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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 25, Number 7, October, pp. 602-606
Development of a Generic Method to the Solid-Phase Extraction
of Acidic Compounds from Complex Matrices
Diane M. Boland[1], Michael F. Burke[1], Tracy Mitchell[2],
and Paul Madley[2]
[1]Department of Chemistry, University of Arizona, P.O. Box 210041, Tucson,
Arizona 85721 and [2]International Sorbent Technology Ltd., Hengoed, CF827RJ,
United Kingdom
A mixed-mode solid-phase extraction procedure was developed for
the isolation and purification of acidic compounds from complex biological matrices.
Urine samples were spiked with several acidic drugs and diluted in ammonium
acetate buffer. Isolute HAX columns (a mixed-mode phase consisting of both hydrophobic
and ion-exchange ligands) were conditioned with methanol and ammonium acetate
prior to sample loading. Once the samples were loaded, the cartridges were rinsed
sequentially with ammonium acetate and a 50:50 ratio of methanol and deionized
water. The analytes were eluted with an 80:20 ratio of methanol and acetic acid.
The eluates were evaporated to dryness and reconstituted to a final volume with
a 98:2:0.1 ratio of deionized water, acetonitrile, and trifluoroacetic acid.
Samples were analyzed by high-performance liquid chromatography. The absolute
recoveries for most of the tested acidic drugs exceeded 80% at an original concentration
of 1 mg/mL. Hydrophobic and ion-exchange sorbents were also investigated separately;
however, the retention of the analytes suffered during sample application as
well as the purity of the eluted extract. Results on anion-exchange columns
show that the correct choice of counter-ion is extremely important to the retention
of acidic analytes. The highest absolute recoveries were obtained when acetate
was the counter-anion on the ion-exchange sorbent.
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