Microfluidic membrane suppressor module design and evaluation for capillary ion chromatography.

A microfluidic ion-suppression module for use in ion-exchange chromatography has been developed and evaluated. The device consists of an ion-exchange membrane clamped between two polymer chips featuring a 200×100µm (width×depth) eluent channel (l=60mm), and a 300×150µm regenerant channel (60mm), respectively. The suppression efficacy using a Nafion membrane was compared with that of a styrene-sulfonate grafted fluorinated ethylene propylene (FEP) membrane. The latter was found to outperform Nafion in terms of lowest attainable background signal (suppression efficacy) and dynamic suppression range. Increasing the suppressor temperature or the sulfuric acid regenerant concentration led to an extension of the operational suppression range, this however at the cost of an increased background signal due to enhanced diffusion, inducing sulfate bleed. Under optimized operating conditions, the microfluidic suppressor provided a dynamic capacity of 0.35µEq./min, being compatible with gradient separations applying up to 70mM KOH in combination with 400µm i.d. capillary columns operated at the optimal flow velocity. The applicability of the miniaturized suppressor is demonstrated for both isocratic and gradient separations of mixtures of inorganic anions. Band-broadening characteristics of the suppressor were optimized with respect to a commercial capillary hollow-fiber suppressor, yielding comparable overall system efficiency, e.g., 8500 plates for nitrate recorded on a 150mm long capillary column. A second chip device was also constructed, featuring suppression at both sides of the eluent flow path. This double-sided suppressor allowed to increase sample throughput and operate at eluent flow rates of 10µL/min, while maintaining efficient suppression characteristics.

Protein Nitrogen Determination by Kjeldahl Digestion and Ion Chromatography.

We report development and validation of a simple, rapid, and accurate method for the quantitation of protein nitrogen, which combines Kjeldahl digestion and ion chromatography with suppressed conductivity detection and requires nanomolar amount of nitrogen in samples (≥10 µg protein). The mechanism of suppressed conductivity detection does not permit analysis of samples containing copper (present in Kjeldahl digestion solution) and aluminum (present in many vaccines as adjuvants) due to precipitation of their hydroxides within the suppressor. We overcame this problem by including 10 µM oxalic acid in Kjeldahl digests and in the eluent (30 mM methanesulfonic acid). The chromatography is performed using an IonPac CS-16 cation exchange column by isocratic elution. The method reduces the digestion time to less than 1 h and eliminates the distillation and titration steps of the Kjeldahl method, thereby reducing the analysis time significantly and improving precision and accuracy. To determine protein nitrogen in samples containing non-protein nitrogen, proteins are precipitated by a mixture of deoxycholate and trichloroacetic acid and the precipitates are analyzed after dissolving in KOH. The method is particularly useful for biological samples that are limited and can also be applied to food, environmental, and other materials.

Determination of Inosine Monophosphate in Meat Products by Ion Chromatography with Suppressed Conductivity Detection / 分析化学

A new method was developed for the separation and determination of inosine monophosphate (IMP) by ion chromatography (IC) with suppressed conductivity detection. Separation was achieved on an anion-exchange column Ionpac AS11-HC of high capacity within a short time. 30 mmol/L KOH produced by an EGC-KOH eluent generator was used for isocratic elution. No interferences existed between the seven common inorganic anions and IMP. Under the optimum conditions, the linear range of the calibration curve for IMP was 1. 0-200 mg/L, with correlation coefficient ( R2 ) of 0. 999. The relative standard deviations (RSDs) for retention time, peak height and peak area of IMP were 0. 16%, 0. 94% and 0. 86%, respectively, indicating good reproducibility of the method. The method was successfully applied to the determination of IMP in meat products, with spiked recovery ranging from 86. 0% to 110. 0%. This simple, accurate and reliable method could be served as a rapid and effective analytical tool for meat flavoring research.