Anal. Chem. 1984, 56, 1803-1808
that this complicating effect will be generally controllable by the use of an appropriate positive ion modifier so that conditions within the ECD can be further tailored for the observance of electron capture reactions, alone. Registry No. CH3NH2,74-89-5; anthracene, 120-12-7.
LITERATURE CITED (I) Lovelock. J. E. Anal. Chem. 1963, 35, 474. (2) Grimsrud, E. P.; Stebblns, R. G. J . Chromafogr. 1078, 155, 19. (3) Andrawes, F. F.; Gibson, E. K.; Bafus, D. A. Anal. Chem. 1980, 52, 1377. (4) Campbell, J. A. Grlmsrud, E. P.; Hageman, L. R. Anal. Chem. 1983, 55,1335. ( 5 ) Wlzner, M. A.; Slnghawangcha, S.; Barkley, R. M.; and Slevers, R. E. J . Chromatogr. 1982, 239, 145. (6) Wentworth, W. E.; Becker, R. S. J . Am. Chem. SOC. 1062, 8 4 ,
4263. (7) Wojnarovits, L.; Foldlak, G. J . Chromafogr. 1081, 206, 511. (8) Grimsrud, E. P. Anal. Chem. 1078, 50, 382. (9) Grimsrud, E. P.; Kim, S. H.; Gobby, P. L. Anal. Chem. 1079, 51, 223. (IO) Grimsrud, E. P.; Kim, S. H. Anal. Chem. 1079, 51, 537.
1803
(11) Gobby, P. L.; Grimsrud, E. P.; Warden, S. W. Anal. Chem. 1980, 5 2 , 473. (12) Grimsrud, E. P.;Connolly, M. J. J . Chromafogr. 1082, 239, 397. (13) Connolly, M. J.; Knighton, W. B.; Grlmsrud, E. P. J . Chromafogr. 1983, 265, 145. (14) Knighton, W. B.; Grlmsrud, E. P. Anal. Chem. 1982, 5 4 , 1892. (15) . . Grimsrud. E. P.: Miller, D.; Stebbins, R. G.; and Kim, S. H. J . Chromatogr. 1980, 797, 51. (16) Slegel, M. W.; Fite, W. L. J . Phys. Chem. 1976, 80,2871. (17j KeGarIe, P. Annu. Rev. Phys. Chem. 1977, 28,445. (18) Meot-Ner (Maunter), M. J . Phys. Chem. 1080, 8 4 , 2716. (19) Slegel, M. W.; McKeown, M. C. J . Chromafogr. 1076, 122, 397. (20) Wentworth, W. E.; Chen, E. C. M. J . Chromafogr. 1079, 786, 99. (21) Rosenstock, H. M; Draxl, K; Steiner, B. W.; Herron, J. T. J . Phys. Chem. Ref. Data Suppl. 1977, 6(1), 163,190,218,224. (22) Grimsrud, E. P.; Valkenburg, C. A. J . Chromafogr ., in press; Proceedings of the 20th Internatlonal Symposlum for Advances in Chromatography, April 16-19,1984,New York, Paper No. 32.
RECEIVED for review February 28,1983. Accepted May 1,1984. This work is supported by the National Science Foundation under Grant No. CHE-8119857.
Gas Chromatographic Analysis of Mixtures Containing Aldonic Acids, Alditols, and Glucose Jacob Lehrfeld Northern Regional Research Center, Agriculture Research Service, U.S. Department of Agriculture, Peoria, Illinois 61604
A method for the slmultaneous determination of aldonic acids, aldltols, and glucose has been developed. Samples are derlvitlzed and then resolved by gas-liquid chromatography. During the derlvltlratlon procedure, aldonic acids are converted to N-alkylaldonamlde acetates, alditols are converted to aldltol acetates, and glucose Is converted to an N-alkylglucosylamlne acetate. A sample containing arabitol, xylitol, mannitol, glucitol, galactitol, glucose, ribonlc acid, xylonlc acid, mannonlc acid, gluconic acid, and galactonlc acid was derlvltlred and then resolved on a 3% SP 2340 glass column In 18 mln.
The analysis of complex carbohydrate mixtures, such as those found in fermentation broths, requires a method capable of simultaneously determining aldonic acids, alditols, and some sugars, usually glucose. For trace analysis, gas-liquid chromatography (GLC) is preferred over high-performance liquid chromatography (HPLC) because of its greater sensitivity and selectivity. A number of derivatives have found wide application but are of limited use with the mixtures under study. The alditols are readily identified as their acetates on an ECNSS-M column (1). The common method for their preparation requires that the sample be heated in a mixture of pyridine and acetic anhydride. Unfortunately, this treatment dehydrates the aldonic acids (2). In addition, glucose could potentially form at least four different anomers due to mutarotation. Trimethylsilyl ethers have been used for the separation of a wide range of carbohydrates (3). However, neutral sugars, such as glucose, and aldonic acids can give multiple peaks. A method for converting the aldonic acid to a single 1,4-lactone requires that the acid be dissolved in 2 N hydrochloric acid and the solution be evaporated to dryness
(4). Unfortunately, evaporation of solutions containing hydrochloric acid results in the formation of a constant boiling azeotrope containing 20% HC1 (5), which can cause dehydration (6) and/or reversion of susceptibile sugars. The procedure to be described gives well-resolved single peaks for glucose, for the five aldonic acids studied, and for the common alditols. It is based on the facile conversion of aldonic acids to aldonolactones and their subsequent reaction with propylamine to form an N-propylaldonamide. Glucose, on the other hand, reacts with propylamine to form an Npropylglucosylamine. Subsequent Amadori rearrangement and Maillard-type reactions (7) are prevented by acetylation of the mixture with acetic anhydride and pyridine. The alditols are not affected by propylamine and are converted into their peracetates. This is the first report to describe the suitability and advantages of the peracetylated N-propylaldonamides and N-propylglucosylamine for the analysis of mixtures containing aldonic acids and glucose in the presence of alditols.
EXPERIMENTAL SECTION Materials. n-Propylamine, n-butylamine, n-amylamine, nhexylamine, pyrrolidine, galactitol, and D-glUCitOl, D-Xylose, Dribose, L-arabinose, D-mannose, D-glucose, and D-galactose were obtained from Aldrich Chemical Co. ~-Mannose-l,4-lactone, D-mannitOl, xylitol, and D-arabitol were obtained from Sigma DChemical Co. Sodium D-gluconate, ~-galactono-1,4-lactone, glucono-1,5-lactone,phenyl @-D-ghcopyranoside,and myo-inositol were obtained from Pfanstiehl Laboratory, Inc. Ammonium xylonate and potassium ribonate were a gift from M. E. Slodki. GLC coated support (3% SP 2340 on 100/120 mesh Supelcoport) was obtained from Supelco. Cation exchange resin (AG 50W-X8 200-400 mesh H+) was obtained from Bio-Rad Laboratory. GLC Analysis. Analysis by GLC was performed on a Packard Instrument Model 428 gas chromatograph equipped with dual
This article not subject to U.S. Copyright. Published 1984 by the American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 11, SEPTEMBER 1984 Table I. Response Factors ( K ) and GLC Retention Times for Alditol Acetates, N-Propylglucosylamine Acetate, and N-Propylaldonamide Acetates
9.10
u a . l 0
a al
--
a
b
0 W
0 W
I
I
I
I
I
2
4
6
8
10
I
I
I
12 14 16 18
Time, min.
Flgure 1. Separation of peracetyhted N-propylaldonamides and aklfiols by gas-liquid chromatography on a SP-2340 packed glass column (1 m X 2 mm id.) and temperature programmed from 190 to 260 "C at a rate of 5 "Clmin: (1) arabitol acetate, (2)xylitol acetate, (3) mannitol acetate, (4)galactitol acetate, (5)glucitol aacetate, (6) inositol acetate, (7) N-propylribonamide acetate, (8) N-propylglucosylamine acetate, @,lo)N-propylxylonamide acetate, phenyl Psglucopyranoslde acetate, (1 1) N-propylmannonamide acetate, (12) N-propylgluconamide
acetate, and (13) N-propylgalactonamide acetate. flame ionization detectors and dual electrometers. Two samples can be run simultaneously. The peracetylated derivatives were separated on a glass column (1m X 2 mm i.d.) packed with 3% SP 2340. The temperature was programmed from 190 to 260 "C at a rate of 5 "C/min. Recommended temperature maximum for SP 2340 is 275 "C. Nevertheless, the columns have remained usable for over a year in spite of some loss in resolution and some increase in tailing. Helium flow rate was 20 mL/min. A mixture of peracetylated N-propylaldonamides, N-propylglucosylamine, and alditols can readily be resolved by GLC on a SP 2340 column in 18 rnin (Figure 1). Conversion of Carboxyl to Lactone. A sample (1 mL) containing ammonium xylonate (15 mg) and potassium ribonate (15 mg) was passed through a column (60 mm X 6 mm i.d.1 containing approximately 1.5 mL of cation exchange resin. A column can conveniently be prepared from a 51/2-in.Pasteur pipet (plugged with a 3-mm glass bead or piece of glass wool) topped with a reservoir connected to the pipet with a piece of Tygon tubing. The sample was washed onto the column with water (1 mL) and then eluted with 6 mL of water. The remaining holdup volume was forced through with rubber bulb. The combined eluent was evaporated in vacuo on a Buchler vortex evaporator at 45 "C. After removal of the water, the temperature was raised to 85 "C and maintained there for 2 h. Conversion to the lactone was greater than 98% in all samples tested. Preparation of N-Propylaldonamides, N-Propylglucoeylamine, and Alditol Peracetates. A mixture of lactones (1-3 mg of each ribonolactone, xylonolactone, ~-mannono-l,4lactone, ~-glucono-1,5-lactone,and ~-galactono-1,4-lactone), glucose (3 mg), and alditols (1-3 mg of each D-arabitol, xylitol, D-mannitol, dulcitol, D-sorbitol, and myo-inositol) was placed in a 16 x 125 mm culture tube and dried in vacuo for 2 h at 85 " C to ensure that the lactones in the sample were entirely in the lactone form. Pyridine (0.5 mL) was added and the mixture was heated to dissolve the sugars. Because propylamine boils at 48 "C, the solution was cooled and propylamine (0.5 mL) was added; the tube was sealed with a Teflon-lined screw-cap and heated at 55 "C for 90 min in an aluminum heating block. (For butylamine, amylamine, hexylamine, and pyrrolidine the temperature was raised to 60 "C.) The tube was cooled, the cap removed, and nitrogen was bubbled in, while reheating to 55 "C, till the sample was dry. After 5-20 min, depending on the nitrogen flow rate, pyridine (0.5 mL) and acetic anhydride (0.5 mL) were added, and
Acetate
K
ret time, min
arabitol xylitol mannito1 galactitol glucitol myo-inositol N-propylglucosylamine phenyl 8-D-glucopyranoside N-propylmannonamide N-propylgluconamide N-propylgalactonamide
0.97 1.00 0.95 0.97 0.97 1.00
4.3 5.3 6.6 7.0
0.70
11.5 12.6
0.85 0.97 0.98 0.92
7.6
8.3 14.0 14.7
15.5
the mixture was heated at 90 "C for 40 min with periodic shaking to ensure complete solution. The sample is generally suitable for GLC as is; however, when smaller quantities are used, the tailing due to the pyridine and acetic anhydride may interfere with the quantitation of the early peaks. In that case, the solvent may be removed by bubbling nitrogen through the solution and reconstituting with 100 pL of chloroform, methylene chloride, or acetone. Optimization of N-Propylglucosylamine Formation. Propylamine (4 mL) was added to a pyridine solution (4 mL) containing 44.6 mg of glucose. An aliquot (0.5 mL) was immediately added to sixteen 16 X 125 mm culture tubes, which were then sealed with Teflon-lined screw-caps, and heated at 55 "C in an aluminum heating block. Tubes were removed at timed intervals (15, 30, 45, 60, 90, and 120 min) and cooled, and the solvents were removed by bubbling nitrogen through the reheated solutions. The residues were acetylated with pyridine (0.5 mL) and acetic anhydride (0.5 mL) at 90 "C for 45 min and analyzed by GLC. A second series was run at 20 "C. A t 55 "C conversion to N-propylglucosylamine was 97% after 60 min and 99% after 120 min. At 20 "C conversion to N-propylglucosylamine was 3% after 30 rnin and 8% after 120 min. Optimization of N-Propylaldonamide Formation. DGlucono-1,5-lactone (32 mg), ~-mannono-1,4-lactone(31 mg), ~-galactono-l,4-lactone(30 mg), and phenyl 8-D-glucopyranoside (15 mg) were dissolved in pyridine (2.5 mL) and propylamine (2.5 mL) was added. The mixture was mixed rapidly and then aliquota (0.5 mL) were added to a series of 16 X 125 mm culture tubes, which were sealed with Teflon-lined screw-caps and placed in a heating block at 55 "C. Tubes were removed at 15-min intervals cooled to 25 "C, and uncapped; the solvent was evaporated from the reheated solution with a stream of nitrogen. The residues were acetylated and analyzed as previously described. Quantitation. A series of standard solutions containing 1-7 mg of arabitol, xylitol, mannitol, glucitol, galactitol, glucose, mannono-l,4-lactone, glucono-1,5-lactone, and galactono-1,4lactone were prepared and treated as described in the Experimental Section. Each tube contained 3 mg of inositol as an internal standard. Samples at four concentration levels were analyzed in triplicate. Peak areas were integrated by a Modcomp computer. Calibration curves (relative detector response vs. milligrams of sugar) were calculated for each component and were found to have correlation coefficientsin the range of 0.997 to 0.999 and relative response factors of 0.7 to 1.0 (Table I). The methodology can be extended to samples containing 10 pg of sugar by increasing the sensitivity of the electrometer and by reducing the sample volume to 100 pL. Samples containing 1-5 fig have been analyzed but standard deviations are large. For example a sample containing 2 fig had a standard deviation of f l . An injection containing 10 ng gives a barely detectable signal.
RESULTS AND DISCUSSION Complex mixtures containing aldonic acids, alditols, and glucose can readily and rapidly be determined by this GLC procedure. Figure 1 demonstrates the application of the method to a synthetic mixture containing six alditols, five aldonic acids, and glucose. Phenyl P-D-glucopyranoside (12.2 min) or myo-inositol(7.9 min) is a good internal standard for
ANALYTICAL CHEMISTRY, VOL. 56, NO. 11, SEPTEMBER 1984
1805
Table 11. GLC Retention Times of Peraoetylated N-Alkylaldonamides on SP-2340"~~ N-propyl
N-butyl
amide N-amyl
D-ribon-
10.4
D-XylOn-
12.2
10.9 12.6 14.4 15.0 16.0 11.7
11.4 13.0 15.0 15.6 16.6 11.9
peracetylated aldonamide
L-mannonD-gluconD-galactonD-glucosylaminec
14.0 14.7 15.5 11.5
N-pyrrolidinyl
N-hexyl
12.3 11.7 16.3 15.3 14.5
12.0 13.6 15.4 15.9 16.7 12.4
-d
"GLC conditions were as follows: initial temp, at 190 O C ; programmed at 5 OC/min to 260 O C . *Phenylfl-D-glucopyranoside tetracetate was used as an internal standard and had a retention time of 12.2 min. CGlucose derivatives. dAn N-pyrrolidinyl peak could not be detected. Table 111. Conversion of Aldoses to Corresponding Peracetylated N-Propylaldosylamines
A N.Propyl
peracetylated N-propylamine
ret time: min
c w
ribosyl arabinosyl xylosyl mannosyl glucosyl
0
galactosyl
8.0 7.4 7.4 13.3 11.5 11.5
.10
7 W Y) 0 e
P W
-
a
L
0 V
W
75 85 89 62 99 85
"The gas chromatograph contained a glass column (1m X 2 mm i.d.) packed with 3% SP 2340 and the temperature was programmed from 190 "C at a rate of 5 OC/min. % amine = (peak area of amine)/(total peak areas of all components) X 100.
\ 0 4
% amineb
8 1216 0 4
8 1218 0 Time, min
4
8 1216
Figure 2. Separation of peracetylated phenyl po-glucopyranoslde (9), N-alkylrlbonamlde (7), and N-alkylxylonamlde (10): (A) N-alkyl =
n-propyl; (B) N-alkyl = n-amyl; (C) N-alkyl = n-hexyl.
quantitating the N-propylaldonamides. Peak 9,10 contains two unresolved components: the peracetates of phenyl 0-D-glucopyranoside and N-propylxylonamide. It would seem that the presence of xylonic acid would prevent the method from being utilized or require that another internal standard be found. The solution to this problem points out the versatility of this method. Butylamine, amylamine, hexylamine, and pyrrolidine can be used to form the corresponding aldonamides (Table 11). All of the respective derivatives, Le., N-butylaldonamide, N-amylaldonamide, N-hexylaldonamide, and N-pyrrolidinaldonamide, separate well on the same GLC column under the same conditions. The N-hexylaldonamides have longer retention times than the corresponding N amylaldonamides, the corresponding N-butylaldonamides, and the corresponding N-propylaldonamides. Consequently, by using amylamine, we can resolve peak 9,lO into two separate peaks. If hexylamine were used the alternate problem of overlap by peaks 7 and 9 would occur (Figure 2). This strategy would not work if glucose (peak 8) were present. Similarily, if an unusual component were in the fermentation mixture being investigated and it overlapped, for example, the N-propylmannonamide peak, one could readily use the same analytical methodology but change the amine used so as to change the retention time of the mannonamide and, consequently, pull the peaks apart. The procedure is simple, can be run in one tube, and requires around 6 h. Since many samples can be processed simultaneously, the time required/sample is much less. Aldonic acids in the salt form, such as might be found in a fermentation mixture, must first be converted to the free acid by passing them through an acidic cation exchange resin. Aldonic acids form ladones spontaneously when their aqueous solutions are evaporated and concentrated (8). A model study
done with sodium gluconate demonstrated that 2 h in vacuo at 85 "C was sufficient to convert gluconic acid fo gluconolactone. The protocol was repeated with all the aldonic acids studied with similar results. All the lactones studied could be converted into their corresponding amide within 15 min at 55 "C. As expected (8), the 1,5-ladones reacted more rapidly than the 1,4-lactones. For example, D-glucono-1,5-lactonewas completely converted in 2 min at 20 OC, whereas ~-galactono-l,4-lactone(55%) and ~-mannono-l,4-lactone(27%) were not. Subsequent acetylation is complete within 30 min, and the peracetylated derivatives are heat stable. The N-alkylaldonamides, unlike the lactones (2),do not form dehydration products when heated in pyridine-acetic anhydride. This was confirmed by GC/MS. Chemical ionization with isobutane gave a molecular ion (MH+) of 432 for N-propylgluconamide. Glucose, on the other hand, forms a glucosylamine. This stucture was confirmed by GC/MS of the N-butylglucosylamine, with isobutane for chemical ionization. A strong molecular ion MH+ was obtained at 446. Similar derivatives were formed with other common sugars. Unfortunately, the degree of transformation to the amine was not as complete (99%) as that found with glucose (Table 111). For identification purposes, the lower and variable percent conversion is tolerable but not for quantitation. The rate of formation of N-propylglucosylamine is markedly slower than amide formation. Consequently, if reducing sugars are not present in the sample, the reaction time can be reduced to 30 min. In summary, the method for analyzing complex mixtures of alditols, aldonic acids, and glucose is simple, requires minimal number of transfers, and is readily adapted for small or large numbers of samples. A moderate number of samples can be completely analyzed, from start to finish, in 1day. The ability to use various amines for derivatization gives this method unusual versatility.
ACKNOWLEDGMENT I thank R. D. Plattner for the GC/MS data.
1806
Anal. Chem. 1984, 56, 1806-1808
LITERATURE CITED (1) Sloneker, J. H. Methods Carbohydr. Chem. 1072, 6 , 20-24. (2) Nelson, C. R.; Gratzl, J. S. Carbohydr. Res. 1078, 60, 267-273. (3) SweeleY, c. c.; Bentley. R.; Maklta, M.; Wells, w. w. J . Am. Chem. SOC. 1063, 85, 2497-2507. (4) Morrlson, I. M.; Perry, M. B. Can. J. Blochem. 1066,44, 1115-1126. (5) Stecher, P. G. "The Merck Index", 7th ed.; Merck: Rahway, NJ, 1960;pp 530-531. (6) Newth, F. H. Adv. Carbohydr. Chem. 1051, 6 , 83-106. (7) Hcdge, J. E.; Rlst, C. E. J. Am. Chem. SOC. 1053. 75, 316-322.
(8) Stanek, J.; Cerny, M.; Kocourek, J.; Pacak. J. "The Monosaccharldes"; Academlc Press: New York, 1963;p 660.
R E C E ~ for J J review February 6, 1984. Accepted May 1,1984. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.
Determination of Selenium(IV) in Seawater by Gas Chromatography after Coprecipitation with Hydrous Iron(I I I) Oxide K. W. Michael Siu* and Shier S. Berman Division of Chemistry, National Research Council of Canada,' Montreal Road, Ottawa, Ontario, Canada K I A OR9
Selenium( I V ) concentratlon in seawater was determined by gas chromatography with electron capture detection after coprecipltatlon with hydrous iron( I II)oxide. Quantitatlve precipitation of Se(1V) was obtained at pH 5.0. Following a brlef, 15 min, stlrrlng and settilng period, the copreclpltate was filtered and dissdved in hydrochloric acid. Selenium was derlvatlred to 5-nitroplarselenoi, extracted into toluene and Introduced into the chromatograph. The detection limit was 1 pg injected or 5 ng of Se/L of seawater using a 200-mL sample. The precislon was 8 % at the 0.025 pg of Se/L level.
The concentration and fate of selenium in the marine environment have received considerable interest recently. This is due partially to the dual nature of selenium, whose essential and toxic levels are not that far apart. Gas chromatography (GC) has been used to determine selenium in a large array of materials after derivatization to form volatile piazselenols. Because of its high sensitivity, the electron capture detector (ECD) is used almost exclusively. The application of this technique has been reviewed ( I ) . Recently, we reported the analyses of marine sediments (2). This paper deals with analysis of open seawater. Selenium exists in seawater principally as Se(1V) and -(VI). It is debatable as to which oxidation state is thermodynamically more stable in seawater; however, both species usually coexist. The ratio of Se(1V) to Se(V1) varies from region to region and also along depths within a particular region (3). The various analytical techniques that are suitable for the determination of selenium in environmental waters have been discussed recently (3). Most methods require some form of preconcentration due to the very low quantities of selenium in natural waters. Gas chromatography has been used to determine various inorganic selenium species after derivatization to form 4,6-dibromopiazselenol(4)or 5-nitropiazselenol (5). For the former derivative, the reagent 1,2-diamino-3,5dibromobenzene is not commercially available. While the reagent for the latter, 1,2-diamino-4-nitrobenzene7 is available, its use in direct open ocean water analysis is not without drawbacks. The extraction efficiency of 5-nitropiazselenol is only about 70% at a toluenelaqueous ratio of 100, a ratio often 'NRCC 23343. 0003-2700/84/0356-1606$01.50/0
necessary for unpolluted waters. This means that experimental conditions have to be strictly controlled to obtain reproducible selenium recovery. Further, the large sample size (100-500 mL) requires addition of about 20 mg or more of derivatization reagent, whose reaction side-products with seawater are coextracted with piazselenol. This results in a complex chromatogram, and in most cases, requires capillary GC to resolve the piazselenol peak from the others. We find a 15-m SE-30 column performs satisfactorily. However, precision of the analysis is low, and each chromatographic run takes about half an hour (6). Some form of preconcentration seems desirable. It is well-known that a host of elements coprecipitates with hydrous iron(II1) oxide. Depending on the pH of the medium, which influences the surface charge of the precipitates, either cations or anions may be coprecipitated (7). Selenite @eo:-) is one of the anions that have been studied. Most methods call for addition of a surfactant, typically sodium lauryl sulfate, to facilitate collection of hydrous iron(II1) oxide (7-10).While it is true that precipitates from low ionic strength solutions are often colloidal and difficult to filter, those from solutions of high salt content, such as seawater, are often coarse and filter well, thus making addition of the collector surfactant unnecessary. It is interesting to note that selenium(V1) is not coprecipitated by hydrous iron oxide. Both previous work (11) and our results in a preliminary study show that practically no Se(V1) is brought down. Thus the coprecipitation process is species selective. Quite a few analytical techniques have used hydrous iron(111) oxide for selenium(1V) preconcentration including spectrophotometry (8, II), atomic absorption (7,9 ) , and neutron activation (IO). Spectrophotometry and atomic absorption necessitate dissolution of the collected hydrous oxide. Further, many procedures require the removal of iron (usually by ion exchange) prior to determination (7,8, 11) This paper discusses the rapid coprecipitation of selenium(1V) from seawater with hydrous iron(II1) oxide, the derivatization of selenium to 5-nitropiazselenol, and its subsequent determination by GC-ECD.
EXPERIMENTAL SECTION Instrumentation. A Varian VISTA 6000 GC equipped with a constant-currentECD was used. The column, held isothermally at 200 "C, was a 1-m borosilicate tube packed with 5% OV-225
Published 1984 by the Amerlcan Chemical Society
