Chemical Pollutants in Air, Water, Soil, and Solid Wastes Phần 5 ppt

sed-The total phenolic compounds in an aqueous sample can be determined by a colorimetric method using 4-aminoantipyrine.. Phthalates can be extracted from 1 L of aqueous sample extrac-b

Phenols are organic compounds containing an –OH group attached to anaromatic ring The structure of phenol, the prototype compound of this class, is

Although the presence of other substituents in the ring can produce an array

of diverse compounds of entirely different properties, the chemical analysis ofmost phenols, however, can be performed in the same way This is attributed to(1) the acidic nature of the phenolic –OH group, and (2) that the –OH group canform derivatives

Trace amounts of phenols may occur in many natural waters as well as indomestic and industrial wastewaters Chlorination of such waters can producechlorophenols

Several phenolic compounds occurring in industrial wastewaters, soils, iments, and hazardous wastes are classified as U.S EPA priority pollutants Theseare presented in Table 2.23.1

sed-The total phenolic compounds in an aqueous sample can be determined by

a colorimetric method using 4-aminoantipyrine This reagent reacts with phenoliccompounds at pH 8 in the presence of potassium ferricyanide to form a coloredantipyrine dye, the absorbance of which is measured at 500 nm The antipyrinedye may also be extracted from the aqueous solution by chloroform The absor-bance of the chloroform extract is measured at 460 nm The sample may bedistilled before analysis for the removal of interfering nonvolatile compounds

The above colorimetric method determines only ortho- and meta-substitutedphenols and not all phenols When the pH is properly adjusted, certain para-substituted phenols, which include methoxyl-, halogen-, carboxyl-, and sulfonicacid substituents, may be analyzed too

OH

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Phosphorus occurs in natural waters, wastewaters, sediments, and sludges

The main sources of phosphorus released into the environment include fertilizers,

many detergents and cleaning preparations, and boiler waters to which phosphates

are added for treatment From an analytical standpoint, phosphorus is classified

into three main categories:

3 Organically bound phosphorus

Orthophosphate and condensed phosphate are a measure of inorganic

phos-phorus The latter is also termed as “acid-hydrolyzable phosphate.” However,

during mild acid hydrolysis, a small amount of phosphorus from organic

phos-phorus compounds may be released To determine suspended and dissolved forms

of phosphorus, the sample should be filtered through a 0.45 μm membrane filter,

and the filtrate and the residue analyzed separately

ANALYSIS

The analytical steps are outlined in Figure 2.24.1

SAMPLE PREPARATION

For the determination of acid-hydrolyzable phosphorus content of the sample,

which is the difference between the orthophosphate in the untreated sample and

the phosphate found after mild acid hydrolysis, the sample is first acidified with

H2SO4and then hydrolyzed by boiling for 1.5 to 2 h The sample may also be

2.24

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PHTHALATE ESTERS

Phthalates are the esters of phthalic acid having the following general structure:

where R′ and F′′ are alkyl, alkenyl, and aryl groups These substances are used

as plasticizers of synthetic polymers such as polyvinyl chloride and celluloseacetate Lower aliphatic phthalates are used in the manufacture of varnishes andinsecticides

Many phthalates are found in trace quantities in wastewaters, soils, andhazardous wastes, often leaching out into the liquid stored in plastic containers

or PVC bags

The acute toxicity of phthalates is very low, exhibiting symptoms of nolence and dyspnea in test animals only at high doses Some of these substancesare listed as U.S EPA priority pollutants

som-Phthalates are analyzed by GC, LC, and GC/MS techniques after the tion and concentration of the samples Aqueous samples may be directly analyzed

extrac-by HPLC Phthalates can be extracted from 1 L of aqueous sample extrac-by repeatedextraction with methylene chloride using a separatory funnel Phthalates havingmuch greater solubility in methylene chloride, partition into this solvent and isseparated The extract is concentrated by boiling off methylene chloride andexchanged to hexane to a volume of 1 to 5 mL Alternatively, 1 L aqueous sample

is passed through a liquid-solid extraction cartridge containing octadecyl groupbonded-silica Phthalates adsorbed on the adsorbent surface are eluted with meth-ylene chloride Phthalates in soils and other solid matrices may be extracted bysonication or Soxhlett extraction using methylene chloride The extract isexchanged to hexane during concentration If the extract is to be analyzed byGC/MS, the solvent exchange to hexane is not necessary and the methylenechloride extract may be directly injected

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To eliminate the interference effect of other contaminants and for dirtysample extracts, cleanup may become necessary The extract is either passedthrough a florisil column or an alumina column and the phthalate esters are elutedwith ether-hexane mixture (20% ethyl ether in hexane, v/v)

The sample extract may be analyzed by GC or GC/MS A 2- to 5-µL aliquot

of the extract is injected into a GC and the phthalates are detected by an electroncapture detector, a flame ionization detector (FID), or a photoionization detector.Some of the chromatographic packed or capillary columns that may be used forthe phthalate analysis are listed below:

• Packed column: 1.5% SP-2250/1.96% SP-2401 on Supelcoport (100/120 mesh), 3% OV-1 on Supelcoport (100/120 mesh), and 3% SP-2100 on Supel- coport (100/120 mesh).

• Capillary column: Fused silica capillary column containing 95% dimethyl polysiloxane and 5% diphenyl polysiloxane (e.g., 30 m, 0.53 mm ID, 1.5 µm Rtx-5); 5% diphenyl polysiloxane, 94% dimethyl polysiloxane, and 1% vinyl polysiloxane (e.g., PTE-5, SPB-5, DB-5, or equivalent, 15 or 30 m × 0.53 mm ID).The column temperatures in the analysis may be maintained between 150°and 220°C Benzyl benzoate or n-butyl benzoate may be used as internal standard.GC/MS analysis is a positive confirmatory test that identifies the compoundsbased on their characteristic ions Table 2.25.1 lists the characteristic ions for somecommonly occurring phthalates, which have been listed as U.S EPA priority pollutants.Aqueous samples containing phthalates at concentrations higher than 10 ppmmay be directly injected into GC and measured by FID

High performance liquid chromatography techniques may be successfullyapplied to analyze phthalate esters A 15 or 25 cm column filled with 5 or 10 µmsilica-based packings is suitable Short columns (3.3 cm × 4.6 mm), commonlycalled 3 × 3 columns, offer sufficient efficiency and reduce analysis time andsolvent consumption Phthalate esters resolve rapidly on a 3 × 3 Supelcosil LC-8column (3 µm packing) at 35°C and detected by a UV detector at 254 nm.Acetonitrile-water is used as mobile phase (flow rate: 2 ml/min; injection volume:

1 mL) Other equivalent columns under optimized conditions may be used

AIR ANALYSIS

Analysis of phthalates in air may be performed by sampling 1 to 200 L airand collecting the esters over a 0.8 µm cellulose ester membrane The phthalatesare desorbed with carbon disulfide and the eluant is injected into a GC equippedwith an FID A stainless steel column 2 m × 3 mm OD, containing 5% OV-101

on 100/120 Chromosorb W-HP was originally used in the development of thismethod (NIOSH Method 5020) for dibutyl phthalate and bis(2-ethylhexyl)phtha-late Any other equivalent GC column listed above may also be used

The EPA Methods in Table 2.25.2 list only a specific number of phthalates.Any other phthalates not listed under the methods, however, may be analyzedusing the same procedures

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POL YCHLORINATED BIPHENYLS (PCBS)

Polychlorinated biphenyls (PCBs) are a class of chlorosubstituted biphenylcompounds that were once widely used as additives in transformer oils, lubricat-ing oils, and hydraulic fluids These substances have high boiling points, exhib-iting high chemical and thermal stability, and flame resistance However, because

of their high toxicity and possible carcinogenic action in humans, these substancesare no longer being used In the U.S., PCBs were made under the trade nameAroclor Table 2.26.1 presents the common Aroclors, their CAS numbers, andthe chlorine contents Each Aroclor is a mixture of several isomers The generalstructure of the biphenyl ring is as follows:

PCBs can be conveniently determined by most of the common analyticaltechniques which include GC-ECD, GC-HECD, GC-FID, GC/MS, HPLC, NMR,and enzyme immunoassay Among these, GC-ECD and GC/MS are by far themost widely used techniques for the determination of PCBs in the environmentalsamples at a very low level of detection While the former can detect the PCBs

at subnanogram range, the mass selective detector (GC/MS) identifies the ponents relatively at a higher detection range, 10 to 50 times higher than the ECDdetection level GC/MS, however, is the best confirmatory method to positivelyconfirm the presence of PCBs, especially in heavily contaminated samples Aque-ous and nonaqueous samples must be extracted into a suitable solvent prior totheir analysis

com-Being mixtures of several components, each Aroclor produces multiplepeaks The common GC columns that can readily separate the chlorobiphenylcomponents include 3% SP-2100, OV-1, DB-5, and SPB-5 Other equivalentcolumns or conditions can be used in the GC and GC/MS analyses Table 2.26.2

presents some of the commonly used columns and conditions for analysis

2 3 4

2.26

POLYCHLORINATED DIOXINS AND

Chlorosub-ANALYSIS

Chlorinated dioxins and dibenzofurans are best analyzed by GC/MS niques, using both low- and high-resolution mass spectrometry A measuredamount of sample is extracted with a suitable solvent The solvent extract con-taining the analytes is concentrated down to a small volume and then subjected

tech-to cleanup for the removal of interferences The extract is injected ontech-to the GC

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3 2 1 10

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9 8 7 6

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column for the separation of individual compounds The chlorinated dioxins anddibenzofurans are then identified from their characteristic mass ions using aGC/MS in selective ion monitoring (SIM) mode

SAMPLE EXTRACTION AND CLEANUP

Aqueous samples are extracted with methylene chloride A 1-L volume ofsample is repeatedly extracted in a separatory funnel The methylene chlorideextract is exchanged to hexane during concentration to a volume of 1 mL.Nonaqueous samples, such as soils, sediments, sludges, fly ash, and tissues may

be extracted by Soxhlett extraction or sonication Methylene chloride, toluene,hexane, or a combination of these solvents may be used for extraction Sludgescontaining 1% or more solids should be filtered The aqueous filtrates and thesolid residues are extracted separately They are then combined prior to cleanupand analysis

Chlorinated compounds such as PCBs, haloethers, chloronaphthalenes, etc.,which may be present in several orders of magnitude higher than the analytes ofinterest, can interfere in the analysis These interfering substances may beremoved from the solvent extracts as follows

Acid-Base Partitioning

The hexane extract is shaken with 1:1 H2SO4 in a small separatory funnelfor 1 min and the bottom H2SO4 layer is discarded Such acid wash may berepeated two or three times The extract is then repeatedly washed with 20%KOH solution Contact time must be minimized because KOH could degradecertain chlorinated dioxins and dibenzofurans If acid-base washing is performed,the sample extract should be washed with 5% NaCl solution each time after acidand base washes, respectively Acid–base partitioning cleanup may, however, beomitted completely if the sample is expected to be clean

Silica Gel Cleanup

This cleanup may be performed only if the alumina cleanup does not removeall interferences A silica gel column containing anhydrous Na2SO4 on the top ispreeluted with 50 mL 20% benzene/80% hexane solution The extract is then

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loaded onto the column and the analytes are eluted with the above benzene-hexanemixture

Carbon Column Cleanup

If significant amounts of interferences still remain in the sample extract afterperforming the above cleanup procedures, the extract may be subjected to a furthercleanup step Prepare a mixture of active carbon AX-21 and Celite 545, containing8% and 92%, respectively This is heated at 130°C for several hours and packedinto a chromatographic column This carbon column is preeluted with tolueneand hexane, respectively The sample extract is now loaded onto the column andthe analytes are subsequently eluted with toluene The eluant is concentrated foranalysis

GC/MS ANALYSIS

The polychlorinated dioxins and dibenzofurans are separated on a fused silicacapillary column A 60 m long and 0.25 µm ID DB-5, SP-2330, or equivalentcolumn having 0.2 µm film thickness should adequately resolute most isomers.The mass spectrometer must be operated in SIM mode The 13C-analogs ofisomers may be used as internal standards The analytes are identified from theirrelative retention times and characteristic masses In low resolution MS, thecharacteristic masses for 2,3,7,8-TCDD are 320, 322, and 257 Use either 37Cl4-2,3,7,8-TCDD or 13C12-2,3,7,8-TCDD as an internal standard The m/z for thesetwo internal standards are 328 and 332, respectively

When using high resolution mass spectrometry (HRMS), the characteristicm/z for 2,3,7,8-TCDD are 319.8965 and 321.8936 The m/z for the corresponding

37Cl4- and 13C12-isomers in HRMS are 327.8847 and 331.9367, respectively.The quantitation is performed by the internal standard method The SIMresponse for the isomers at their primary characteristic m/z are compared againstthe internal standard(s) A detection limit in the range of 2 to 5 ppt (0.002 to0.005 µg/L) can be achieved for aqueous samples concentrated as above andanalyzed using low resolution mass spectrometry method A lower detection limit

in 0.01 to 1 ppt range may be achieved by HRMS technique

SAMPLE PRESERVATION AND HOLDING TIME

Samples must be refrigerated and protected from light If residual chlorine

is present, add Na2S2O3 (80 mg/L sample) Samples must be extracted within

7 days of collection and subsequently analyzed within 40 days

Silica (SiO2) occurs in high abundance all over the earth It occurs in theform of sand and quarts It is also present in rocks and silicate minerals It isfound in natural waters at varying concentrations from 1 to 100 mg/L

Silica in water may be analyzed by the following methods:

1 Gravimetric method

2 Ammonium molybdate colorimetric method

3 Atomic absorption spectrophotometric methodMethods 1 and 2 are presented below Method 3 is discussed in brief undermetal analysis

GRAVIMETRIC METHOD

Silica and silicates (SiO32– and SiO44–) react with hydrochloric or perchloricacid to form silicic acid, H2SiO3 Evaporation of the solution precipitates dehy-drated silica Upon ignition, dehydration is completed The reaction steps aresummarized below:

The residue after ignition is weighed along with its container This residueconsists of dehydrated silica plus any nonvolatile impurities in the sample

SiO or silicates HCl/HClO H SiOevaporation

partially dehydrated SiO

where W1 is the weight of crucible and contents before HF treatment and W2 isthe weight of crucible and contents after volatilization of SiF4.

no chlorine ion (test with AgNO3; addition of a few drops of AgNO3 reagent tothe washing should not produce white precipitate or turbidity)

Transfer the filter paper and residue to a platinum crucible Dry at 110°C.Heat the covered crucible (keeping a little opening) gradually to 1200°C Cool

in a desiccator and weigh Repeat the ignition, cooling, and weighing untilconstant weight is attained

Moisten the residue with distilled water Add a few drops of 1:1 H2SO4

followed by 10 mL HF (48% strength) Evaporate the mixture slowly to dryness.Ignite the residue at 1200°C Record the constant weight Determine the concen-tration of dissolved silica in the sample from the above equation

AMMONIUM MOLYBDATE COLORIMETRIC METHOD

Under acid condition (at pH ~1) silica reacts with ammonium molybdate toform a yellow colored heteropoly acid, silicomolybdic acid The reactions areshown below:

Phosphate reacts with ammonium molybdate too, similarly forming yellowphosphomolybdic acid The presence of phosphate, therefore, interferes in thetest The addition of oxalic acid or citric acid destroys phosphomolybdic acidcomplex but not silicomolybdic acid complex The intensity of color developed

is proportional to the concentration of silica in the sample

An additional color development step may often be required to confirm theyellow color of silicomolybdic acid The latter is reduced to a dark blue substance

by treating with aminonaphthalo sulfonic acid The color of heteropoly blueformed is more intense than the yellow color of silicomolybdic acid The lattertest is more sensitive and can give a detection limit of 50 µg silica/L when using

a spectrophotometer

Certain forms of silica and many polymeric silicates do not react with nium molybdate These complex silicates may be decomposed to simple molybdate-reactive silica by high temperature digestion or fusion with sodium bicarbonate

As a more sensitive alternative test or an an additional confirmatory test,add 2 mL of aminosulfonic acid reducing reagent 5 min after adding oxalic acidsolution Let the solution stand for 5 min and then measure the absorbance at

815 or 650 nm (at the latter wavelength the sensitivity is reduced.) Plot a separatecalibration curve Read the concentration of analyte from the calibration curve

Reagent

• Reducing agent: to 300 mL of NaHSO3 solution (~20% strength), add 100 mL

of solution containing 1 g 1-amino-2-naphthol-4-sulfonic acid and 2 g Na2SO3 Filter and store the reagent in a plastic bottle in the dark at 4°C Discard this solution when it becomes dark.

© 1997 by CRC Press LLC