Dual-Purpose Photometric-Conductivity Detector for Simultaneous and Sequential Measurements in Flow Analysis

This work presents a new dual-purpose detector for photometric and conductivity measurements in flow-based analysis. The photometric detector is a paired emitter-detector diode (PEDD) device, whilst the conductivity detection employs a capacitively coupled contactless conductivity detector (C4D). The flow-through detection cell is a rectangular acrylic block (ca. 2 x 2 x 1.5 cm) with cylindrical channels in Z-configuration. For the PEDD detector, the LED light source and detector are installed inside the acrylic block. The two electrodes of the C4D are silver conducting ink painted on the PEEK inlet and outlet tubing of the Z-flow cell. The dual-purpose detector is coupled with a sequential injection analysis (SIA) system for simultaneous detection of the absorbance of the orange dye and conductivity of the dissolved oral rehydration salt powder. The detector was also used for sequential measurements of creatinine and the conductivity of human urine samples. The creatinine analysis is based on colorimetric detection of the Jaffe reaction using the PEDD detector, and the conductivity of the urine, as measured by the C4D detector, is expressed in millisiemens (mS cm(-1))

Quality control of gasohol using a micro-unit for membraneless gas diffusion

This work describes the development of a new spectrophotometric flow technique suitable for monitoring of ethanol content in gasohol fuel. Membraneless gas-diffusion (MBL-GD) was applied with one-step aqueous extraction of gasohol (1:2 gasohol/water). Segments of aqueous extract and color developing reagent were allowed to flow into two separate channels in the MBL-GD device. Inside the device, ethanol vapor can diffuse across a small headspace between the two channels (donor and acceptor). Introduction of an air-segment behind the zone of acceptor reagent to stop dispersion of the colored zone greatly improves the rapidity of analysis using this MBL-GD technique. Two methods were developed for quality control of gasohol by measuring ethanol content. Method I is suitable for direct calibration of E5 and E10. Method II is recommended for E20. These methods have high accuracy with good precision (% RSD: 1 to 4.9, n&#8201;=&#8201;45) and have a sample throughput of 26 samples per hour. E10 samples were compared with analysis using a standard GC method. </p

An equation for fitting distance-based measurements with analyte concentrations: From discrete segments simulation to closed-form solution

In this study, an equation for fitting the band lengths in µPADs to the concentrations/amount of analyte added to the µPAD sample area is derived. A simulation of the band formation is carried out using a discrete segment model. The detector channel is divided into equal segments with the same amount of reagent R in each segment. The sample moves into the channel in steps corresponding to segments of the same size as the detector segment. Each sample segment contains analyte A at C mole ratio to reagent R. Assuming a stoichiometric ratio of 1:1 for reaction between A and R, there will be formation of only one product band in each detector segment. By examining the number of bands (n) formed after N steps, a set of linear algebraic equations is derived to determine the number of bands (n) for any integer values of N and C. By extrapolating this result to real positive numbers, we obtain the equation L=a.CA/(b + CA), where L represents the band length, and CA represents the concentration/amount of analyte. The equation represents a rectangular hyperbola

Method Development for Separation of Active Ingredients in Cold Medicines by Micellar Electrokinetic Chromatography

Separation of nine commonly used active ingredients in cold medicines, were demonstrated by micellar electrokinetic chromatography. The ingredients included paracetamol, chlorpheniramine maleate, diphenhydramine hydrochloride, triprolidine hydrochloride, phenylpropanolamine hydrochloride, dextromethorphan hydrobromide, loratadine, aspirin and caffeine. Effects of buffer concentrations, pH, organic modifiers and capillary length were investigated. The optimum conditions were achieved in 10 mM sodium dihydrogenphosphate-sodium tetraborate buffer, pH 9.0, containing 50 mM sodium dodecyl sulfate and 28% v/v acetonitrile using the effective length of 50 cm, the separating voltage of +15 kV and the capillary temperature of 30°C. Separation of all peaks was obtained within 28.4 min with a resolution of 1.2

Development of a Simple Reversible-Flow Method for Preparation of Micron-Size Chitosan-Cu(II) Catalyst Particles and Their Testing of Activity

A simple flow system employing a reversible-flow syringe pump was employed to synthesize uniform micron-size particles of chitosan-Cu(II) (CS-Cu(II)) catalyst. A solution of chitosan and Cu(II) salt was drawn into a holding coil via a 3-way switching valve and then slowly pumped to drip into an alkaline solution to form of hydrogel droplets. The droplets were washed and dried to obtain the catalyst particles. Manual addition into the alkaline solution or employment of flow system with a vibrating rod, through which the end of the flow line is inserted, was investigated for comparison. A sampling method was selected to obtain representative samples of the population of the synthesized particles for size measurement using optical microscopy. The mean sizes of the particles were 880 &plusmn; 70 &micro;m, 780 &plusmn; 20 &micro;m, and 180 &plusmn; 30 &micro;m for the manual and flow methods, without and with the vibrating rod, respectively. Performance of the flow methods, in terms of rate of droplet production and particle size distribution, are discussed. Samples of 180 &micro;m size CS-Cu(II) particles were tested for catalytic reduction of 0.5 mM p-nitrophenol to p-aminophenol by 100-fold excess borohydride. The conversion was 98% after 20 min, whereas without the catalyst there was only 14% conversion

Contactless conductivity sensor employing moist paper as absorbent for in-situ detection of generated carbon dioxide gas

This work presents an unconventional use of capacitively coupled contactless conductivity detector (C4D) for detection of gas absorption by moist paper with potential application for chemical analysis. To be suitable for measuring conductivity of moist paper absorbent, the C4D sensor was therefore designed in planar configuration. A layer of dry filter paper, only 20 mm x 25 mm in size, was placed on the C4D sensor and the device installed inside a specifically designed vaporization chamber. A vial (16 mm i.d., 8 mm high) containing a 150-mu L solution of sodium bicarbonate was placed alongside. The filter paper was loaded with 110 mu L of deionized water through an injection hole in the cover lid. A 100-mu L aliquot of 2 M hydrochloric acid solution was directly dispensed into the vial through a second hole in the lid to generate CO2 gas from the bicarbonate solution. It was observed that the C4D sensor gave real-time response that corresponded to the absorption of the gas and subsequent production of H+ and HCO3- in the moist paper. The monitored signal reached a constant value at 160 s after the addition of the acid. Chemistry of the absorption process and equivalent circuit for the C4D are proposed. Direct measurement of cement powder was chosen to demonstrate the potential use of this device for quantifying the CaCO3 content of the cement. The calibration curve for 0.5-3 mg CaCO3 was linear for signals recorded at 160 s: V-dc = (0.172 +/- 0.005) center dot (mg CaCO3) + (0.016 +/- 0.009), with coefficient of determination of 0.9965. Linear calibrations were also observed when the signals were monitored at various time less than 160 s. The limit of quantitation (3 SD of intercept/slope) was 0.17 mg CaCO3. The method provided acceptable precision with %RSD of 4.6 (2 mg CaCO3, n = 10). (C) 2020 Elsevier B.V. All rights reserved