Somchai Lapanantnoppakhun

Determination of ethanol in liquor by near-infrared spectrophotometry with flow injection

A simple procedure for the determination of ethanol in a liquor by near-infrared (NIR) spectrophotometry with flow injection (FI) is proposed. A liquor sample is equilibrated off-line with dried chloroform to extract ethanol into the organic phase. The extract is injected into a carrier stream of dried chloroform passing through a home-made flow through cell (1 mm path length) sitting in a NIR spectrophotometer for continuous monitoring of absorbance at 2305 or 2636 nm. The ethanol content can be evaluated from a calibration established by a plot of change in absorbance versus concentration of ethanol standard solutions. Optimization of the system will be discussed. A calibration is linear in the range of 20-50% (v/v) ethanol. A throughput of 240 injections h(-1) can be obtained. The procedure is validated by comparing the results with an analysis using gas chromatography.

Stopped-flow injection simultaneous determination of phosphate and silicate using molybdenum blue.

Kinetic information for the phosphate-molybdate-ascorbic acid reaction can be obtained by making use of a very simple manually operated stopped-flow injection (FI) system. Various parameters (concentrations of reagents, flow rate, mixing coils, and volume of flow cell) were investigated for determination of phosphate. A stopped-FI system should be arranged for low degree of mixing (of reactants) and low dispersion so that good signals of rate changes will be observed. Simultaneous determination of phosphate and silicate by the stopped-FI technique is proposed, using a laboratory-made semi-automatic stopped-FI Analyzer with LED-based photometer. It is based on kinetic separation of phosphate and silicate using molybdenum blue. The proposed procedure has been demonstrated for the application to water samples. The results obtained agree with that of a standard method.

Flow injection in-valve-mini-column pretreatment combined with ion chromatography for cadmium, lead and zinc determination

A flow injection (FI) in-valve-mini-column packed with Chelex-100 resin is proposed for on-line sample pretreatment for some metal ions, namely, Cd(II), Pb(II) and Zn(II), prior to simultaneous determination using ion chromatography (IC). A solution containing a mixture of the cations was first passed through the in-valve-mini-column, followed by on-line elution. The eluate was then flowed further to an injection valve and was injected into an ion chromatograph. Conditions of the system were optimized. A single standard calibration was possible. The recoveries of cations were found to be in the range of 95-105%. The developed method was applied to the accurate analysis of zinc ore samples.

Webcam camera as a detector for a simple lab-on-chip time based approach.

A modification of a webcam camera for use as a small and low cost detector was demonstrated with a simple lab-on-chip reactor. Real time continuous monitoring of the reaction zone could be done. Acid-base neutralization with phenolphthalein indicator was used as a model reaction. The fading of pink color of the indicator when the acidic solution diffused into the basic solution zone was recorded as the change of red, blue and green colors (%RBG.) The change was related to acid concentration. A low cost portable semi-automation analysis system was achieved.

Determination of trace iron in beer using flow injection systems with in-valve column and bead injection

Three flow injection (FI) systems were investigated for the determination of trace iron in beer: an FI-in-valve column-flame atomic absorption spectrophotometry (FI-FAAS) system, a spectrophotometric FI system with a column placed at the detection point, and an FI-spectrophotometric system with bead injection (FI-BI). Cationic exchange resin Dowex 50W X8 and iminodiacetate chelating resin, Chelex-100, were employed for the FI-spectrophotometric and FI-FAAS systems, respectively. The FI-in-valve column, packed with the resin, enhances the FAAS performance. The spectrophotometric FI system with a column (packed with Chelex-100) placed at the detection point (in a cell holder of a spectrophotometer) is based on the formation of iron (II)-1,10-phenanthroline complex sorbed onto the resin. No eluent has been found to be suitable. The FI-BI for renewable microcolumn has been proven to be an alternative. The FI-FAAS and FI-BI procedures provide online sample preseparation and preconcentration for the determination of iron in beer. Both are simple, rapid, and economical. The procedures also involve sample preparation (decarbonation and suppression of tannin interference by adding ascorbic acid) and standard addition. The results obtained by FI-FAAS and FI-BI agree with those of AOAC spectrophotometric method.

Determination of diphenhydramine hydrochloride in some single tertiary alkylamine pharmaceutical preparations by flow injection spectrophotometry

A simple and rapid spectrophotometric method with flow injection is proposed for determination of diphenhydramine hydrochloride in some single tertiary alkylamine pharmaceutical preparations (capsule and syrup). It is based on ion pair formation with bromocresol green in a pH 3 buffer which a yellow ion pair compound is extracted into chloroform layer. An aqueous layer containing excess bromocresol green is injected into a carrier stream of 0.01 M borax solution and absorbance of the stream is continuously monitored at 610 nm. Diminution of the bromocresol green is related to an amount of diphenhydramine hydrochloride that can be evaluated from a calibration graph established by a plot of diphenhydramine hydrochloride concentration (micro gm l(-1)) and peak height (mV). Optimization will be discussed. The calibration graph is linear over the concentration ranges of 5-21 and 75-188 micro gm l(-1). A throughput of 100 injections h(-1) can be obtained. Application to assay for capsule and syrup samples has been demonstrated. The method is validated by comparing the results with HPLC analyses.

Exploiting sequential injection analysis with lab-at-valve (LAV) approach for on-line liquid-liquid micro-extraction spectrophotometry.

Sequential injection analysis (SIA) with lab-at-valve (LAV) approach for on-line liquid-liquid micro-extraction has been exploited. Sample, reagent and organic solvent were sequentially aspirated into a coil attached to a central port of a conventional multiposition selection valve, where the extraction process was performed. The aqueous and organic phases were separated in a conical separating chamber LAV unit attached at one port of the valve. The organic phase containing extracted product was then monitored spectrophotometrically. The system offers a novel alternative on-line automated extraction in a micro-scale and has been successfully demonstrated for the assays of diphenhydramine hydrochloride (DPHH) in pharmaceutical preparations and anionic surfactant in water samples.

Flow Injection/Sequential Injection Chromatography: A Review of Recent Developments in Low Pressure with High Performance Chemical Separation

This review focuses on the developments of the various parts of instrumentation and the operation of low to medium pressure flow injection and sequential injection chromatography (FIC and SIC) systems. The report and discussion include solution delivery system, separation column, flow cell and detector, mobile phase management, and online sample pretreatment. Applications of FIC and SIC and their differences as compared to HPLC are also presented.

Exploiting green analytical procedures for acidity and iron assays employing flow analysis with simple natural reagent extracts

Green analytical methods employing flow analysis with simple natural reagent extracts have been exploited. Various formats of flow based analysis systems including a single line FIA, a simple lab on chip with webcam camera detector, and a newly developed simple lab on chip system with reflective absorption detection and the simple extracts from some available local plants including butterfly pea flower, orchid flower, and beet root were investigated and shown to be useful as alternative self indicator reagents for acidity assay. Various tea drinks were explored to be used for chromogenic reagents in iron determination. The benefit of a flow based system, which allows standards and samples to go through the analysis process in exactly the same conditions, makes it possible to employ simple natural extracts with minimal or no pretreatment or purification. The combinations of non-synthetic natural reagents with minimal processed extracts and the low volume requirement flow based systems create some unique green chemical analyses.

Simple lab-on-chip approach with time-based detection

A simple lab-on-chip approach with time-based detection is proposed. A platform is made from a piece of acrylic differently shaped channels for introducing sample and reagent(s) using flow manipulation. Time-based changes involving migration of the reaction zone are monitored. The changes can be visually monitored by using a stop-watch with naked eyes observation. Some applications for the determination of ascorbic acid, acetic acid and iron in real samples with different chemistries were demonstrated.