Microfluidic chip-capillary electrophoresis for two orders extension of adjustable upper working range for profiling of inorganic and organic anions in urine.

To meet the need for onsite monitoring of urine anions, a microfluidic chip-capillary electrophoresis device was designed, fabricated and tested to extend the upper CE working range for an enhancement up to 500 fold (100 fold for sample dilution and 5 folds for CE injection) in order to analyze highly variable anionic metabolites in urine samples. Capillaries were embedded between two PMMA plates with laser-fabricated microchannel patterns to produce the microfluidic chip-capillary electrophoresis to perform standard/sample dilution and CE injection with adjustable dilution ratios. A circular ferrofluid valve was incorporated on-chip to perform cleanup and conditioning, mixing and dilution, injection and CE separation. Under optimized conditions, a complete assay for four samples can be achieved within an hour for 15 anions commonly found in urines. Satisfactory working ranges (0.005-500 mM) and low detection limits (0.5-6.5 µM based on S/N =2) are obtained with satisfactory repeatability (RSD, n=5) 0.52-0.87% and 4.1-6.5% for migration time and peak area, respectively. The working ranges with two orders adjustable upper extension are adequate to cover all analytes concentrations commonly found in human urine samples. The device fabricated shows sufficiently large experimentally verifiable enhancement factor to meet the application requirements. Its reliability was established by more than 94% recoveries of spiked standards and agreeable results from parallel method comparison with conventional ion chromatography method. The extension of the upper CE working range enables flexible onsite dilution on demand, a quick turn-around of results, and a low-cost device suitable for bedside monitoring of patients under critical conditions for metabolic disorders.

Analysis of organic acids and inorganic anions in beverage drinks by capillary electrophoresis.

To meet the need for a new and validated analytical method for simultaneous determination of inorganic and organic acid anions in beverage drinks, a capillary zone electrophoresis (CZE) procedure had been developed based on a new background electrolyte (BGE) system containing 3 mmol/L 1,3,5-benzenetricarboxylic acid (BTA), 15 mmol/L tris(hydroxymethyl)aminomethane and 1.5 mmol/L tetraethylenepentamine (TEPA) at pH 8.4. Baseline separation of anions commonly found in beverage drinks could be achieved in less than 14 min with indirect UV detection at 240 nm. Comigration problems for hydroxycarboxylic acids could be solved using TEPA as BGE additive. The results indicate excellent repeatability for migration time (RSD, 0.27-0.67%, n = 5) and good precision for both peak height (RSD, 3.2-4.2%, n = 5) and peak area (RSD, 3.1-4.5%, n = 5). Under the optimized conditions and using corrected peak area for quantitation, an excellent linear dynamic range (with correlation coefficient > 0.997 in a concentration range from 0.005 to 2.0 mmol/L) and low detection limit (1-4 micro mol/L) were obtained for all the anions investigated. The applicability and reliability of the CE procedure developed were established by parallel method determination using established ion chromatography procedure for the analysis of inorganic and organic acid anions in orange juice and wine samples. Our CZE procedure provided a sensitive and economic technique for simultaneous determination of inorganic and organic acid anions in orange juice, red and white wine samples.