Determination of the plasticizer N-butylbenzenesulfonamide and the pharmaceutical Ibuprofen in wastewater using solid phase microextraction (SPME)

A rapid, inexpensive and solvent-free method for the simultaneous determination of the polyamide plasticizer N-butylbenzenesulfonamide (NBBS) and the widely used pharmaceutical Ibuprofen by solid phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MSD) in wastewater samples was developed. Besides the optimized analytical conditions, results of investigations with varying analytical parameters are reported. Problems, which may occur during the analytical procedure (e.g. salt deposits, adsorption phenomena, carry-over), are discussed. For the determination of Ibuprofen, it is important to carry out the extraction under acidic conditions with sufficiently buffered samples; the GC/MSD system must be very clean and well maintained. SPME allows an extraction of Ibuprofen without derivatization of its carboxylic group. For quantification in complex matrices, the standard addition technique is necessary. Limit of detection and limit of determination are 0.1 μg/L for both analytes. NBBS and Ibuprofen were detected in several raw and treated wastewater samples from municipal wastewater treatment plants in the range from < 0.1 to 3.5 μg/L. Received: 13 March 1998 / Revised: 16 June 1998 / Accepted: 19 June 1998     

Optimization of in situ derivatization SPME by experimental design for GC-MS multi-residue analysis of pharmaceutical drugs in wastewater

This paper presents the development of a procedure, which enables the analysis of nine pharmaceutical drugs in wastewater using gas chromatography‐mass spectrometry (GC‐MS) associated with solid‐phase microextraction (SPME) for the sample preparation. Experimental design was applied to optimize the in situ derivatization and the SPME extraction conditions. Ethyl chloroformate (ECF) was employed as derivatizing agent and polydimethylsiloxane‐divinylbenzene (PDMS‐DVB) as the SPME fiber coating. A fractional factorial design was used to evaluate the main factors for the in situ derivatization and SPME extraction. Thereafter, a Doehlert matrix design was applied to find out the best experimental conditions. The method presented a linear range from 0.5 to 10 μg/L, and the intraday and interday precision were lower than 16%. Applicability of the method was verified from real influent and effluent samples of a wastewater treatment plant, as well as from samples of an industry wastewater and a river.     

Stir bar sorptive extraction for the analysis of short‐chain chlorinated paraffins in water

An optimised method using stir bar sorptive extraction (SBSE) and a thermal desorption‐GC‐electron capture detector (GC‐ECD) for the determination of short‐chain chlorinated paraffins from water samples was developed. Recoveries near to 100% were obtained by using 20 mm×0.5 mm (length×film thickness) PDMS commercial stir bars from 200 mL spiked water samples and 20% methanol addition with an extraction period of 24 h. Method sensitivity, linearity and precision were evaluated for surface water and wastewater spiked samples. A LOD of 0.03 and 0.04 μg/L was calculated for surface and wastewater, respectively. The precision of the method given as an RSD was below 20% for both matrices. The developed method was applied for the analysis of two real samples from a contaminated river and a wastewater treatment plant. Results were in accordance with those obtained using a previously developed method based on solid phase microextraction (SPME).     

Application of solid-phase microextraction and gas chromatography-mass spectrometry for the determination of chlorophenols in leather

This paper proposes a new analytical procedure based on the headspace solid‐phase microextraction (HS‐SPME) technique and gas chromatography‐selected ion monitoring‐mass spectrometry (GC‐SIM‐MS) for the determination of 16 phenols extracted from leather samples. The optimized conditions for the HS‐SPME were obtained through two experimental designs – a two‐level fractional factorial design followed by a central composite design – using the commercial SPME fiber polyacrylate 85 μm (PA). The best extraction conditions were as follows: 200 μL of derivatizing agent (acetic anhydride), 20 mL of saturated aqueous NaCl solution and extraction time and temperature of 50 min and 75°C, respectively. All optimized conditions were obtained with fixed leather sample mass (250 mg), vial volume (40 mL) and phosphate buffer pH (12) and concentration (50 mmol/L). Detection limits ranging from 0.03 to 0.20 ng/g, and relative standard deviation (RSD) lower than 10.23% (n=6) for a concentration of 800 ng/g (chlorophenols) and 1325 ng/g (2‐phenylphenol) in the splitless mode were obtained. The recovery was studied at three concentration levels by adding different amounts of phenols to the leather sample and excellent recoveries ranging from 90.0 to 107.2% were obtained. The validated method was shown to be suitable for the quantification of phenols in leather samples, as it is simple, relatively fast and sensitive.     

Determination of polycyclic aromatic hydrocarbons in aqueous samples by microwave assisted headspace solid-phase microextraction and gas chromatography/flame ionization detection

The novel pretreatment technique, microwave-assisted heating coupled to headspace solid-phase microextraction (MA-HS-SPME) has been studied for one-step in situ sample preparation for polycyclic aromatic hydrocarbons (PAHs) in aqueous samples before gas chromatography/flame ionization detection (GC/FID). The PAHs evaporated into headspace with the water by microwave irradiation, and absorbed directly on a SPME fiber in the headspace. After being desorbed from the SPME fiber in the GC injection port, PAHs were analyzed by GC/FID. Parameters affecting extraction efficiency, such as SPME fiber coating, adsorption temperature, microwave power and irradiation time, and desorption conditions were investigated.Experimental results indicated that extraction of 20 mL aqueous sample containing PAHs at optional pH, by microwave irradiation with effective power 145 W for 30 min (the same as the extraction time), and collection with a 65 μm PDMS/DVB fiber at 20 °C circular cooling water to control sampling temperature, resulted in the best extraction efficiency. Optimum desorption of PAHs from the SPME fiber in the GC hot injection port was achieved at 290 °C for 5 min. The method was developed using spiked water sample such as field water with a range of 0.1-200 μg/L PAHs. Detection limits varied from 0.03 to 1.0 μg/L for different PAHs based on S/N = 3 and the relative standard deviations for repeatability were <13%. A real sample was collected from the scrubber water of an incineration system. PAHs of two to three rings were measured with concentrations varied from 0.35 to 7.53 μg/L. Recovery was more than 88% and R.S.D. was less than 17%. The proposed method is a simple, rapid, and organic solvent-free procedure for determination of PAHs in wastewater.     

Determination of organic pollutants in coking wastewater by dispersive liquid–liquid microextraction/GC/MS

A method based on dispersive liquid–liquid microextraction coupled with GC/MS was developed for quantitative analysis of the major organic pollutants listed in the United States Environmental Protection Agency method 8270 and the 15 European‐priority polycyclic aromatic hydrocarbons in coking wastewater. The major parameters such as extraction solvent, dispersive solvent, solution pH, and extraction time were systematically optimized. The optimum extraction conditions were found to be: 15 μL mixture of 2:1 v/v carbon tetrachloride and chlorobenzene as the extraction solvent, 0.75 mL ACN as the dispersive solvent, solution pH of 8, and extraction time of 2 min. For the major pollutants listed in the United States Environmental Protection Agency 8270, the linear ranges were 0.1 to 100 mg/L, the enrichment factors ranged from 452 to 685, and the relative recoveries ranged from 67.5 to 103.5% with RSDs of 4.0–9.1% (n = 5) at the concentrations of 10 mg/L under the optimum extraction conditions. For the 15 polycyclic aromatic hydrocarbons, the linear ranges were 0.1 to 100 μg/L, the enrichment factors ranged from 645 to 723, and the relative recoveries ranged from 94.5 to 107.6% with RSDs of 4.6–9.0% (n = 5) at the concentrations of 10 μg/L. The usefulness of the developed method was demonstrated by applying it in the analysis of real‐world coking wastewater samples.     

Solid‐phase microextraction based on polyaniline doped with perfluorooctanesulfonic acid coupled to HPLC for the quantitative determination of chlorophenols in water samples

A porous and highly efficient polyaniline‐based solid‐phase microextraction (SPME) coating was successfully prepared by the electrochemical deposition method. A method based on headspace SPME followed by HPLC was established to rapidly determine trace chlorophenols in water samples. Influential parameters for the SPME, including extraction mode, extraction temperature and time, pH and ionic strength procedures, were investigated intensively. Under the optimized conditions, the proposed method was linear in the range of 0.5–200 μg/L for 4‐chlorophenol and 2,4,6‐trichlorophenol, 0.2–200 μg/L for 2,4‐dichlorophenol and 2–200 μg/L for 2,3,4,6‐tetrachlorophenol and pentachlorophenol, with satisfactory correlation coefficients (>0.99). RSDs were <15% (n = 5) and LODs were relatively low (0.10–0.50 μg/L). Compared to commercial 85 μm polyacrylate and 60 μm polydimethylsiloxane/divinylbenzene fibers, the homemade polyaniline fiber showed a higher extraction efficiency. The proposed method has been successfully applied to the determination of chlorophenols in water samples with satisfactory recoveries.     

Determination of organophosphorus pesticide residues in vegetables using solid phase micro-extraction coupled with gas chromatography–flame photometric detector

An adequate and simple analytical method based on solid-phase microextraction (SPME) followed by gas chromatography–flame photometric detection (GC–FPD) for the determination of eleven organophosphorus pesticide residues (i.e., ethoprophos, sulfotep, diazinon, tolclofos-methyl, fenitrothion, chlorpyrifos, isofenphos, methidathion, ethion, triazophos, leptophos) in vegetables samples (cabbage, kale and mustard) was developed. Important parameters that influence the extraction efficiency (i.e., fibre type, extraction modes, extraction time, salt addition, desorption time and temperature) were systematically investigated. Four types of commercially available fibres (i.e., 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS), 65 μm polydimethylsiloxane/divinylbenzene (PDMS/DVB), 100 μm polydimethylsiloxane (PDMS), and 85 μm polyacrylate (PA)) were evaluated. PA fibre exhibited the best performance and was used for the rest of the studies. The optimised extraction conditions were: extraction time, 30 min at room temperature; stirring speed, 1275 rpm; salt content, 10% NaCl; desorption time and temperature, 11 min at 260 °C; and no pH adjustment of the sample extract. The method was validated over the range 0.1–100 μg/L. Repeatabilities were satisfactory, ranging between 2.44% and 17.9% for all analytes. The limits of detection and quantitation ranged from 0.01 to 0.14 and 0.03 to 0.42 μg/L, respectively. The method was applied to twenty local vegetable (cabbage, kale and mustard) products. Chlorpyrifos (0.22–1.68 μg/kg) was the most detected pesticide in the tested samples. The obtained values are however lower than the Maximum Residue Limits (MRLs) as stipulated in the Food Act & Regulations of Malaysia.     

Application of solid-phase microextraction for the determination of pyrethroid residues in vegetable samples by GC-MS

A solid-phase microextraction (SPME) method has been developed for the determination of 7 pyrethroid insecticides (bifenthrin, lambda-cyhalothrin, permethrin, cyfluthrin, cypermethrin, fenvalerate, and tau-fluvalinate) in water, vegetable (tomato), and fruit (strawberry) samples, based on direct immersion mode and subsequent desorption into the injection port of a GC/MS. The SPME procedure showed linear behavior in the range tested (0.5-50 microg L(-1) in water and 0.01-0.1 mg kg(-1) in tomato) with r(2) values ranging between 0.97 and 0.99. For water samples limits of detection ranged between 0.1 and 2 microg L(-1 )with relative standard deviations lower than 20%. Detection limits for tomato samples were between 0.003 and 0.025 mg kg(-1) with relative standard deviations around 25%. Finally, the SPME procedure has been applied to vegetable (tomato) and fruit (strawberry) samples obtained from an experimental plot treated with lambda-cyhalothrin, and in both cases the analyte was detected and quantified using a calibration curve prepared using blank matrix. SPME has been shown to be a simple extraction technique which has a number of advantages such as solvent-free extraction, simplicity, and compatibility with chromatographic analytical systems. Difficulties with the correct quantification in a complex matrix are also discussed.     

Rapid wide-scope screening of drugs of abuse, prescription drugs with potential for abuse and their metabolites in influent and effluent urban wastewater by ultrahigh pressure liquid chromatography-quadrupole-time-of-flight-mass spectrometry

In the present work, a rapid method with little sample handling has been developed for determination of 23 selected volatile organic compounds in environmental and wastewater samples. The method is based on headspace solid-phase microextraction (SPME) followed by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) determination using triple quadrupole analyzer (QqQ) in electron ionization mode. The best conditions for extraction were optimised with a factorial design taking into account the interaction between different parameters and not only individual effects of variables. In the optimized procedure, 4 mL of water sample were extracted using a 10 mL vial and adding 0.4 g NaCl (final NaCl content of 10%). An SPME extraction with carboxen/polydimethylsiloxane 75 μm fiber for 30 min at 50°C (with 5 min of previous equilibration time) with magnetic stirring was applied. Chromatographic determination was carried out by GC-MS/MS working in Selected Reaction Monitoring (SRM) mode. For most analytes, two MS/MS transitions were acquired, although for a few compounds it was difficult to obtain characteristic abundant fragments. In those cases, a pseudo selected reaction monitoring (pseudo-SRM) with three ions was used instead. The intensity ratio between quantitation (Q) and confirmation (q) signals was used as a confirmatory parameter. The method was validated by means of recovery experiments (n=6) spiking mineral water samples at three concentration levels (0.1, 5 and 50 μg L(-1)). Recoveries between 70% and 120% were generally obtained with relative standard deviations (RSDs) lower than 20%. The developed method was applied to surface water and wastewater from a wastewater treatment plant and from a municipal solid-waste treatment plant. Several compounds, like chloroform, benzene, trichloroethylene, toluene, tetrachloroethylene, dibromochloromethane, xylenes and bromoform were detected and confirmed in all the samples analyzed.     

Gas chromatographic–mass spectrometric methodology using solid-phase microextraction for the multiresidue determination of pesticides in surface waters

Solid-phase microextraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS) and selected ion monitoring (SIM) was used for the analytical determination of priority pesticide residues. Fibers coated with a 65-µm film thickness of polydimethylsiloxane divinylbenzene (PDMS-DVB) were used to extract 31 pesticides of different chemical groups. The quality parameters of the method demonstrated a good precision with detection limits of 1–56?ng/L. Linearity was controlled in the range of 0.1–50?µg/L. The proposed method was applied for the trace-level determination of the target pesticides in surface water samples including three rivers and one lake at the Epirus region (north-west Greece) for a period of one year. The results demonstrate the suitability of the SPME–GC–MS approach for the analysis of multi-residue pesticides in environmental water samples.     

Low‐density solvent‐based vortex‐assisted surfactant‐enhanced emulsification liquid–liquid microextraction and its application

For the first time, the low‐density solvent‐based vortex‐assisted surfactant‐enhanced emulsification liquid–liquid microextraction, followed by GC‐flame photometric detection has been developed for the determination of eight organophosphorus pesticides in aqueous samples. A small volume of organic extraction solvent (toluene) was dispersed into the aqueous samples by the assistance of surfactant and vortex agitator. The extraction was performed in a special disposable polyethylene pipette, allowing using the reagents with lower density than water as extraction solvents. The influence parameters were systemically investigated and optimized: toluene (30 μL) and Triton X‐100 (0.2 mmol/L) were used as the extraction solvent and the surfactant, respectively, and the extraction was performed for 1 min under room temperature without adding sodium chloride. Under the optimum conditions, the validation parameters such as the RSD (n = 6; 2.1–11.3%), LOD (0.005 and 0.05 μg/L), and linear range (0.1–50.0 μg/L with correlation coefficients (0.9958–0.9992) showed the method was satisfying. The proposed method has been successfully applied to the determination of the organophosphorus pesticides in real samples with recoveries between 82.8 and 100.2%.     

Application of solid phase microextraction for the determination of soil fumigants in water and soil samples

The potential of solid phase microextraction (SPME) for the determination of the soil fumigants 1,3-dichloropropene (1,3-DCP) and methyl isothiocyanate (MITC) in environmental samples such as soil and water samples has been investigated. Direct immersion SPME followed by GC/ECD/NPD analysis allowed the rapid determination of the two fumigants in water samples, with very little sample manipulation, giving an LOD of 0.5 microg L(-1). Precision, calculated as relative standard deviation (RSD) for six replicates at three concentration levels, was found to be lower than 20% at the concentration levels tested. For the analysis of soil samples, headspace (HS)-SPME combined with GC/ECD/NPD analysis has been applied. Quantification using matrix-matched calibration curves allowed determination of both analytes (MITC and 1-3-DCP) with a LOD of 0.1 microg kg(-1) (RSD < 10%) for the two concentration levels assayed (0.02 and 0.2 mg kg(-1)). The HS-SPME procedure developed in this paper was applied to soil samples from experimental green house plots treated with metham-Na, a soil disinfestation agent that decomposes in soil to MITC. The absence of sample manipulation as well as the low solvent consumption in SPME methodology are among the main advantages of this analytical approach.     

Solid‐phase microextraction with a graphene‐composite‐coated fiber coupled with GC for the determination of some halogenated aromatic hydrocarbons in water samples

In this work, a graphene composite was coated onto etched stainless‐steel wire through a sol–gel technique and it was used as a solid‐phase microextraction (SPME) fiber. The prepared fiber was characterized by SEM, which revealed that the fiber had a highly porous structure. The application of the fiber was evaluated through the headspace SPME of five halogenated aromatic hydrocarbons (chlorobenzene, bromobenzene, 1,3‐dichlorobenzene, 1,2‐dichlorobenzene, and 1,2,4‐trichlorobenzene) in water samples followed by GC with flame ionization detection. The main factors influencing the extraction efficiency, including headspace volume, extraction time, extraction temperature, stirring rate, ionic strength of sample solution, and desorption conditions, were studied and optimized. Under the optimum conditions, the linearity of the method ranged from 2.5 to 800.0 μg/L for 1,2,4‐trichlorobenzene and from 2.5 to 500.0 μg/L for chlorobenzene, bromobenzene, 1,3‐dichlorobenzene, and 1,2‐dichlorobenzene, with the correlation coefficients (r) ranging from 0.9962 to 0.9980, respectively. The LODs (S/N = 3) of the method for the analytes were in the range between 0.5 and 1.0 μg/L. The recoveries of the method for the analytes obtained for the spiked water samples at 50.0 and 250.0 μg/L were from 76.0 to 104.0%.     

Rapid determination of bisphenol A in drinking water using dispersive liquid‐phase microextraction with in situ derivatization prior to GC‐MS

This paper described a novel approach for the determination of bisphenol A by dispersive liquid‐phase microextraction with in situ acetylation prior to GC‐MS. In this derivatization/extraction method, 500 μL acetone (disperser solvent) containing 30.0 μL chlorobenzene (extraction solvent) and 30.0 μL acetic anhydride (derivatization reagent) was rapidly injected into 5.00 mL aqueous sample containing bisphenol A and K₂CO₃ (0.5% w/v). Within a few seconds the analyte was derivatized and extracted at the same time. After centrifugation, 1.0 μL of sedimented phase containing enriched analyte was determined by GC‐MS. Some important parameters, such as type and volume of extraction and disperser solvent, volume of acetic anhydride, derivatization and extraction time, amount of K₂CO₃, and salt addition were studied and optimized. Under the optimum conditions, the LOD and the LOQ were 0.01, 0.1 μg/L, respectively. The experimental results indicated that there was linearity over the range 0.1–50 μg/L with coefficient of correlation 0.9997, and good reproducibility with RSD 3.8% (n = 5). The proposed method has been applied for the analysis of drinking water samples, and satisfactory results were achieved.     

PDMS extraction bars for the determination of volatile aromatic hydrocarbons in water and wastewater

In this study, the preparation and application of extraction bars of PDMS were investigated to preconcentrate and determine benzene, toluene, ethylbenzene, and xylene in water and wastewater by means of HPLC with fluorescence detection. Aliquot samples from hospital wastewater were used as the model effluent. The independent variables for the sorptive extraction were as follows: ionic strength (added amounts of NaCl); pH; temperature and time of absorption; temperature and time of desorption. Under optimized conditions, by using a factorial design, the suspended extraction bars could allow the determination of benzene, toluene, ethylbenzene, and xylene (1.20 ± 0.05 μg/L; 10.40 ± 0.02 μg/L; 1.80 ± 0.04 μg/L; 15.9 ± 0.04 μg/L, respectively) in hospital effluent (fortified samples), by recoveries of 71.9 ± 4.9 to 74.8 ± 5.6%. This procedure represents an innovation that eliminates the time‐consuming stage of vacuum microfiltration, and allows the determination of volatile organic compounds by HPLC. As far as we know, this procedure is original and represents an important contribution to the field.     

Determination of organophosphorus insecticides in natural waters using SPE-disks and SPME followed by GC/FTD and GC/MS

Two methods for the analysis of ten organophosphorus insecticides in natural waters using solid phase extraction disks containing C₁₈ and SDB and solid phase microextraction fibers containing polyacrylate (PA) are developed. Bromophos ethyl, bromophos methyl, dichlofenthion, ethion, fenamiphos, fenitrothion, fenthion, malathion, parathion ethyl and parathion methyl were determined by GC/MS and GC/FTD. The SPE-disks require only 1000 mL of sample and provide a method limit of detection in the range of 0.01–0.07 μg/L and recovery rates from 60.7 to 104.1%. The solid phase microextraction (SPME) technique requires 2–5 mL of water sample and provides a method limit of detection in the range of 0.01 to 0.05 μg/L for all detectors and the recoveries compared to distilled water ranged from 86.2 to 119.7%. The proposed methods were applied to the trace level screening determination of insecticides in river water samples originating from different Greek regions.     

Speciation of inorganic and tetramethyltin by headspace solid‐phase microextraction and gas chromatography–mass spectrometry

A headspace solid‐phase microextraction (HS‐SPME) method coupled to GC‐MS was developed in order to determine trace levels of tetramethyltin (TeMT) and inorganic tin (iSn) after ethylation to tetraethyltin (TeET) in various matrices. The derivatization of iSn and the extraction of both TeMT and iSn as TeET were performed in one step. Sodium tetraethylborate (NaBEt₄) was used as derivatization agent and the volatile derivatives were absorbed on a PDMS‐coated fused silica fiber. The conditions for the HS‐SPME procedure were optimized in order to gain in repeatability and sensitivity. Several critical parameters of GC‐MS were also studied. The detection of TeMT and iSn as TeET peaks was performed by the SIM mode. The precision of the proposed method is satisfactory providing RSD values below 10% for both tin species and good linearity up to 10 μg/L. The developed method was successfully applied to the determination of tin species in several samples like canned fish, fish tissues, aquatic plants, canned mineral water and sea water. The proposed HS‐SPME‐GC‐MS method was proved suitable to monitor the concentration levels of toxic tin compounds in environmental and biological samples.     

Solid-phase microextraction of N-nitrosamines

A method was developed for the extraction of seven N-nitrosamine compounds from water by solid-phase microextraction (SPME). The method developed requires a total analysis time of only 1.25 h for both extraction and detection (versus 3-20 h for other isolation techniques). Three gas chromatography (GC) detection systems were tested with the SPME method, nitrogen chemiluminesence detection (NCD), nitrogen-phosphorus detection (NPD) and chemical ionization mass spectrometry (CI-MS), with method detection limits (MDLs) found in the ng/L range. This method was used to analyze wastewater samples and showed excellent selectivity of extraction. The detection limits of this method for N-nitrosodimethylamine (NDMA) range from 30 to 890 ng/L as a function of detector type. The excellent selectivity of SPME in addition to the fast analysis time would make this method ideal for general surveys, wastewater analysis and laboratory studies (e.g. degradation kinetics or formation potential).     

A convenient method for epichlorohydrin determination in water using headspace-solid-phase microextraction and gas chromatography

A simple procedure for epychlorohydrin determination in water is presented. In order to optimize the epichlorohydrin extraction conditions in water using headspace (HS)-solid-phase microextraction (SPME), followed by gas chromatography, an experimental design in two steps is performed. Firstly, a 2(5-2) fractional factorial design for screening the significant variables is used. Secondly, a central composite design for optimizing them is carried out. The best experimental conditions are the followings: poly(dimethysiloxane)-divinylbenzene coating fiber; 20 min extraction time; 5 degrees C extraction temperature; 300 g/L sodium chloride; and 20 mL HS volume in a 40-mL vial. Using the previous extraction conditions with gas chromatography (GC)-flame ionization detection equipment, a limit of detection (LOD) of 1.8 microg/L and a relative standard deviation (RSD) of 3.8% (for 25 microg/L) are obtained. With a GC electron capture detection equipment the RSD is 6.6% (for 5 microg/L), and the LOD found is lower (0.08 microg/L). The method is applied to the analysis of water from four treatment plants at the entrance and effluent stream. The standard addition method is used to quantitate the epichlorohydrin that is found in the raw water of the three wastewater treatment plants.