Biomedical Engineering Reference
In-Depth Information
AMPs was carried out using a C18 column, whereas opiates, PCP, cocaine, and
BEG were separated on a PFP column. This is an example of a good analytical
method that needs a time-consuming sample preparation and two chromatographic
runs for the achievement of the best performances [
115
] .
10.2.5
m SPE
Solid phase extraction usually needs at least 0.5 ml of sample, so it is not suitable
when a small amount of sample is available. A method based on m -SPE-HPLC-MS/
MS for simultaneous determination of stimulants and hallucinogens was developed
[
66
]. Amphetamine, methamphetamine, MDA, MDE, MDMA, cocaine, BEG, mes-
caline, ketamine, PCP, psilocybine were the target analytes. Extraction was carried
out using C18 tips, adapted to automatic pipettes. These tips are made of a fiberglass,
functionalized with apolar chains of octadecylsilane in a monolithic structure. Only
90 ml of OF is required: these were mixed with 10 ml of methanol containing deuter-
ated ISTDs (one for each class of substances). The mixed solution was sonicated
and centrifuged to precipitate proteins. The whole supernatant was then rescued and
passed through the tip by loading and releasing five times with the pipette. The
analytes elution was achieved using 100 ml of methanol. The analytes were sepa-
rated using a reversed phase C18, packed with 3 mm average diameter particles. The
complete separation of all substances occurs in 12 min.
Authors calculated the value of matrix effect comparing two calibration curves:
one created with blank samples, fortified after the extraction process, and the other
with standard solutions. Matrix effects, intended as ion suppression, calculated by
comparing the slopes of those curves are lower than 6 % for each analyte.
10.3
Urine
Urine samples are often submitted to enzymatic cleavage of gluconic or sulfuric
acid conjugates of drugs and/or their metabolites. This kind of treatment is a prereq-
uisite for the sensitive GC-MS analysis of drugs excreted into urine in conjugated
form, but it is not strictly required in LC-MS(/MS) analysis, because this technique
allows the direct analysis of such conjugates, e.g., glucuronides of opiates [
116-
118
] .
Nevertheless, many of the recently published methods for LC-MS(/MS)-based urine
analysis still include enzymatic conjugate cleavage.
Andersson et al. have recently proposed a direct injection LC-MS/MS method
for the identification and quantification of amphetamine, methamphetamine, MDA,
and MDMA in urine drug testing. The samples were prepared for analysis by
fivefold dilution with ultrapure water [
119
]. A gradient elution was performed using
two solvents: 25 mM formic acid containing 1 % acetonitrile and 25 mM formic
acid containing 90 % acetonitrile. Authors observed matrix effects, in terms of ion
suppression, about 25-fold. This method was used for real sample analysis and
