Biomedical Engineering Reference
In-Depth Information
offers great potential for routine urine drug testing as the time for sample preparation
can be shortened since no extraction and derivatization is needed. Same authors in
2007 had proposed direct injection of urine sample for confirmatory analysis of opi-
ates and their glucuronide metabolites [
118
] .
Peters noted in a recent review [
52
] that only a few works published have used
simple dilution for the preparation of urine samples. The dilution factors ranged from
5- to 50-fold. Eichhorst et al. also used (tenfold) dilution in their procedure, but only
after urine samples had been submitted to enzymatic conjugate cleavage [
120
] .
10.3.1
LLE
Maquille et al. [
121
], due to the physicochemical properties (i.e., polarity and ion-
ization state) of the investigated drugs (opiates, amphetamine, cocaine and metabo-
lites), concluded that LLE should be selected. To automate the sample preparation
procedure, this team proposed urine extraction by supported liquid-liquid extrac-
tion (SLE), a promising technique that appeared in 1997 [
122
], which can be easily
automated in a 96-well plate format. It has been demonstrated that matrix effect is
signi fi cantly minimized.
10.3.2
SPE
Fernandez et al. [
123
] proposed a high throughput analysis of THC-COOH. It is rare
that one finds LC-MS/MS application to only one analyte, but sometimes there are
specific requests. THC-COOH exists in both the free and glucuronide form, so authors,
in order to improve sensitivity, performed sample enzymatic conjugate cleavage by
basic hydrolysis. Similar hydrolysis procedures have been described by other authors
[
97,
124,
125
]: these strong hydrolysis conditions can only be applied to molecules
like THC or THC-COOH which are very resistant, thus, multiclass analysis address
“softer” enzymatic hydrolysis. Elution of the analytes from the cartridge was achieved
by the application of the LC mobile phases: 0.1 % formic acid and acetonitrile during
the chromatographic run. Whilst the elution step was being performed, a new car-
tridge was conditioned, loaded, and washed in the left clamp. Although the analyte
has a carboxylic group, the authors selected ESI in positive ionization mode to create
their MRM experiments with [M+H]
+
as precursor ion.
The use of online SPE in the column-switching mode is particularly adapted to
illicit drug analyses, on the other hand the offline SPE on multiwell plates is qualified
for multianalyte procedures: since each sample is independently extracted, this for-
mat is compatible with different separation techniques working with different
mechanisms (reversed or normal phase, ion exchange, etc.); reduces contamination
risk; presents a great advantage in analyses where a legal aspect has to be taken into
account; it does not require a particular technical skill [
62
] .
Berg et al. [
126
] have developed a method for the determination of opiates and
cocaine in urine. Sample preparation was performed by adding ISTDs and 0.5 ml of
