Characterization of human placental alkaline phosphatase by activity and protein assays, capillary electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Placental alkaline phosphatase (PLAP) that had been isolated from human placenta was further purified using subsequent ion-exchange chromatography (IEC), affinity chromatography (AC) and centrifugal membrane concentration (CMC). During the process, the PLAP samples from the different stages of purification were characterized regarding purity and activity. This was accomplished by combining Lowry analysis, enzymatic activity assay, capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE) and matrix-assisted laser desorption/ionisation time of flight mass spectrometry (MALDI-TOF-MS). The sample obtained after IEC had a rather low specific activity (6.8 U/mg) and appeared to contain several major contaminants, among which was human serum albumin (HSA). AC followed by CMC yielded PLAP with a specific activity of 128 U/mg. The purity and identity of the protein was indicated by MALDI-TOF-MS yielding a spectrum with one major peak at m/z 58,101. Interestingly, CZE of the pure PLAP revealed a cluster of peaks, which probably reflects the presence of various glycoforms and/or oligomers. The same analytical approach was used to characterize commercially available PLAP. This sample showed a moderate specific activity (15 U/mg) and appeared to be highly impure containing various other proteins.

Towards a general approach for the impurity profiling of drugs by micellar electrokinetic chromatography

A general micellar electrokinetic chromatographic (MEKC) strategy for the impurity profiling of drugs was developed involving a sodium dodecyl sulfate (SDS) and a cetyltrimethylammonium bromide (CTAB) MEKC system. With this combination, in principle, each sample component passes the detector in at least one of the two MEKC systems provided that separation buffers of the same pH are used in both systems. In order to select the proper MEKC systems, the electroosmotic flow (EOF) and micelle migration time (t(mc)) were determined for separation buffers of several pH values, containing various amounts of surfactant and organic modifier. The selectivity of the MEKC systems was studied using a mixture of compounds with a wide range of physico-chemical properties. The final selection of two adequate MEKC systems for this approach was based on the requirements that the t(mc) (i.e., analysis time) of both systems was below 20 min and that the t(mc)/t(eof) ratio was above 3 or 2 for the SDS and CTAB system, respectively. Furthermore, the systems should provide high efficiency, exhibit differences in selectivity and use moderate concentrations of modifier and surfactant, so that, if needed, further optimization is possible. The selected MEKC systems contained 60 mM SDS or 10 mM CTAB, respectively, in a phosphate buffer (pH 7.5) with 10% acetonitrile. Some test compounds with extreme mobilities were used to demonstrate the suitability of the MEKC approach to detect each component of a sample. The potential of the proposed MEKC combination for impurity profiling was demonstrated by the analysis of fluvoxamine with several impurities at the 0.1% level.

Capillary electrochromatography of basic compounds using octadecyl-silica stationary phases with an amine-containing mobile phase

The capillary electrochromatographic (CEC) analysis of basic compounds on octadecyl-silica stationary phases (Hypersil ODS and Spherisorb ODS I) was studied. A basic drug (fluvoxamine) and one of its possible impurities were used as test compounds. With an eluent of acetonitrile-phosphate buffer (pH 7.0), the compounds could be baseline-separated; however, broad and tailing peaks were obtained. To minimise detrimental interactions with residual silanol groups, the pH of the mobile phase was lowered to 2.5, but the plate numbers were still quite low (<2.6x10(4) plates/m). Addition of a masking agent (hexylamine or triethylamine) to the mobile phase resulted in much better peak efficiencies (ca. 1x10(5) plates/m). Therefore, the influence of the amine concentration and pH of the mobile phase on the CEC performance (peak width, peak tailing, electroosmotic flow, selectivity) was investigated in detail. Highest efficiencies (2.8x10(5) plates/m) could be obtained with the Spherisorb column, while the Hypersil column offered a better selectivity. Furthermore, the results show that the residual silanol groups are (at least partly) responsible for the separation of the basic compounds and that the amount of injected sample has an unusually large effect on the peak efficiency. The usefulness of the system for impurity profiling was demonstrated with a mixture containing fluvoxamine and its stereoisomer (a possible impurity) at the 0.1% level. The general effectiveness of amine additives in CEC was illustrated by the separation of a mixture of five structurally different basic drugs yielding plate numbers in the 1x10(5)-3x10(5) plates/m range. Comparison with capillary electrophoretic analysis revealed a unique selectivity of the CEC system which is based on both electrophoretic mobility and chromatographic partitioning.

Liquid chromatography-Fourier-transform infrared spectrometry

Over the past years the coupling of liquid chromatography (LC) and Fourier-transform infrared spectrometry (FT-IR) has been pursued primarily to achieve specific detection and/or identification of sample constituents. Two approaches can be discerned in the combination of LC and FT-IR. The first and simpler approach is to use a flow cell through which the effluent from the LC column is passed while the IR spectra are continuously recorded. The second approach involves elimination of the LC solvent prior to IR detection using an interface which evaporates the eluent and deposits the analytes onto a substrate. This paper provides a general overview of flow-cell based IR detection and briefly discusses early solvent-elimination interfaces for LC-FT-IR. A more comprehensive description is given of interface systems which use spraying to induce rapid eluent evaporation, and which basically represent the state-of-the-art in LC-FT-IR. Finally, the interface systems suitable for reversed-phase LC are summarized and the perspectives of LC-FT-IR are discussed. The overview indicates that flow-cell LC-FT-IR has rather poor detection limits but can be useful for the specific and quantitative detection of major constituents of mixtures. Solvent-elimination techniques, on the other hand, provide much better sensitivity and enhanced spectral quality which is essential when unambiguous identification of low-level constituents is required.

Profiling of cocaine by micellar electrokinetic chromatography

The potential of micellar electrokinetic chromatography (MEKC) for the profiling of cocaine samples is described. An MEKC system containing sodium dodecyl sulfate (SDS) and methanol was optimized using a test mixture of cocaine, its common impurities (benzoylecgonine, norcocaine, tropacocaine, and trans-cinnamoylcocaine), and several degradation products. The effect of pH, percentage modifier, and concentration surfactant on the separation has been investigated. The optimal separation buffer for cocaine samples consisted of 75 mM SDS, 17.5% methanol, and 25 mM borate (pH 8.3) and was well suited to separate components of diverse polarity in one run. Various cocaine seizures have been analyzed with the MEKC system and their signatures were compared. The electrokinetic chromatograms obtained were characteristic, and differences and similarities among the samples could easily be observed. Several impurities were identified in the samples by means of migration times and comparison of recorded and library UV spectra. The composition of the samples was determined semiquantitatively using relative corrected peak areas.

Choice of capillary electrophoresis systems for the impurity profiling of drugs

In order to develop a strategy for the impurity profiling of drugs, the possibilities of some capillary electrophoresis systems were investigated. A mixture containing a drug and some of its possible impurities has been used as a model problem. The test compounds were investigated by capillary zone electrophoresis (CZE) and by micellar electrokinetic chromatography (MEKC). The pH of the CZE buffer was varied, but the two stereoisomers could not be separated. Moreover, CZE is not suitable for neutral compounds. In MEKC, two different types of surfactants, sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB), have been used and the effect of type and concentration modifier on the separation and the elution window was studied. In the SDS system, both the resolution and the elution window could be increased considerably by the addition of modifier. The use of two MEKC systems of different selectivity seems to be a combination with high potential for the impurity profiling of drugs.

Lanthanide luminescence quenching as a detection method in ion chromatography. Chromate in surface and drinking water

Dynamic quenching of Eu(III) and Tb(III) luminescence by inorganic anions as a detection method in ion chromatography was investigated. To obtain a high luminescence intensity, lanthanide(III) complexes are formed with ligands which make indirect excitation of the ions possible. Only a few anions (e.g., nitrite, chromate) induce efficient dynamic luminescence quenching. Chromate is an efficient quencher of Tb-acac luminescence. Samples of tap water and surface water, spiked with chromate, were injected into a high-performance liquid chromatographic system with post-column addition of the luminescent complex. In this way, a detection limit of 1.1 . 10(-7) M (13 ppb) of chromate could be obtained.