Page 126 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

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in experiments performed in negative ionization mode. Between the two
instruments used, better matching results were obtained through the latter
mode which was also used for library data collection.
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Gergov et al. presented a very straightforward approach for the appli-
cation of LC/ESI/MS/TOF in toxicological screening. The features of TOF/MS
were utilized, i.e., high mass accuracy and high sensitivity over the full spec-
trum. On this base a library was established containing 433 toxicologically
relevant compounds (parent drugs and their metabolites), expanded simply
by the calculation of their monoisotopic masses. The mass range for com-
pounds included in the library extended from 105 to 734 Da. This library
was used for the identification of drugs in urine extracts, using gradient
elution in an ACN–ammonium acetate buffer at pH 3.2. The retention data
of drugs were stored but not used for identification in this study. The results
of LC/MS/TOF screening were in concordance with the results of GC and
TLC screening, run in parallel. According to the authors, the method is very
promising and allows screening for compounds with known formula even
without reference compounds. This is of practical value, particularly for
metabolites, due to the frequent lack of available reference standards. The
screening for metabolites using LC/ESI/MS/TOF was done by the same group
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in consecutive study. Ten previously analyzed autopsy urine samples were
subjected to LC/ESI/MS/TOF and the results were compared with the library
of theoretical masses of metabolites. Several metabolites of drugs (amitrip-
tyline, methadone, etc.) were identified.

2.6.2.2 Undirected Screening using LC/MS/MS Procedures
(QQQ, qTOF, and qIT)
An intralaboratory reproducibility of mass spectra obtained with similar or
different instruments is of primary relevance for the establishment and use
of mass spectra libraries. Weinmann, Gergov, and Goerner compared mass
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spectra obtained with two identical (Sciex API 365) and one different (Sciex
API 2000) LC/MS/MS in three laboratories. Methadone, benzoylecgonine,
and diazepam were used as test substances. Product ion spectra of proto-
nated quasi-molecular ions of more than 400 compounds were similar for
all laboratories. Also, in-source CID spectra showed good similarity with
the product ion spectra. The last point is very important because in the first
step of LC/MS screening, the in-source generated mass spectra are collected
and eventually confirmed in MS/MS analysis. Gergov et al. presented a
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LC/ESI/MS/MS screening procedure for 238 therapeutic and illicit drugs
extracted from blood with organic solvents at acidic and basic pH. Only a
positive ionization mode was applied. For each compound, the transition
from protonated quasi-molecular ion to one most intense or most specific
fragment was monitored. Also, retention time and peak area were used for

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