Biomedical Engineering Reference
In-Depth Information
0.67 M Sørensen phosphate buffer (pH 7.4) before mixed mode cation exchange
SPE on Oasis MCX SPE cartridges. Chromatographic separation was performed at
60 °C on a UPLC BEH C18 column. Authors assessed that high pH mobile phase
provided narrow and symmetrical peaks and repeatable retention times due to less
silanol interactions, increased retention, and increased load capacity; this was pos-
sible due to the use of a column compatible with both low pH and high pH mobile
phases. In literature there are several applications of MCX-SPE for urine sample
pretreatment. For example Aturki et al. [
127
] used MCX-SPE for urine sample pre-
treatment, but after the centrifugation of samples and filtration of supernatant. Urine
sample was loaded into the cartridge that was then dried under a stream of nitrogen
for 5 min. The cartridge was washed with phosphoric acid (10 mM, 2 ml), acetic
acid (100 mM, 1 ml), and methanol (2 ml). Retained analytes were eluted with 4 ml
of 3 % ammonia solution in methanol.
10.3.3
m SPE
A
m -SPE
approach was proposed for urine sample by Ellison et al. [
128
] . This group
used Disposable Pipette Extraction (DPX). DPX incorporates pipette tips that contain
solid-phase sorbent material loosely confined with a screen at the bottom narrow end
of the tip and a barrier near the top. DPX tips were selected as containing sorbent with
strong cation-exchange (CX) and reversed-phase characteristics. DPX-CX 1-ml tips
were used to extract drugs of abuse from the prepared urine samples. No conditioning
step was performed prior to extraction. The tips were loaded with the sample solution
by slowly aspirating the solution using an attached syringe device (in place of a
pipette) and vortex mixing for ~10 s (by holding the syringe with attached tip inside a
small test tube) to allow the solution to thoroughly mix with sorbent and create a gel
of high surface area. Extraneous material was washed from the tips by adding 500 m l
of distilled water to the top of the sorbent and dispensing. Authors, in this way, devel-
oped a comprehensive extraction for 6-MAM, BEG, morphine, codeine, oxycodone,
amphetamine, methamphetamine, MDMA, PCP, THC-COOH, and pentobarbital.
Recoveries were measured between 80 and 105 %.
Another mSPE-based method has recently been proposed by Napoletano et al.
[
67
]. Previously cited procedure applied at OF samples was exported with very
slight modifications to urine and plasma samples. Recovery in urine were verified at
SAMSHA cutoff concentration values [
129
], they ranged from 56 % for amphet-
amine and 90 % for PCP; RSD was always less or equal to 10 % and matrix effects,
valuated as reported above, were less or equal to 10 %.
10.4
Hair Analyses of Drugs of Abuse
Although sample collection would seem easier than other matrices such as urine and
plasma, this requires caution and has been encoded to be as significant as possible
