10 years of MS instrumental developments--impact on LC-MS/MS in clinical chemistry

The combination of liquid chromatography and mass spectrometry (LC-MS) is a powerful and indispensable analytical tool that is widely applied in many areas of chemistry, medicine, pharmaceutics and biochemistry. In this review recent MS instrumental developments are presented as part of a special issue covering various aspects of liquid chromatography tandem mass spectrometry (LC-MS/MS) in clinical chemistry. Improvements, new inventions as well as new combinations in ion source technology are described focusing on dual or multimode sources and atmospheric pressure photoionization (APPI). Increasing demands regarding sensitivity, accuracy, resolution and both quantitation and identification guarantee on-going improvements in mass analyzer technology. This paper discusses new hybrid MS instruments that can perform novel scan modes as well as high-resolution mass spectrometers (HRMS) that finally seem to be able to overcome, or at least significantly reduce, their weaknesses in quantitative applications. Ion mobility-mass spectrometry (IMMS) itself is not an invention of the last 10 years, but a lot of progress was made within the last decade that reveals the potential benefits of this combination. This is clearly reflected by the increased number of commercially available instruments and the various designs of IMMS are covered in detail in this review. Selected applications for all these instrumental developments are given focusing on the perspective of clinical chemistry.

Microemulsion electrokinetic chromatography with on-line atmospheric pressure photoionization-mass spectrometric detection of medium polarity compounds

In this paper, we present the determination of pharmaceuticals employing microemulsion electrokinetic chromatography (MEEKC) with atmospheric pressure photoionization-mass spectrometric (APPI-MS) detection. This recent hyphenated technique allows to overcome some disadvantages of MEEKC, namely its inherent incompatibility with MS detection. Important parameters like microemulsion (ME) composition, the composition of the sheath liquid and APPI-MS detection parameters have been investigated. Using the optimized set of parameters, the eight selected substances could be detected down to concentrations between 3 mg L(-1) (phenacetin) and 41 mg L(-1) (diltiazem). Switching to the MS2 mode, the use of specific transitions for the detection of each analyte provided improved detection limits in the range of 0.6 mg L(-1) (carbamazepine) to 6 mg L(-1) (metoprolol). Calibration curves were linear over one to two orders of magnitude with correlation coefficients better than 0.98.

Microemulsion Electrokinetic Chromatography with On-Line Atmospheric Pressure Photoionization Mass Spectrometric Detection

In the present paper we report, for the first time, the successful on-line coupling of microemulsion electrokinetic chromatography (MEEKC) with mass spectrometric (MS) detection using an atmospheric pressure photoionization interface. Microemulsions (MEs) including mostly volatile ingredients and classical MEs based on nonvolatile buffer components and sodium dodecyl sulfate (SDS) as surfactant were compared with respect to their compatibility with MS detection. The investigations performed revealed that MEs with up to 3% SDS and buffers containing sodium borate can be employed without significant suppression of the MS signals. A test mixture of nine substances could be separated by MEEKC using a ME consisting of 0.8% octane, 2% SDS, 6.6% butanol, and 90.6% of 20-mmol ammonium hydrogencarbonate buffer (pH 9.5). Operating the MS instrument in the MS(2) mode provided improved signal/noise ratios for analytes leading to characteristic MS-MS transitions. Thereby, limits of detection ranging between 0.5 (carbamazepine) and 5 microg mL(-1) (phenacetin) could be obtained.

Determination of antidepressants in surface and waste water samples by capillary electrophoresis with electrospray ionization mass spectrometric detection after preconcentration using off-line solid-phase extraction

A method for the quantitative determination of seven major antidepressants in surface waters and sewage treatment plant effluents by CE using ESI-MS is presented. Calibration curves for the selected analytes were prepared in Milli-Q purified water and Danube river water extract covering a concentration range of at least one order of magnitude. LODs achieved were between 6 and 13 microg/L for Trazodone and 39 and 53 microg/L for Sertraline in the Milli-Q purified water and Danube river water matrix, respectively. For sample preparation eight different SPE materials were investigated. Best results were obtained for a resin based on hydrophilic divinylbenzene (recoveries from Milli-Q purified water 93-96%; from Danube river water 85-99%). Finally, a series of eight sewage treatment plant effluents were investigated with respect to their content in the selected antidepressants. Six of these samples were tested positive for antidepressants, in particular Venlafaxine, Citalopram and Trazodone in concentrations between 36 and 322 ng/L.

Development of an analytical method for the determination of antidepressants in water samples by capillary electrophoresis with electrospray ionization mass spectrometric detection

A method for the quantitative determination of major antidepressants in aqueous matrices by CE using ESI-MS is presented. Several aqueous, nonaquoeus, and mixed aqueous/organic solvent BGEs including inorganic and organic acids were investigated with respect to their suitability for the separation of the selected analytes. Finally, due to the necessity to employ MS detection if the developed method should be suitable also for environmental samples, only MS-compatible electrolytes were taken into account. Based on this fact optimum results were obtained with a system consisting of 1.5 M formic acid and 50 mM ammonium formate in ACN/water (85/15). Linear calibration plots could be obtained for all solutes over a concentration range of almost two orders of magnitude, and the LODs achieved were in the range of 3-6 microg/L for trazodone and 39-43 microg/L for sertraline with the TOF instrument and the single quadrupole instrument in the SIM mode, respectively. This fact allowed the assumption that the presented method can be regarded as suitable for the determination of antidepressants even in the trace amounts commonly present in environmental samples. Spiking of river water and sewage plant effluent extracts with the selected solutes showed that no interferences from the matrix usually found in such samples can be expected. Finally the quantitative determination of the seven antidepressants in environmental samples was used to benchmark the performance of CZE coupled to a single quadrupole MS and a TOF-MS.

Residue analysis of the pharmaceutical diclofenac in different water types using ELISA and GC-MS

A highly sensitive and specific indirect competitive enzyme-linked immunosorbent assay (ELISA) for the determination of diclofenac in water samples was developed. With pure water, the limit of detection (LOD, S/N = 3) and IC50 were found to be 6 ng/L and 60 ng/L, respectively. The analytical working range was about 20-400 ng/L. Highest cross-reactivity (CR) of 26 tested pharmaceuticals, metabolites, and pesticides was found for 5-hydroxydiclofenac (100%). Other estimated values were well below 4% and, therefore, are negligible. The assay was applied for the determination of diclofenac in tap and surface water samples as well as wastewater collected at 20 sewage treatment plants (STPs) in Austria and Germany. Humic substances were identified as main interference in surface water. Wastewater samples which were only submitted to filtration and dilution yielded about 25% higher diclofenac concentrations using the ELISA compared to GC-MS. However, the ELISA turned out to be a simple, inexpensive, and accurate method for the determination of diclofenac both in influent and effluent wastewater after rather simple sample preparation, i.e., filtration, acidification, and readjustment to neutral pH-value, and at least 10-fold dilution with pure water.

Studies on the metabolic fate of 111In-labeled antibodies

Indium-111-labeled antibodies, though providing superior photon flux to iodine-labeled antibodies, can exhibit high levels of accumulation in some non-target organs. In an effort to understand the nature of this non-target uptake we have evaluated the molecular weight of 111In species retained in several tissues by radio-FPLC (sizing chromatography) following injection of [111In]DTPA 5G6.4, a murine monoclonal antibody, into normal mice. Blood, liver and kidneys were removed, and liver and kidneys were homogenized at several time points after antibody injection. The proportion of 111In-containing species was found to vary with the tissue and with time. Analysis of blood showed only radiolabeled antibody. In the liver, several 111In species were identified with molecular weights compatible with intact antibody, [111In]transferrin, and low molecular weight complexes, with an increase in the proportion of [111In]transferrin and low molecular weight species occurring over time. While the same molecular weight species were also identified in the kidneys, the kidneys contained the largest percentage of low molecular weight species which increased over time. When 125I-labeled 5G6.4 was injected and the tissues similarly analyzed, only radioactive material with the molecular weight of intact antibody was detected. Comparison of two methods of purification of [111In]labeled antibody after labeling revealed a significant difference in the organ uptake of radiolabeled products for 111In. Although dialysis was sufficient for the removal of labile 111In, as determined by TLC, subsequent sizing chromatography on Bio-Gel P-60 dramatically dropped the hepatic and renal uptake of 111In relative to blood and diminished the proportion of the low molecular weight species present on sizing FPLC of extracts from tissues.(ABSTRACT TRUNCATED AT 250 WORDS)