A. Kunkel et H. Watzig, Pharmacokinetic investigations with direct injection of plasma samples: Possible savings using capillary electrophoresis (CE), ARCH PHARM, 332(5), 1999, pp. 175-178
Capillary electrophoresis (CE) is often regarded as a separation technique
of choice because of its high selectivity and its cost advantages compared
to LC, RSD% of 0.5% have become standard for quality control assays. Using
CE, sample pretreatment can often be significantly reduced, leading to nota
ble savings of labor and regent costs. Moreover, errors from sample pretrea
tment are avoided. A number of pharmaceuticals (e.g. acetaminophen, salicyl
ic acid, sulfamethoxazole, theophylline, tolbutamide, and trimethoprim) hav
e been determined in human plasma on underivatized fused silica capillaries
by MEKC without sample pretreatment, the total analysis time being only 10
min. An sodium dodecyl sulfate-containing berate buffer (60 mM with 200 mM
SDS) at pH 10 has been used. Between runs, proteins adsorbed to the capill
ary wall are removed by a rinsing regimen consisting of SDS buffer and eith
er acetonitrile (e.g. 50% v/v) or isopropanol (e.g. 10% v/v). Other rinsing
approaches are discussed (salts, enzyme containing solutions, organic solv
ents, sodium hydroxide, hydrofluoric acid). The separation system is tested
in a concentration range between 10 ng/mL and 100 mu g/mL, the detection l
imit being about 5 ng/mL. The sensitivity has been substantially improved c
ompared to preceding work using field-amplified injection mechanisms and ef
ficient computer algorithms that take advantage of multiwavelength detectio
n. Correlations between the limit of quantitation (LOQ), the limit of detec
tion (LOD) and the signal/noise ratio are discussed. A day-to-day precision
for relative peak areas of 1 to 2% relsdv (n > 40) has been reached in the
upper concentration range. Thus, not only drug monitoring but also pharmac
okinetic investigations from blood plasma have become possible without furt
her sample pretreatment.