1980
Anal. Chem. 1980, 52, 1980-1982
Determination of Traces of Low Aliphatic Amines by Gas Chromatography Kazuhiro Kuwata, * Yoshiaki Yamazaki, and Michiko Uebori Environmental Pollution Control Center, 62-3, 1 Chome, Nakarnichi, Higashinari-ku, Osaka City 537, Japan
Traces of low aliphatic amines in environmental, food, and biological samples are usually determined by gas chromatography (GC). A number of gas chromatographic columns, such as 0.5% PEI 40M + 0.3% potassium hydroxide on graphitized carbon black ( I ) , 4% PEG 20M + 0.8% potassium hydroxide on Carbopack B ( 2 , 3 ) , 15% diglycerol + 5% tetraethylenepentamine (TEP) + 2% potassium hydroxide on Chromosorb W (3),2% TEP on Graphon (3),28% Penntwalt 223 + 4% potassium hydroxide in Gas Chrom R ( 3 ) , Chromosorb 103 ( 3 ) ,a n d 10% Amine 220 + 10% potassium hydroxide on Chromosorb W ( 3 ) ,are discussed with respect t o resolution of the amines and the accuracy of the determined values. These columns, however, give poor separation for the Cz-C3 amine isomers. When water is injected into the columns with a sample, ghost peaks are often produced and retention times of the amines tend to be changed. The columns except Chromosorb 103 are limited to use for isothermal analysis a t relatively low temperatures and are difficult to use for t h e simultaneous determination of the C1-C4 amines. Recently, a n excellent GC column packed with 4.8% PEG 20M + 0.3% potassium hydroxide on Carbopack B was reported to determine nanogram levels of C1-CI aliphatic amines ( 4 ) . The column offers complete separation of the C2-C3amine isomers and is less affected by water than the other columns are. However, t h e preparation of the column seems t o be difficult for routine analysis, and information on its practical use is not discussed in detail. In this article, a convenient and long-life GC column packed with Chromosorb 102 treated with trimethylchlorosilane (Chromosorb 102 TMCS) and coated with 5% potassium hydroxide is reported to separate traces of C1-C4 aliphatic amines. A few applications for determination of the amines in gas samples and environmental samples are presented.
EXPERIMENTAL SECTION Reagents a n d Materials. Aliphatic amine hydrochlorides used as standards were from Tokyo Kasei Kogyo (Tokyo, Japan) and Eastman Kodak Co. (Rochester, NY). Potassium hydroxide and trimethylchlorosilane (TMCS) used were from Wako Pure Chemical Industries (Osaka, Japan). Chromosorb 102 (80-100 mesh) was a product of Johns-Manville Co. (Denver, CO). The stock solutions containing lo00 wg/mL of a free amine were made by dissolving the amine hydrochloride in distilled water. Standards of lower concentrations were made by neutralizing a part of the stock solution with 0.1 N potassium hydroxide solution and by appropriately diluting the solution with distilled water. Preparation of t h e Analytical Column. Ten grams of Chromosorb 102 was added to 5% (v/v) TMCS in 50 mL of toluene in a flask. The mixture was placed under vacuum for a minute, allowed to stand for 5 min, filtered through a sintered glass funnel, washed with 100 mL of toluene and then with 50 mL of methanol, and dried at 80-90 "C after a preliminary air-dry. The Chromosorb 102 TMCS was added t o 25 mL of methanol containing 0.5 g of potassium hydroxide in a flask. The mixture was dried under gentle vacuum and gentle heating in a rotary evaporator. The analytical column was made by packing the material into a 2 m X 2 mm i.d. glass tube and conditioning at 200 "C for 3 days. During the conditioning 10 pL of water was injected 30 to 40 times to ensure preparation of the stable column. Prior to use of the column, 10 pL of water was injected a few times at 170 "C. Apparatus. A Varian (Walnut Creek, CA) 2700 gas chromatograph with a flame ionization detector (FID) and a Hewlett-Packard (Avondale, PA) 5830A gas chromatograph with an FID and a nitrogen-phosphorus flame ionization detector (NP0003-2700/80/0352-1980$01 .OO/O
Table I. Retention Times of C,-C, Aliphatic Amines retention timea f SD,b min amine isothermalC programmedd me thylamine 1.05 f 0.005 6.68 f 0.007 dimethylamine 1.54 k 0.005 7.58 i 0.007 ethylamine 1.83 i 0.005 7.88 i 0.007 trimethylamine 2.26 i 0.010 8.23 i. 0.005 isopropylamine 3.49 i 0.011 9.11 f 0.005 9.91 i 0.005 n-propylamine 4.83 i 0.011 tert-bu tylamine 5.91 f 0.017 10.49 i 0.005 diethylamine 7.03 i 0.009 11.11 i 0.005 sec-butylamine 8.87 i 0.014 12.04 i 0.007 is0 butylamine 9.79 i 0.018 12.53 t 0.005 n-butylamine 12.17 f 0.027 13.65 i 0.006 Average value in five runs. SD, standard deviation. Isothermal at 70 ' C for first 4 Isothermal at 150 C. min and programmed from 7 0 to 1 7 0 C at 30 C/min. FID) were used. The working conditions were as follows: carrier gas, nitrogen 50 mL/min; injection temperature, 170 "C; column temperature, 100-170 "C; FID temperature, 200 "C; NP-FID temperature, 250 "C.
RESULTS AND DISCUSSION Chromosorb 102 modified with potassium hydroxide produced a good separation of C1-C4 aliphatic amines. A satisfactory separation of the amines was obtained on Chromosorb 102 loaded with 20% potassium hydroxide (Figure 1). However, it is difficult to regularly pack such highly alkalized material into the column in a n ordinary room because of its high hygroscopicity, and the material may damage the column tubings and parts of the instrument. Treatment of Chromosorb 102 with TMCS successfully reduced t h e necessary amount of the alkali on the material. T h e amount of 5% potassium hydroxide on Chromosorb 102 TMCS was enough to produce excellent separation of the C1-C4 amines (Figure 1). A base line separation of the Cz-C3 amine isomers was achieved on the column. The column could be also used for temperature programming analysis (Figure 2). This was convenient for the analysis of various types of samples since the amines vaporized from a condensed sample or thermally desorbed from an adsorbent may be trapped a t the head of the column a t a relatively low temperature a n d then determined a t a raised temperature. Table I reports the accuracy of retention times of the C1-CI amines obtained on the column by isothermal and temperature programming operations. T h e relative standard deviations of the retention times were less than 0.5% more than on a day when the analytical conditions were not changed. When the quantitation was done by peak area (height X width at half-height), excellent linear calibration graphs for the individual amines were obtained over the range from 10 to 700 ng by the FID and from 1 t o 50 ng by t h e NP-FID, where the standard deviations of determined values were less than 3 % . The NP-FID, which is selectively sensitive t o nitrogencontaining compounds ( 5 ) ,improved the analytical accuracy for low nanogram levels of the amines. If, other than the amines, minor organic substances which may cause ghost peaks to disturb the analysis are present in the sample, use of the NP-FID is recommended. Table I1 reports t h a t low nanogram levels of the amines can be accurately determined by the NP-FID. T h e detection limits with t h e NP-FID, defined as responses to twice the background peaks in the blank C 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 12, OCTOBER 1980
I '12
Table 11. Accuracy of Determination of Low Nanogram Levels of Aliphatic Amines amt of amine responsea injec- peak areaCt ted, ng SD,':' arbitrary
amine
0
5
10
15
Retention time, min Flgure 1. Separation of C,-C, aliphatic amines. Peak identity: (1) methylamine, (2) dimethylamine, (3) ethylamine, (4) trimethylamine, (5) isopropylamine, (6) n-propybmine, (7) tert-butylamine, (8) diethylamine. (9) sec-butylamine, (10) isobutylamine. ( 1 1) n-butylamine. Amount of each amine was 100 ng. Column conditions: (A) Chromosorb 102 coated with 20% potassium hydroxide; (8) Chromosorb 102 TMCS coated with 5 % potassium hydroxide: temperature 150 OC.
211 3L 5
Table 111. Concentrations of C,-C, Aliphatic Amines in Synthetic Air Samplesa sample Ab methylamine dimethylamine
isopropylamine n-propylamine tert-butylamine diethylamine sec-butylamine
'I
isobutylamine n-butylamine
nl,oLA-
11
0
15
Retent ion t i m e , mtn Figure 2. Separation of C1-C4 aliphatic amines by temperature programming operations. For peak identity see Figure 1. (A) Isothermal at 70 OC for first 4 min, programmed from 70 to 170 OC at 30 'C/min, and detected by FID; amount of each amine was 100 ng. (B) Isothermal at 120 OC for first 5 min, programmed from 120 to 160 OC at 10 OC/min, and detected by the NP-FID; amount of each amine was 1 ng.
test where 2 WLof water was injected, were 0.2 ng for methylamine, 0.1 ng for dimethylamine, and 0.05 ng for ethylamine and the C+2, amines. The relative standard deviations of determined values of the amines near the detection limits were less than 12%. After successive analyses of samples containing high concentrations of the amines, 1&20 pL of water should be injected to flush away traces of the amines adsorbed in the injection port and t h e column tubings.
%
-~
trimethylamine
I
RSD,b
1.0 998 t 27.8 2.79 methylamine 1.0 827 i 15.0 1.81 dimethylamine 1.0 595 i 16.1 2.71 ethylamine 1.0 893 i 22.3 2.50 trimethylamine isopropylamine 1.0 1009 t 23.8 2.36 1.0 817 i 19.1 n-propylamine 2.34 tert-butylamine 1.0 403 i 12.1 3.00 diethylamine 1.0 1162 t 30.9 2.66 sec-butylamine 1.0 701 t 4.9 0.70 is0 butylamine 1.0 607 i 6.1 1.00 n-bu tylamine 1.0 325 i 7.4 2.28 a Isothermal at 120 ' C for first 5 min, programmed from 120 to 1 6 0 C at 1 0 C/min, and detected by the NP-FID. RSD, relative standard deviation. Average value in six runs. SD, standard deviation.
ethylamine
h, I
1981
sample Bb
sample C b
0.38 18.6 i 1.13 97.0 ?; 3.34 (85.0) (93.0) (97.0) 94.4 i 4.58 4.00 t 0.35 19.6 i 0.31 (100.0) (98.0) (94.4) 3.62 t 0.26 20.0 i 0.57 94.0 t 3.00 (90.5) (100.0) (94.0) 3.96 i 0.61 19.6 i 1.03 102.4 I 1.36 ('38.0) (102.4) (99.0) 3.22 i 0.22 19.9 i 0.28 96.4 i 5.46 (80.5) (99.5) (96.4) 4.08 t 0.27 20.2 i 0.76 102.0 t 1.36 (102.0) (102.0) (101.0) 3.24 1 0.51 18.3 i 0.48 98.4 i 4.90 (81.0) (98.4) (91.5) 3.36 i 0.41 19.7 i 0.40 91.6 i 6.48 (91.6) (98.5) (84.0) 3.24 i 0.39 18.3 i 0.92 89.2 f 4.18 (81.0) (91.5) (89.2) 3.94 i 0.62 17.5 1 0.49 92.8 t 8.10 (98.5) (87.5) (92.8) 3.40 i 0.58 21.5 i 0.89 105.0 i 6.10 (85.0) (107.5) (105.0) 3.40
i
concn of amine 4.00 20.0 100.0 calcd, ng/L a Five liters of an experimental air sample was prepared in each run and analyzed by GC with the FID via the concentration method ( 6 ) . Concentxation (ng/L) of amine found i standard deviation ( % recovery). Concentration is average value in five runs at 20 C. Although such problems caused by water injected with a sample were minor for this column compared with those for previous columns ( 1 - 4 ) , injection of too much water still produced a few problems. The response of the NP-FID was lowered or extinguished for 5-40 s by passing 1-5 mg of water. Because the water fraction eluted between methylamine and dimethylamine peaks, determination of both amines tended to be affected by the injection of too much water. Three milligrams of water seemed to be the maximum while ensuring the determination of 1-ng levels of both amines. In the case of a sample containing dimethylamine, analysis should be started a t a relatively low temperature and run a t a higher temperature after the dimethylamine is eluted. The retention times of the amines were apparently not changed by injecting up to 10 mg of water with a sample. T h e retention times, especially for the C4 amines, tended to be shortened by more than 10 mg of water, but the peak areas were not changed.
1982
Anal. Chem. 1980, 52, 1982-1982
Amines in synthetic air samples were trapped on an alkalized Porasil A column and thermally desorbed (6). T h e amine vapors carried by nitrogen gas (50 mL/min) were trapped at the head of the analytical column a t 70 "C for 4 min and then determined by the FID by programming from 70 to 170 "C a t 30 "C/min. Results shown in Table I11 indicate that this column is appropriate for the routine determination of C1-CI aliphatic amines in gas samples. Sixty liters of ambient air around a poultry farm and around a rendering plant were sampled at 1L/min by using a 30-mL fritted bubbler with 10 mL of 0.01 N sulfuric acid solution. The sample was evaporated to 1 mL under reduced pressure and gentle heating, neutralized with 1.0 N potassium hydroxide solution, and brought to 2 mL with water (7). One to two microliters of the sample was analyzed by GC with the NP-FID. Figure 3 shows that low ppb (v/v) levels of the aliphatic amines in air polluted from these sources could be successfully determined. These results have demonstrated that the column can be successfully applied to the determination of traces of low aliphatic amines in gas samples and polluted ambient air.
(Ai
II
Retention t i m e , min
LITERATURE CITED
Figure 3. Analysis of ambient air around emission sources sampled at 20 OC. For analytical conditions see Figure 28. (A) Emission gas from a poultry farm: (1) trimethylamine (1.65 ng) 22.4 ppb (vlv). ( 8 ) Ambient air around a rendering plant: (1) dimethylamine (0.51 ng), 9.1 ppb; (2) trimethylamine (0.26 ng), 3.5 ppb; (3) diethylamine (0.08 ng), 0.9 ppb.
(1) Di Corcia, A.; Liberti, A,; Sarnperi, R . J . Chromatogr. Sci. 1974, 12, 7 10-714. (2) Di Corcia, A,; Samperi, R. Anal. Chem. 1974, 4 6 , 977-981. (3) Dunn, S. R.: Simenhoff. M. L.; Wesson. L. G., Jr. Anal. Chem. 1976, 48, 41-43. (4) Di Corcia. A.: Samperi, R.; Severini, C. J . Chromatogr. 1979. 170, 325-329. ( 5 ) Burgett. C. A.; Smith, D. H.: Bente. H. B. J . Chromatogr. 1977, 134, 57-64. (6) Kuwata, K.; Yamazaki, Y.; Uebori, M. Bunseki Kagaku 1980, 29, 170-175. (7) Mosiec, A. R.; Andre, C. E.; Viets, F. G., Jr. Environ. Sci. Techno/.1973, 7, 642-644.
T h e column with minimal background peaks was obtained by injecting 10 MLof water 30 to 40 times during the conditioning at 200 O C . The water injected here seemed to give no unfavorable effects on the column quality. The column could be easily reproduced and successively used for more than 5 months without deterioration of the characteristics.
RECEIVED for review March 28, 1980. Accepted July 3, 1980.
Hand Polishing of Quartz Windows John R. Sutter Depatfment of Chemistry, Howard University, Washington, D.C. 20059
During the course of our research, we have found it necessary on occasion to repolish a scratched or chipped quartz window that was needed immediately; for example, the quartz windows in a Gibson-Durrum stopped-flow apparatus. The actual polishing technique is identical to that used for infrared windows made of NaCl or KBr-400- and then 600-mesh grits are used depending on the extent of the damage, with a final polish using Barnesite grit, rouge. In the case of quartz, water may be used to form the paste. The problem is to find a suitable surface to polish on. We have found that a sheet or square of Teflon makes an excellent lap, since the property of the slick Teflon surface, that it does not abrade with the piece being worked on, makes it almost perfect. The Teflon sheet is placed on a hard, flat surface; less support is needed when using a thicker Teflon block. A square of size
0003-2700/80/0352-1982$01 .OO/O
suitable to the work at hand is all that is required. We have hand polished many quartz windows with absolutely no "lemon peel" effect and, with proper rotation of the work, the windows will remain flat. The larger the window, the easier this is to accomplish. Small windows can be easily held and manipulated by placing them in a length of polyethylene or other tubing of correct size. A pair of stopped-flow windows can be polished in an hour or so and the results are really quite beautiful. We further see no objection to draping a Teflon sheet in a mold for the polishing of convex lenses, but we have not had the need to try this. RECEIVED for review March 27,1980. Accepted May 28,1980.
0 1980 American Chemical Society
