Page 82 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

1522_C02.fm Page 70 Wednesday, November 12, 2003 9:36 AM

New possibilities of LC/APCI/MS were demonstrated by the group of
Blair. APCI corona discharge generated low-energy electrons from the
31
nitrogen sheath gas, which ionized suitable analytes through electron capture.
This technique has been named electron capture APCI-MS and was applied
to the analysis of pentafluorobenzyl derivatives of various drugs and biomol-
ecules like steroids, prostaglandins, thromboxane, and amino acids. The
sensitivity of electron capture APCI was 25- to 100-fold higher than negative
ion APCI for underivatized compounds.

2.2.2.2 Choice of Mass Analyzer (Q vs. QQQ vs. IT
vs. qTOF)
It goes without saying that the use of tandem mass spectrometry instead of
single stage quadrupole gives obvious advantages concerning specificity and
sensitivity. The main obstacle of LC/MS/MS is the price. However, in the last
few years some manufacturers launched lower-cost bench-top tandem instru-
ments that may be widely applicable in forensic toxicological laboratories.
Some research groups performed comparative studies concerning vari-
32
ous mass analyzers applied in LC/MS. Clauwaert et al. applied the
LC/ESI/qTOF/MS for quantitative measurements of MDMA and its metab-
olite MDA in body fluids. The LOQ was 1 mg/l and the linear dynamic range
extended over four decades. It was concluded that this technique achieves
the linear dynamic range for LC/ESI/MS/MS. Zhang and Henion compared
33
the applicability of LC/ESI/qTOF/MS and LC/ESI/MS/MS for quantitative
analysis of idoxifene in human plasma. The drug and its deuterated analog
as an internal standard was isolated from plasma using a semiautomated 96-
well hexane extraction and separated on a 30 mm ¥ 2 mm CN column. This
column could separate target compound from the matrix, which was not
possible with the ODS column. For the TOF/MS instrument, an exact mass
of the protonated quasi-molecular ion was measured (m/z 524.1441), whereas
a MS/MS instrument was applied in SRM mode, using m/z 524.2 as a parent
ion and m/z 97.9 as a product ion. The comparison showed that the
LC/MS/MS technique was about ten times more sensitive than LC/qTOF/MS
(the LOQs for idoxifene were 0.5 mg/l and 5 mg/l, respectively). Both methods
showed satisfactory dynamic range. In conclusion, the authors stated that
LC/qTOF/MS might be used to complement LC/MS/MS in certain cases.
Comparison between an ion trap and single-stage quadrupole mass spec-
trometer was done for GC/MS by Vorce et al. The authors compared the
34
sensitivity, precision, and stability of ion ratios obtained for both mass ana-
lyzers, using urine extracts spiked with amphetamine, methamphetamine,
THC-carboxylic acid, phencyclidine, morphine, codeine, 6-monoacetylmor-
phine, and benzoylecgonine on five concentration levels for each drug. The
sensitivity of the ion trap used in the full-scale mode was comparable to

© 2004 by CRC Press LLC