Abstract: Fecal sterol has been proposed as a chemical indicator
of human fecal pollution even when fecal coliform populations have
diminished due to water chlorination or toxic effects of industrial
effluents. This paper describes an improved derivatization procedure
for simultaneous determination of four fecal sterols including
coprostanol, epicholestanol, cholesterol and cholestanol using gas
chromatography-mass spectrometry (GC-MS), via optimization study
on silylation procedures using N-O-bis
(trimethylsilyl)-trifluoroacetamide (BSTFA), and
N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide
(MTBSTFA), which lead to the formation of trimethylsilyl (TMS) and
tert-butyldimethylsilyl (TBS) derivatives, respectively. Two
derivatization processes of injection-port derivatization and water bath
derivatization (60 oC, 1h) were inspected and compared. Furthermore,
the methylation procedure at 25 oC for 2h with
trimethylsilydiazomethane (TMSD) for fecal sterols analysis was also
studied. It was found that most of TMS derivatives demonstrated the
highest sensitivities, followed by methylated derivatives. For BSTFA
or MTBSTFA derivatization processes, the simple injection-port
derivatization process could achieve the same efficiency as that in the
tedious water bath derivatization procedure.
Abstract: Fecal coliform bacteria are widely used as indicators of
sewage contamination in surface water. However, there are some
disadvantages in these microbial techniques including time consuming
(18-48h) and inability in discriminating between human and animal
fecal material sources. Therefore, it is necessary to seek a more
specific indicator of human sanitary waste. In this study, the feasibility
was investigated to apply caffeine and human pharmaceutical
compounds to identify the human-source contamination. The
correlation between caffeine and fecal coliform was also explored.
Surface water samples were collected from upstream, middle-stream
and downstream points respectively, along Rochor Canal, as well as 8
locations of Marina Bay. Results indicate that caffeine is a suitable
chemical tracer in Singapore because of its easy detection (in the range
of 0.30-2.0 ng/mL), compared with other chemicals monitored.
Relative low concentrations of human pharmaceutical compounds (<
0.07 ng/mL) in Rochor Canal and Marina Bay water samples make
them hard to be detected and difficult to be chemical tracer. However,
their existence can help to validate sewage contamination. In addition,
it was discovered the high correlation exists between caffeine
concentration and fecal coliform density in the Rochor Canal water
samples, demonstrating that caffeine is highly related to the
human-source contamination.
Abstract: Fecal sterol has been proposed as a chemical indicator
of human fecal pollution even when fecal coliform populations have
diminished due to water chlorination or toxic effects of industrial
effluents. This paper describes an improved derivatization procedure
for simultaneous determination of four fecal sterols including
coprostanol, epicholestanol, cholesterol and cholestanol using gas
chromatography-mass spectrometry (GC-MS), via optimization study
on silylation procedures using N-O-bis
(trimethylsilyl)-trifluoroacetamide (BSTFA), and
N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide
(MTBSTFA), which lead to the formation of trimethylsilyl (TMS) and
tert-butyldimethylsilyl (TBS) derivatives, respectively. Two
derivatization processes of injection-port derivatization and water bath
derivatization (60 oC, 1h) were inspected and compared. Furthermore,
the methylation procedure at 25 oC for 2h with
trimethylsilydiazomethane (TMSD) for fecal sterols analysis was also
studied. It was found that most of TMS derivatives demonstrated the
highest sensitivities, followed by methylated derivatives. For BSTFA
or MTBSTFA derivatization processes, the simple injection-port
derivatization process could achieve the same efficiency as that in the
tedious water bath derivatization procedure.