A new method for the efficient extraction and determination of volatile aliphatic amines by means of single-drop microextraction (SDME) in combination with microchip electrophoresis and contactless conductivity detection has been developed. An experimental approach for interfacing real world samples with chip electrophoresis is presented. The method consists of an optimized protocol for extraction via ultrasound assisted headspace SDME and the separation and determination of the target analytes with a novel microfluidic device. Five volatile, short-chained aliphatic amines, methylamine, dimethylamine, trimethylamine, diethylamine and triethylamine, were determined. The analytes were separated using a PMMA microchip with an 8.7 cm long separation channel and integrated thin-film gold electrodes for capacitively coupled contactless conductivity detection (C 4 D). The determinations were carried out in a His/MES buffer (His/MES ratio of 80 : 20 at pH 6.6). Various parameters for the extraction and determination of the target analytes were optimized and applied to complex sample matrices like shrimp. The five analytes could be separated in less than 40 s applying a separation voltage of 3.8 kV. A linear concentration dependence was found within the range from 0.1 to 10 ppm for the ethylamine species and from 0.5 to 10 ppm for the methylamines. The limits of detection were all well below 400 ng/mL. The proposed method is simple, quick, presents low levels of waste, works with small sample quantities and is suitable for quantification of aliphatic amines in seafood samples like shrimp or fish from where they are naturally developing upon biodegradation. In the present study the accelerated decay of shrimp tissue due to improper storage was monitored.
The separation of complex mixtures such as biological or environmental samples requires high peak capacities, which cannot be established with a single separation technique. Therefore, multidimensional systems are in demand. In this work, we present the hyphenation of the two most important (orthogonal) techniques in ion analysis, namely, ion chromatography (IC) and capillary electrophoresis (CE), in combination with mass spectrometry. A modulator was developed ensuring a well-controlled coupling of IC and CE separations. Proof-of-concept measurements were performed using a model system consisting of nucleotides and cyclic nucleotides. The data are presented in a multidimensional contour plot. Analyte stacking in the CE separation could be exploited on the basis of the fact that the suppressed IC effluent is pure water.
Two tubular capacitively coupled contactless conductivity detection (C(4)D) cells with different geometric dimensions were evaluated with regard to their main analytical characteristics under non-separation and separation conditions in conjunction with liquid chromatography. A comparison of the performance of the tubular cells to a previously tested thin-layer detection cell was drawn. Additionally, using a theoretical model the experimental results were compared with sets of calculated values and partially enabled to model the complex behavior of C(4)D detection in combination with high-performance liquid chromatography (HPLC). While cell 1 is characterized by a geometric cell volume of 0.6 μL, a wall thickness of 675 μm, and an inner diameter of 125 μm, the respective values for cell 2 are 2.3 μL, 200 μm, and 250 μm. The main analytical parameters were evaluated using a potassium chloride (KCl) solution. The limits of detection were 0.4 μM KCl (5.7 × 10(-6) S m(-1)) for cell 1 and 0.2 μM KCl (3.2 × 10(-6) S m(-1)) for cell 2, which compares well to the previously found 0.2 μM for the thin-layer cell. A pair of linear ranges was found for both cells in a concentration interval ranging from 1 × 10(-6) to 1 × 10(-4) M (corresponding to 1.5 × 10(-5) to 1.5 × 10(-3) S m(-1)) KCl, respectively. Furthermore, the detector cells were applied to the HPLC separation of a model compound system consisting of benzoic acid, lactic acid, octanesulphonic acid, and sodium capronate. Separation of the compounds was achieved with a Biospher PSI 100 C18 column using 60% aqueous acetonitrile mobile phase. Calibration curves for the examined model system were well correlated (r² > 0.997), and it was found that under separation conditions the arrangement with the lower cell volume (cell 1) yields higher sensitivity and respectively lower limits of detection for all model compounds. Compared with the thin-layer cell, the tubular cells show better overall performance in regard to the determined analytical characteristics.
A method for conducting fast and efficient capillary electrophoresis (CE) based on short separation capillaries in vertical alignment was developed. The strategy enables for high-throughput analysis from small sample vials (low microliter to nanoliter range). The system consists of a lab-made miniaturized autosampling unit and an amperometric end-column detection (AD) cell. The device enables a throughput of up to 200 separations per hour. CE-AD separations of a dye model system in capillaries of only 4 to 7.5 cm length with inner diameters (ID) of 10 or 15 μm were carried out under conditions of very high electric field strengths (up to 3.0 kV/cm) with high separation efficiency (half peak widths below 0.2 s) in less than 3.5 s migration time. A non-aqueous background electrolyte, consisting of 10 mM ammonium acetate and 1 M acetic acid in acetonitrile, was used. The practical suitability of the system was evaluated by applying it to the determination of dyes in overhead projector pens.
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