Downloaded via KAROLINSKA INST on January 23, 2019 at 09:34:21 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
(2) J. C. Arcos and M. F. Argus, “Chemical Induction of Cancer", Vol. II A, Academic Press, New York, NY, 1974, p 386. (3) "The Health Consequences of Smoking", January 1973, DHEW Publication No. (HSM) 73-8704. (4) P. S. Larson and H. Silvette, "Tobacco—Experimental and Clinical Studies", Supplement II, The Williams and Wilkins Co., Baltimore, MD, 1972. (5) “The Health Consequences of Smoking, A Report to the Surgeon General: 1971", DHEW Publication No. (HSM) 71-7513. (6) R. L. Stedman, Chem. Rev., 68, 153 (1968). (7) A. P. Swain, J. E. Cooper, R. L. Stedman, and F. G. Bock, Beitr. Tabakforsch., 5, 97 (1969). (8) F. G. Bock. A. P. Swain, and R. L. Stedman, J. Nat. Cancer Inst., 44, 1305 (1970). (9) D. Hoffman and E. L. Wynder, Cancer, 27, 848 (1971). R. L. Miller, W. J. Chamberlain, and R. L. Stedman, Tob. Sci., 13, 21 (10)
(12) R. L. Stedman, R. L. Miller, L. Lakritz, and W. J. Chamberlain, Chem. Ind. (London), 394 (1968). (13) B. L. Van Duuren, J. Nat. Cancer Inst., 21, 1 (1958). (14) D. Hoffmann and E. L. Wynder, Cancer, 27, 848 (1971). (15) H. J. Kllmlsch and L. Stadler, J. Chromatogr., 67, 175 (1972). (16) H. J. Kllmlsch, Fresenlus Z. Anal. Chem., 264, 275 (1973). (17) W. O. Atkinson, "Production of Sample Cigarettes for Tobacco and Health Research", Unlv. of Kentucky Tobacco and Health Conference— 1970, Lexington, KY. (18) K. Rothwell, Ed., "Standard Methods for the Analysis of Tobacco Smoke", Research Paper II, Tobacco Research Council, Lodon, 1972. (19) H. C. Plllsbury, C. C. Bright, K. J. O'Connor, and F. W. Irish, J. Assoc. Off. Agrie. Chem., 52, 458 (1969). (20) A. P. Swain, J. E. Cooper, and R. L. Stedman, Cancer Res., 29, 579 (1969).
(1969). (11) E. L. Wynder and D. Hoffmann, "Tobacco and Tobacco Smoke: Studies in Experimental Carcinogenesis", Academic Press, New York and London, 1967, p 730.
Received for review December 20, 1974. Accepted February 7, 1975. Reference to a company or product name does not imply approval or recommendation by the USDA.
Quantitative Gas Chromatographic Determination of Ethanolamines as Trimethylsilyl Derivatives Ryszard Piekos, Krzysztof Kobylczyk, and Janusz Grzybowski Institute of Chemistry and Analytics, Faculty of Pharmacy, Medical Academy, 80-416 Gdansk, Poland
Individual components of ethanolamine mixtures, comprising mono-, di-, and triethanolamine are usually determined by chemical methods. The methods are said to be nonspecific and mostly inaccurate. Their brief characterization is to be found in the work of Brydia and Persinger
U).
Direct gas chromatographic determination of ethanolam-
ines is complicated by their low volatility owing to the strong hydrogen bonding character which causes tailing chroma(1). The best separation was achieved by vacuum tography with a copper tube, 0.5 m by 0.3 cm, packed with diatomaceous earth, grain size 0.25-0.5 mm, impregnated with 25% polyethylene glycol 6000, and operated at 195 °C with helium carrier gas flow rate of 18 ml/min (2). A more convenient procedure has been developed by Brydia and Persinger (1), who converted ethanolamines to their trifluoroacetyl derivatives and determined them by gas chromatography. This method turned out to be simple and rapid, and provided impurity information which was unobtainable from the chemical method. However, when an ethanolamine mixture contained water, trifluoroacetic acid was liberated which tailed badly. A slight tailing of the derivative peak was also observed with new columns, which disappeared after several analyses. These shortcomings have now been eliminated by con-
version of ethanolamine mixtures to their trimethylsilyl (TMS) derivatives prior to separation. The trimethylsilylation method has been used widely for the separation and gas chromatographic determination of compounds carrying -OH, -NH, -NH2, -COOH, and -SH groups (3-5). More recent works on related analyses are: that of Champion and Jones (6), concerning determination of other alkanolamines by gas chromatography of acetyl derivatives and that of Cancalon and Klingman (7) on the determination of ethanolamine and other hydroxy amines as trifluoroacetyl and trifluoroacetyl/trimethylsilyl derivatives.
EXPERIMENTAL Apparatus. A Pye 104 gas chromatograph equipped with a flame ionization detector was used. The chromatograms were recorded on a Philips PM 8010 chart recorder. Chromatographic Columns. Glass columns were used (152.4 cm = 5 feet long X 0.4-cm i.d.) packed with 3% OV-1 coated on 100/120 mesh Diatomite CQ. The columns were preheated overnight at 240 °C with a carrier gas flow rate of 60 ml/min. Operating Parameters. The detector temperature was 210 °C, and the injection port was maintained at 190 °C. Argon and nitrogen were used as carrier gases at a flow rate of 19 ml/min. The chart speed was 1 cm/min. Injections were made with a 1 µ syringe, and injected volumes varied between 0.4 and 0.7 µ . The volumes were dependent on the magnitude of correction factors of the TMS derivatives considered. When the triethanolamine content of a mixture exceeded 90%, 0.7 µ was injected, since the TMS derivative of the amine has the greatest correction factor. In case of a high (>90%) monoethanolamine content, a 0.4-µ1 injection was satisfactory. For the remaining cases, intermediate volumes were employed. The column temperature was isothermal at 130 °C for 2 min and 15 sec, then programmed to 180 °C at 49°/min, and held at 180 °C until the analysis has been completed. An attenuation of the order of 5 X 104 resulted in a stable base line even with a fast rate of temperature increase employed. Peak area was calculated by multiplying the width of a peak at half-height by peak height at maximum. Chemicals. The trimethylsilylation agent, A,0-bis(trimethylsilyl)acetamide (BSA), was prepared according to the method of Klebe et al. (S), and had bp 71-73 “C/35 mm Hg. Monoethanolamine (>99%) was the product of Carlo Erba, Milan, Italy, and diand triethanolamine were pure commercial products manufactured by POCh, Gliwice, Poland. Procedure. About 0.02 ml of an ethanolamine mixture was added to a 2-ml stoppered test tube, followed by 1 ml of BSA. An exothermic reaction ensued. The content was then shaken for 1 min to obtain a homogeneous solution, and maintained in a water bath at 60 °C for 20-30 min, or for 2 hr at room temperature. The time was reduced by half with binary mixtures containing monoand triethanolamine, since each of them could be derivatized quantitatively much more readily than diethanolamine. Under the conditions indicated, complete trimethylsilylation of ethanolamANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
·
1157
Table I. Response Factors and Derivative Data for Components of Ethanolamine Mixtures Tris-TMS derivative
AbbreviaComponent
tion
Monoethanolamine Diethanolamine Triethanolamine
MEA DEA TEA
Bp/mm Hg Mol
20
*20 j 4
D
Relative
Approx.
response
retention
(7)
(7)
(7)
factor
time, min
80°/4 74°/2 119V2
1.4345 1.4290 1.4310
0.8551 0.8692 0.8945
0.22 0.63 1.00
1.95 5.42 8.20
Wt
277.64 321.69 365.74
n
Table II. Weight Per Cent Analyses of Trimethylsilyl Derivatives of Ethanolamines by Gas Chromatography Determined0
Added MEA
DEA
TEA
MEA
DEA
TEA
32.0 17.1
33.2 24.7 65.8 94.2
34.8 58.2 16.7 2.9 98.1 2.0 5.0 98.0 65.6 2.5
32.0 17.1 17.4 2.8
33.8 24.4 65.9 94.2
1.1
1.1
34.2 58.5 16.6 3.0 97.8
17.5 2.9 0.8
1.1
96.0 2.0 95.7 2.0 4.1 90.9 4.2 90.6 0 2.0 2.1 0 34.4 0 34.3 0 0 97.5 97.1 0 All results are averages of two determinations.
Figure 1. Chromatogram of trimethylsilyl derivatives of ethanolamines
ines occurred. One-half microliter samples were usually introduced into the gas chromatograph by means of a l-µ syringe.
RESULTS AND DISCUSSION Under the conditions employed, BSA reacts with the hydroxyl and the amino groups of the ethanolamines as shown in the following general equation: OSi(CH3)3 H2 N (C H2 C H2 OH )3_ „ +
3CH3C(:0)NHSi(CH3)3
3CH3C^ XNSi(CH3)3 +
—>-
[(CH3)3Si]X(CH2CH2OSi(CH3)3]3.„ (1)
where
=
0, 1, 2.
The products of these reactions were verified by preparation of the derivatives and comparison of their physicochemical characteristics with those reported in the literature (9). The side product of silylation, N-trimethylsilylacetamide (MSA), had retention time of ca. 1.5 min and eluted along with the excess of BSA. Reactions of the ethanolamines with BSA are quantitative under the conditions of the method. Derivative prepa1158
·
ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
2.3 5.2 97.9 65.7 2.9
ration is simple and rapid. Complete elution of all volatile derivatives requires less than ten minutes, and overall analysis time including calculations takes about one hr. In case of binary mixtures comprising mono- and triethanolamine, the time is reduced by half. Peak X in the chromatogram (see Figure 1) is due to incompletely silylated di- and/or triethanolamine in which only two hydroxyls have been silylated. Thus, it may be useful for monitoring the completeness of trimethylsilylation of the two amines. Figure 1 shows a chromatogram of an almost completely trimethylsilylated mixture which contained 4.2% of monoethanolamine (MEA), 90.6% of diethanolamine (DEA), and 5.2% of triethanolamine (TEA). For quantitative trimethylsilylation, a slight extension of the silylation time is required. Commercial ethanolamines contain low concentrations (
