Dialysis-solid-phase extraction combined on-line with non-aqueous capillary electrophoresis for improved detectability of tricyclic antidepressants in biological samples.

Dialysis-solid-phase extraction (SPE) sample pretreatment is combined on-line with non-aqueous capillary electrophoresis for the determination of tricyclic antidepressants in urine and serum. After clean-up and enrichment, the water is removed from the sample matrix and the analytes are eluted from the cartridge by means of an organic solvent. Next, the eluate is transported to the capillary and the injection is performed electrokinetically. This injection, which does not suffer from an adverse sample matrix effect because of the SPE step, results in further analyte concentration. The detection limits are in the 0.02-0.1 microg/ml range and the day-to-day repeatabilities are between 2.5 and 9.5%, which is quite satisfactory.

On-line dialysis-SPE-CE of acidic drugs in biological samples.

A fully automated method is presented for the determination of acidic drugs in urine and serum using on-line dialysis-solid-phase extraction (SPE)-capillary electrophoresis (CE) with UV detection. With non-steroidal anti-inflammatory drugs (NSAIDs) as test compounds, detection limits in the biological samples were 0.05-1.0 microgram ml-1. Calibration plots were linear over two orders of magnitude and the within-day and between-day repeatability were better than 10%. The CE capillary and SPE column were used for over 500 analyses; the dialysis membrane was replaced after 250 analyses. A general protocol for dialysis-SPE-CE which can be used for amphoteric and acidic drugs was devised. The present results show that this protocol has general validity and can be recommended for future work on other classes of drugs.

Coupling of biological sample handling and capillary electrophoresis.

The analysis of biological samples (e.g., blood, urine, saliva, tissue homogenates) by capillary electrophoresis (CE) requires efficient sample preparation (i.e., concentration and clean-up) procedures to remove interfering solutes (endogenous/exogenous and/or low-/high-molecular-mass), (in)organic salts and particulate matter. The sample preparation modules can be coupled with CE either off-line (manual), at-line (robotic interface), on-line (coupling via a transfer line) or in-line (complete integration between sample preparation and separation system). Sample preparation systems reported in the literature are based on chromatographic, electrophoretic or membrane-based procedures. The combination of automated sample preparation and CE is especially useful if complex samples have to be analyzed and helps to improve both selectivity and sensitivity. In this review, the different modes of solid-phase (micro-) extraction will be discussed and an overview of the potential of chromatographic, electrophoretic (e.g., isotachophoresis, sample stacking) and membrane-based procedures will be given.

On-line dialysis solid-phase extraction coupled to capillary electrophoresis.

A fully automated dialysis solid-phase extraction (SPE) sample preparation procedure is coupled on-line to capillary electrophoresis (CE) for the first time. The system is used to determine sulfonamides in serum and urine. The dialysis unit serves to remove proteins and particulate matter. Reconcentration of the analytes is performed with a small SPE column while (in)organic salts and other interferences are removed simultaneously. Finally, the analytes are desorbed and injected, via a homemade interface, into the CE system. Limits of detection (LOD) of 0.05-0.1 and 0.05-0.3 microg/mL are obtained in urine and serum, respectively. The within-day and between-day precisions are in the range of 2-6% and 3-8%, respectively, for a concentration of five times the LOD. The dialysis SPE-CE system was used over a period of six months for the analysis of over 500 serum and urine samples without problems such as clogging of the CE capillary or SPE column.

At-line solid-phase extraction for capillary electrophoresis: application to negatively charged solutes.

The analysis of complex biological samples with capillary electrophoresis (CE) requires proper sample pretreatment. In this paper the applicability of solid-phase extraction (SPE) coupled at-line with CE is studied, by using a laboratory-made interface. A fresh (disposable) SPE cartridge is used for each sample to prevent carry-over effects. The sample handling procedure is performed parallel with the analysis of the previous sample, to improve sample throughput. Using this set-up, negatively charged test compounds (some non-steroid anti-inflammatory drugs) can be determined in serum and urine. The method is linear over at least two decades and detection limits are around 40 microg/l. A single capillary, flushed only once a week with a sodium hydroxide solution, was used without problems for the analysis of ca. 900 samples during 1 year. The robustness of the system was very good: no blocking of loop, interface or capillary was found during this period. Furthermore, the system was successfully used for overnight runs.

A novel pyrroleninone cross-link from bovine dentine.

The aim was to identify suspect collagen cross-links in dentine, eluting close to known cross-links in ion-exchange HPLC. Bovine tooth roots as source of dentine were powdered, demineralised, reduced, and acid-hydrolysed. Cross-linking amino acids were isolated from the acid hydrolysate by size exclusion, adsorption, and sequential ion exchange chromatography. In addition to dihydroxylysinonorleucine and hydroxylysylpyridinoline, an unknown cross-link was isolated (V-2). The ultraviolet, mass, and nuclear magnetic resonance spectra support the proposed structure of V-2, a trimeric amino acid with a pyrroleninone nucleus.

Capillary electrophoresis of the collagen crosslinks HP and LP utilizing absorbance, wavelength-resolved laser-induced fluorescence and conventional fluorescence detection.

A capillary electrophoretic (CE) method is presented for the determination of the collagen crosslinks hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP). Various detection techniques are compared, i.e. UV-Vis diode-array absorbance detection (DAD) and fluorescence detection both in the laser-induced fluorescence (LIF) and the conventional fluorescence mode. LIF detection was performed using a frequency-doubled Rhodamine dye laser pumped by an excimer laser, for excitation at 290 and 325 nm. The emission was measured with an intensified diode-array detector mounted on a spectrograph to obtain wavelength-resolved spectra. Relevant concentration detection limits were achieved only by using LIF detection, i.e. 200 nM of HP and LP in a 30 mM phosphate buffer (pH 2.0). Linear calibration curves were obtained from the detection limits up to the maximum concentration available, 23 microM for HP and 4.2 microM for LP, respectively for both fluorescence modes. The identity of the migrating compounds was confirmed by on-line recording of both the absorption and the fluorescence spectra.

Determination of phenprocoumon in plasma and urine using at-line solid-phase extraction-capillary electrophoresis.

The use of capillary electrophoresis (CE) for the analysis of biological samples is rather problematic because of the large number of interferences present in the matrix. One of the possibilities to solve such problems is to couple solid-phase extraction (SPE) at-line with CE, a technique developed in our laboratory. In this study at-line SPE-CE is performed for the determination of the anticoagulant phenprocoumon in biological fluids. Plasma samples are injected after the addition of 1 vol.% of formic acid to release the drug from binding proteins, while urine samples can be directly injected. The procedure is linear between 0.2 and 30 microg ml(-1) with a correlation coefficient, r2, of 0.9996. The detection limit in plasma is 0.1 microg ml(-1), which is fully adequate in view of the concentrations, that have to be dealt with in practice. The phenprocoumon concentration in a plasma sample of a patient treated with the anticoagulant was 3.8 microg ml(-1).

Evaluation of phytic acid as a buffer additive for the separation of proteins in capillary electrophoresis.

The use of phytic acid to improve protein analysis by capillary electrophoresis (CE) is becoming more and more popular. Due to its size and number of negative charges (up to 12) it provides a high ionic strength combined with a low conductance resulting in an efficient decrease of wall adsorption for proteins. Because of its twelve acidic groups, phytic acid can be used as a buffer over a wide pH range (pH 2-11). The limited wall adsorption of proteins using phytic acid-containing buffers is observed for buffers with a pH of 5.5 and higher. With a monoprotic buffer, most of the investigated proteins show wall adsorption at the pH values studied. In case of a phytic acid buffer, wall adsorption is reduced by a factor of 2-4. The use of phytic acid both as a modifier and as a pH buffer results in more pronounced differences between the various protein mobilities compared with the use of monoprotic buffers. As a result this feature can be used to improve resolution in protein separations.