Narong Praphairaksit

Lab-on-Paper with Dual Electrochemical/ Colorimetric Detection for Simultaneous Determination of Gold and Iron

A novel lab-on-paper device combining electrochemical and colorimetric detection for the rapid screening of Au(III) in the presence of a common interference, Fe(III), in industrial waste solutions is presented here. With dilute aqua regia (0.1 M HCl + 0.05 M HNO(3)) as the supporting electrolyte, square wave voltammetry on paper provided a well-defined reduction peak for Au(III) at approximately 287 +/- 12 mV vs Ag/AgCl. Under the optimized working conditions, the calibration curve showed good linearity in the concentration range of 1-200 ppm of Au(III) with a correlation coefficient of 0.997. The limit of detection (LOD) of the proposed method is 1 ppm. Interferences from various cations were also studied. Fe(III) is the only metal that affects the electrochemical determination of Au(III) when present above a 2.5-fold excess concentration of that of the Au(III). To overcome this limitation, a colorimetric method was used to simultaneously detect Fe(III) as a screening tool. The procedure was then successfully applied to determine Au(III) in gold-refining waste solutions. The results are in agreement with those obtained from inductively coupled plasma-atomic emission spectrometry (ICP-AES).

Dissociation of polyatomic ions in the inductively coupled plasma

Abstract A general method for identifying the origin of a particular polyatomic ion is described. Based on a postulated dissociation reaction, measured ion signal ratios (e.g. Ar 2 + /Ar + ) are combined with mass bias corrections and estimates of the density of the neutral product (usually Ar, O or H atoms) to determine a gas kinetic temperature T gas . The temperature can also be measured by the reduction in pressure when the ICP is sampled (compared to room temperature argon), or by other means. Dissociation energies and spectroscopic constants for the ions are necessary. For the particular instrument used, some of the findings of this study are: (a) ArO + and ArN + can be either dissociated (if the plasma potential is high) or created (if the plasma potential is low) by collisions between the sampler and skimmer; (b) the strongly-bound oxide ions O 2 + and MO + for the rare earths are observed at levels consistent with T gas ∼5300 K in a ‘hot’ plasma, but ClO + is formed in excess; and (c) the abundances of most other polyatomic ions like H 2 O + and ArH + correspond to higher densities than would be expected in the ICP itself.

An externally air-cooled low-flow torch for inductively coupled plasma mass spectrometry

Abstract A low-flow torch specifically designed for inductively coupled plasma mass spectrometry (ICP-MS) was developed and evaluated. The outside of the torch is cooled externally by pressurized air flowing at ∼70 l min−1 through a fourth tube sealed onto the usual ‘outer’ tube of a standard minitorch. This external air flow merely cools the outer tube of the torch and does not enter the plasma. Although plasmas can be sustained at operating power as low as 400 W with a 2 l min−1 outer Ar flow, somewhat higher power and flows are advisable. A stable and analytically useful plasma can be obtained at 850 W with an outer Ar flow rate of only 4 l min−1. Under optimum operating conditions, the externally air-cooled plasma produces comparable sensitivities, M2+/M+ signal ratios, matrix effects and other analytical figures of merit as those produced by a conventional torch while using much less argon. MO+/M+ signal ratios are slightly higher with the externally cooled torch.

Low flow, externally air cooled torch for inductively coupled plasma atomic emission spectrometry with axial viewing

Abstract The torch wall is cooled largely by air passing through a cooling jacket added to the outside of a Fassel torch. The plasma is viewed axially through a cooled cone interface centered on the axial channel. The outer argon gas flow can be reduced to 7 l min −1 with no compromise in performance or torch lifetime. The plasma exhibits the same ‘robustness index’ and interference effects from Na as the conventional, high-flow ICP supplied with the particular spectrometer used. Detection limits (DL) for lines at ∼200 nm are poorer by approximately a factor of two, while those for lines at ∼400 nm are actually better than values typically seen for the same lines by axial viewing of a conventional, high-flow ICP.

Microfluidic Paper-based Analytical Devices for Determination of Creatinine in Urine Samples

Simple, low-cost and portable microfluidic paper-based analytical devices (μPADs) for determination of creatinine in urine samples were developed. The methodology was based on Jaffé reaction between the creatinine and picric acid in alkaline conditions, generating a colorimetric creatinine-alkaline picrate complex. The product exhibits an orange color that is clearly visible on the μPADs. The color intensity of the complex, which is indicative of the concentration of creatinine, is then quantitatively determined using ImageJ software. Various experimental parameters were optimized to achieve the best performance of the μPADs. Under the optimum conditions, a wide linear range was obtained in the range of 0.2 - 1 mM with a limit of detection and limit of quantitation of 0.08 and 0.26 mM, respectively. The accuracy of the proposed method was in good agreement with the standard Jaffé method. Finally, the developed devices were successfully applied for the determination of creatinine in urine samples.