A low-cost method for determination of calcium carbonate in cement by membraneless vaporization with capacitively coupled contactless conductivity detection

This work presents a flow analysis method for direct quantitation of calcium carbonate in cement without pretreatment of the sample. The method is based on online vaporization of CO₂ gas following acidification of the sample inside a small chamber that has a flow of acceptor solution passing around it. Solubilization of the CO₂ gas into the acceptor stream changes the conductivity of the acceptor solution causing an increase of signal at the capacitively coupled contactless conductivity detection (C⁴D) placed at the outlet of the vaporization chamber. This chamber is an adaption from previous work reported on ‘membraneless vaporization’ (MBL-VP).The method can be used in the quality control of production of mixed cement. These cement materials usually have calcium carbonate contents at high concentration range (e.g., 33-99% (w/w) CaCO₃). Analysis of samples by this method is direct and convenient as it requires no sample pretreatment. The method is low-cost with satisfactory accuracy and acceptable precision.     

Determination of iodide by detection of iodine using gas-diffusion flow injection and chemiluminescence

This work describes development of a flow injection (FI) system for determination of iodide, based on the chemiluminescence (CL) reaction between iodine and luminol. Iodide in the sample zone is oxidized to iodine. Employment of a gas-diffusion (GD) unit allows for selective detection of the generated CL (425 nm). Preliminary results showed for concentrations of less than 2 mg L⁻¹, that signals were irreproducible and that the calibration was not linear.In order to solve these problems, a method of ‘membrane conditioning’ was investigated, in which iodide stream was continuously merged with oxidant to generate I₂ that conditioned the GD membrane and tubing. This minimized surface interaction between the active surface and the I₂ generated from the samples, thus improving both precision and sensitivity. By employing membrane conditioning, it has been possible to reliably detect concentrations down to 0.1 mg L⁻¹.At the optimized condition, an excellent linear calibration (r² = 0.999) was obtained from 0.1 to 1.0 mg L⁻¹. The method was successfully applied to determine iodide in some pharmaceutical products such as potassium iodide tablets and a liquid patent medicine. However, for vitamin tablets, ascorbic acid was found to interfere seriously by causing a negative signal.     

Chemometrics-assisted cross injection analysis for simultaneous determination of phosphate and silicate

This work presents a novel method for simultaneous spectrophotometric determination of phosphate and silicate by using a cross injection analysis (CIA) coupled with the use of partial least squares (PLS) for data evaluation. The detection principle is based on the well-known ‘molybdenum blue’ method. The molybdate ions in the presence of stannous chloride in acidic medium give phosphomolybdenum blue and silicomolybdenum blue as products. In this work, all the liquids, including sample and reagents were simultaneously introduced into a CIA platform by using two peristaltic pumps for controlling the x-channel and y-channel flow which was automatically manipulated by using in-house control board. Crossflow provides sufficient mixing inside the platform prior detection of the absorption spectra of blue complexes in the wavelength of 400–900 nm. Since spectra of the blue colour product of phosphate and silicate are resemblant, these two analytes therefore reciprocally interfere with one another. This results in difficulty in simultaneous analysis of phosphate and silicate. In this work, PLS was utilised as assistor of CIA system for simultaneous analysis of phosphate and silicate using molybdenum blue reaction without using any modification of reagents and addition of selective masking agent. The calibration ranges are 0.1–6 mgP L^?1 and 5–100 mgSi L^?1 for phosphate and silicate, respectively. By using CIA coupled with PLS for data evaluation, the analysis of two analytes was achieved within 1.5 min with only single injection. The developed system was applied to natural water samples and the system was validated with the conventional methods. By statistical paired t-test, there was no evidence of significant difference at 95% confidence level (t_stat = 2.28, t_critical = 2.31 and t_stat = 0.62, t_critical = 2.31 for phosphate and silicate, respectively). This implied that the chemometrics-assisted CIA system was successfully developed for simultaneous spectrophotometric determination of phosphate and silicate.     

A membraneless gas diffusion unit: design and its application to determination of ethanol in liquors by spectrophotometric flow injection

This work presents new design of a gas diffusion unit, called ‘membraneless gas diffusion (MGD) unit’, which, unlike a conventional gas diffusion (GD) unit, allows selective detection of volatile compounds to be made without the need of a hydrophobic membrane. A flow injection method was developed employing the MGD unit to determine ethanol in alcoholic drinks based on the reduction of dichromate by ethanol vapor. Results clearly demonstrated that the MGD unit was suitable for determination of ethanol in beer, wine and distilled liquors. Detection limit (3S/N) of MGD unit was lower than the GD unit (GD: 0.68%, v/v; MGD: 0.27%, v/v). The MGD design makes the system more sensitive as mass transfer is more efficient than that of GD and thus, MGD can perfectly replace membrane-based designs.     

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 I₃⁻–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 μl). 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.