substances Consequently, if both chemicals are detected in the test atmosphere, the results should be reported as phosphoric acid, with a note indicating that the reported concentration includes any diphosphorus pentoxide present.
9.1.5.4 When present in workplace air, sulfur trioxide, sulfur dioxide and volatile organic sulfur compounds exist as gases or vapours and do not interfere with the sampling method
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Preparation for sampling
Before using the samplers, ensure they are clean by dismantling them and soaking in a detergent solution Rinse thoroughly with water, wipe with absorbent tissue, and allow to dry before reassembling Alternatively, a laboratory washing machine can be used for cleaning.
9.2.2 Loading the samplers with filters
Ensure that clean samplers are loaded with appropriate membrane or quartz fiber filters, and label each sampler for unique identification Finally, seal the samplers with their protective cover or plug to avoid contamination.
9.2.3 Setting the volumetric flow rate
Perform the following in a clean area, where the concentration of sulfuric acid and phosphoric acid is minimal
Connect each sampler to a sampling pump using flexible tubing to prevent leaks Remove the protective cover from each sampler, activate the sampling pump, and attach the flowmeter to measure the flow through the sampler's inlet orifice Set the desired volumetric flow rate, then switch off the pump and seal the sampler to avoid contamination during transport.
If necessary, allow the sampling pump operating conditions to stabilise before setting the volumetric flow rate
Retain one unused loaded sampler from each batch of 10 prepared, ensuring a minimum of three samplers are kept Handle these samplers with the same care as those used for sampling, particularly regarding their storage and transport to and from the sampling position, while ensuring that no air is drawn through the filters.
Sampling position
To ensure accurate sampling, position the sampler within the worker's breathing zone, ideally near the mouth and nose, such as by fastening it to the worker's lapel Additionally, attach the sampling pump in a way that minimizes inconvenience, either by securing it to a belt around the waist or placing it in a convenient pocket.
When assessing worker exposure to sulfuric or phosphoric acid, it is crucial to consider whether the process may cause a significant discrepancy between actual exposure levels and those recorded by a lapel-mounted sampler If such a difference is likely, it is essential to position the sampler as close as possible to the worker's nose and mouth to ensure accurate measurement.
When conducting static sampling to evaluate a worker's exposure in situations where personal sampling is unfeasible, it is essential to place the sampler close to the worker and at their breathing height If uncertainty arises, the sampling position should be determined at the location where the risk of exposure is deemed highest.
When conducting static sampling to assess the background levels of sulfuric acid or phosphoric acid in the workplace, it is essential to choose a sampling location that is adequately distanced from work processes This ensures that the results remain unaffected by emissions of sulfuric acid or phosphoric acid from nearby sources.
Collection of samples
To initiate sampling, first remove the protective cover or plug from the sampler and activate the sampling pump It's essential to document the time and volumetric flow rate at the beginning of the sampling period If the sampling pump includes an integral timer, ensure it is reset to zero Additionally, if applicable, measure and record the atmospheric temperature and pressure at the start of the sampling using the thermometer and barometer.
If the temperature or pressure at the sampling location differs from the conditions under which the volumetric flow rate was established, adjustments to the volumetric flow rate may be necessary prior to sampling.
At the conclusion of the sampling period, it is essential to document the time and calculate the duration of the sampling Verify the malfunction indicator and/or the integral timer reading; if the sampling pump was not functioning correctly during the sampling period, the sample is deemed invalid Measure and record the volumetric flow rate using the flowmeter Additionally, if necessary, measure and record the atmospheric temperature and pressure at the end of the sampling period with the thermometer and barometer.
Accurately document the sample identity and all pertinent sampling information To determine the mean volumetric flow rate, average the flow rates recorded at the beginning and end of the sampling period If necessary, also calculate the mean atmospheric temperature and pressure The volume of air sampled at standard atmospheric conditions can be calculated by multiplying the mean flow rate (in litres per minute) by the duration of the sampling period (in minutes).
Transportation
9.5.1 Samplers that collect airborne particles on the filter
For samplers that collect airborne particles on filters, except when using quartz fibre filters, it is essential to remove the filter from each sampler and place it in a labelled filter transport cassette, ensuring it is securely closed Alternatively, samples can be transported to the laboratory in the original samplers It is crucial to handle strong acids like sulfuric and phosphoric acid with care, preventing the collected sample from contacting the walls of the transport container.
When utilizing quartz fibre filters, promptly transfer the filter into a screw-cap polyethylene vessel using clean PTFE tweezers Accurately pipette 4.0 ml of the extraction solution into the vessel, secure it with a plastic cap, and gently shake to mix.
NOTE Anecdotal evidence (Reference [24]) suggests that it is necessary to extract sulfate from quartz fibre filters immediately after sampling to achieve quantitative recovery of sulfuric acid
9.5.2 Samplers with an internal filter cassette
For samplers equipped with an internal filter cassette, it is essential to remove the filter cassette from each sampler and secure it with its lid or transport clip, unless quartz fibre filters are being used.
When utilizing quartz fibre filters, promptly transfer the filter into a screw-cap polyethylene vessel using clean PTFE tweezers Rinse the internal surfaces of the filter cassette with 4.0 ml of extraction solution, seal the vessel with a plastic cap, and gently shake to ensure proper mixing.
9.5.3 Samplers of the disposable cassette type
9.5.3.1 For samplers of the disposable cassette type, except when using quartz fibre filters (see 9.5.3.2), transport the samples to the laboratory in the samplers in which they were collected
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When utilizing quartz fibre filters, promptly transfer the filter into a screw-cap polyethylene vessel using clean PTFE tweezers Rinse the internal surfaces of the filter cassette with 4.0 ml of extraction solution, seal the vessel with a plastic cap, and gently shake to ensure proper mixing.
NOTE Anecdotal evidence suggests that it is necessary to extract sulfate from quartz fibre filters immediately after sampling to achieve quantitative recovery of sulfuric acid
Extraction can be performed in samplers that have adequate capacity and are watertight, provided that the sample inlet and outlet orifices are sealed with protective plugs In this scenario, the extraction solution should be introduced through the air inlet orifice, while ensuring that the sample inlet and outlet orifices remain sealed Additionally, the sampler must be kept in an upright position during transportation.
9.5.4 Transport of samples to the laboratory
Transport samples to the laboratory in a specially designed container that prevents damage during transit and is clearly labeled for proper handling.
9.5.4.2 Ensure that the documentation which accompanies the samples is suitable for a “chain of custody” to be established (see, for example, ASTM D 4840 [14] )
CAUTION — Use suitable personal protective equipment (including gloves, face shield or safety glasses, etc.) while carrying out the analysis.
Preparation of test and calibration solutions
10.1.1 Selection of the extraction solution
When preparing test solutions for the determination of sulfuric acid or phosphoric acid, choose between using water or the appropriate eluent based on the analytical technique and separator column specified in sections 6.1, 6.2.4, 6.3.10, or 6.3.12.
10.1.2 Preparation of test solutions from filter sampling
To ensure thorough mixing, swirl each screw-cap polyethylene vessel or sampling cassette, keeping the filter fully submerged Agitate the mixture in an ultrasonic bath for 15 minutes, then let the immersed filters rest at room temperature for 1 hour, swirling or agitating occasionally.
When using a disposable cassette type sampler for extraction, it is essential to remove the protective plug from the sample inlet orifice To prevent spillage and contamination of the sample solution, the sampler must be kept in an upright position while placed in the ultrasonic bath.
10.1.2.1.2 Filter each sample solution through a membrane filter (7.2.3.6) using a disposable syringe (7.2.3.7), dispensing each filtrate into an individual, labelled, autosampler vial (7.2.3.8)
Open the filter transport cassettes or sampler filter cassettes and carefully transfer each filter into a labeled 50 ml beaker using clean PTFE tweezers.
Disposable cassette-type samplers can be used for extraction if they have adequate capacity and are watertight when sealed with a protective plug The extraction solution should be introduced through the air inlet, and the samplers must be kept upright in the ultrasonic bath to prevent spillage and contamination of the sample solutions.
Accurately pipette 4.0 ml of extraction solution into each beaker If the sampler type allows airborne particles to adhere to its internal surfaces, use the extraction solution to wash any particulate material into the beaker For PTFE filters, add 0.1 ml of ethanol due to their hydrophobic nature.
10.1.2.2.3 Swirl gently to mix the contents, ensuring that the filter remains completely immersed Agitate for
15 min in an ultrasonic bath (7.2.5) and then allow the immersed filters to sit for 1 h at room temperature, swirling or agitating occasionally
10.1.2.2.4 Filter each sample solution (10.1.2.2.3) through a membrane filter (7.2.3.6), e.g by using a disposable syringe (7.2.3.7), dispensing each filtrate into an individual, labelled, autosampler vial (7.2.3.8)
To ensure accurate measurements, prepare at least five calibration solutions with sulfate and phosphate concentrations ranging from 2 mg l⁻¹ to 20 mg l⁻¹ Use precise pipetting to transfer the required volumes of the sulfate and phosphate working standard solutions into labeled one-mark volumetric flasks Dilute each solution to the mark with water, then stopper and mix thoroughly It is essential to prepare these calibration solutions fresh each day for optimal results.
Instrumental analysis
10.2.1.1 Set up the ion chromatograph in accordance with manufacturer’s instructions
10.2.1.2 Install a sample loop that gives a suitable injection volume, e.g 50 àl
10.2.1.3 Adjust the detector to measure to a suitable measuring range
10.2.1.4 Adjust the flow rate of the eluent (6.2.4, 6.2.5, 6.3.10 and 6.3.12) to a value that is compatible with the columns used, e.g 1,5 ml min −1
10.2.1.5 Adjust the flow rate of the regeneration solution to a suitable value
Inject the calibration solutions into the ion chromatography system in ascending order of concentration Measure the conductivity of the sulfuric acid or phosphoric acid peak for each calibration solution using peak area mode.
10.2.2.2 Use the instrument's computer to generate a calibration function using a linear regression Repeat the calibration if the coefficient of determination, r 2 u 0,999
NOTE If r 2 u0,999, it is possible that the removal of an erroneous calibration point and reprocessing of the data will yield an acceptable calibration
Inject the laboratory blank solutions and the blank and sample test solutions into the ion chromatography system to conduct conductivity measurements Utilize the stored calibration function to ascertain the concentration of sulfuric acid or phosphoric acid in milligrams per liter.
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After the initial calibration, analyze the calibration blank solution and a mid-range calibration solution following every 10 test solutions If the concentration of sulfate or phosphate in the continuing calibration blank (CCB) exceeds the method detection limit, or if the concentration in the continuing calibration verification (CCV) varies by more than ±5%, corrective actions must be taken Options include using the instrument software to adjust for sensitivity changes or suspending analysis to recalibrate the instrument In either scenario, reanalyze the affected test solutions or, if reanalysis is not feasible, adjust the data to reflect the sensitivity change.
Analyze reagent and laboratory blank solutions, as outlined in section 10.4.1.1, along with quality control solutions specified in section 10.4.2.1 Utilize the results to effectively monitor the method's performance according to the guidelines in sections 10.4.1.2 and 10.4.2.2.
If sulfate or phosphate concentrations exceed the upper limit of the linear calibration range, dilute the test solutions to bring them within this range and repeat the analysis Ensure to add an appropriate volume of extraction solution during dilutions to match the matrix of the diluted test solutions with that of the calibration solutions, and make sure to record the dilution factor, \( f_{\text{dilution}} \).
NOTE For samples expected to have very high concentrations of sulfate or phosphate, it may prove necessary to dilute the test solutions before they are first analysed.
Estimation of detection and quantification limits
10.3.1 Estimation of the instrumental detection limits
To estimate the instrumental detection limits for sulfate and phosphate, follow the procedures outlined in sections 10.3.1.2 and 10.3.1.3 under the specified analytical conditions It is essential to repeat this estimation whenever there are significant changes in the experimental conditions.
The instrumental detection limit is useful for identifying changes in instrument performance, but it should not be confused with the method detection limit Typically, the instrumental detection limit is lower than the method detection limit, as it only considers variability from individual instrument readings without accounting for contributions from the sample matrix.
10.3.1.2 Prepare a test solution with sulfate and phosphate concentrations near the anticipated instrumental detection limits, by diluting the working standard solution (6.4.3) by an appropriate factor
To determine the instrumental detection limits for sulfate and phosphate, conduct a minimum of 10 ion chromatographic measurements on the test solution Calculate these limits as three times the sample standard deviation of the mean concentration values.
10.3.2 Estimation of the method detection limit and quantification limit
To estimate the method detection limit and quantification limit under the specified analytical conditions, follow the procedures outlined in sections 10.3.2.2 and 10.3.2.3, which are based on the approach detailed in Reference [15] It is essential to repeat this estimation whenever there are significant changes to the experimental conditions.
To enhance detection capabilities, it is essential to fortify a minimum of 10 filters with sulfate and phosphate concentrations near the expected method detection limit, such as 1.5 µg of sulfate or phosphate This can be achieved by spiking each filter with 0.1 ml of a solution that has been appropriately diluted from the working standard solution.
Perform ion chromatographic measurements on the test solutions obtained from each spiked filter after extracting the filters Calculate the method detection limit as three times the sample standard deviation of the mean concentration value, and determine the quantification limit as ten times the same standard deviation.
Quality control
10.4.1 Reagent blanks and laboratory blanks
To ensure the integrity of sample analysis, it is essential to carry reagent blanks and laboratory blanks throughout the entire sample preparation and analytical process This practice helps identify potential contamination from laboratory activities Reagent and laboratory blank solutions should be prepared at a frequency of at least one per 20 samples or a minimum of one per batch.
If reagent and laboratory blank results are unexpectedly high compared to prior data, it is essential to investigate potential contamination from laboratory processes or the sampling filter batch Taking appropriate corrective measures will help prevent recurrence of this issue.
To ensure method accuracy during sample preparation and analysis, it is essential to carry spiked samples and spiked duplicate samples throughout the entire process These samples, which consist of filters with known amounts of sulfate and phosphate added, help estimate percentage recovery relative to the true spiked value Spiking can be achieved by adding known volumes of sulfate and phosphate working standard solutions, prepared from stock solutions sourced differently than those used for calibration Quality control samples should be processed at a frequency of at least one per 20 samples or a minimum of one per batch.
To ensure the effectiveness of the method, it is essential to monitor performance by creating control charts that display the relative percentage recoveries and the relative percentage differences between spiked samples and their duplicates If the quality control results suggest that the method is not performing as expected, it is crucial to identify the underlying issues, implement corrective measures, and reanalyze the samples if needed For comprehensive guidance on utilizing quality control charts, refer to ASTM E 882.
To ensure the accuracy of analytical methods for sulfuric acid or phosphoric acid, it is essential to analyze suitable certified reference materials (CRMs) before routine use This analysis helps confirm that the percentage recovery aligns satisfactorily with the certified values CRMs can be obtained from reputable sources such as the European Commission and the National Institute for Standards and Technology (NIST).
Laboratories conducting regular air analysis for sulfuric acid or phosphoric acid should consider participating in an appropriate external quality assessment or proficiency testing scheme, provided such a scheme is available to them.
For details on current proficiency testing schemes, consult resources like the European Information System on Proficiency Testing Schemes (EPTIS) at www.eptis.bam.de or reach out to a national accreditation organization.
Measurement uncertainty
Laboratories should estimate and report measurement uncertainty following ISO Guide 98:1995 The process begins with creating a cause and effect diagram to identify sources of random and systematic errors These errors are then estimated or determined experimentally and compiled into an uncertainty budget The combined uncertainty is multiplied by a coverage factor, typically 2, to yield an expanded uncertainty, providing a confidence level of approximately 95% in the calculated value.
NOTE 1 References [19] and [20] describe the application of cause and effect analysis to analytical methods
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Precision can be assessed using quality control data, and the error related to instrumental drift can be estimated by assuming a rectangular probability distribution This estimation involves dividing the allowable drift before the instrument requires recalibration.
NOTE 3 Systematic errors include those associated with method recovery, sample recovery, preparation of working standard solutions, dilution of test solutions, etc
Calculate the mass concentration, ρ acid , in milligrams per cubic metre, of sulfuric acid or phosphoric acid in the air samples at ambient conditions, using Equation (2):
V f ρ ρ ρ acid =( anion,1 × 1 × dilution ) (− anion,0 × 0 )× conversion
The mean concentration of sulfate or phosphate in the field blank test solutions is denoted as \$\rho_{\text{anion},0}\$, measured in milligrams per liter In contrast, \$\rho_{\text{anion},1}\$ represents the concentration of sulfate or phosphate in the sample test solution, also expressed in milligrams per liter.
V is the volume, in litres, of the air sample;
V 0 is the volume, in millilitres, of the field blank test solutions;
The volume of the sample test solution, denoted as V1, is measured in millilitres The dilution factor, represented as f_dilution, equals 1 for neat solutions Additionally, the conversion factor from anion to acid concentration varies, with f_conversion being 1.021 for sulfate and 1.0318 for phosphate.
Sample collection and stability
Laboratory tests using sulfuric acid mist demonstrated a collection efficiency exceeding 95% across a concentration range of 0.5 mg m⁻³ to 10 mg m⁻³ on 0.45 µm pore-size PTFE filters Additionally, a recovery rate of over 95% for sulfuric acid or phosphoric acid was observed four weeks post-sample collection In contrast, quartz fiber filters achieved a recovery rate between 97% and 100% for sulfuric acid or phosphoric acid after the same duration.
Quantification limits
The quantification limit of the method for both phosphate and sulfate, estimated as prescribed in 10.3.2, is
1 mg l −1 For a sample solution volume of 4 ml and an air sample volume of 420 l, this is equivalent to
0,01 mg m −3 of sulfuric acid or phosphoric acid.
Upper limits of the analytical range
The upper limit of the analytical range is governed by the maximum permissible loading of the sample filter
It has been demonstrated (Reference [23]) that no breakthrough occurs for quartz fibre filters at sample © ISO 2007 – All rights reserved 23
Bias and precision
Laboratory experiments indicate that the analytical method demonstrates minimal bias, with the mean analytical recovery from spiked filters ranging from 97% to 100% for both phosphoric acid and sulfuric acid (Reference [23]).
The coefficient of variation (CV) analysis, which reflects analytical variability, was determined from the analysis of spiked filters It was found that the CV for phosphoric acid ranges from 0.7% to 3.2%, while for sulfuric acid, it ranges from 0.5% to 2.6% (Reference [23]).
Uncertainty of sampling and analysis method
The expanded uncertainty of the method, using a coverage factor of 2, has been estimated to be