Biomedical Engineering Reference
In-Depth Information
Bond Elut (Agilent) and CBA ISOLUTE (International Sorbent technology) both
representing an irregular end-capped mixed-mode phase of a weak cation exchanger
(carboxylic acid) and a mid-polarity sorbent.
N
-butyl-scopolamine was extracted
accordingly from equine urine [
78
]. Elution of analytes was achieved by the use of
a methanolic solution acidified either with 1 M HCl [
54
] or 1 % formic acid [
78
]
allowing competition between QTA and hydronium ions. Recoveries were between
96 and 103 % [
54
] (Table
4
).
In contrast, alkalized solvents were used to elute hyoscyamine [
48
] and atropine
and scopolamine [
11
] from cation exchange adsorbent by inducing deprotonation of
protonated TTA thus neutralizing the analytes and preventing from attractive ionic
interaction.
In addition to the silica-based materials mentioned above, modern polymers are
widely used for TTA and QTA sample preparation allowing SPE not impaired by
undesirable silanol activities. HLB Oasis (Waters) is the tradename for a hydro-
philic-lipophilic balance reversed-phase sorbent enabling lipophilic interaction to
benzene moieties and hydrophilic interactions to pyrrolidone groups as present in
the macroporous copolymer of poly(divinylbenzene-co-
N
-vinylpyrrolidone).
Elution of analytes is often performed with solvents containing MeOH or ACN.
Applying this adsorbent TA such as atropine and scopolamine were extracted from
human viscera [
15
] , human serum [
97-
99
] , human urine [
12
] as well as from rat
plasma and brain microdialysate [
77
]. Furthermore, this hydrophilic-lipophilic bal-
ance phase was also suitable for extraction of the QTA trospium from human and rat
plasma [
77,
84
] and methyl scopolamie from rat plasma [
77
] (Table
4
).
More conventional SPE procedures make use of single cartridges or tubes that
may be processed in a multiple-port vacuum manifold for simultaneous preparation
of a reasonable number of samples. Further improvement of sample throughput and
reduced manual working steps was realized by an automated design originally pre-
sented by Oertel et al. for scopolamine analysis in a PK study using atropine as IS
[
97
]. An ASPEC XL sample processor (Gilson) operated with Oasis HLB cartridges
was used for microanalytical preparation of just about 200 ml serum for each sam-
ple. Any preconditioning, sample loading, washing and elution step was carried out
automatically. Liquid flow was established by high air pressure at the top of car-
tridge in contrast to typical vacuum applied at the bottom of the device. At last,
evaporation of eluates required an additional manual working step. However, recov-
ery of scopolamine was found to be only 51 % independent of the concentration
yielding an appropriate LOQ of 20 pg/ml [
97
] (Table
4
). Interday precision was
adequate (5.9-14.1 %).
The same instrumental design was also applied by Stetina et al. to quantify sco-
polamine in human serum for a PK study [
98
] (Table
4
).
Automation for improved throughput was also established by the use of 96-well
plates allowing the extraction of smallest sample volumes in the microliter range.
Callegari et al. recently published a method to extract the QTA trospium from 50 m l
plasma and brain homogenate samples using HLB Oasis sorbent [
77
] (Table
4
).
A satisfying LOQ (0.1 ng/ml) was obtained when adding atropine as IS thus allowing
