Kanchana Uraisin

Simple flow injection system for colorimetric determination of iodate in iodized salt

This work presents a flow injection (FI) system that was developed for determination of iodate. The system utilizes the oxidation of iodide by the analyte to iodine, which subsequently forms tri-iodide. In the presence of starch, the blue I(3)(-)-starch complex is developed within the sample zone and can be colorimetrically detected at 590 nm. Optimization was carried out to make the system suitable for quantitating iodate added to table salts. To prevent accumulation of the blue complex residue on walls of tubing and the flow cell, a port was placed in the system for injection of 10(-3) M thiosulfate plug (100 mul). An injection of this cleaning solution after each sample injection is recommended to avoid positive baseline shift. By means of the paired t-test, the amounts of iodine (mg I kg(-1)) were statistically compared with the results determined by titration and by iodide ion selective electrode. No significant disagreement at 95% confidence was observed. The proposed system is very simple, uses common chemicals and provides rapid analysis (65 injections per h) with high precision (R.S.D.=0.66%, n=10). A detection limit of 2 mg I kg(-1) salt can be achieved.

A miniaturized chemiluminescence detection system for a microfluidic paper-based analytical device and its application to the determination of chromium(III)

A miniaturized detection system for chemiluminescence that is generated on a microfluidic paper-based analytical device (μPAD) was developed using optical fibers and was applied to the determination of Cr(III). The μPAD was fabricated by wax printing and consisted of 6 separate channels in a parallel alignment. Each channel was composed of an injection zone for a reagent solution, a reaction zone, and a waste zone. The μPAD was placed on a plastic holder equipped with 6 optical fibers to collect chemiluminescence (CL). The other ends of the optical fibers were bundled and introduced into a small photomultiplier tube module to obtain the CL signals. The CL reaction was based on luminol oxidation by hydrogen peroxide in the presence of Cr(III), which catalyzed the reaction in an alkaline medium. The reaction conditions, including the use of an enhancer and a masking agent, were optimized to obtain high sensitivity and selectivity. Under the optimal conditions, a linear range was obtained at 0.05 to 1.00 ppm with a detection limit of 0.02 ppm. The analysis time was less than 1 min per one μPAD in order to obtain 6 measurements of differing concentrations with a precision of <6.5%. This method was successfully applied to the determination of Cr(III) spiked into natural water samples at the sub-ppm range.

Spectrophotometric determination of bromide in water using the multisyringe flow injection analysis technique coupled to a gas-diffusion unit

A novel spectrophotometric method for the determination of bromide has been developed using the Multisyringe Flow Injection Analysis technique (MSFIA). This method is based on the decolorization of methylene blue by the bromine released from the oxidation of bromide by bromate under acidic conditions. By incorporating a gas-diffusion unit into the MSFIA system the transferred bromine reacts with methylene blue in the acceptor stream. The decrease of the methylene blue absorbance is monitored at 745 nm. The oxidation conditions are not strong enough to oxidize chloride to chlorine, which is a major component of both natural and seawater. The proposed method provides linearity for the determination of bromide over a range of 1 × 10−5 mol L−1 to 6 × 10−5 mol L−1 in 5 × 10−2 mol L−1 of chloride, with a correlation coefficient (r2) of 0.9939, and a precision of 3.1% (%RSD for 3 × 10−5 mol L−1 Br− in 5 × 10−2 mol L−1 Cl−, n = 10). The limit of detection (3σ) is 0.5 × 10−5 mol L−1. The proposed method has been applied to the determination of Br− in water samples, obtaining recoveries in the analysis of spiked tap, natural, and seawater samples in the range of 90–106%.

Direct injection of human serum and pharmaceutical formulations for glucosamine determination by CE-C4D method

A simple CE-C(4)D method has been developed for the determination of glucosamine by direct injection of human serum and pharmaceutical samples. Glucosamine was electrokinetically injected and analysed in its protonated form using 20mM MES/His (pH 6) as background electrolyte in order to separate it from the matrix and to provide a better response to the C(4)D detector. Separation of glucosamine in human serum and pharmaceutical samples was performed in 3 min without the need for protein precipitation or matrix removal. Good precision in terms of %RSD for the migration time and peak area were less than 1.91% (n = 10). The conductivity signal was linear with glucosamine concentration in the range 0.10-2.50mg/mL, with a detection limit of 0.03 mg/mL. Recoveries of glucosamine in serum and pharmaceutical samples were 86.5-104.78%. The method was successfully applied for the determination of the glucosamine content in pharmaceutical formulations and validated with high performance liquid chromatography (HPLC). Good agreements were observed between the developed method, label values and the HPLC method. Glucosamine could be detected in spiked serum sample by direct injection. This was not possible by HPLC due to co-eluting interferences.

Reagent-free analytical flow methods for the soft drink industry: Efforts for environmentally friendly chemical analysis

The evolution of an entirely green analytical system for industrial quality control of carbonated drinks is described. The developed flow system is capable of providing analytical data of the dissolved CO2, sucrose, and color of a sample consecutively in real-time. The system has been carefully designed on the basis of “reagent-free”, meaning that no added chemicals are required for the analysis. The system first vaporizes CO2 from the soft drink in a gas–liquid separation chamber, with a channel for a flow of pure water as the CO2 acceptor. The dissolved CO2 alters the conductivity of the water stream, which is directly related to the concentration of CO2 in the soft drink. The sucrose content is measured based on the “schlieren effect”, the sample plug flows out of the vaporization chamber into a colorimeter with a near-infrared/light-emitting diode (NIR/LED) as light source. The schlieren effect arises at the boundary of pure water and soft drink with refraction of light in proportion to the sugar concentration. The system also measures the absorbance of the sample using an RGB-LED. The related principles and preliminary experiments as proof of concept are described as well as the construction of the flow system for this completely reagent-free analyzer. A simple flow injection system using the schlieren effect was also developed for rapid quantitative analysis of sugar in noncarbonated soft drinks.

Simple in‐house flow‐injection capillary electrophoresis with capacitively coupled contactless conductivity method for the determination of colistin

An in-house flow-injection capillary electrophoresis with capacitively coupled contactless conductivity detection method was developed for the direct measurement of colistin in pharmaceutical samples. The flow injection and capillary electrophoresis systems are connected by an acrylic interface. Capillary electrophoresis separation is achieved within 2 min using a background electrolyte solution of 5 mM 2-morpholinoethanesulfonic acid and 5 mM histidine (pH 6). The flow-injection section allows for convenient filling of the capillary and sample introduction without the use of a pressure/vacuum manifold. Capacitively coupled contactless conductivity detection is employed since colistin has no chromophore but is cationic at pH 6. Calibration curve is linear from 20 to 150 mg/L, with a correlation coefficient (r(2) ) of 0.997. The limit of quantitation is 20 mg/L. The developed method provides precision, simplicity, and short analysis time.

Green analytical method for simultaneous determination of salinity, carbonate and ammoniacal nitrogen in waters using flow injection coupled dual-channel C4D

A flow injection analysis system (FIA) for the simultaneous determination of salinity, carbonate and ammoniacal nitrogen has been developed and reported in this paper. FIA incorporating membrane units was used, not only for the separation of the gaseous carbon dioxide and ammonia, but also for on-line dilution in the salinity measurement. The sample was injected via a 10-port valve with two sample loops. One loop was used for salinity and carbonate measurements and the second loop for ammoniacal nitrogen determination. A dual-channel capacitively coupled contactless conductivity detector was assembled in a single shielding box. Input voltage from the same AC power supply was fed to the input electrodes of both C4D cells. One channel of the C4D was used to monitor the change in conductivity of an acceptor stream that carried a zone of the water sample that has passed through the on-line dilution unit. Conductivity of this zone relates directly to the salinity of the sample. The same sample zone was next acidified to generate carbon dioxide gas that diffused through a hydrophobic membrane of the first gas diffusion (GD) unit. The zone of dissolved carbon dioxide in acceptor stream of water flowed into the same C4D cell as for the salinity measurement, but arriving at a later time. Concurrently, the second channel of the C4D monitored the change in conductivity of the acceptor stream in the second GD unit due to the diffusion of ammonia gas generated by the reaction of base with the sample injected from the second sample loop. The change in conductivity at this second C4D cell correlates with the concentration of ammoniacal nitrogen present in the sample. The proposed method is low cost, simple, rapid and sensitive. The limit of quantitation for salinity, carbonate and ammoniacal nitrogen are 0.31mmolL-1, 1.85 µmol L-1, respectively. Throughput of 20 samples h-1 for simultaneous analysis can be achieved with RSD of less than 3.8%. The system had been applied to the determination of salinity, carbonate and ammoniacal nitrogen in 15 water samples, with results in agreement with those obtained using comparison methods.

Green analytical flow method for the determination of total sulfite in wine using membraneless gas–liquid separation with contactless conductivity detection

A green analytical flow method was developed for the determination of total sulfite in white wine. The method employs the membraneless vaporization (MBL-VP) technique for gas–sample separation allowing direct analysis of wine. Sulfite in an aliquot of sample was converted to SO2 gas via acidification. Dissolution of the gas into the water acceptor led to a change in the conductivity of the acceptor which was monitored using a ‘capacitively coupled contactless conductivity detector’ (C4D) flow cell. Only a minute amount of common acid (100 μL of 1.5 mol L−1 H2SO4) is used. The MBL-VP unit was incorporated into the flow system to separate the SO2 gas from the wine sample using the headspace above the donor and acceptor compartments as a virtual membrane. The method provides a linear working range (10–200 mg L−1 sulfite) which is suitable for most wines with calibration equation y = (0.056 ± 0.002)x + (1.10 ± 0.22) and r2 = 0.998. Sample throughput is 26 samples h−1. The lower limit of quantitation (LLOQ = 3SD of blank per slope) is 0.3 mg L−1 sulfite for 20 s diffusion time with good precision (%RSD = 0.8 for 100 mg L−1 sulfite, n = 10). We also present a simple modification of the MBL-VP unit by the addition of a third cone-shaped reservoir to provide two acceptor zones leading to improvement in sensitivity of more than three-fold without use of heating to enhance the rate of diffusion of SO2.

Catalytic remediation of phenol contaminated wastewater using Cu–Zn hydroxide nitrate

This work highlights an application of Cu–Zn hydroxide nitrate (denoted as 6Cu–Zn) as a highly effective and reusable catalyst for catalytic wet peroxide oxidation of phenol under mild conditions (35 °C). PXRD and XANES experiments were carried out to confirm a single phase of copper hydroxide nitrate in the 6Cu–Zn sample. The catalytic activity of 6Cu–Zn for degrading phenol was reported in terms of the percent phenol conversion, and chemical oxygen demand (COD) removal efficiency. Treatment of 100, 200, and 500 ppm aqueous phenol solutions with H2O2/6Cu–Zn resulted in complete phenol degradation within 10 min. The 6Cu–Zn catalyst can be reused for up to five consecutive runs while maintaining complete phenol conversion and COD removal efficiency (greater than 90%) after water washing. This work introduces a simple, mild, energy efficient and effective pretreatment method for highly toxic wastewater which could be applied prior to feeding the pretreated wastewater to subsequent conventional treatment units.

Spectrophotometric determination of cobalt in horse urine using 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline as chromogenic reagent

Cobalt has been reported for being abused as an illegal doping agent due to its ability as an erythropoiesis-stimulating agent for enhancing performance in racehorses. Since 2015, cobalt is listed as a prohibited substance by the International Federation of Horseracing Authorities (IFHA) with a urinary threshold of 0.1 μg cobalt per mL urine. To prevent the misuse of cobalt in racehorse, a simple method for detection of cobalt is desirable. In this work, the detection of cobalt is based on the spectrometric detection of the complex formation between cobalt(II) and 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline at pH 4. The absorbance of the complex is monitored at 602 nm. The metal:ligand ratio of the complex is 1:2. The calibration graph was linear in the range of 0 – 2.5 μM {Absorbance = (0.0825 ± 0.0013)[Co2+] + (0.0406 ± 0.0003), r2 = 0.999} and the detection limit (3 SD of intercept)/slope) was 0.044 μM. The proposed method has been successfully applied to horse urine samples with the recoveries in the range 91 – 98%.