Anal. Chem. 1984, 56, 1281-1285 Artr, R. J.; Schweighardt, F. K. J . Ll9. Chromafogr. IS80, 3 , 1807. Selucky, M. L. Anal. Chem. 1983, 55, 141. Klesment, I. J. Chromafogr. 1974, 97, 705. Hettmann, E., Ed. “Chromatography: A Laboratory Handbook of ChromatOaraDhlC and ElectroDhoretic Methods”, 3rd ed.; Van NostrandReinthd! New York, 1975; p 179. (30) Strothers, J. B. “Carbon-13 Nmr Spectroscopy”; Academic press: New York, 1972; p 70. (31) Latter, S. R.; Solli, H.; Douglas, A. G.; DeLange, F.; DeLeeuw, J. W. Nature (London) 1979, 279, 405. (32) Bellamy, L. J. “The Infrared Spectra of Complex Molecules”, 3rd ed.;
(26) (27) (28) (29)
1281
Chapman and Hall: London, 1975; Vol. 1. (33) Ben, G. B.; Harvey, T. G.; Matheson, T. W.; Pran, K. C. Fuel 1983, 62, 1445.
RECEIVED for review July 11, 1983. Resubmitted December 12,1983. Accepted February 21,1984. This work was supported by the National Energy Research, Development and Demonstration Council of Australia.
Determination of Aldicarb, Aldicarb Oxime, and Aldicarb Nitrile in Water by Gas ChromatographyIMass Spectrometry Michael L. Trehy and Richard A. Yost*
Department of Chemistry, University of Florida, Gainesville, Florida 32611 John J. McCreary
Department of Environmental Engineering Science, University of Florida, Gainesville, Florida 32611
A technlque for the analysls of aldlcarb and two of Its degradation products is described, The use of a short caplilary column coupled to a mass spectrometer Is found to facllltate the analysis of the thermally labile carbamate pestlclde. Methane and lsobutane chemlcai ionization reagent gases are evaluated. The llmlts of detection for aldlcarb, aidlcarb oxime, and aldlcarb nltrlle are 0.3 ng, 1.2 ng, and 0.15 ng, respectively. Application of the technlque to the study of the fate of aldlcarb In anaeroblc groundwaters Is described. Aldicarb Is found to slowly hydrolyze to aidicarb oxime in sterile anaerobic groundwater at pH 8.2; in the presence of a hlgh concentrationof anaeroblc mlcroorganisms, however, aldlcarb rapidly degrades to aidicarb nltrlie.
Aldicarb is a carbamate pesticide manufactured by Union Carbide and sold under the trademark Temik. Analysis for aldicarb and its degradation byproducts is of concern since aldicarb is extensively used in agriculture and has been detected in groundwaters in agricultural areas (1). This report describes a GC/MS method to selectively detect aldicarb (I) (2-methyl-2-(methylthio)propanal0-[(methylamino)carbonyl]oxime), aldicarb nitrile (11) (2-methyl-2(methylthio)propanenitrile), and aldicarb oxime (111) (2methyl-2-(methylthio)propanaloxime). Aldicarb oxime and aldicarb nitrile are found to be the major byproducts of aldicarb formed in spiked anaerobic water samples.
c H3
H
I
I
CH,SCCH=NOCNCH,
I
I1
0
CH, 1
CH,
I
CH3SCCSN
I
CH, I1
CH3
I
CH,SCCH=NOH
I
c H, 111
Methods which have been reported for the analysis of aldicarb include thin-layer chromatography (TLC) (2,3), liquid chromatography (LC) with various detectors (mass spectrometer (4), ultraviolet detector ( 5 ) )and postcolumn derivitization and fluorometric detection (6, 7)), and gas chromatography (GC) with various detectors (Hall detector (8), mass spectrometer (GC/MS) (9), flame ionization detector (2), and esterification and detection with an electron capture detector (10)). Only the LC and TLC methods avoid degra0003-2700/84/0356-1281$01.50/0
dation of aldicarb. Aldicarb is thermally labile and rapidly degrades in the injection port or on the column in all the GC methods reported. The thermal degradation product of aldicarb has been identified as aldicarb nitrile by matching the retention time with that of a synthesized standard on a Carbowax 20M packed column (2). Mass spectra obtained in this study for the thermal degradation of aldicarb observed on a 30-m Carbowax 20M capillary column are consistent with their identification. The use of short columns to facilitate faster analyses and to avoid thermal degradation has been reported (11,12). A 1-m SE-30 packed column has been used for the analysis of carbaryl residues in foods with some success (12). Here we show that this approach can minimize degradation of aldicarb, permitting the detection of aldicarb itself. A major drawback to the use of GC methods for the analysis of aldicarb is that aldicarb not only degrades during the GC analysis to aldicarb nitrile, but may also degrade chemically in the environment to aldicarb nitrile. Thus, if aldicarb nitrile is not removed prior to GC analysis by a Florisil separation (13), this environmental degradation product will give a positive interference for aldicarb. The formation of aldicarb nitrile from aldicarb in environmental samples has been suspected (14) although only the oxidized forms of the nitrile have been detected in aerobic systems. It has been found that from 3 to 12% of the aldicarb applied degrades to either 2-methyl-2-(methylsulfinyl)propanenitrile or 2-mesyl-2methylpropanenitrile in potatoes (10%) (15),soils (5%) (16)) sugar beets (5%) (141, and aqueous cultures of soil fungi (3 to 11% depending on type of soil fungus) (17).
EXPERIMENTAL SECTION Apparatus. A Finnigan gas chromatograph/triple-stage quadrupole mass spectrometer/data system was used in this study. Electron energies of 70 and 100 eV were used for electron ionization (EI)and chemical ionization (CI),respectively. The chemical ionization reagent gas was methane or isobutane at an ionizer pressure of 107 Pa. The mass spectrometer was tuned with FC43 (perfluorotributylamine). The E1 spectra for aldicarb and aldicarb oxime were similar to those in the NBS library. Nitrogen collision gas was introduced at 0.23 Pa and collision energies were 10-20 eV for collisionally activated dissociation (CAD) spectra. The continuous dynode electron multiplier was operated at 850-900 V with the conversion dynodes at &3000 V. The gain was set for A/V. Selected ion monitoring for the 0 1984 American Chemical Soclety
1282
ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
nine positive ions (86,89, 116, 134, 150, 151, 202, 207, and 223) in a total scan time of 0.273 s was used for quantitative analysis. The capillary columns were inserted directly into the ion source. Reagents and Standard Compounds. Standards of aldicarb, aldicarb oxime, aldicarb sulfoxide,aldicarb oxime sulfoxide, and aldicarb sulfone were obtained from the U.S. EPA Pesticides & Industrial Chemicals Repository (MD-8),Research Triangle Park, NC 27711. Stock solution were prepared in methylene chloride and stored at 4 "C. Aldicarb nitrile was synthesized by using a published procedure (18). A 17.8-g sample of aldicarb was extracted from 416 g of Temik by two extractions with methanol (400 mL and 300 mL). The methanol extract was concentrated to 200 mL and then added slowly to 300 mL of distilled water. The precipitated white aldicarb crystals were collected on a Buchner funnel and washed with 20 mL of distilled water. Then 17 g of the extracted aldicarb was refluxed in a 250-mL round-bottom flask in 50 mL of cyclohexene for 67 h. The cyclohexene was separated from a lower layer of viscous oil and concentrated by evaporating the cyclohexene by passing a stream of air over the surface. The liquid residue was distilled under vacuum to obtain aldicarb nitrile with a boiling point of 71 "C at 5.2 kPa. Gas Chromatographic Conditions. [l] A 2.6-m fused silica bonded phase (J & W DB5, SE54 equivalent) capillary column operated at 14 kPa with helium as a carrier gas was used for the analysis of aldicarb and aldicarb oxime. Splitless injection was used with the sweep off for 30 s. The injection port was operated at 130 "C and a clean silanized glass insert was used to minimize loss of sample due to degradation and adsorption. The interface temperature was 135 "C and the column temperature was programmed from 40 to 100 "C at a rate of 20 "C/min after a hold of 1min. Aldicarb oxime eluted after 64 s while aldicarb eluted after 207 s. Ethyl benzoate, used as an internal standard, had a retention time of 76 s. [2] A 9-m fused silica DB5 capillary column was necessary to separate aldicarb nitrile from the solvent peak. Analysis for aldicarb nitrile was performed with the injection port at 60 "C and the interface at 100 "C. Splitless injection was used with the sweep off for 12 s. The column was programmed from 30 "C to 100 "C at 20 "C/min after a hold of 1 min. Helium was used as the carrier gas at a pressure of 28 kPa. Aldicarb nitrile had a retention time of 120 s. [3] A 30-m Carbowax 20M fused silica capillary column was employed for the evaluation of the thermal degradation products of aldicarb. Splitless injection was used with the sweep off for 30 s. The injection port was operated at 250 "C while the interface was maintained at 200 "C. The column temperature was programmed from 50 "C to 180 "C at 20 "C/min with an initial hold of 4 min and a final hold at 180 "C for 6 min. The helium carrier pressure was 98 kPa. Extraction Efficiencies. Aldicarb, aldicarb oxime, aldicarb sulfoxide, aldicarb oxime sulfoxide, and aldicarb sulfone were separately spiked into pH 5.7 buffered water at 10 to 30 ppm concentrations. Each aqueous sample was extracted with vigorous shaking for 2 min in a 250-mL separatory funnel with methylene chloride. The concentration of each compound in the aqueous layer was then determined by its UV absorption. Extraction efficiencies for aldicarb, aldicarb oxime, and aldicarb oxime sulfoxide were also evaluated on the basis of their concentrations in the organic layer as determined by GC/MS. Aldicarb sulfoxide and aldicarb sulfone were also evaluated by use of MS with direct probe sample introduction. Aldicarb nitrile did not absorb in the spectral range from 220 to 800 nm. Its extraction efficiency was determined by GC/MS analysis of spiked methylene chloride samples before and after partitioning with deionized water. The relative standard deviation for the analysis was 2.5%. Degradation Experiments. Aldicarb was spiked into either anaerobic well water containing approximately 2 ppm of hydrogen sulfide or into anaerobic well water containing approximately 8 ppm of oxygen. Anaerobic samples were prepared inside an "Atmos" bag with a stream of nitrogen gas constantly purging the bag. Samples for four experiments involving the fate of aldicarb in groundwater were set up: (1)sterile anaerobic groundwater at pH 8.2; (2) microorganism-enriched anaerobic groundwater at pH 6.8; (3) anaerobic groundwater with ground limestone from
-
Table I. Comparison of the Partition Coefficients Determined for Aldicarb and Five of Its Degradation Byproducts for Extraction of Water Samples with Methylene Chloride (This Study) with That Obtained by Using Chloroform (3) compound aldicarb aldicarb oxime aldicarb sulfoxide aldicarb oxime sulfoxide aldicarb sulfone aldicarb nitrile
methylene chloride 140 12 1.0
0.047 5.2 >190
chloroform 25.8 1.66
0.95 0.15 3.45
the Floridan aquifer at pH 7.0-7.4; (4) aerobic groundwater from a shallow well at pH 5.5. Each of the water samples was spiked with aldicarb at a concentration of 1-3 ppm. After various incubation periods, each water sample was extracted with methylene chloride in a rotary shaker for 30 min by using a 1 to 11.5 ratio of methylene chloride to water. The extracts were analyzed by GC/MS and via the direct probe.
RESULTS AND DISCUSSION Partition Coefficients. The partition coefficients obtained for the extraction of aqueous samples with methylene chloride are compared with those reported with chloroform (3) in Table I. The partition coefficients for the two different solvents were found to parallel one another closely. However, the extraction efficiency obtained for aldicarb sulfoxide by using a single extraction of spiked water with a 1:11.5 ratio of methylene chloride to water was considerably lower than that reported for two consecutive extractions using a 1:lO ratio (4). Efficient extraction of aldicarb sulfoxide has been reported for four consecutive extractions of water with chloroform if a ratio of 1:2 chloroform to water is used (8). In our experiments, for a single extraction with methylene chloride of water in a ratio of 1:11.5,aldicarb, aldicarb nitrile and aldicarb oxime were extracted with 99%, 102%, and 44% extraction efficiencies, respectively. Chromatography. Aldicarb partially degrades and gives a positive interference for aldicarb nitrile when an injection port temperature of 130 "C is used. However, aldicarb nitrile does not interfere with the analysis for aldicarb in this procedure because only a small portion of the aldicarb injected is degraded. The presence of the intact molecule is demonstrated by the appearance of the (M+ 1)+ion in methane and isobutane CI and by matching the E1 spectra obtained with that of standards, as shown in Figure la-c. Analysis for the intact aldicarb molecule (as opposed to a thermal degradation product) is of distinct advantage since it is possible to differentiate between aldicarb and aldicarb nitrile without the use of a florisil cleanup procedure. The 3-m DB5 capillary column was found to provide greater sensitivity and reproducibility in the analysis for aldicarb than the 9-m DB5 capillary column. Aldicarb elutes at a lower temperature on the short column due to the reduced column pressures in the GC/MS system and the greatly shortened length. A representative gas chromatogram is shown in Figure 2. The use of on-column injection techniques in conjugation with the use of short capillary columns would quite likely improve the sensitivity of the technique. On the longer columns normally used for GC/MS analysis, aldicarb does not elute in a reasonable time at temperatures low enough to avoid thermal degradation. The use of a short SE54 capillary column produced poorer limits of detection for aldicarb than with the DB5 column, possibly due to adsorption on the column. We also observed that the condition of the injection port had considerable influence on the sensitivity and linearity of the aldicarb analysis. A clean silanized glass insert was necessary to obtain a linear
ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
1
1283
B
4i
TIME (SEC)
I
191
41
1 1
(d)
Figure 2. Reconstructed chromatogram of a methylene chloride extract of water spiked with aldicarb, peak C. The presence of aldicarb oxime formed by hydrolysis of aidicarb during the 91-day incubation period is shown by peak A. Peak B is due to ethyl benzoate which was used as an internal standard. Table 11. Response for Aldicarb and Aldicarb Nitrile versus Temperature of Injection Port When Aldicarb is Injected at a Concentration of 1.28 mg/mL area for "C
area for aldicarb (I) in counts
60 100 140 180 220
142 110 2854550 8100290 4367700 1531320
temp,
I34
I
1
1082 10 1 1 7
104 964 358 706 862202
ratio of IIiI 0.0076 0.0035 0.0130 0.0821 0.563
I
172
1 1
(f)
aldicarb nitrile (11) in counts
(i)
I
,r.1, 5i
150
IO0
ZOO
M/Z Figure 1. Mass spectra for aldicarb, aldicarb oxime, and aldicarb nitrile: (a)E1 aldicarb; (b) +CI(methane)aldicarb; (c)+CI(isobutane) aldicarb: (d) E1 aldicarb oxime; (e) +CI(methane)aldicarb oxime: (f) +CI(isobutane) aldicarb oxime: (9) E1 aldicarb nitrile; (h) +CI(methane)aklicarb nitrile; (i) +CI(isobutane) aldicarb nitrile. The spectra were obtained
with the source at 100 O C .
response from 1.5 ng to 150 ng injected. The limit of detection for aldicarb was 0.3 ng at a S I N ratio of 3. Aldicarb oxime does not thermally degrade even with an injection port temperature of 350 O C (3). The narrow peak width of aldicarb oxime necessitated the use of a fast scan
repetition rate (0.27 slscan) in order to obtain sufficient data points to quantitate the 1.5 s wide peak. Aldicarb oxime was found to have a linear response from 1.2 ng to 150 ng, with a LOD of 1.2 ng. The analysis for aldicarb nitrile is complicated by the formation of aldicarb nitrile from aldicarb in a hot injection port. Aldicarb nitrile can be selectively determined, however, if the injection port is maintained at 60 "C. A sample containing 1.28 X lo3ppm aldicarb produces a 1.3 ppm response for aldicarb nitrile due to its formation in the injection port. The variation in the observed responses for aldicarb nitrile and aldicarb as the temperature of the injection port is increased is shown in Table 11. The linear dynamic range for aldicarb nitrile was found to be from 0.15 ng to 150 ng with a LOD of 0.15 ng. The determination of aldicarb sulfoxide and aldicarb sulfone was not possible with the 2.6-m capillary column. Aldicarb sulfoxide is less volatile than aldicarb and appears to be even more thermally labile than aldicarb. Since these compounds can be analyzed by direct probe insertion, the use of even shorter capillary columns could provide a means €or their analysis as well. Mass Spectrometry. The isobutane CI spectra for aldicarb and its degradation byproducts are characterized by the formation of abundant MH+ ions. The CI sensitivity obtained with methane was four times greater than that obtained with isobutane; however, this gain in sensitivity is offset by the higher chemical background due to ionization of methylene chloride. In addition to the MH+ 116 (5.4% relative abundance) ion, for aldicarb nitrile, the isobutane spectra for aldicarb nitrile contains the (M + 57)+ ion, 172 (100% RA), corresponding to the addition of isobutane ion to the aldicarb nitrile molecule. The methane CI spectrum for aldicarb nitrile contains the
1284
ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984 172
I I
3.0
I
I
I
r
(ai
89
I 57
I
I \
I
89 I
I 50
191
1
1
1
I00
I50
200
MI2
Figure 3. The collision induced daughter spectra of (a)positive ion 172 due to aldicarb nitrile In isobutane CI and (b) positive ion 191 due to aldicarb in isobutane CI.
I
+
MH+ (11.4% RA), the (M + 29)' (1.4% RA), and the (M 41)' (0.6% RA) ions. The E1 spectrum for aldicarb nitrile is characterized by the presence of an abundant molecular ion, 115 (59.5% RA). It has been reported that aldicarb dehydrates on a 2% OV-17 column based on the presence of a 172 ion (M - 18)+in the isobutane CI spectrum (9). Our data suggest that this corresponds instead to the (M 57)+ ion (172) of the nitrile. In order to confirm that the 172 ion in the isobutane CI spectrum of aldicarb nitrile was indeed the (M C4H9)+ion, the CAD daughter spectrum for the 172 ion was acquired. The major fragments were 57 (C4H7)+,89 (C4H,S)+, and 116 (172 - C&)+ as shown in Figure 3a. In contrast, the CAD daughter spectrum of the MH+ ion (191) of aldicarb does not yield a 57 ion or a (191 - C4H8)+ion as shown in Figure 3b. Degradation of Aldicarb in Spiked Water Samples. The rate of hydrolysis of aldicarb to aldicarb oxime in sterile anaerobic groundwater a t pH 8.2 is shown in Figure 4. The retention time on the short DB5 capillary column and on the 30-m Carbowax 20M capillary column matched those of aldicarb oxime, as did the mass spectra (CI, EI, and CAD). Quantitation was performed by using selected ion monitoring (SIM) with ethyl benzoate as an internal standard. In order to obtain greater precision in the data, all the samples were run in a single day. The samples that had been previously extracted with methylene chloride and stored in sealed septum bottles at 4 "C were analyzed at a rate of 6 samples/h. The half-life for aldicarb at pH 8.2 in sterile anaerobic water was 43 days. Essentially all of the degraded aldicarb can be accounted for by the formation of aldicarb oxime. Aldicarb oxime was found to be stable in alkaline conditions as high as pH 11 for 2 weeks. In the presence of a high concentration of microorganisms or in the presence of ground limestone, aldicarb degraded rapidly with the formation of aldicarb nitrile under anaerobic conditions. In these samples 85% of the original aldicarb had degraded in less than 2 weeks. Aldicarb nitrile was found in these samples to account for 100% of the degraded aldicarb. This is of particular interest since aldicarb nitrile gives a positive interference for aldicarb when GC methods are used which employ standard columns. A Florisil cleanup procedure is not necessary when using the short column method employed in this study because the intact aldicarb molecule is determined. The conversion of aldicarb to aldicarb nitrile probably involves an intramolecular rearrangement both in the gas phase for thermal degradation in the injection port and in aqueous solutions in the presence of microorganisms or ground limestone. This pathway has been suggested as the mechanism
+
+
A
If
0
M 20
0
IO0
80
40
60
TIME (DAYS)
Figure 4. The rate of hydrolysis of aldicarb (0)to aldicarb oxime (0). The half-life of aldicarb at pH 8.2 was estimated to be 43 days. for the synthesis of aldicarb nitrile from aldicarb employed in this study (18). Aldicarb, I, thermally degrades to aldicarb nitrile, 11, and (methy1amino)methanoic acid, IV. The base
I
I/
IV
peak in the CAD daughter spectra of the MH+ ion for aldicarb is the 116 ion which corresponds to the aldicarb nitrile MH+ ion. The base peak in the negative methane CI spectra for aldicarb is the 74 ion, the (methy1amino)methanoate ion.
CONCLUSION This technique overcomes several disadvantages of methods currently used for aldicarb and its degradation byproducts. In the case of GC analysis. by conventional length columns, aldicarb nitrile gives a positive interference for aldicarb, and thus a time-consuming cleanup procedure is necessary. Aldicarb nitrile cannot be detected by LC with UV detection because it does not absorb in the UV. The postcolumn fluorometric technique used in LC requires that the analyte hydrolyze with the formation of methylamine which may react with o-phthaldehyde to form a fluorophore. Aldicarb nitrile does not hydrolyze to form methylamine and thus is not detected. The use of GC/MS with short capillary columns has been shown to permit analysis for thermally labile pesticides and offers the advantage of confirmation of identity and rapid analysis. Up to six samples per hour can be analyzed for aldicarb by this technique. Further, the possibility of misidentification is greatly reduced.
ACKNOWLEDGMENT We are grateful to Joe Delfino for fruitful discussions. We also wish to thank Matthew Monsees for assisting in setting up the anaerobic water samples and LC analysis of aldicarb residues which will be the subject of another report. We deeply regret the untimely death of John J. McCreary whose insight and leadership was of great assistance to his
Anal. Chem. 1984, 56, 1285-1288
students and peers. His wit and humor will be sorely missed by his friends and students.
Registry No. I, 116-06-3;11,1646-75-9;111,10074-86-9;water, 7732-18-5. LITERATURE CITED (1) Guerrera, A. A. J.-Am. Water Works Assoc. 1981, 73 (4), 190-199. (2) Knaak, J. 6.;Tallant, M. J.; Sulllvan, L. J. J. Agric. Food Chem. 1966, 14,573-578. (3) Metcalf, R . L.; Fukuto, T. R.; Collins, C.; Borck, K.; Burk, J.; Reynolds, H. T.; Osman, M. F. J. Agric. Food Chem. 1966, 14,579-584. (4) Wright, L. h.; Jackson, M. D.; Lewis, R. G. Bull. Environ. Contam. Toxicol. 1982, 28, 740-747. (5) Sparaclno, C. M.; Hines, J. M. J. Chromatogr. Scl. 1976, 14, 549-556. (6) Move. H. A,: Scherer, S. J.: St. John, P. A. Anal. Left. 1977, IO, 1049-1 073. (7) Krause, R. T. J . Chromatogr. 1979, 185,615-824. (8) . . Galoux, M.; Van damme, J.-C.; Bernes, A.; Potvin, J. J . Chfomatogr. 1979, 177,245-253. I
.
1285
.
(9) Muszkat, L.; Aharonson, N. Inf J. Mass Spectrom. Ion Phys . 1983, 4. 8_. .323-328. .~~ Moye, H. A. J. Agric. FoodChem. 1975, 23,415-418. Yost, R. A.; Fetterolf, D. D.; Hass, J. R.; Harvan, D. J.; Weston, A. F.; Skotnicki, P. A.; Simon, N. A,, submitted to Anal. Chem. Riva, M.; Carisano, A. J. Chromafogr. 1969, 42,464-469. United States Food and Drug Administration Pesticide Analytical Manual; US. Government: Rockvilie, MD, 1970; Volume 11, Pesticide Reg. Sectlon 120.269 Aldicarb. (14) Rouchaud, J.; Moons, C.; Meyer, J. A. Pesfic. Sci. 1980, 1 1 , 483-492. (15) Andrawes, N. R.; Bagiey, W. P.; Herrett, R. A. J. Agric. Food Chem. 1971, 19,731-737. (16) Andrawes, N. R.; Bagley, W. P.; Herrett, R . A. J . Agric. FoodChern. 1971, 19,727-730. (17) Jones, A. S. J. Agric. Food Chem. 1976, 24, 115-117. (18) Payne, L. K.; Stansbury, H. A., Jr.; Weiden, M. H. J. J. Agric. Food Chem. 1966, 14,356-365. ~~
RECEIVED for review December 27,1983. Accepted February 21, 1984. This project was supported by a State of Florida STAR grant. Funds for the GC/MS/DS were provided by the National Science Foundation.
Determination of Elemental Iodine by Gas Chromatography with Electron Capture Detection S. J. Fernandez,* L. P. Murphy, and R. A. Rankin Exxon Nuclear Idaho Co., P.O. Box 2800, Idaho Falls, Idaho 83401
A gas chromatography/electron capture detector (GC/ECD) technique has been developed to determine elemental iodine In toluene and cyclohexane solvents. The retentlon Index based on the alkyl Iodide and n-paraffin series was determined. Sufflclent resolution was obtalned to resolve I, from alkyl Iodides. A detection iimlt of 39 ng of I, was obtalned. A dlssoclatlve electron capture mechanism was proposed for the ECD response to 12. Radlotracer studles established the I, was transmitted through the column without conversion to an organlc lodlde. The utlllty of the developed technlque was mass spectrometry standdemonstrated on a AgI in ",OH ard solutlon. An accuracy of 23% and a preclsion of 12% were demonstrated.
Potentially, the most environmentally significant emissions from nuclear facilities are the radioactive isotopes of iodine. The many alkyl iodides, aromatic iodides, and inorganic iodides that may be formed during nuclear and chemical processes complicate the measurement of liquid and gaseous iodine compounds at the submicrogram level. Castello et al. ( I ) published the gas chromatographic separation and identification of several alkyl iodides using glass columns filled with tricresyl phosphate on DMCS treated Chromosorb W. Castello et al. (1)also proposed a homologous series of iodoalkanes as a reference for the calculation of the retention indexes of ECD sensitive substances. Corkill and Giese (2)used fused silica capillary columns coated with either SE52 or SE54 to analyze the iodothyronines. A gas chromatographic separation of Iz and methyl iodide prior to mass spectrometric analysis was developed in this laboratory (3). The analysis of I, by packed column gas chromatography is
more difficult than the analysis of organic iodides because I2 is less volatile and more reactive than the organic iodides of environmental significance. In this article the analysis of 12 by GC/ECD is investigated as a function of detector, injector, and column temperatures. The calculated retention indexes are compared to the results of Patte, Echeto, and Laffort ( 4 ) .
EXPERIMENTAL SECTION Apparatus. The separation and measurement of iodine compounds were performed with a Varian Model 3700 gas chromatograph equipped with a 63Nielectron capture detector. Two columns were used: a 30 cm X 0.3 cm stainless steel column of 10% OV-101 on Chromosorb W-Hp 80/100 mesh obtained from Varian Instrument Group (Palo Alto, CA); and a 300 cm X 0.3 cm nickel column of 5% SE-30 on Chromosorb W-HP, SO/lOO mesh obtained from Alltech Associates (Arlington Heights, IL). All experiments were performed with a 30 cm3/min flow N2 or 90% Ar/lO% CHI carrier gas. The column was operated isothermally at 100 "C for the retention index experiments. Reagents. The methyl iodide, ethyl iodide, 1-iodopropane, and 2-iodopropane were obtained from Aldrich Chemical Co. (Milwaukee, WI) and used without further purification. The toluene, benzene, and cyclohexane were "distilled-in-glass" grade obtained from Burdick and Jackson (Muskegon, MI) and used without further purification. The elemental iodine was resublimed grade obtained from Fisher Scientific Co. (Pittsburgh, PA). Iodine Compound Mixture Preparation. Alkyl iodide solutions were prepared by volumetric dilution; the I2 solutions were prepared by weighing I2 crystals to fO.l mg, dissolving the crystals in toluene or cyclohexane, and preparing subsequent serial dilutions volumetrically. RESULTS AND DISCUSSION Retention Index. The retention index was determined in the manner of Castello et al. ( I ) and Patte et al. ( 4 ) at 100
0003-2700/84/0356-1285$01.50/00 1984 American Chemical Society
