Tandem measurements of iron and creatinine by cross injection analysis with application to urine from thalassemic patients.

This work presents development of a method for the dual determination of Fe(III) and creatinine using cross injection analysis (CIA). Two CIA platforms connected in series accommodated sample and reagents plugs aspirated via y-direction channels while water was pumped through the x-direction channel toward a flow-through cell of a diode array UV-vis. detector. Iron was detected from the colorimetric reaction between Fe(II) and 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-(3-sulfopropyl)amino) aniline (5-Br-PSAA), with prior reduction of Fe(III) to Fe(II) by ascorbic acid. The Jaffe's reaction was employed for the detection of creatinine. Under the optimal conditions, good linearity ranges were achieved for iron in the range 0.5 to 7 mg L(-1) and creatinine in the range 50 to 800 mg L(-1). The CIA system was applied to spot urine samples from thalassemic patients undergoing iron chelation therapy, and was successfully validated with ICP-OES and batchwise Jaffe's method. Normalization of urinary iron excretion with creatinine is useful for correcting the iron concentration between urine samples due to variation of the collected urine volume.

A flow system for the determination of metal speciation in soil by sequential extraction.

A flow extraction system with on-line and off-line flame atomic absorption spectrometric (FAAS) detection was developed to speed up, facilitate, and improve the accuracy of sequential extraction for metal speciation in solid materials. A flow extraction system with off-line detection was more advantageous than the on-line detection. In the proposed system, extraction was performed in a closed extraction chamber where extractants were flowing through sequentially. The extract from each extraction was collected in 4-10 fractions to obtain a total of approximately 180 ml for subsequent FAAS determination. The system is simple, easy to construct and operate. It has less risk of contamination and human error. A widely used three-step sequential extraction scheme was used to evaluate the novel system by analyzing Ca, Fe, Mn, Cu, and Zn in a certified reference material. The extraction time for three-step sequential extraction of soil sample was 4 h. The analytical results for Ca, Fe, Mn, Cu, and Zn of a soil certified reference material using the proposed system were compared with those of the conventional batch extraction.

A novel continuous-flow sequential extraction procedure for metal speciation in solids.

A continuous-flow extraction system was developed to speed up, facilitate, and improve the accuracy of the chemical fractionation of metals in solid materials. A three-step sequential extraction scheme was used to evaluate the novel system by analyzing calcium (Ca), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in a soil certified reference material (National Institute of Standards and Technology [NIST] SRM 2710). In the proposed system, extraction occurred in a closed chamber through which extractants were passed sequentially. The extracts were collected in a number of subfractions for subsequent name atomic absorption analysis. Apart from the advantages of simplicity, speed, and less risk of the contamination that flow analysis systems usually possess, the continuous-flow system can improve the accuracy of chemical fractionation of metals by sequential extraction. The system ensures that extraction is performed at designated pH values without any need of adjustment. Variation of sample weight to chamber volume ratios from 1:12 to 1:40 had no effect on the extractability of the metals studied. In the extraction of the acid soluble fraction, concentrations of acetic acid in the range 0.11 to 0.5 mol L(-1) had no significant effect on the amounts of metals extracted, except Fe. Increasing the concentration of hydroxylamine in the reducible fraction step from 0.04 to 0.5 mol L(-1) affected the extraction efficiency for Fe, Mn, and Zn. The extraction profile, rather than a single value of extracted concentration, of each element offers additional information about the kinetics of leaching processes and chemical associations between elements in the solid materials.

Simple flow injection for screening of total antioxidant capacity by amperometric detection of DPPH radical on carbon nanotube modified-glassy carbon electrode.

An amperometric flow injection (FI) method suitable for evaluation of 'total antioxidant capacity' (TAC) is presented. In this method, a carrier stream of a solution of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(•)) continuously flows through an electrochemical cell, furnished with a carbon nanotube modified-glassy carbon electrode (CNT/GC) as the working electrode. At the applied voltage of 0.05V (vs. Ag/AgCl), DPPH(•) is reduced resulting in a constant electric current. For measurement of the TAC, a sample zone containing antioxidant(s) is injected into the carrier stream therein reduction reaction of DPPH(•) occurring within the sample zone. The decreased amount of the radical in the sample zone leads to a drop of the amperometric signal at the CNT/GC electrode. We have also compared the performance of the CNT/GC electrode to the unmodified GC electrode using cyclic voltammetry. The sensitivity of the CNT/GC electrode was more than twenty five times greater than the bare GC electrode. The study of the sweep rate dependence showed that the cathodic and anodic current of 0.1mM DPPH solution varied linearly (r(2)=0.998) with the square root of the scan rate, from 0.02 to 0.12 Vs(-1). These results demonstrated that the CNT/GC electrode is appropriate for the quantitation of antioxidants via amperometric detection of the residual concentration of non-reacted DPPH(•). We obtained linear calibrations for all the antioxidants tested including gallic acid, catechin, quercetin, caffeic acid and Trolox. The system offers rapid sample throughput (45 samples h(-1)) and good precision of 3.2% R.S.D., for 20 µL-injection of 2.5 µM Trolox (n=30). This method was applied to evaluate the TAC of extracts of some Thai indigenous vegetables.

Sequential injection analysis with electrochemical detection as a tool for economic and rapid evaluation of total antioxidant capacity.

This work presents a new flow-based coupled electrochemical technique for evaluation of "total antioxidant capacity (TAC)". A sequential injection (SI) with amperometric detection was applied to the TAC analysis of commercial instant ginger infusion beverages using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. Besides having chromogenic properties, the ABTS reagent behaves as an electroactive species at the glassy carbon electrode in phosphate buffer pH 7.0, the decrease of the cathodic current signal of the ABTS(+) radical after reaction with antioxidants can be monitored. The SI system, furnished with an in-house electrochemical detection cell (ECD), was optimized with respect to the applied potential, sample and reagent volume, and flow rate to the detector. Gallic acid was used as the standard antioxidant and the capacity was reported as gallic acid equivalent (GAE) unit. TAC measurements of ginger infusions at the optimum condition were performed using the proposed technique and also with the classical batch spectrophotometric ABTS assay. TAC values obtained from our method and the standard method are in good agreement (r(2)=0.956). The SI-amperometric technique provided satisfactory precision (4.11% RSD) with rapid sample throughput (40 samples h(-1)). Also using this method, the consumption of the expensive ABTS reagent was greatly reduced.

A reagent-free SIA module for monitoring of sugar, color and dissolved CO2 content in soft drinks.

This work presents a new sequential injection analysis (SIA) method and a module for simultaneous and real-time monitoring of three key parameters for the beverage industry, i.e., the sugar content (measured in Brix), color and dissolved CO(2). Detection of the light reflection at the liquid interface (the schlieren effect) of sucrose and water was utilized for sucrose content measurement. A near infrared LED (890+/-40 nm) was chosen as the light source to ensure that all the ingredients and dyes in soft drinks will not interfere by contributing light absorption. A linear calibration was obtained for sucrose over a wide concentration range (3.1-46.5 Brix). The same module can be used to monitor the color of the soft drink as well as the dissolved CO(2) during production. For measuring the color, the sample is segmented between air plugs to avoid dispersion. An RGB-LED was chosen as the light source in order to make this module applicable to a wide range of colored samples. The module also has a section where dissolved CO(2) is measured via vaporization of the gas from the liquid phase. Dissolved CO(2), in a flowing acceptor stream of water resulting in the change of the acceptor conductivity, is detected using an in-house capacitively coupled contactless conductivity detector (C(4)D). The module includes a vaporization unit that is also used to degas the carbonated drink, prior the measurements of sucrose and color within the same system. The method requires no chemicals and is therefore completely friendly to the environment.

Low cost telemetry with PC sound card for chemical analysis applications.

This work describes the development of a telemetric system in conjunction with a computer sound card for recording of signals. For signal transmission, a transmission wireless microphone was utilized, making the telemeter compatible with the sound card normally equipped inside a personal computer. The developed telemeter is a low-cost apparatus capable of remote monitoring. With the sampling rate of 10Hz, 100% accuracy was obtained up to a distance of 30m. The precision was good (%RSD=0.03-0.09), with relatively low noise. The effective signal range was from 0 to 2V, with approximately 1100 working steps (greater than 10bit A/D). The telemetric system was shown to be suitable for wireless recording of outputs from spectrophotometer and pH meter. Potential applications in chemical analysis were demonstrated.

Membraneless vaporization unit for direct analysis of solid sample.

A new apparatus, called 'membraneless vaporization' (MBL-VP) unit was designed and developed for direct analysis of solid samples. Solid analyte was converted into a gaseous form which then reacts with an indicator reagent. Change in absorbance was used to quantitate the analyte. Stirring with a magnetic bar was employed to facilitate the evaporation of the gas. Unlike the pervaporation technique, hydrophobic membrane was not required for this MBL-VP technique. Application of the membraneless technique for direct determination of calcium carbonate in calcium supplements, has shown to be very precise (R.S.D.=2.5% for 0.16 mmol CO3(2-)), with detection limit of 0.5 mg CaCO3. Results by this method agreed well with flame atomic absorption spectrometric method. Sample throughput was 20 samples h(-1).

Pervaporation-flow injection with chemiluminescence detection for determination of iodide in multivitamin tablets.

This paper describes the use of a pervaporation (PV) technique in a flow injection (FI) system for selective improvement in iodide analysis. Iodide in the sample zone is oxidized to iodine, which permeates through a hydrophobic membrane. Detection of the diffused iodine is achieved using the chemiluminescent (CL) emission at 425nm that results from the reaction between iodine and luminol. The method was applied for the analysis of some pharmaceutical products, such as nuclear emergency tablets and multivitamin tablets. Ascorbic acid present in multivitamin samples interfered seriously with the analysis, and off-line sample treatment using anion exchange resin was employed to successfully remove ascorbic acid before the analysis. Ascorbic acid was flushed from the column using 0.4M sodium nitrate followed by elution of iodide with 2M sodium nitrate. The detection limit (3S.D.) of the system was 0.5mgl(-1), with reproducibility of 5.2% R.S.D. at 5mgl(-1). Sample throughput was determined as 30injectionsh(-1). There was good agreement between iodide concentrations from extracted samples determined using four different methods, i.e., PV-FI, gas diffusion-flow injection, potentiometry and ICP-MS. A comparison of the analytical features of the developed pervaporation system with these of the previously reported chemiluminescence gas diffusion-flow injection previously reported is also described.

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.

Determination of trace amounts of bromide by flow injection/stopped-flow detection technique using kinetic-spectrophotometric method.

A simple, sensitive and selective method for the determination of bromide in seawater by using a flow injection/stopped-flow detection technique was examined. The detection system was developed for a new kinetic-spectrophotometric determination of bromide in the presence of chloride matrix without any extraction and/or separation. The detection was based on the kinetic effect of bromide on the oxidation of methylene blue (MB) with hydrogen peroxide in a strongly acidic solution. Large amounts of chloride could enhance the sensitivity of the method as an activator. The decolorisation of the blue color of MB was used for the spectrophotometric determination of bromide at 746nm. A stopped-flow approach was used to improve the sensitivity of the measurement and provide good linearity of the calibration over the range of 0-3.2mugml(-1) of bromide. The relative standard deviation was 0.74% for the determination of 2.4mugml(-1) bromide (n=5). The detection limit (3sigma) was 0.1mugml(-1) with a sampling frequency of 12h(-1). The influence of potential interfering ions was studied. The proposed method was applied to the determination of bromide in seawater samples and provided satisfactory results.

Method development based on all injection analysis for the determination of phosphorus in soil and sediment extracts.

In this work, we have modified the technique of all injection analysis (AIA) by changing the position of the detector. The detection is then located as a part of the circulatory loop. With this new detector position, we could monitor for many numbers of circulation. The sensitivity was improved by using the cumulative signal data obtained when the number of circulation rounds was increased. The dilution effect using this new detector location was also less than that with the previous system. We employed a four-channel peristaltic pump to aspirate four types of liquids into the system together at one time. The AIA method was then developed for determination of phosphorus in soils and sediment extracts. The method was optimized for the new harmonized scheme of extraction that has been developed by the European Commission.

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 (425nm). Preliminary results showed for concentrations of less than 2mgL(-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 I(2) that conditioned the GD membrane and tubing. This minimized surface interaction between the active surface and the I(2) generated from the samples, thus improving both precision and sensitivity. By employing membrane conditioning, it has been possible to reliably detect concentrations down to 0.1mgL(-1). At the optimized condition, an excellent linear calibration (r(2) = 0.999) was obtained from 0.1 to 1.0mgL(-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.

Simple and selective method for determination of iodide in pharmaceutical products by flow injection analysis using the iodine-starch reaction.

This work exploited the well-known iodine-starch reaction for development of a simple flow-injection (FI) method for determination of iodide in pharmaceutical samples. Iodide in an injected zone was oxidized to iodine. A gas diffusion unit enables selective permeation of iodine through a hydrophobic membrane. Detection was made very selective for elemental iodine by employing formation of the I(3)(-)-starch complex. The detection limit (3 S/ N) of the system was 1 mg I L(-1). For a liquid patent medicine used for asthma treatment we suggested modification of the system. Direct injection of this sample, which contains a particularly high concentration level of iodide (ca. 9000 mg I L(-1)), can be achieved by coupling a dialysis unit to the FI system. This has increased the working range to 6000-10,000 mg I L(-1) without employing complicated nanoliter injection.

Sequential extraction of phosphorus in soil and sediment using a continuous-flow system.

Distribution and mobility of phosphorus in soil and sediment are usually studied by sequential extraction. In the extraction procedure, a sample is treated with a series of reagents to distinguish the phases to which phosphorus is associated such as carbonate and iron or manganese oxides, etc. There have been a number of extraction schemes presented for phosphorus. At present, all of the existing schemes are carried out batchwise. Phosphorus contents derived from all sequences are operationally defined and depend on experimental conditions. An extraction procedure, which is a continuous-flow-based technique, was recently proposed by our group for metals in soils and sediments. The extraction is carried out in a closed chamber through which extractants are passed sequentially. In this paper, the system was investigated using the extraction scheme of Hieltjes and Lijklema to study distribution of phosphorus in three certified reference materials (CRMs). A number of fractions were collected for each reagent for subsequent colorimetric determination. The results are compared with those obtained from a batch extraction. The summation of phosphorus contents of all phases were compared with the certified values and with the values obtained from total digestion. These results have demonstrated that the continuous extraction system developed is also applicable for fractionation of phosphorus. Advantage and disadvantage are discussed.

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.

Flow-injection determination of iodide ion in nuclear emergency tablets, using boron-doped diamond thin film electrode.

The electrochemical determination of iodide was studied at boron-doped diamond thin film electrodes (BDD) using cyclic voltammetry (CV) and flow-injection (FI) analysis, with amperometric detection. Cyclic voltammetry of iodide was conducted in a phosphate buffer pH 5. Experiments were performed using glassy carbon (GC) electrode as a comparison. Well-defined oxidation waves of the quasi-reversible cyclic voltammograms were observed at both electrodes. Voltammetric signal-to-background ratios (S/B) were comparable. However, the GC electrode gives much greater in the background current as usual. The potential sweep rate dependence exhibited that the peak current of iodide oxidation at 1mM varied linearly (r(2) = 0.998) with the square root of the scan rate, from 0.01 to 0.30Vs(-1). This result indicates that the reaction is a diffusion-controlled process with negligible adsorption on BDD surface, at this iodide concentration. Results of the flow-injection analysis show a highly reproducible amperometric response. The linear working range was observed up to 200muM (r(2) = 0.999). The detection limit, as low as 0.01muM (3sigma of blank), was obtained. This method was successfully applied for quantification of iodide contents in nuclear emergency tablets.

Continuous and stopped flow injection for catalytic determination of total iodine in urine.

This paper describes the use of flow injection (FI) techniques for the determination of iodine in urine, based on the catalytic effect of iodide in the redox reaction between Ce(IV) and As(III). The proposed procedures minimize errors in the conventional batch method arising from the reading of absorbance at a fixed time after addition of Ce(IV) reagent. Two FI systems, for the continuous and stopped modes of operation were assembled. In the continuous-FI system, a thermostated bath was used to increase the sensitivity. However this is not necessary for the stopped-FI system. The two systems are comparable in terms of sensitivity, sample throughput and detection limit. The continuous-FI and the stopped-FI exhibited detection limits (3 sigma) of 2.3 and 3 micrograms I l-1 respectively. Both systems have equal sample throughputs of 35 samples h-1. Calibration plots for both techniques are linear. The FI procedures provide very short analysis times compared to the batch procedure. Using the linear regression test, there is no significant difference between the results from the four methods, i.e., continuous-FI, stopped-FI, conventional method and ICP-MS. The proposed methods are readily applicable for automation and can be an alternative to the conventional procedure for the survey of the iodine deficiency disorder. A condition for sample digestion is also proposed to reduce the amount of chloric acid required for complete digestion. Kinetic information of the reaction can also be obtained from the stopped flow mode.