Spectrophotometric flow-injection analysis of mercury(II) in pharmaceuticals with p-nitrobenzoxosulfamate

A new, simple and rapid spectrophotometric FI method for the accurate and precise determination of Hg(II) in pharmaceutical preparations has been developed. The method is based on the measuring the decrease of absorbance intensity of p-nitrobenzoxosulfamate (NBS) due to the complexation with Hg(II). The absorption peak of the NBS, which is decreased linearly by addition of Hg(II), occurs at 430 nm in 2×10⁻⁴ mol l⁻¹ HNO₃ as a carrier solution. Optimization of chemical and FI variables has been made. A micro column consisting of several packing materials applied instead of reaction coil was also investigated. A background level of Fe(III) maintained in reagent carrier solution with NBS was found useful for sensitivity and selectivity. Under the optimized conditions, the sampling rate was over 100 h⁻¹, the calibration curve obtained were linear over the range 1-10 μg ml⁻¹, the detection limit was lower than 0.2 μg ml⁻¹ for a 20 μl injection volume, and the precision [S_r=1% at 2 μg ml⁻¹ Hg(II) (n=10)] was found quite satisfactory. Application of the method to the analysis of Hg(II) in pharmaceutical preparations resulted a good agreement between the expected and found values.     

Flow-injection determination of europium after on-line reduction

A zinc reductor minicolumn is used in a flow-injection system for reduction of europium(III) to europium(II). Europium(II) is indirectly determined either spectrophotometrically by oxidation with iron(III) and reaction of the iron(II) formed with 1,10- phenanthroline, or spectrofluorimetrically by reaction with cerium(IV) and measurement of the cerium(III) produced. The reductor functions efficiently at flow rates up to 1 ml min^?1, which allows sample injection rates up to 100 h^?1. Linear calibration is achieved for 10–200 and 0.5–4 μg ml^?1 with detection limits of 2.5 and 0.25 μg ml^?1, by spectrophotometry and spectrofluorimetry, respectively.     

Chemiluminescence determination of barbituric acid using Ru(phen)(3)(2+)-Ce(IV) system

A chemiluminescence (CL) method for the determination of barbituric acid (BA) was proposed, which is based on the enhancement of BA to the CL intensity of Tris-(1,10-phenanthroline)ruthenium(II) (Ru(phen)₃²⁺)-cerium(IV) (Ce(IV)) system. The concentration of BA is proportional to the CL intensity in the range of 5.0×10⁻³-2.0 μg ml⁻¹. The detection limit is 6.9×10⁻⁴ μg ml⁻¹. The relative standard deviation (R.S.D.) of determining 11 samples containing 0.20 μg ml⁻¹ BA is 3.2%. This CL method has been successfully applied to the determination of BA in the synthetic samples. The mechanism of CL reaction was studied.     

Determination of paraquat in human blood plasma using reversed-phase ion-pair high-performance liquid chromatography with direct sample injection

This report describes the determination of paraquat (PQ) in human blood plasma samples by a direct-injection reversed-phase ion-pair chromatographic method. Blood plasma filtrate was injected directly into the LiChrospher® RP-18 alkyl-diol silica (ADS) precolumn integrated in a column switching system using a mixture of 3% 2-propanol and 10 mM sodium octane sulfonate (SOS) in a 0.05 M phosphate buffer (pH 2.8). After washing with this phase, the ADS precolumn was back-flushed with the analytical mobile phase consisting of 40% of methanol and 10 mM SOS in a 0.05 M phosphate buffer (pH 2.8) at a flow rate of 1.0 ml min⁻¹, in order to carry the analyte to a conventional reversed-phase analytical column, where the separation of PQ was achieved and finally detected by UV at 258 nm. The recoveries of PQ from human blood plasma samples ranged between 95.0 and 99.5% at nine different concentrations (from 0.05 to 3.00 μg of PQ ml⁻¹) with coefficients of variation <2.5% (n=3). The precision expressed as relative standard deviation was below 3.5% for between-day and below 4.3% for within-day measurements (n=5). The detection limit (signal-to-noise ratio, S/N>3) was 0.005 μg ml⁻¹ with an injection volume of 200 μl. The proposed method is promising for the identification and quantification of PQ at low concentration levels and is suitable for its analysis in human blood plasma samples from intentional or accidental poisonings cases with a sample throughput of 5 samples per hour.     

Influence of ultrasonic waves on phosphate determination by the molybdenum blue method

Polymeric bonds between molybdate monomeric ions in acidic medium were broken by 40 kHz ultrasonic wave irradiation, improving the reaction kinetics with o-phosphate in the presence of ascorbic acid. It could be assumed that the ultrasonic wave irradiation of molybdate solution in acidic medium during 1.0 min was sufficient to increase the rate of the molybdenum blue formation. The approach was applied to the o-phosphate determination in natural waters. Precise results were obtained in the range from 0.05 to 0.50 μg ml⁻¹ (r=0.9994; N=6), and the detection limit was estimated as 0.027 μg ml⁻¹ PPO₄. Advantages over the classical analogous procedure are emphasised.     

Simultaneous determination of Sb(III) and Sb(V) by partial least squares regression

A method for simultaneous spectrophotometric determination of Sb(III) and Sb(V) using multivariate calibration method is proposed. This method is based on the development of the reaction between the analytes and pyrogallol red at pH 2.00. The selection of variables was studied. A series of synthetic solutions containing different concentrations of Sb(III) and Sb(V) were used to check the prediction ability of the partial least squares model. The calibration curves were linear over the range of 0.3-3.4 and 0.3-3.0 μg ml⁻¹ for Sb(III) and Sb(V), respectively. The detection limits were 0.177 and 0.200 μg ml⁻¹ for Sb(III) and Sb(V), respectively.     

Development of integrated chemiluminescence flow sensor for the determination of adrenaline and isoprenaline

A novel integrated chemiluminescence (CL) flow sensor for the determination of adrenaline and isoprenaline is developed based on the enhancing effect of analytes on CL emission of luminol oxidized by periodate in alkaline solution. The analytical reagents luminol and periodate are immobilized on anion exchange resins, respectively, and packed in a glass tube to construct a reagentless sensor. The proposed sensor allows the determination of adrenaline and isoprenaline over the range from 2.0×10⁻⁸ to 1.0×10⁻⁵ g ml⁻¹ and 2.0×10⁻⁷ to 5.0×10⁻⁵ g ml⁻¹, respectively. The detection limits are 7.0×10⁻⁹ g ml⁻¹ for adrenaline and 5.0×10⁻⁸ g ml⁻¹ for isoprenaline with a relative standard deviation of 1.7% for the 1.0×10⁻⁷ g ml⁻¹ adrenaline (n=11) and 2.1% for 1.0×10⁻⁶ g ml⁻¹ isoprenaline (n=11). The sample throughput was 60 samples h⁻¹. The sensor has been successfully applied to the determination of adrenaline and isoprenaline in pharmaceutical preparations.     

The determination of chromium(VI) in natural waters by differential pulse polarography.

A method utilizing differential pulse polarography for the determination of chromium(VI) in natural water is described. Additions of 0.62 μg Cu(II) ml^-1 and 0.55 μg Fe(III) ml^-1 did not interfere with the determination of 0.050 μg Cr(VI) ml^-1. The natural water samples containing chromium(VI) were buffered to approximately pH 7 with 0.1 M ammonium acetate and 0.005 M ethylene diamine and analyzed. Natural water samples of chromium content from 0.035 μg ml^-1 to 2.0 μg ml^-1 may be analyzed directly without further preparation. The detection limit is 0.010 μg ml^-1.     

Determination of citrate in tablets and of oxytetracycline in serum using europium (III) luminescence

A direct method for the determination of citrate and oxytetracycline in samples containing complex matrices like tablets or serum has been developed using the luminescence of the ternary complex formed with Eu(III) ions. The triplet-state energy level of oxytetracycline (OxTc), the excitation maximum (412 nm) and the luminescence lifetime of Eu-OxTc (58 μs) were determined. A 17-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. This is accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu (III) and citrate (C = 1 · 10^− 4 mol L^− 1) and pH 7.2. For determination of citrate, the optimal concentrations of Eu(III) and OxTc are 1 : 0.5 (C_Eu = 1 · 10^− 4 mol L^− 1, C_OxTc = 5 · 10^− 5 mol L^− 1) at pH 7.2. The linear range for determination of OxTc in serum is 0.25-250 μg mL^− 1, and for citrate in tablets from 0.5 to 10.0 μg mL^− 1 (2.3 · 10^− 6- 4 · 10^− 5 mol L^− 1). The detection limit was 0.1 μg mL^− 1 for OxTc and 0.2 μg mL^− 1 (1 · 10^-6 mol L^− 1) for citrate, respectively. A comparison of the new method with other methods for determination of citrate is given.     

A rapid spectrophotometric method for the determination of transparent exopolymer particles (TEP) in freshwater

A simple and rapid spectrophotometric method is proposed for the determination of transparent exopolymer particles (TEP) in freshwater samples. In this method, TEP reacts with excess of alcian blue solution yielding a low solubility dye-TEP complex. After centrifugation, the concentration of the remaining dye in the supernatant was determined at 602 nm and its concentration was related to the concentration of TEP in freshwater. The effect of alcian blue concentration from 1.5×10⁻³ to 9.0×10⁻³% (m/v), solution pH from 2.5 to 6.9 and stirring time from 20 to 120 s on the analytical curve was investigated. Under the optimum conditions established, such as alcian blue concentration of 3.0×10⁻³% (m/v); pH of 4.0 (0.2 mol l⁻¹ acetate buffer solution) and stirring time of 1 min, the analytical curve was linear from 0.50 to 10 μg ml⁻¹ (A=0.34−0.037[GX]; r²=0.9999; where A is the absorbance and [GX] the gum xanthan concentration in μg ml⁻¹) with a detection limit of 0.10 μg ml⁻¹. The recovery of TEP (as gum xanthan) for two samples ranged from 95.3 to 108 and the relative standard deviations (R.S.D.s) were lower than 0.8% for gum xanthan solutions at concentrations of 1.0 and 1.5 μg ml⁻¹ (n=8). The results obtained for TEP in freshwater samples using the proposed spectrophotometric method and those obtained using a literature method are in agreement at the 95% confidence level and within an acceptable range of error.     

A novel tetrachlorothallate (III)-PVC membrane sensor for the potentiometric determination of thallium (III)

A novel tetrachlorothallate (III) (TCT)-selective membrane sensor consisting of tetrachlorothallate (III)-2,3,5-triphenyl-2-H-tetrazolium ion pair dispersed in a PVC matrix plasticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1×10⁻³-4×10⁻⁶ M thallium (III) at 25 °C with an anionic slope of 56.5±0.5 over the pH range 3-6. The lower detection limit and the response time are 2×10⁻⁶ M and 30-60 s, respectively. Selectivity coefficients for Tl(III) relative to a number of interfering substances were investigated. There is negligible interference from many cations and anions; however, iodide and bromide are significantly interfere. The determination of 0.5-200 μg ml⁻¹ of Tl(III) in aqueous solutions shows an average recovery of 99.0% and a mean relative standard deviation of 1.4% at 50.0 μg ml⁻¹. The direct determination of Tl(III) in spiked wastewater gave results that compare favorably with those obtained by the atomic absorption spectrometric method. The electrode was successfully applied for the determination of thallium in zinc concentrate. Also the tetrachlorothallate electrode has been utilized as an end point indicator electrode for the determination of thallium using potentiometric titration.     

Chemiluminescence determination of ultramicro DNA with a flow-injection method

A high sensitive flow-injection chemiluminescence method for determination of calf thymus DNA and herring sperm DNA has been developed. The method is based on the chemiluminescence reaction of Rhodamine B-cerium(IV)-thermally denatured DNAs in sulfuric acid media. The proposed procedure allows quantitation of DNAs in the range 2.6×10⁻⁵ to 0.26 μg ml⁻¹ for calf thymus DNA and 5.0×10⁻⁸ to 5.0×10⁻⁵ μg ml⁻¹ for herring sperm DNA with correlation coefficients 0.9998 and 0.9996 (both n=11), respectively. The detection limits (3σ) are 6.5×10⁻⁶ μg ml⁻¹ for calf thymus DNA and 4.3×10⁻⁸ μg ml⁻¹ for herring sperm DNA. The possible mechanism of chemiluminescence in the system is discussed.     

Novel preconcentration technique using bis(2-ethylhexyl) hydrogen phosphate (HDEHP) loaded porous polytetrafluoroethylene (PTFE) filter tube as a sorbent: Its application to determination of In(III) in seawater by ICP-MS with air segmented discrete sample introduction

Novel preconcetration method involving porous polytetrafluoroethylene (PTFE) filter tube impregnated bis(2-ethylhexyl) hydrogen phosphate (HDEHP) as a sorbent was studied to establish it as a practical preconcentration method for ultra trace analysis with ICP-MS. A 1 ng portion of In(III) in 1000 ml of matrix free solution or 700 ml of synthetic seawater was quantitatively complexated with HDEHP adsorbed onto porous PTFE filter tube by passing the solution through the micro pore of the filter tube. Preconcentrated In(III) was then quantitatively recovered provided that the elution, which consists of a cyclical filtering 0.1 ml of 8 mol dm⁻³ hydrochloric acid through the filter tube for 1 min; therefore, up to 10000- and 7000-fold of enrichment was attained for matrix free solution and synthetic seawater, respectively. To introduce a 0.1 ml of the eluted solution to ICP-MS, flow injection method with air segmented discrete sample introduction (ASDI) was also studied by using manually operated simple valve system. By using ASDI, good linearity of calibration curve (r = 0.99997) was observed from 0.01 to 5.0 ng ml⁻¹ of In(III). Good reproducibility was also shown in measurements of 0.1 ml of 5 ng ml⁻¹ of In(III) (R.S.D. = 1.9%, n = 5). The average recovery and R.S.D. of the results for the five duplicates determination of 0.1 ng of In(III) spiked to 200 ml of synthetic seawater were 99 and 2.4%, respectively. The method was applied to the determination of In(III) in coastal seawater sampled at north east of Hachijyo Island, Japan; using 200 ml of sample, 2000-fold preconcentration of In(III) was performed within 30 min for five samples. The analytical detection limit and the blank were 9.8 and 21 pg l⁻¹, respectively. The average concentration was determined to be 96 pg l⁻¹, and R.S.D. of the results was 3.7% (n = 3).     

Fluorimetric determination of ascorbic acid with o-phenylenediamine

A simple and sensitive fluorimetric method for the determination of ascorbic acid (AA) is described. The method is based on the condensation reaction between AA and o-phenylenediamine (OPDA) in the absence of the oxidant. The fluorescence intensity is measured at excitation and emission wavelengths of 360 and 430 nm, respectively. Under optimum condition, a linear relationship is obtained between the fluorescence intensity and the concentration of AA in the range of 0.05-40 μg ml⁻¹. The detection limit is 0.006 μg ml⁻¹, which is obviously lower than that of other fluorimetric methods reported.     

Semi-online preconcentration of Cd, Mn and Pb on activated carbon for GFASS

This paper presents a method whereby trace elements in NH₄Cl-NH₃ medium are adsorbed on activated carbon in a micro-flow-injection (FI) semi-online sorbent extraction preconcentration system and then determined by graphite furnace atomic absorption spectrometry (GFAAS). The analytical performance of the proposed method for determining Cd, Mn and Pb was studied. A microcolumn packed with activated carbon was used as a preconcentration column (PCC). The metals to be determined were preconcentrated onto the column for 60 s and then rinsed with 0.02% (v/v) HNO₃ and eluted with 30 μl of 2 mol l⁻¹ HNO₃. Compared with the direct injection of 30 μl of aqueous sample solution, enrichment factor of 32, 26, and 21 and detection limits (3σ) of 0.4, 4.7, and 7.5 ng l⁻¹ for Cd, Mn and Pb, respectively, were obtained with 60 s sample loading at 3.0 ml min⁻¹ for sorbent extraction, 30 μl of eluate injection, and peak area measurement. The precisions (RSD, n=6) were 2.8% at the 0.05 μg l⁻¹ level for Cd, 3.0% at the 0.3 μg l⁻¹ level for Mn, and 3.1% at the 0.5 μg l⁻¹ level for Pb. The experimental results indicate that the procedure can eliminate the fundamental interferences caused by alkali and alkaline earth metals and the application of it to the determination of Cd, Mn and Pb in some water samples is successful.     

A novel nonenzymatic fluorescent sensor for glucose based on silica nanoparticles doped with europium coordination compound

Amino-functionalized luminescent silica nanoparticles (LSNPs) doped with the europium(III) mixed complex, Eu(TTA)₃phen with 2-thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline(phen) were synthesized successfully using an revised Stöber method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR), and fluorescence spectroscopy were performed for characterizing the synthesized nanoparticles. In the presence of glucose, the fluorescence intensity of the amino-functionalized LSNPs was enhanced due to the enhanced fluorescence resonance energy transfer. Based on fluorescence-enhancing effect, a simple and sensitive method for the determination of glucose was proposed. Under the optimized experimental conditions, the enhanced fluorescence intensity ratio (ΔF/F₀) was linear with the concentration of glucose (c) in the range of 0.0-180 μg ml⁻¹ with a detection limit of 0.8 μg ml⁻¹ (S/N = 3). The R.S.D. values were 0.33% and 0.37% at the levels of 22.5 and 100 μg ml⁻¹, respectively. The proposed method was applied to the determination of glucose in synthetic samples with satisfactory results. The proposed method was also performed to the analysis of blood glucose in human serum samples and the results were in good agreement with clinical data provided by the hospital, which indicates that the method presented here is not only simple, sensitive, but also reliable and suitable for practical applications.     

Determination of phenylurea herbicides in aqueous samples using partitioned dispersive liquid-liquid microextraction

Partitioned dispersive liquid-liquid microextraction (PDLLME), using THF as the dispersive solvent and dichloromethane as the extraction solvent, was utilized to isolate and concentrate phenylurea herbicides (PUHs) from aqueous samples. In PDLLME, a dispersive solvent should be able to partition in the organic extractant droplets to effectively extract the polar organic compounds from aqueous samples. The mixture of the water-immiscible extractant and the partitioned dispersive solvent was obtained by centrifugation, dried under low pressure, reconstituted in methanol-water mixture (1:1), and injected into a HPLC system for the determination of PUHs. The enrichment factors of the PUHs ranged from 68 to 126 under the optimal conditions. The linear range was 0.5-100 ng ml⁻¹ for each analyte, the relative standard deviations of PUHs were in the range of 1.5-5.9% (n = 5), and the detection limits (signal-to-noise ratio of 3) ranged from 0.10 to 0.28 ng ml⁻¹ for the herbicides. The range of intraday precision (n = 5) for PUHs at the levels of 0.5, 5, and 50 ng ml⁻¹ were 3.0-5.9%, 1.8-3.3%, and 2.2-3.6%, respectively. The range of interday precision (n = 5) at 0.5, 5, and 50 ng ml⁻¹ were 0.4-1.8%, 1.2-2.4%, and 0.9-2.3%, respectively. The recoveries of PUHs from three spiked river water samples, at a level of 10 ng ml⁻¹, were 91.2-104.1%. Due to its rapidity, ease of operation, and high recovery, PDLLME can be utilized to isolate and concentrate organic environmental contaminants such as PUHs from aqueous samples.     

Electrochemical hydride generation atomic absorption spectrometry for determination of cadmium

An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead-tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett-Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml⁻¹of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml⁻¹ and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml⁻¹. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.     

Flow injection kinetic spectrophotometric determination of trace amounts of Se(IV) in seawater

A simple, accurate, sensitive and selective flow injection catalytic kinetic spectrophotometric method for rapid determination of trace amounts of selenium is proposed in this paper. The proposed method is based on the accelerating effect of Se(IV) on the reaction of ethexlenediamine tetrecetic acid disodium salt (EDTA) and sodium nitrate with ammonium iron(II) sulfate hexahydrate in acidic media. The absorbance intensity was registered in this reaction solution at 440 nm. The calibration graph is linear in the range of 5 × 10⁻⁹-2 × 10⁻⁷ and 2 × 10⁻⁷-2 × 10⁻⁶ g ml⁻¹. The detection limit is 2 × 10⁻⁹ g ml⁻¹. The relative standard deviation was 3.4% for 5 × 10⁻⁸ g ml⁻¹ Se(IV) (n = 11), 2.7% for 5 × 10⁻⁷ g ml⁻¹ Se(IV) (n = 11). This method is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to determination of Se(IV) of seawater samples.     

Ultra-trace level determination of hydroquinone in waste photographic solutions by UV-vis spectrophotometry

A simpler UV-vis spectrophotometric method was investigated for hydroquinone (HQ) determination using KMnO₄ as oxidizing agent for conversion of HQ to p-benzoquinone (BQ) as well as signal enhancer. Various parameters such as analytical wavelength, stability time, temperature, pH, solvent effect and interference of chemicals were checked and parameters optimized by using 1 μg ml⁻¹ standard solution of HQ. Beer's Law was applicable in the range of 0.07-2 μg ml⁻¹ and 0.005-0.05 μg ml⁻¹ at 245.5 nm and at 262 nm for aqueous standard solutions of HQ with linear regression coefficient value of 0.9978 and 0.9843 and detection limit of 0.021 μg ml⁻¹ and 0.0016 μg ml⁻¹ HQ, respectively. Standard deviation of 1.7% and 2.4% was true for 1 μg ml⁻¹ and 0.03 μg ml⁻¹ HQ solution (n = 11) run at respective wavelengths. The method was successfully applied to dilute waste photographic developer samples for free HQ determination.