Biomedical Engineering Reference
In-Depth Information
(LC-MS). LC-MS combines the power of MS detection with the versatility of LC,
which allows chromatographic separation of thermally unstable analytes, as well as
compounds with a wide range of polarities without performing derivatization
processes. For this reason, LC-MS and LC-MS/MS applications for the analysis of
antidepressants have significantly grown over the last decade.
2
Sample Preparation for Antidepressants
LC-MS(MS) Analysis
In the early stages of LC-MS, it was thought that the high selectivity provided by this
technique could effectively eliminate intereferences caused by endogenous matrix
compounds, and thus, the need for sample cleanup [
26
]. However, nowadays, it is
well known that one limitation associated to LC-MS analysis is the suppression or
enhancement on the analyte response when coeluting undetected compounds com-
pete with the analyte in the ionization process [
27,
28
] . This phenomenon, generi-
cally known as matrix effect, may affect several validation parameters, such as the
limit of detection, linearity, precision, and accuracy. Therefore, matrix effect may
diminish method sensitivity and the reliability of quantitative results [
29
] . One of the
main strategies to overcome matrix effect is to minimize the presence of these coelut-
ing interferences through a more effective sample cleanup; thus, this step should be
always taken into consideration when developing an LC-MS method.
Most of the published analytical methods for the determination of antidepres-
sants were developed in plasma, serum, whole blood, and urine, which are the most
useful matrices for clinical and toxicological analysis of these therapeutic com-
pounds. However, albeit few, some LC-MS methodologies have also been described
for the analysis of several antidepressants in hair [
30-
33
] , oral fl uid [
34,
35
] , breast
milk [
36
], or typical forensic matrices such as gastric content, bile, vitreous humor,
brain, liver, lung, and/or muscle [
37-
40
] .
Some biological matrices, such as hair and internal organs, require a special
pretreatment prior to extraction. Hair samples must be washed to avoid external
contamination, including an initial organic solvent, followed by aqueous washes
[
41
]. After cutting or powdering, the hair matrix is usually disintegrated to extract
the analytes from its inner structure. Ultrasonication in methanol (MeOH) [
31,
32
]
or incubation in HCl [
33
] has been employed to extract antidepressants from the
hair structure. Internal organs should be initially homogenized, and this process
was usually performed in water or basic buffers by means of a blender or an ultra-
sonicator [
37-
40
]. In addition, urine hydrolysis is sometimes performed to break
glucuronide conjugates or some metabolites. b-Glucuronidase was employed for
urine hydrolysis of mirtazapine [
42
] and bupropion metabolites conjugates [
43, 44
] ,
and HCl was used for hydrolysis of 4-hydroxy-3-metoxy paroxetine metabolite
[
45
], prior to sample extraction.
Several sample preparation or extraction procedures have been described for the
analysis of antidepressants, from the most simple protein precipitation to online
