Ebook Hazardous chemicals handbook Part 2

(BQ) Part 2 book Hazardous chemicals handbook has contents: Monitoring techniques, radioactive chemicals, safety by design, operating procedures, marketing, transport of chemicals, chemicals and the environment sources and impact, conversion tables and measurement data,...and other contents.

Monitoring techniques

As mentioned in Chapters 4, 5 and 16 chemicals can be a nuisance or pose safety, health and environmental risks, or become wasteful of expensive resources if allowed to escape excessively and uncontrollably into the general or workplace environment Escapes can result from inadequate process control, errors in operation or maintenance, incomplete understanding of the process, etc Such problems can arise from both: periodic emissions of chemicals due to the need to open, or enter, the ‘system’ occasionally (e.g during sampling, cleaning, line-breaking) including both planned and unplanned releases (e.g due to accidents, human error) and, continuous low-level fugitive emissions from normally-closed points, e.g valve seals, flange gaskets, pump seals, drain valves.

The need to monitor the impact of activities involving chemicals on the environment may stem from sound management practice or to satisfy a host of specific legal requirements Thus, in the

UK under the Environmental Protection (Prescribed Substances and Processes) Regulations 1991, operators must apply BATNEEC to prevent or minimize the release of prescribed substances into the environment, or to render harmless any emissions The prescribed substances for release into the air are given in Table 10.1 No prescribed process may be operated without an authorization from the Environment Agency and air pollutants which must be measured and the frequency of monitoring are set out in the authorization Compliance with emission limits for municipal waste incineration plants (Table 10.2) also requires monitoring.

Table 10.1 Prescribed substances for release into the air

Oxides of sulphur and other sulphur compounds

Oxides of nitrogen and other nitrogen compounds

Oxides of carbon

Organic compounds and partial oxidation compounds

Metals, metalloids and their compounds

Asbestos, glass fibres and mineral fibres

Halogens and their compounds

Phosphorus and its compounds

Particulate matter

In addition to pollution episodes, risks may arise due to atmospheric oxygen concentrations fluctuating beyond its normal level of 21% posing health (page 72) or fire hazards Fire and explosion dangers may also arise from the presence of flammable gases, vapours, or dusts in the atmosphere (Chapter 6).

Thus, as illustrated by Table 17.13 monitoring emissions of hazardous chemicals into the environment may be required for a variety of reasons such as:

10

308 MONITORING TECHNIQUES

• Assessing fire or explosion risks from atmospheres containing flammable gas, vapour or dust.

• Determining oxygen content of the working atmosphere.

• Determining sources of leaks of toxic, flammable, or nuisance pollutants.

• Identifying unknown pollutants.

• Assessing process efficiency and control.

• Assessing environmental risk from effluent discharges or for formal environmental impact assessment.

• Determining employee exposure to known toxic substances.

• Providing data for internal company environmental audits.

• Investigation of the causes of accidents.

• Investigation of the cause and nature of problems (e.g local complaints of odour) or pollution incidents.

Selected general analytical techniques for

monitoring environmental pollution

Stages in environmental monitoring include obtaining representative samples of the environment

in question and subsequent analysis of physical, chemical or microbiological attributes Monitoring techniques range from sophisticated in-line, continuous sampling and instantaneous analysis linked to audible/visual alarms or features to control the pollution; samplers running continuously, e.g throughout a normal day for subsequent analysis; to grab samples (i.e samples collected over

a short time span of, e.g., a few minutes) Continuous monitoring is common in personal dosimetry studies where an appropriate collection device samples air wherever a worker is throughout a specified period, e.g 15 minutes or 8 hours (page 111) A selection of common analytical techniques include the following.

Gases and vapours

Atomic absorption/emission spectrometry

Metal ions are most commonly measured using atomic absorption spectrometry In this technique

Table 10.2 Selected emission limits for municipal waste incineration (units: mg/m 3 )

the test sample is aspirated into a flame where chemical reduction of metal ions to metal atoms occurs Light is emitted at the discrete absorption wavelength for the metal A disadvantage is the need for a separate lamp for each element Emission spectrometry is therefore preferred Here test material is heated and vaporized using a DC or inductively-coupled plasma generator, after which

an optical emission spectrum as a function of wavelength is recorded An advantage of this technique is that a range of metals or metalloids can be analysed simultaneously.

Chemiluminescence

Here a chemical reaction produces a molecule with electrons in an excited state Upon decay to the ground state the liberated radiation is detected One such example is the reaction between ozone and nitric oxide to form nitrogen dioxide emitting radiation in the near infra-red in the 0.5–3µ region The technique finds use for measuring nitric oxide in ambient air or stack emissions.

Chromatography

This technique permits the separation of a mixture of compounds by their partition between two immiscible heterogeneous phases, one of which is stationary It detects substances qualitatively and quantitatively The chromatogram retention time is compound-specific, and peak-height indicates the concentration of pollutant in the sample Detection systems include flame ionization, thermal conductivity and electron capture With gas chromatography the mixtures to be separated are in the vapour phase under the operating conditions of the equipment A gas is used as the mobile phase to carry the sample over a column of stationary phase Flame ionization detection operates

by ionisation of molecules in a hydrogen flame and detection of the current change using a pair

of biased electrodes The current signal is directly related to the number of carbon atoms in the sample Thermal conductivity detectors measure the change in electrical resistance of a heated filament as gas flows over it It is most suitable for gases with very high, or very low, conductivity Traditionally gas chromatography is a laboratory analysis but portable versions are now available for field work.

In classical liquid chromatography a solution of solute percolates under gravity through a column packed with finely-divided solid when different compounds elute at different rates In

high-performance liquid chromatography (HPLC) the liquid is eluted from a packed column

under high pressure using solvent Detection systems include differential refractive index, diode array, electrochemical and ultra-violet-visible absorption HPLC is used for analysis of less volatile compounds in liquid samples than those in gas chromatography.

Because of its sensitivity (<1 ppm), ion chromatography has become extremely popular for analysis of ions in solution It is a column-based method for separating ions similar to HPLC but using ion exchange columns and either high- or low-conductivity eluent The most common detectors are electrical conductivity and ultra-violet absorption It finds wide use in air pollution monitoring of rain waters, impinger solutions and filter extracts for anions such as sulphate, nitrate, chloride, and cations, including ammonia and metals.

Colorimetry

Use is made of colour changes resulting from reaction of pollutant and chemical reagents: colour intensity indicates concentration of pollutant in the sample Reaction can take place in solution or

on solid supports in tubes or on paper strips, e.g litmus or indicator paper Quantitative assessment

of colour formation can also be determined using visible spectroscopy Instruments are calibrated

GASES AND VAPOURS 309

of filters to remove interfering species.

Ion-selective electrodes are a relatively cheap approach to analysis of many ions in solution The emf of the selective electrode is measured relative to a reference electrode The electrode potential varies with the logarithm of the activity of the ion The electrodes are calibrated using standards of the ion under investigation Application is limited to those ions not subject to the same interference as ion chromatography (the preferred technique), e.g fluoride, hydrogen chloride (see Table 10.3).

Table 10.3 Examples of applications of ion-selective electrodes

of the spectrum in which the pollutant shows peak absorption as opposed to scanning the entire spectrum Table 10.4 identifies principal absorption peaks for selected gases One advantage of IR

is that the detector does not ‘react’ with the gases and the major functional components are protected and easily removed for maintenance Since IR detection is potentially sensitive to temperature, the instrument requires approximately 15 minutes to equilibrate prior to use Water vapour can seriously affect performance.

Table 10.4 Main IR absorption peaks for selected gases

Compound specific analysers

Several instruments are available that are designed to monitor a specific compound rather than a wide range of substances The detection system varies according to the pollutant A selection is given in Table 10.6.

Mass spectrometry

This technique relies on the formation of ions by various means in a high-vacuum chamber, their acceleration by an electrical field and subsequent separation by mass/charge ratio in a magnetic field and the detection of each species It can be used for both inorganic and organic substances,

be very sensitive, and be of value in examining mixtures of compounds especially if linked to glc Usually this is a laboratory technique but portable or ‘transportable’ models are now available.

Ultra-violet spectrometry

Outermost valency electrons in atoms are excited by ultra-violet radiation The excited electrons return to the ground state liberating energy by disassociation, re-emission, fluorescence, or phosphorescence The level of UV radiation absorbed follows the Beer–Lambert law (page 312) The peak wavelength for selected gases is given in Table 10.5 Photo ionization detectors (PIDs) use ultraviolet light to ionize gas molecules such as volatile organic compounds; the free electrons collected at electrodes result in a current flow proportional to the gas concentration The lamp requires constant cleaning and hence may have limited life expectancy.

GASES AND VAPOURS 311

Automatic aerosol mass concentration can be achieved directly by collecting particles on a surface followed by use of a piezoelectric or oscillation microbalance, or by β-attenuation sensing techniques, or indirectly using light scattering The piezoelectric microbalance contains an electrostatic precipitator to deposit particles onto a vibrating silica crystal The change in resonance frequency is converted into mass concentration using a microprocessor Oscillating balances operate on the principle that air at 50°C (to avoid condensation) passes through a filter attached

to the top of a tapered glass tube which vibrates at its natural frequency As material is deposited

on the filter the oscillation frequency changes directly in proportion to the increased mass Beta gauges rely on the principle that when low-energy β particles pass through a material the intensity

of the beam is attenuated according to Beer–Lambert law:

Table 10.6 Selected examples of compound specific instruments

Ion selective electrodeOxidation to NOx and chemiluminescence

Infra-red

ChemiluminescenceCoulometry

Coulometry

UV fluorescence

Optical microscopy

This technique is invaluable for measurement of particle size, for counting the number of particles and for identification of particles by:

• morphology, e.g by comparison with standard particles, and

• refractive index using polarized light microscopy.

Electron microscopy

With a resolution of 0.01 µm this technique outperforms optical light microscopy (0.1 µm) and

is used, e.g., to examine fine particles such as metal fume When linked to other facilities such as dispersive X-ray analysis, quantitative data can be obtained.

Monitoring water quality

Water is essential to man both directly and indirectly through agriculture and industry in which vast quantities are used for cooling, energy production, irrigation, refrigeration, washing, solvents etc Risk of contamination can render water dangerous, unpleasant, or unusable Point sources of water pollution include domestic and industrial waste whilst non-point sources include agricultural and urban run-offs Analysis of water is important for estimating the nature and concentration of contaminants and hence fitness for use Artificial contaminants are mainly of domestic and

MONITORING WATER QUALITY 313

314 MONITORING TECHNIQUES

industrial origin, and are increasing in similarity because of the expanding domestic use of chemicals (cosmetics, detergents, paints, garden insecticides and fertilizers) Water quality can be assessed by direct analysis of chemical substances or by indirect effects, e.g pH, colour, turbidity, odour, impact on dissolved oxygen content.

Chemical pollutants are classified as inorganic or organic The former include metals (e.g Mn,

Fe, Cu, Zn, Hg, Cd, As, Cr), anions (e.g Cl–, SiO32–, CN–, F–, NO3–, NO2–, PO4– – –, SO3– –,

SO4– –, S––), and gases (Cl2, NH3, O2, O3) Methods for the examination of waters and associated materials published by the UK Department of the Environment are listed in Table 10.7 Selected methods for metal analysis are summarized in Table 10.8 Sampling protocols are described in, e.g., BS 6068 and BS EN 2567 Examples of BS methods for analysis of chemical contaminants

in water are illustrated by Table 10.9 Biological methods are also given in BS 6068.

Monitoring land pollution

Sources of land pollution include transport accidents, spillage during chemical handling, loss of containment from storage tanks, leakage and landfill of waste effluent An appreciation of the processes governing retention, degradation and removal of pollutants and the behaviour of specific pollutants in soil are essential in devising correct sampling and analytical strategies for assessing land contamination Even soil itself varies in dynamics and composition from one site to another Constituents include solid phase materials (such as complex mixtures of clays, minerals, organic matter), liquid aqueous phase of solutions (e.g natural minerals, fertilizers, pesticides and industrial wastes) and gaseous phase components (e.g oxygen, nitrogen, carbon dioxide, oxides of nitrogen, ammonia, hydrogen sulphide) The determination of toxic elements and organic substances in soils is a requisite of some EC directives as a means of controlling environmental pollution Analyses are important when certain types of waste are recycled, e.g by spreading sludge from water purification units on land, composting from household refuse The choice of analytical method will be dictated by accuracy, sensitivity etc Some key techniques are summarized in Table 10.10 and selected BS methods for monitoring soil quality are listed in Table 10.11.

Monitoring air pollution

Sampling

Differences exist between the monitoring of pollution levels in ambient and workplace air These reflect the differences in levels of contaminant, environmental standards, purposes for which data are used, etc (see also Table 16.8) Thus, although similarities may exist in detection techniques, the sampling regimes, analytical details and hardware specifications may differ for assessment of the two environments In general, atmospheric levels of contaminants are much lower in ambient air than those encountered in the workplace As a result larger volumes of sample are often needed for ambient air analyses This can be achieved using pumps of larger flow rate capacities, or by longer sampling times.

Atmospheric monitoring involves first obtaining samples of the air with subsequent analysis of the samples collected Examples of sampling techniques for gases and vapours are given in Table 10.12 Air samples can be pumped into instruments for direct analysis and data readout Alternatively, they are collected in air-tight bags, or absorbed in liquids, or onto solid sorbents, for subsequent laboratory analysis using techniques such as those described on page 308 Common solid sorbents

Table 10.7 Methods for the examination of water and associated materials published by the UK Department of the Environment

A review and methods for the use of epilithic diatoms for detecting and monitoring changes in river water quality, 1993Chlorphenylid, Flucofuron and Sulcofuron Waters (Tentative Methods based on methylation and GC-ECD, ion-pair HPLC andhydrolysis of Sulcofuron to 4-chloro-3-trifluoromethylaniline by GC-ECD), 1993

Cyanide in Waters etc (by Reflux Distillation followed by either Potentiometry using a Cyanide Selective Electrode orColorimetry, or Continuous Flow Determination of Cyanide or Determination by Microdiffusion), 1988

Determination of Aldicarb and other N-methyl carbamates in Waters (by HPLC or Confirmation of total Aldicarb residues andother N-methyl carbamates in waters by GC), 1994

Determination of the pH Value of Sludge, Soil, Mud and Sediment; and the Lime Requirement of Soil (Second Edition) (byDetermination of the pH Value of Sludge, Soil, Mud and Sediment or by Determination of the Lime Requirement of Soil),1992

Flow Injection Analysis, An Essay Review and Analytical Methods

Information on Concentration and Determination Procedures in Atomic Spectrophotometry, 1992

Isolation and Identification of Giardia Cysts, Cryptosporidium Oocysts and Free Living Pathogenic Amoebae in Water etc.,1989

Kjeldahl Nitrogen in Waters [including Mercury Catalysed Method, Semi-automated Determination of Kjeldahl Nitrogen(Copper Catalysed, Multiple Tube, Block Digestion Method followed by Air Segmented Continuous Flow Colorimetry)Determination of Kjeldahl Nitrogen in Raw and Potable Water (Hydrogen Peroxide, Multiple tube, Block DigestionMethod followed by Manual or Air-Segmented Continuous Flow Colorimetry) Semi-automated Determination of KjeldahlNitrogen (Copper/Titanium Catalysed, Multiple Tube, Block Digestion Method followed by Distillation and Air SegmentedContinuous Flow Colorimetry), Air-segmented Continuous Flow Colorimetric Analysis of Digest Solutions for Ammonia],1987

Linear Alkylbenzene Sulphonates (LAS) and Alkylphenol Ethoxylates (APE) in Waters, Wastewaters and Sludges by HighPerformance Liquid Chromatography, 1993

Phenylurea herbicides (urons), Dinocap, Dinoseb, Benomyl, Carbendazim and Metamitron in Waters [e.g determination ofphenylurea herbicides by reverse phase HPLC, phenylurea herbicides by dichloromethane extraction, determination byGC/NPD, phenylurea herbicides by thermospray LC-MS, Dinocap by HPLC, Dinoseb water by HPLC, Carbendazim andBenomyl (as Carbendazim) by HPLC], 1994

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g Phosphorus in Waters, Effluents and Sludges by phosphomolybdenum blue method, Phosphorus in Waters and Acidic Digests by Spectrophotometry-phosphovanadomolybdate method, Ion Chromatographic Methods for the Determination of Phosphorus Compound,Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination ofMolybdate Reactive Silicon-1-amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acidreduction method, Pretreatment Methods to Convert Other Forms of Silicon to Soluble Molybdate Reactive Silicon,Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992

Spectrophotometry-Sulphate in Waters, Effluents and Solids (2nd Edition) [including Spectrophotometry-Sulphate in Waters, Effluents and Some Solids by BariumSulphate Gravimetry, Sulphate in waters and effluents by direct Barium Titrimetry, Sulphate in waters by InductivelyCoupled Plasma Emission Spectrometry, Sulphate in waters and effluents by a Continuous Flow Indirect SpectrophotometricMethod Using 2-Aminoperimidine, Sulphate in waters by Flow Injection Analysis Using a Turbidimetric Method, Sulphate

in waters by Ion Chromatography, Sulphate in waters by Air-Segmented Continuous Flow Colorimetry using MethylthymolBlue], 1988

Temperature Measurement for Natural, Waste and Potable Waters and other items of interest in the Water and SewageDisposal Industry, 1986

The Determination of 6 Specific Polynuclear Aromatic Hydrocarbons in Waters [Using High-Performance LiquidChromatography,Thin-layer Chromatography], 1985

The Determination of Taste and Odour in Potable Waters, 1994

Use of Plants to Monitor Heavy Metals in Freshwaters [Methods based on Metal Accumulation and on Techniques other thanAccumulation], 1991

MONITORING AIR POLLUTION 315

316 MONITORING TECHNIQUES

Table 10.8 Methods for analysis of metal content of water

Spectrophotometry–Colorimetry One of most useful and versatile 10–5 to 10–7 M

methods but can be time consuming (10–9 with pre-concentration)Kinetic analysis (metal ion acts Sensitive, highly selective, only 10–8 to 10–9 M

Atomic absorption

spectrophotometry:

interfering effects important

Flame and spark emission Not very accurate Gives multi- 10–5 to 10–8 M

Neutron activation analysis Specialized, expensive 10–9 to 10–10 M

Ion-selective electrodes Highly selective but insensitive 10–5 to 10–6 M

and imprecisePolarography: Restricted to electroactive metals

Anodic stripping voltametry Applicable to few metals and 10–8 to 10–10 M

dependent on metal speciation

for gases and vapours (Table 10.13) include silica gel, activated charcoal, or organic resins Silica gel is most useful for polar compounds whereas charcoal finds wide use for non-polar substances Subsequently, the pollutant is generally removed from the solid phase by thermal desorption or by solvent extraction The advantages and disadvantages of the two desorption techniques are summarized in Table 10.14 Their versatility is illustrated by Table 10.15 for use of charcoal Pumps vary from large, stationary high-volume versions to pocket-size devices for use in personal dosimetry when operators wear sampling devices in the form of tubes or badges in lapels

to collect air sampled in their breathing zone Passive samplers are also available for monitoring gases and vapours in air These are inexpensive devices which do not require a mechanical pump but rely on the concentration gradient between the air and sorbent material and the resultant molecular diffusion of the pollutant towards the sorbent according to Fick’s law:

Q = DdC/dZ

where Q = molar flux (mol cm–2s–1),

D = diffusion coefficient (cm2s–1),

C = concentration (mol cm–3)

Z = diffusion path length (cm).

Because of the low rates of molecular diffusion, assessment of workplace air quality using passive samplers usually entails sampling for a working shift, and exposure periods of one to four weeks tend to be needed to measure concentrations in ambient air.

Gases and vapours

Analyses of gases and vapours tend to utilize the techniques described on page 308 Many of these methods were traditionally limited to laboratory analyses but some portable instruments are now available for, e.g., gas chromatography (Table 10.16) and non-dispersive infra-red spectrometry (Table 10.17).

Table 10.9 Selected British Standard methods for monitoring water quality

long-chain fatty acids spectrophotometry

cyanogen chloride

sulphosalicylic acidinorganically bound total

pH

calcium and magnesium EDTA titrimetricnonionic surfactants Dragendorff reagentanionic surfactants methylene blue titrationarsenic, cadmium, cobalt, atomic absorption spectrometrycopper, lead, magnesium, spectrometry

nickel, zinc

chemical oxygen demand

sodium and potassium atomic absorption spectrometry

and by flame emissionspectrometry

spectrometryorganochlorine compounds gas chromatographydissolved anions (bromide, liquid chromatographychloride, nitrate, nitrite,

phosphate, sulphate, chromate,iodide, sulphite, thiocyanate,thiosulphate, chlorate, chlorite) liquid chromatographyorganic nitrogen and gas chromatographyphosphorus

atomic emission spectrometry

free and total chlorine titrimetric or colorimetric

dissolved oxygen iodometry or electrochemical probe

MONITORING AIR POLLUTION 317

318 MONITORING TECHNIQUES

hydrocarbon oil index solvent extraction and gas

chromatographyhalogenated hydrocarbons gas chromatography(volatile)

total organic carbon anddissolved organic carbonorganically bound halogenalpha and beta activitysuspended solids filtration through glass fibreelectrical conductivity turbidity

dissolved organic carbon

ammonium, potassium,manganese, calcium,magnesium, strontium, barium ion chromatography

BS EN 13395 nitrate and nitrite nitrogen flow analysis and spectrometry

Table 10.9 Cont’d

Table 10.10 Common instrumental techniques for soil analysis

• Phosphorus or mineral nitrogen Spectrophotometry

• Alkaline earth metals and transition metals Flame atomic absorption spectrometry

• Aluminium, boron, silicon Inductively coupled plasma atomic emission spectrometry

• Lead in soil slurries Electrothermal atomic absorption spectrometry

• Toxic organic compounds High pressure liquid chromatography

One of the most commonly used portable, gas detection systems is based on colour indicator tubes employed, in the main, for grab sampling Tubes are available to detect over 300 substances (Table 10.18) and, using a combination of tubes, a range of concentrations can be measured The technique relies on a manually-operated bellows or piston pump to aspirate a fixed volume of atmosphere through a glass tube containing crystals (e.g silica gel or alumina) impregnated with

a reagent which undergoes a colour change upon reaction with a specific pollutant or class of pollutant The length of stain that develops is proportional to the concentration of contaminant and the tube is generally calibrated to permit direct read-off in parts per million Sample lines of several metres between the pump and tube allow atmospheres to be sampled, e.g., inside vessels A smaller number of special tubes (Table 10.18(b)) are available for longer-term monitoring and these

are used in conjunction with battery-powered pumps operating at a flowrate of 10–20 ml/s Again the average concentrations can be read off directly after an exposure period of, e.g., 8 hours Direct-reading colorimetric diffusion tubes requiring no pump are available for a small number of substances (Table 10.18(c)) Because of their simplicity, colour indicator tubes are widely used but their limitations must be appreciated; sources of inaccuracy are given in Table 10.19 Portable or fixed multi-point colorimetric detectors are available which rely on paper tape impregnated with the reagent A cassette of the treated paper is driven electrically at constant speed over a sampling orifice and the stain intensity measured by an internal reflectometer to provide direct read out of concentration of contaminant in sample Such instruments are available for a range of chemicals including the selection given in Table 10.20.

Flammable gases

Flammable atmospheres can be assessed using portable gas chromatographs or, for selected compounds, by colour indicator tubes More commonly, use is made of ‘explosimeters’ fitted with Pellistors (e.g platinum wire encased in beads of refractory material) The beads are arranged in a Wheatstone bridge circuit The flammable gas is oxidized on the heated catalytic element, causing the electrical resistance to alter relative to the reference Instruments are calibrated for specific compounds in terms of 0–100% of their lower flammable limit Recalibration

or application of correction factors is required for different gases These types of sensor are subject to ‘poisoning’ by certain chemicals such as silicone, sulphur, and halogen compounds Points to consider are listed in Table 10.21.

Semiconductors resembling Pellistors are also available, e.g a platinum/rhodium filament is used to heat a pellet of doped oxide which absorbs any flammable gas passing over it, causing the electrical conductivity to alter and subsequently the voltage in the electrodes attached to the pellet Amplification of the signal registers a deflection on the meter Again, errors can arise if the instrument is used for gases other than those for which it is calibrated These sensors offer a long life expectancy; they are not restricted to flammable substances.

Table 10.11 Selected British Standard methods for monitoring soil quality

pHeffective cation exchange capacity barium chloride reagent

organic and total carbon elementary analysis

water- and acid-soluble sulphate barium chloride reagentpotential cation exchange capacity

cadmium, chromium, cobalt, copper, extraction with aqua regia withlead, manganese, nickel, and zinc flame and electrothermal atomic

absorption spectrometrypolynuclear aromatic hydrocarbons high performance liquid

chromatography

trace elements extraction with DTPA or digestion with

hydrofluoric and perchloric acids

BS 8855 coal tar derived phenolic compounds

FLAMMABLE GASES 319

Table 10.12 Selected examples of sampling techniques for air contaminants

or highly reactive

in other agents

Gases or vapours of Absorption with Fritted or sintered Water, acid, 1–15 (depends 95–100 May plug if large

included

or highly reactive or jet impaction

in other agents

with absorbing agents

Table 10.13 Common sorbent materials and applications

• Anasorb activated charcoal Solvent desorption Polar organic compounds

• Anasorb graphitized charcoal Various grades for collection of substances of a range of

volatilities

compounds

chlorinated organic compounds

• Polyurethane foam Halogenated compounds including PCBs, dioxins, furans

and organophosphorus compounds

• Porous polymer Various types usually for solvent desorption; suitable for a

range of organic compounds including highly polarsubstances

inorganic acid gases, methanol, nitro compounds

compounds Suitable for low ambient concentrations

Table 10.14 Thermal desorption of sorbed gas from sample tubes

Advantages over solvent extraction

Elimination of sample preparation and handling of toxic solvents such as carbon disulphide

Absence of solvent simplifies chromatograph

Increased sensitivity

Sample tubes can be reused

Greater range of detection systems to which the desorbed gas can be subjected (e.g chromatography, infra-red and ultravioletspectroscopy, colorimetry)

Limitations

Certain resins undergo degradation even below 250°C

Test sample may be thermally unstable

Not all compounds readily desorb

The entire test sample is used with no opportunity for repeat analyses

Toxic particulates

Airborne particulates include dust, fume and aerosols Many such particles are invisible to the naked eye under normal lighting but are rendered visible, by reflection, when illuminated with a strong beam of light This is the ‘Tyndall effect’ and use of a dust lamp provides a simple technique for the rapid assessment of whether a dust is present, its flow pattern, leak sources, the effects of ventilation, etc More sophisticated approaches are needed for quantitative data Whether personal, spot or static sampling is adopted will depend upon the nature of the information required.

Air in the general atmosphere, or in the breathing zone of individuals, may be collected using

a pump coupled to a means of isolating particulate matter for subsequent analysis or determination (Table 10.23) It is important to differentiate between ‘total inhalable dust’ i.e., the fraction of airborne material which enters the nose and mouth during breathing and is hence available for deposition in the respiratory tract, and ‘respirable dust’, i.e the fraction which penetrates to the gas exchange region of the lung For this purpose techniques for separating dust or aerosol

TOXIC PARTICULATES 321

Table 10.15 Charcoal tube user guide

Two concentration ranges are given for most substances The low range is approximately 1%–15% of the TLV and the high range 15%–200% TLV The user shouldselect from these two ranges the expected mean concentration.

(2) A sampling rate is recommended for each concentration range and for a 2 hr, 4 hr, or 8 hr sampling period Each sampling rate is given in ml/min and has beencalculated to provide a minimum tube loading of at least 0.01 mg at the minimum concentration shown and not to exceed the recommended tube loading at thehighest concentration shown for that range These figures are based on the use of 100 mg coconut-shell charcoal tubes to the NIOSH recommended design exceptwhere otherwise noted

(3) A recovery of 5% of the total sample from the back-up section of charcoal in a sample tube was defined as the breakthrough point: 50% of this value is shown

as the recommended maximum tube loading, to allow for high humidity or the presence of other substances which reduce the normal tube capacity

(4) The figures given are not intended to be used as exact desorption efficiencies and are only given as a guide when carrying out system calibrations Actualdesorption efficiencies should always be determined at the time of analysis However, these figures represent the best obtainable data from several sources, andany significant deviation should be regarded as a possible indication of a systematic error in the analytical technique The figure given for desorption efficiency

is an average figure The desorption efficiency for a compound will vary with the amount of substance on the tube With reduced tube loadings, in most cases,the desorption efficiency will be lower Significant errors may be introduced when analysing small amounts of substance and an average desorption efficiencyfactor is used

(5) The desorption efficiencies given are directly related to the eluent used All data in the desorption efficiency column correspond to the specific eluent listed:

(6) 100 mg petroleum-based charcoal tubes based on the NIOSH recommended design should be used for sample collection of these compounds

(7) These compounds migrate rapidly to the back-up section of the charcoal tube A 400 mg tube should be used for sample collection with a second 100 mg tube

in series behind the large tube to determine breakthrough

330 MONITORING TECHNIQUES

Table 10.16 Chromatographic column guide for Century organic vapour analyser

Column packingretention time(min:secs)

T 10% 1,2,3-Tris(2-cyanoethoxy) propane on Chromosorb P, AW, 60/80 mesh

(1) Century organic vapour analysers are factory calibrated to measure ‘total organic’ vapours according to a standard(methane) Since different organic vapours interact with the flame ionization detector (FlD) to varying extents, it is vitalthat the instrument user be aware of the magnitude of the variation in order to obtain the most accurate data Each usermust determine relative responses for the individual instrument

(2) For chromatographic work, the OVA can be used with a variety of column lengths and packing materials For highestaccuracy, temperature control for the column is mandatory This is accomplished using the portable isothermal pack (PlP)kit which is supplied with three 8 in (203 mm) columns packed with B, G and T materials respectively Isothermal control

is accomplished non-electrically using an ice-water mixture for 0°C and a seeded eutectic mixture for 40°C The datalisted are for comparison purposes only since retention time for a compound can vary according to the condition of thecolumn packing material, packing procedure and chemical interaction among the components of a vapour mix

A blank in the table indicates that no data are available for the analysis

TOXIC PARTICULATES 333

Table 10.16 Cont’d

Column packingretention time(min:secs)

Table 10.17 Compounds detectable by portable infrared analysis (MIRAN 1A)

1-Chloro-2,3,-Epoxypropane, see Epichlorohydrin

2-Chloroethanol, see Ethylene chlorohydrin

Chloroethylene, see Vinyl chloride

1,2-Diaminoethane, see Ethylenediamine

Dimethylaminobenzene, see Xylidene

Dimethylbenzene, see Xylene

2,6-Dimethylheptanone, see Diisobutyl ketone

Diphenylmethane diisocyanate, see Methylene

bisphenyl isocyanate, MDl

1,2-Epoxypropane, see Propylene oxide

2,3-Epoxy-1-propanol, see Glycidol

Ethanethiol, see Ethyl mercaptan

2-Ethoxyethyl acetate (cellosolve acetate) 8.8 8.25 0.58 0.03

Ethylene glycol monomethyl ether acetate,

see Methyl cellosolve acetate

Glycol monoethyl ether, see 2-Ethoxyethanol

Guthion(R), see Azinphosmethyl

Methyl amyl alcohol, see Methyl isobutyl carbinol

Methyl ethyl ketone (MEK), see 2-Butanone

Methyl isobutyl ketone, see Hexone

Phenylethylene, see Styrene

Tetrachloroethylene, see Perchloroethylene

Tetrachloromethane, see Carbon tetrachloride

2,4,6-Trinitrophenol, see Picric acid

2,4,6-Trinitrophenylmethyl-nitramenine, see Tetryl

The analytical wavelength has usually been chosen as that of the strongest band in the spectrum which is free from interference due to atmospheric water and

CO2 If more than one infra-red absorbing material is present in the air in significant concentration, the use of another analytical wavelength may be necessary

(2) Path lengths are chosen to optimize readings at the exposure limits All measurements were made using a 1 mm slit

(3) Equivalent to the OSHA limit Absorbance less than the tabulated value indicates concentrations below the exposure limits regardless of the presence of interferingcompounds

(4) The concentration that would produce an absorbance equal to the peak-to-peak noise of the instrument

(5) Solid or vapour pressure too low for analysis

(6) Difficult to obtain commercially

342 MONITORING TECHNIQUES

Table 10.18(a) Substances for which colour detector tubes are available from one supplier (Drager) – short-term tubes

10 –150 ppm100–1000 ppm

5 –700 ppm500–100 000 ppm

Bromomethane 20–200 ppm

40–400 ppm500–25 000 ppm

50–1000 ppm100–1200 ppm

5–60%

2.5 –120 ppm0.1 –60 mg/l

5–250 ppm5–700 ppm8–150 ppm10–3000 ppm0.001–0.3 vol %0.3 –7 vol %

Table 10.18(a) Cont’d

TOXIC PARTICULATES 343

Table 10.18(a) Cont’d

Table 10.18(a) Cont’d

TOXIC PARTICULATES 345

Ethylene glycol monoethylether acetate 50 –700 ppm

Table 10.18(a) Cont’d