Anal. Chem. 1980. 52, 2076-2079
2076
Determination of Arenes, Vinyl Chloride, and Other Volatile Haloorganic Compounds in Water at Microgram-per-Liter Levels by Gas Chromatography Rajlnder S. Narang" and Brian Bush Division of Laboratories and Research, New York State Department of Health, Albany, New York 12201
Arenes, vlnyl chloride, and other volatile haloorganic compounds were stripped from water and absorbed on Porapak N in a closed system. They were eluted wRh methanol. The volatile haloorganic compounds were separated by gas chromatography on a 3-m Chromosorb 102 column. Other approprlate columns and a photolonlration detector were used for the anaiysls of vlnyl chloride and the arenes, wfth detection limits of 1 bg/L for ail the compounds.
I n recent years several types of methods have been developed to analyze water for volatile compounds. Impurities have been recovered from head space above a heated sample (1, 2 ) a n d analyzed by gas chromatography with electron capture (EC) detection. Water has been injected directly into a gas chromatograph, and its halogenated organic contaminants were detected with a n EC detector ( 3 ) . T h e main drawback of these methods is that most EC detectors lose their responsiveness when used with aqueous samples. Gas sparging methods (4) are slow and cannot be automated. In the method developed by Grob ( 5 ) organic substances are stripped from water at varying temperatures in a closed system, transferred t o a charcoal adsorbent cartridge, and eluted with carbon disulfide. This method works very well for high-boiling compounds, but recoveries are poor for volatile compounds. Furthermore, t h e solvent used is not compatible with either EC or photoionization (PI) detectors. T h e method we describe is based on Grob's closed-system stripping, b u t the absorbent and eluting solvent have been modified. T h e solvent used is compatible with both EC and PI detectors; i t also makes the procedure semiautomatic because autosamplers can be used on the gas chromatograph. We have extended the method to analysis of various arenes and, with slight modification, to analysis of vinyl chloride, both at microgram per liter levels. E X P E R I M E N T A L SECTION Apparatus. In the system shown in Figure 1,the circulating vapor contacts nothing but stainless steel and glass. The stainless-steel bellows pump (Metal Bellows Corp., Sharon, MA) forces the head space above the sample through the glass adsorption tube (15 cm X 0.62 cm i.d.) at a flow rate of 250 mL/min. The adsorption tube is packed with 2.5-4 cm of Porapak N, 8&100 mesh (Analabs Inc., Milford, MA) sandwiched between plugs of glass wool. The 5-mL graduated tubes used for measuring elution volumes were standardized by weighing 1 g of water in each tube. Those tubes whose l-mL mark deviated from the true volume were discarded. Recovered halogenated organic compounds were analyzed with a Hewlett-Packard 7600 gas chromatograph equipped with an EC detector. A PI detector (HNU Systems, Newton Upper Falls, MA) was fitted to the oven of the chromatograph and connected to the electrometer (Hewlett-Packard Model 7650 A) of the flame ionization detector. Various mixtures were separated on 3 m X 3 mm i.d. columns of silanized Chromosorb 102,2 m X 3 mm i.d. columns of Porapak T, and 2 m X 3 mm i.d. columns of 20% SE-30 0003-2700/60/0352-2076$01 .OO/O
on Gas Chrom Q. When the EC detector was used, chromatograms were recorded with a Hewlett-Packard 3385 automation system. Reagents. The methanol used for extraction was purified by distilling spectro- or nanograde solvent through a l-m Vigreux column at a rate of 60 mL/h. Fractions (150 mL) were collected and checked for interfering substances by the gas chromatographic procedures used for the analysis. Fractions contributing less than 1% to the base line were combined and used for elution. Chromosorb 102 was silanized by treatment with 20% trimethylchlorosilane in toluene for 1 h. It was then filtered and washed, first with toluene and then with methanol, until the filtrate was neutral. The adsorbent tubes of required length are prepared by using conditioned Porapak N, which is prepared by conditioning overnight in 5 cm X 30 cm tubes at 180 "C with a carrier gas flowing through it (He, 20 mL/min). These tubes are washed with methanol (50 mL) under gentle vacuum and reconditioned at 170 "C for 45 min with He (20 mL/min) flowing through them. These tubes are allowed to cool in a solvent-free place and capped with polyethylene caps until ready to use. After each use the tubes are regenerated first by washing with methanol (30 mL) under gentle vacuum followed by conditioning at 170 "C for 45 min with He (20 mL/min) flowing through them. Gas Chromatography. The halogenated volatile materials frequently encountered in New York State were all separated on a 3 mm X 2 mm i.d. column of silanized Chromasorb 102 (argon/methane 955; flow rate, 20 mL/min; column temperature, 170 "C; 63Nidetector, 300 "C; injector, 190 "C). Arenes were separated on a 2 m x 2 mm i.d. column of 20% SE-30 on Gas Chrom Q (column temperature, 40-60 "C at 4 "C/min; injector, 190 "C; helium flow rate, 30 mL/min) and detected with a PI detector (HNU Systems, Newton Upper Falls, MA) at 200 "C. Vinyl chloride was determined on a Porapak T column (80-100 mesh; 2 m X 2 mm i.d.) a t 90 "C (helium flow rate 30 mL/min) with the injection heater switched off, it was detected by PI. Haloorganic compounds were quantitated with the HewlettPackard 3385 automated system, which integrated the peaks with integration function 1 (base line fixed after initial solvent peak; vertical drop from valleys between partially fused peaks). The PI peaks for arenes and vinyl chloride were measured manually; areas were calculated by multiplying the peak height by the width at half-peak height. Stripping Procedures. Assays f o r Haloorganic Compounds and Arenes. The graduated impinger was rinsed twice with the sample at 4 "C and filled to the 50- or 1WmL mark. It was placed in a constant-temperature water bath at 45 "C and connected to the circulating system with Swagelock fittings. During stripping the impinger top should be clamped in place to prevent blowoff. After the sample reached thermal equilibrium (approximately 5 min), the pump was run for 15 min. The adsorption tube was removed from the apparatus and suspended vertically from a clamp so that the bottom of the adsorption tube was near the 2-mL mark of a 5-mL graduated centrifuge tube. Redistilled methanol was then passed through the tube, and the volume collected by gravity elution (1-1.5 mL) was measured. Assays for Vinyl Chloride. The absorption tube was cooled to 0 "C with a thermoelectric cooling unit for 5 min before it was connected to the stripping system. The centrifuge tube was chilled in a methanol-ice mixture contained in a Dewar flask, and the measured eluate was analyzed immediately. 0 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 13, NOVEMBER 1980
2077
Table I. Volume of Collected MeOH Required to Elute Various Compounds from Porapak N Adsorption Tube % recovery
MeOH collected fraction mL I I1 I I1 I I1 I I1
m- or p -
CHC1,
0.5 0.5 0.7 0.5 0.8 0.5 0.9 0.5
I
1.00
I1
0.5
CH,CCl, C,HCl,
97 3 97
99
CHBrC1, C,Cl,
CCI,
benzene
100
100
99
toluene
xylene
o-xylene
98
100
89
100
100
100
98
98
99
95 5 99
99
95 5 99
96
98
98
99
99
100
100
100
100
100
97
98
98
99
99
100
100
100
100
100
100
97
98
98
98
98
100
100
100
100
Table 11. Recoveries of Various Haloorganic Compounds (5%)" spike (vg/L)
Mean
CH,CCl,
93.0 t 8.3 96.5 t 7.6 86.3 t 7.0 87.3 ?r 3.6 87.0 5 3.4
1 2 5 10 20 a
CHCl,
fr
92.0 fr 84.3 t 95.3 f 92.3 fr 93.5 r
3.6 1.3 6.2 3.6 1.7
C,HCl, 81.0 94.3 94.8 91.8 91.3
?r
fr f
i f
4.2 7.5 7.5 2.9 3.0
CHBrCl, 104.3 100.8 98.0 97.3 97.3
fr f
fr
fr fr
8.3 8.3 6.2 1.0 5.3
C,CL 93.0 99.5 93.5 96.3 96.5
f f f f
f
CCl, 3.4 6.2 3.3 3.0 3.5
76.0 92.0 94.3 100.3 88.5
f
fr t ?r
t
4.9 8.3 1.5 6.8 6.0
standard deviations for four strippings at each concentration.
W
2
Qa
AIRFLOW-
W
a
e
SWAGELOK
0
W In W
WATER BATH
-FRI
145') 0
15
30
MINUTES
B PORAPAK N
-2
GLASS WOOL
5 - 3 cm-
Flgure 1. (A) Assembled stripping apparatus. (B)Glass adsorption tube packed with Porapak N.
Standardization. A stock solution of each haloorganic compound or arene (100 mg/L methanol) was prepared and then diluted with water to produce a range of concentrations typical of the types of water samples to be examined. At least five calibration points were obtained before the unknown samples were analyzed. During a series of analyses,every tenth sample stripped was a standard aqueous solution. Standard solutions of vinyl chloride (10 mg/L in methanol) were made up by the method of Fujii (6). Vinyl chloride (0.500 mL at STP)was measured with a gastight syringe and injected into 125 mL of methanol contained in a 125-mL septum-sealed bottle.
RESULTS AND DISCUSSION T h e minimum volume of methanol required to elute each of the various compounds (Table I) from the Porapak N absorption tube was established by stripping 100 m L of a n approximately 20 pg/L solution onto the tube. The tube was eluted with methanol, and two fractions were collected. The
Flgure 2. Separation of haloorganic compounds on silanlzed Chromo& 102. The peaks are as follows: (1) trans-l,2dichloroethylene, (2) 1,1,2-trichlorotrifluoroethane, (3) chloroform, (4) 1,2dichloroethane, (5) l,l, 1-trichbroethane,(6) carbon tetrachloride, (7) trichloroethylene, (8) bromodichloromethane, (9) 1,1,2-trichIoroethane, (10) tetrachioroethylene.
first fractions were of varying volumes; the second was 0.5 mL for every compound. Recoveries of various haloorganic compounds are shown in Table 11, and a chromatogram of all the haloorganic compounds found in New York State waters is shown in Figure 2. Figure 3 shows chromatograms of well water from a polluted area of Long Island and of a chlorinated surface water. The complete separation of l,l,l-trichloroethane, carbon tetrachloride, and trichloroethylene is difficult, but the separation shown is sufficient for quantitation by vertical-drop area measurement. A typical chromatogram of methanolic strippings from a water blank and from 100 m L of water spiked with 0.5 pg of vinyl chloride is shown in Figure 4. Methanol and water, for some unknown reason, gives a negative response on a PI detector. Chromatograms of the volatile arenes are shown in Figure 5. The recovery efficiency for benzene was determined after subtracting the small peak caused by an interfering material in the distilled water used for dilution. If the benzene concentration alone is required and there is no interfering sub-
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pj
ANALYTICAL CHEMISTRY, VOL. 52, NO. 13, NOVEMBER 1980 Polluted well water
p W VI
P W
W
U J
z
0
L
n
0
v)
MINUTES
W [L
Chlorinated surface wale1
v II
W lJ
i
I
15
Flgure 4. Chromatograms of (A) strippings from 100 mL of unspiked water and (B) smppings from 100 mL of water spiked with vinyl chloride (5 pg/L) on a Porapak T column.
a
0 t-
o W
tW
P
3 v, W
z
0
a
v, W E IT W u
IW
0
MINUTES
Figure 3. Haloorganic compounds from polluted well water and chlorinated surface water chromatographed on silanized Chromosorb 102. The peak numbers corresponds to identical peaks in Figure 2, except that peaks 11 and 12 are unidentified.
MINUTES
% meta t
% xylene
(pg/mL)
rneta
para
% calcd
para found
%error
1 2 3 4 5
9.8 17.8 25.1 33.0 40.2
9.8 18.7 27.9 35.3 44.5
19.6 36.5 52.3 68.3 84.7
19.2 34.03 52.3 68.5 83.5
2.0 6.0 0.0 0.2 1.5
8
Flgure 5. Chromatograms of arenes on 20% SE-30. (A) Strippings from 100 mL of blank distilled water gave peak 1. The methanolic solution from 1, spiked with 0.5 pg of benzene/mL, gave peak 2. Strippings from 100 mL of water spiked with 5 pg of benzene/L gave peak 3. (e) The peaks are (4) o-xylene, (5) rn- and p-xylene, and (6) toluene.
Table 111. Photoionization Response of Xylenes spike
I
I
0
method with one automated chromatograph. No one column or detector is suitable for all compounds. Mass spectrometry might be suitable for universal detection, and with multiple-ion monitoring only one column might accomplish the entire analysis a t the required sensitivity. However, many laboratories have only limited access to mass spectrometers, and the pure gas chromatographic method is a useful alternative. Our data show t h a t application of the relatively new PI detector to strippable substances with low electron-capturing properties yields reliable results, with detection limits well below those of the conventional flame ionization detector (7), due in part t o its lack of sensitivity t o methanol. The separation of sample preparation and analysis gives this method greater flexibility than many others. Several chromatographic examinations of the methanol extract can be made on different columns, if required, thus simplifying peak identification and analytical accuracy. In addition, more samples can be handled per day because the extracts can be analyzed on a 24-h basis with conventionally automated chromatographs.
stance, a Tenax GC column can be used for separation, but analysis of the other arenes is then not possible. Indeed, mand p-xylenes were not separated on the SE-30 column, but because their PI detector responses were almost identical (Table HI), their recovery could be determined from the combined peak. Recoveries for vinyl chloride and the arenes are given in Table IV. T h e main aim of this work was to develop a stripping method compatible with a conventional, automated liquid injector for a gas chromatograph so that the efficiency of analysis would be optimized by separating the stripping from the analysis step. This has been achieved, and the range of compounds which can be determined has been demonstrated. Closed-circuit stripping, trapping with Porapak N, and elution with methanol have proven t o be a workable, trouble-free procedure. Twenty-five samples a day can be analyzed by this Table IV. Recoveries of Vinyl Chloride and Various Arenes (%)" spike (pg/L) 5
10 20 a
Mean
f
vinyl chloride 96.0 r 9.8 94.0 f 4.5 93.0 * 6.2
benzene 96.0 101.0 93.0
k
f
t
5.5 3.8 2.5
toluene
o-xylene
91.5 t 1.7 91.7 k 4.6 89.8 ? 6.1
91.8 f 2.4 94.3 i 6.2 90.3 f 4.6
standard deviation for three strippings at each concentration.
m-/p-xylene 92.3 91.0 89.3
f
f f
2.1 7.8 4.8
Anal. Chem. 1980, 52,2079-2083
ACKNOWLEDGMENT We thank Ron Pause for generating spectra of polluted well water samples a n d Terry Fuller for technical assistance.
LITERATURE CITED (1) Bush, B.: Narang, R . S.: Syrotynski, S. Bull. Environ. Contam. Toxicol. 1977, 18, 436. (2) Kaiser. K. L. E.; Oliver, 8 . G. Anal. Chem. 1976, 48, 2207.
2079
(3) Nicholson, A. A.; Meresz, 0. Bull. Environ. Contam. Toxicol. 1975, 14, 453. (4) Bellar, T. A.; Lichtenberg. J.; Kroner, R . C. J . Am. Wafer Works Assoc.
1974, 703. (5) &ob, K.: Gob, J. J . Chromatogr., 1974, 90, 303. (6) Fujii. T. Anal. Chem. 1977, 49, 1985. (7) Driscol, J. N. J . Chromatogr. 1977, 49, 134.
RECEIVED for review March 12,1980. Accepted July 25,1980.
Comparison of Three Commercially Available Gas Chromatographic-Flame Photometric Detectors in the Sulfur Mode J. F. McGaughey' and S. K. Gangwal' Energy, Engineering and Environmental Sciences Group, Research Triangle Institute, Research Triangle Park, North Carolina 27709
Three commercially available flame photometrlc detectors (FPD) in the sulfur mode have been evaluated by Comparing the parameters of dynamic range, llnearky, minimum detection limn, sensitivity, peak shape, selecthrity, and ease of operation. Sulfur compounds used for this study included hydrogen sulflde, carbonyl sulflde, and sulfur dioxide. The experimental parameters were kept as nearly Identical as possible for the three systems wnh only minor equipment modlfications belng necessary. The selection of an FPD should be based on the intended use because none of the systems proved to be superior In all categories.
Accurate determination of low levels of sulfur gases has received considerable attention in recent years (1-15). Usually, the measurement device of choice has been the flame photometric detector (FPD) since its introduction by Brody and Chaney (1) in 1966. In combination with a gas chromatograph (GC), the F P D has become a significant tool for determining individual sulfur gases because of its sensitivity and specificity (2-8). T h e Research Triangle Institute (RTI) has been involved for several years in the determination of sulfur gases [specifically hydrogen sulfide (H,S), carbonyl sulfide (COS), and sulfur dioxide (SO,)] in concentrations ranging from parts per billion to low percent levels. One of the authors recently described the applicability of a novel F P D to the analysis of sulfur emissions from emerging energy technologies (9). RTI also conducts outdoor smog chamber experiments that require the determination of parts per million to parts per billion levels of these sulfur gases. Additionally, RTI, under contract to government and private organizations, carries out both fugitive a n d stack emission measurements from many industries. These analyses constitute a wide range of sulfur concentrations a n d prompted the present instrument study. Three commercial FPDs are currently in use at RTI. Experiments comparing the three systems were conducted to determine the most suitable system to be used for each specific application. I t is believed t h a t the results of this study will aid other investigators in avoiding some of the pitfalls (10-14) Present address: TRW, Inc., Energy Systems Group, Environmental Engineering Division, Research Triangle Park, NC 27709. 0003-2700/80/0352-2079$01 .OO/O
Table I. Cylinder Concentrations label concn (ppm in nitrogen)
measd concn
6.45 100.00
7.03 100.00
4.09 84.60 6.41 95.20
1.12 50.80
50.40
low H,S high H,S
low cos high COS low so, high SO,
(ppm in
nitrogen)
1.12
of F P D (e.g., nonlinearity and compound dependence) and will allow them to advantageously use these instruments for measurement of sulfur gases.
EXPERIMENTAL SECTION FPD. The three systems used in this study were a Varian-3700 FPD (Varian Associates, Walnut Creek, CA), a Perkin-Elmer-3920 FPD (Perkin-Elmer Corp., Norwalk, CT), and a Tracor-560 FPD (Tracor Instruments, Austin, TX). The Perkin-Elmer system had been in use the longest (14 months) at the time of this study. The Varian FPD can be used as both a single- and a dual-flame detector as described by Patterson et al. (15,161. The PerkinElmer and Tracor systems are single-flame detectors. In addition, the electrometer for the Varian instrument is equipped with two filter time constants: 0.2 and 1.2 s. The electrometer was preset at the factory at the lower value and was used throughout this study. The larger value is intended to be used only rarely and in unusually high noise situations. The 0.2-9 mode is necessary in order to detect early peaks with rapidly changing slopes, which was the situation in this study. The Perkin-Elmer or Tracor electrometers do not have this option and the time constant is not specified in the manuals, but presumably they have a time constant comparable to that of the Varian electrometer. GC Column, Gases and Standards. A 6 f t (1.8 m) X 1/8 in. (0.32 cm) 0.d. Teflon (FEP) column packed with Carbopack B/1.5% XE-60/1% H3P04obtained from Supelco, Inc. (Bellefonte, PA), was used for all measurements. Grade 0.5 helium and grade 0.1 hydrogen obtained from Airco (Research Triangle Park, NC) were used as the carrier and fuel gas, respectively. A Bendix (Louisberg, WV) clean air system was used to provide dry hydrocarbon-free air to the detectors. The standard gases used for this evaluation were H2S, COS, and SOz. These were contained in compressed gas cylinders with nitrogen as the balance gas. The concentration of each cylinder was certified by Scott Environmental Technology (Plumsteadville, PA) to within *2%. These concentrations were verified with a 0 1980 American Chemical Society
