Anal. Chem. 1998, 70, 4389-4393
Direct Injection Gas Chromatographic/Mass
Spectrometric Analysis for Denatonium Benzoate
in Specific Denatured Alcohol Formulations
Lay-Keow Ng,*,† Michel Hupe´,† Jean Harnois,‡ and Andre´ H. Lawrence†
Research and Development Division and Excise Laboratory Division, Laboratory & Scientific Services Directorate,
Revenue Canada, Ottawa, Ontario, Canada K1A 0L5
matrixes, such as alcohol toilet preparations,1,2 rapeseed oils3 and
denatured alcohols.4 All these methods involve preconcentration
of Bitrex prior to chromatographic analysis. They are time-
consuming, require a large sample volume, and may suffer errors
inherent to the extraction process. Therefore, a direct approach
which does not involve any sample preparation for the determi-
nation of Bitrex in alcohol formulations is highly desirable.
Quaternary ammonium salts are thermally unstable. They
decompose at elevated temperatures to neutral molecules which
could be vaporized and subsequently analyzed by various separa-
tion techniques. Gas chromatography is an ideal analytical
technique for the determination of quaternary ammonium salts
because the heated injector port of the instrument allows in situ
decomposition of the salts. As such, transformation to neutral
molecules, vaporization, and analysis of the characteristic pyroly-
sates can be performed in a single step. Direct injector pyrolysis
has been previously applied to the analysis of quaternary am-
monium salts.5-7 For example, benzalkonium chlorides were
thermally degraded to alkyldimethylamines upon injection into a
gas chromatograph, and the pyrolysis products were used to
determine the homologous composition of the salt. Similarly,
Bitrex could be assayed by analyzing the nitrogen-containing
pyrolysates. In several Canadian formulations containing Bitrex,
other denaturants such as diethyl phthalate (DEP), camphor, and
sucrose octaacetate (SOA) can also be present. The concentration
levels of these components are usually 30-400 times higher than
that of Bitrex. Trace analysis of Bitrex in the presence of large
amounts of other denaturants requires a highly selective and
sensitive detection technique.
Direct injection GC/ MS was investigated for the analysis
of benzyldiethyl(2,6-xylylcarbamoylmethyl)ammonium ben-
zoate (Bitrex), a quaternary ammonium salt, in various
Canadian denatured alcohol formulations. Bitrex yielded
predominantly a peak due to the neutral diethylamine
derivative (I). The structure of I, elucidated by MS and
NMR, is strongly related to that of the cation of Bitrex.
Compound I was formed from Bitrex in the heated injector
port of the GC via a decomposition reaction similar to
Stevens rearrangement. The response of I was found to
be dependent on the injector port temperature, and the
optimal temperature was determined to be in the range
2 5 0 -3 5 0 °C. The GC/ MS response of I in SIM mode
was used to quantify Bitrex. The effects of the codena-
turants sucrose octaacetate (SOA), diethyl phthalate (DEP),
and camphor, which are present at much higher concen-
tration than Bitrex in several formulations, were also
investigated. The presence of SOA enhanced the re-
sponse of the analyte considerably, while DEP and
camphor had no significant effect. All standard curves
of Bitrex (1 -1 6 ppm) in different alcohol matrixes were
fitted by second-order polynomial functions, with coef-
ficients of determination (R2 ) routinely in the range
0 .9 9 8 -0 .9 9 9 . The analysis time was 1 8 min, and the
within-run precision was <4 %. The results of this study
point to the potential of the GC/ MS technique as a
quantitative tool for Bitrex in various alcohol formulations.
Bitrex, chemically known as benzyldiethyl(2,6-xylylcarbam-
oylmethyl)ammonium benzoate, is a highly bitter compound. It
is among the common substances used for denaturing alcohol.
The Canadian Government Regulations specify the level of Bitrex
in several formulations of specially denatured alcohol to be 7 ppm.
The rate of duty on the denatured alcohols depends on whether
the specifications are met. Various methods based on thin-layer
chromatography and high-performance liquid chromatography
have been applied to the determination of Bitrex in different
The objective of this study was to show that direct injection
GC/ MS operated in a selected ion monitoring mode (SIM) is a
feasible approach for the determination of Bitrex in various alcohol
formulations. Quantification of Bitrex was based on the deter-
mination of a rearranged pyrolysis product (I). The determination
of the structure of I by MS and NMR spectroscopy, and the
analytical characteristics of the technique, are described.
* To whom correspondence should be addressed. E-mail: rlkng@revcan.ca.
Fax: 613-952-7825.
(3) Damon, C. E.; Pettitt, B. C., Jr. J. Chromatogr. 1 9 8 0 , 195, 243-249.
(4) Kovar, J.; Loyer M. J. Liq. Chromatogr. 1 9 8 4 , 7, 2163-2177.
(5) Ng, L.-K.; Hupe´, M.; Harris, A. G. J. Chromatogr. 1 9 8 6 , 351, 554-559.
(6) Barry, B. W.; Saunders, G. M. J. Pharm. Sci. 1 9 7 1 , 60, 645-647.
(7) Lopez, A. F.; Peralta de Ariza, M. T.; Orio, O. A. J. High-Resolut. Chromatogr.
1 9 8 9 , 12, 503-504.
† Research and Development Division.
‡ Excise Laboratory Division.
(1) Glover, M. J.; Blake, A. J. Analyst 1 9 7 2 , 97, 891-896.
(2) Sogden, C.; Mayne, T. G.; Loscombe, C. R. Analyst 1 9 7 8 , 103, 653-656.
S0003-2700(98)00093-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/04/1998
Analytical Chemistry, Vol. 70, No. 20, October 15, 1998 4389