A portable liquid chromatography system based on a separation/detection chip module consisting of a replaceable ultraviolet-visible absorbance or contactless conductivity detection unit.

Recently, there has been a growing demand for miniaturized analytical instruments, including portable HPLC systems, that can enable rapid analysis in the field. This study aimed to develop chip-based separation/detection modules with replaceable detection units for constructing compact HPLC systems to minimize the dead volume. This module provides a tubing-free connection between the column and the detection unit. This study also built detection units for conductivity detection and ultraviolet-visible (UV-Vis) detection to cover a wide variety of inorganic and organic compounds. Furthermore, UV- and Vis-light-emitting diodes were employed for the absorbance detection unit. In addition, portable all-in-one HPLC systems and a handy HPLC system were constructed for ion chromatography and reversed-phase chromatography, demonstrating the successful separation and detection of inorganic ions and several organic compounds.

Simultaneous and direct determination of urea and creatinine in human urine using a cost-effective flow injection system equipped with in-house contactless conductivity detector and LED colorimeter.

This work presents a cost-effective and simple flow injection analysis (FIA) system for simultaneous and direct determination of urea and creatinine in human urine. The FIA system comprises two in-house detectors, a contactless conductivity detector and a light emitting diode (LED) detector. The contactless detector was built as a flow-through detection cell with axial electrodes, commonly known as capacitively coupled contactless conductivity detector (C4D) and the diode detector was fabricated based on the concept of paired emitter detector diodes (PEDD). With appropriate dilution of urine, the sample is directly injected into a stream of glycine-NaOH buffer pH 8.8 (the gas donor stream) and is carried by the carrier through a urease minicolumn for on-line enzymatic hydrolysis. The generated NH3 diffuses from the carrier stream through a porous polytetrafluoroethylene (PTFE) membrane into a stream of deionized water (the acceptor stream) leading to an increase in the signal at the C4D due to the NH3 dissolution in the water. In this system, creatinine is determined based on the Jaffé reaction by merging a stream of alkaline picrate with the gas donor stream. The change in color is detected using the PEDD equipped with two green LEDs. Under the optimum condition, the linear range of urea and creatinine were 30-240 mg L-1 and 10-500 mg L-1, with limits of detection of 9.0 mg L-1 and 0.9 mg L-1, respectively. The proposed system provides satisfactorily good precision (RSD < 3%), with sample throughput of 31 sample h-1 for the two analytes. The FIA system tolerates potential interference commonly found in human urine. The system was successfully applied and validated with selected reference methods.

Simultaneous Determination of Inorganic Anions and Cations in Water and Biological Samples by Capillary Electrophoresis with a Capacitive Coupled Contactless Conductivity Detector Using Capillary Filling Method.

An analytical method for concurrent analysis of inorganic anions and cations has been developed using a capillary electrophoresis (CE)-capacitively coupled contactless conductivity detector (C4D) system. Although hydrodynamic and electrokinetic injection techniques have been widely used in CE, we employed a capillary filling method (CFM) for the analysis of inorganic ions. The procedure is relatively simple and has the advantage that CMF does not require pressure control and vial exchange. Three anions (chloride, sulfate, nitrate) and five cations (ammonium, potassium, sodium, magnesium, calcium) were successfully separated and detected at ppm levels within 80 s using a 9 mM histidine/15 mM malic acid (pH 3.6) containing 50 mM N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate as background electrolyte. Applying this analytical condition, the electroosmotic flow is negligible and anions and cations were migrated concurrently to different polarities according to their electrophoretic mobility. Obtained raw data showed stepwise increases in detected conductivity due to the migration of sample components, which expresses as peak profiles by differentiation of electropherograms. The RSD values of the peak area and migration times for the anions and cations were satisfactory and were less than 5.15 and 2.04%, respectively. The developed method was applied for the analysis of inorganic anions and cations in commercial mineral waters, tap water, urine, and exhaled breath condensate. These results indicate that the CE-C4D system with CFM is suitable for the rapid analysis of inorganic anions and cations in various samples.

[Fabrication of conventional ion chromatography-capacitively coupled contactless conductivity detector].

A conventional ion chromatography-capacitively coupled contactless conductivity detector (IC-C4D) was fabricated. The main parameters, such as the electrode length and gap, tube material and inner diameter, excitation frequency, voltage and waveforms, were optimized. The self-made C4D showed comparable performance to that of a commercial contact conductivity detector. Under the suppressed mode, the limits of detection of common inorganic anions (F-, Cl-, NO2-, Br-, NO3-, and SO42-) were 0.02-0.08 µmol/L. The relative standard deviations (RSDs) for the peak area were less than 1.8% (n=6). The linearities of the six common inorganic anions were achieved in the range of 0.1-10 µmol/L with correlation coefficients (R2)>0.9950. The advantages of such a C4D in a relatively conventional mode include simple structure, low fabrication cost and no electrode fouling, and it will help extend the application of IC.