Determination of total iron in ground waters and multivitamin tablets using a solid-phase reactor with tiron immobilised on amberlite ion-exchange resin in a flow injection system

A method is described for the flow injection determination of total iron as Fe(III) using a solid-phase reactor containing disodium-1,2-dihydroxybenzene-3,5-disulphonate (tiron) as substrate. The iron(III) reacted with tiron to form a complex which absorbs strongly at 667 nm, where it was measured spectrophotometrically. The system has a linear range of 1 to 50 mg L^–1 with a detection limit of 0.67 mg L^–1. It is suitable for the determination of total iron in multivitamin tablets and iron-rich ground waters, with a relative standard deviation of better than 1.1%. The results obtained compared favourably with the certified values and a standard ICP-AES method.     

Development of a voltammetric method for the determination of iron(III) in Zn-Fe alloy galvanic baths

A square wave voltammetric method whith a static mercury drop electrode (SMDE) was developed for the quantitative determination of iron (III) in Zn-Fe alloy galvanic baths. Real alloy bath samples were analyzed by the standard addition method and recovery tests were carried out. 0.50 mol L^–1 sodium citrate (pH 6.0) or 0.20 mol L^–1 oxalic acid (pH 4.0) were applied as supporting electrolytes resulting in both cases in a peak potential of about –0.20 V vs. Ag|AgCl (saturated KCl). The iron (III) concentration in the alloy bath was 9.0 × 10^–4 mol L^–1. A good correlation (r = 0.9999) was achieved between the iron (III) concentration and the peak current in the electrolytes studied, with linear response ranges from 1.0 × 10^–6 to 1.2 × 10^–4 mol L^–1. Interference levels for some metals such as copper (II), lead (II), chromium (III) and manganese (II) that can hinder the Zn-Fe alloy deposition were evaluated; only copper (II) interferes seriously. Received: 4 April 2000 / Revised: 19 June 2000 / Accepted: 22 June 2000     

A rapid automated method for wine analysis based upon sequential injection (SI)-FTIR spectrometry

A new process control methodology for the simultaneous determination of sugars, alcohols and organic acids in wine based on multivariate evaluation of mid-IR transmission spectra of wine samples is presented. In addition to ethanol several lower level wine components (glucose, fructose, glycerol, citric-, tartaric-, malic-, lactic- and acetic acid) were determined. To establish a multivariate calibration model a set of 72 calibration solutions was prepared and measured, using a novel, fully automated sequential injection (SI) system with Fourier transform infrared (FTIR) detection. The resulting spectra were evaluated using a partial least square (PLS) model. The developed PLS model was then applied to the analysis of real wine samples containing 79–91 g L^–1 ethanol, 5.9–8.1 g L^–1 glycerol, 0.4–6.9 g L^–1 glucose, 1.5–7.5 g L^–1 fructose, 0.3–1.6 g L^–1 citric acid, 1.0–1.7 g L^–1 tartaric acid, 0.02–3.2 g L^–1 malic acid, 0.4–2.8 g L^–1 lactic acid and 0.15–0.60 g L^–1 acetic acid, yielding results which were in good agreement with those obtained by an external reference method (HPLC-IR). The short analysis time (less than 3 min) together with high reproducibility makes the newly developed method applicable to process control and screening purposes (average of the standard deviations calculated from four repetitive measurements of six different real samples: ethanol: 0.55 g L^–1, glycerol: 0.037 g L^–1, glucose: 0.056 g L^–1, fructose: 0.036 g L^–1, citric acid: 0.020 g L^–1, tartaric acid: 0.010 g L^–1, malic acid: 0.052 g L^–1, lactic acid: 0.012 g L^–1 and acetic acid: 0.026 g L^–1). Received: 21 January 1998 / Revised: 5 March 1998 / Accepted: 6 March 1998     

Organic solvent-soluble membrane filters for the preconcentration and spectrophotometric determination of iron(II) traces in water with Ferrozine

An organic solvent-soluble membrane filter (MF) is proposed for the simple and rapid reconcentration with subsequent spectrophotometric determination of trace levels of iron (II) in water. Iron (II) is collected on a nitrocellulose membrane filter as ion associate of an anionic complex, which is formed by iron (II) and Ferrozine and a cation-surfactant. The ion-pair compound and the MF can be dissolved in small volumes of 2-ethoxyethanol and the absorbance of the resulting solution is measured at 560 nm against a reagent blank with molar absorptivity of 4.01 × 10⁴ L mol^–1 cm^–1. Beer’s law is obeyed over the concentration range 0–10 μg L^–1 of iron (II) in water and the detection limit is 0.03 μg L^–1 with a 50-fold enrichment factor. The proposed method can satisfactorily be applied to the determination of iron (II) in natural water and sea water. Received: 23 June 1998 / Revised: 21 July 1998 / Accepted: 25 August 1998     

A simple flow injection spectrophotometric determination method for iron(III) based on O-acetylsalicylhydroxamic acid complexation

A simple and rapid flow-injection spectrophotometric method for the determination of iron(III) and total iron is proposed. The method is based on the reaction between iron(III) and O-acetylsalicylhydroxamic acid (AcSHA) in a 2 % methanol solution resulting in an intense violet complex with strong absorption at 475 nm. Optimum conditions for the determination of iron(III) and the interfering ions were tested. The relative standard deviation for the determination of 5 μg L⁻¹ iron(III) was 0.85 % (n = 10), and the limit of detection (blank signal plus three times the standard deviation of the blank) was 0.5 μg L⁻¹, both based on the injection volumes of 20 μL. The method was successfully applied in the determination of iron(III) and total iron in water and ore samples. The method was verified by analysing a certified reference material Zn/Al/Cu 43XZ3F and also by the AAS method.     

Flow injection analysis with in-line solid phase extraction for the spectrophotometric determination of sulfonated and unsulfonated Quinoline Yellow in Cologne

An integrated solid-phase spectrophotometry/ FIA  method is  proposed for the determination of the synthetic colorant matter Quinoline Yellow (QYWS) in the presence of its unsulfonated derivative QYSS. The procedure is based on the retention and preconcentration of the low level QYSS on a C-18 silica gel minicolumn, followed by sequential measurement of its absorbance at λ = 410 nm after its elution with methanol. The applicable concentration range, the detection limit and the relative standard deviation were the following: for QYWS, from 0.10 to 30.0 mg L^–1; 0.013 mg L^–1; and 0.6%; and for QYSS, between 10 and 1,000 μg L^–1; 2 μg L^–1; and 1.3%, respectively. The method was applied to the determination of small amounts of QYSS present in QYWS in Colognes. Percentages of recovery between 98% and 99% were obtained in all instances. The method was also satisfactorily applied to the determination of these compounds in samples of commercial Colognes comparing the results for QYWS with those offered by an HPLC reference method and also validating the results chemometrically. Received: 21 January 2000 / Revised: 17 March 2000 / Accepted: 22 March 2000     

Determination of EDTA in used fixing solutions by capillary electrophoresis

A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm × 75 μm I.D.) filled with a borate buffer (50 mmol L^–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved is 2 × 10^–6 mol L^–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions. Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998     

Flow injection spectrophotometric determination of iron(III) using diphenylamine-4-sulfonic acid sodium salt

A highly sensitive and very simple spectrophotometric flow-injection analysis (FIA) method for the determination of iron(III) at low concentration levels is presented. The method is based on the measurement of absorbance intensity of the red complex at 410 nm formed by iron(III) and diphenylamine-4-sulfonic acid sodium salt (DPA-4-SA). It is a simple, highly sensitive, fast, and low cost alternative method using the color developing reagent DPA-4-SA in acetate buffer at pH 5.50 and the flow-rate of 1 mL min⁻¹ with the sample throughput of 60 h⁻¹. The method provided a linear determination range between 5 μg L⁻¹ and 200 μg L⁻¹ with the detection limit (3S) of 1 μg L⁻¹ of iron(III) using the injection volume of 20 μL. FIA variables influencing the system performance were optimized. The amount of iron(III) and total iron in river and seawater samples was successfully determined. Repeatability of the measurements was satisfactory at the relative standard deviation of 3.5 % for 5 determinations of 10 μg L⁻¹ iron(III). The accuracy of the method was evaluated using the standard addition method and checked by the analysis of the certified material Std Zn/Al/Cu 43 XZ3F.     

Determination of EDTA in used fixing solutions by capillary electrophoresis

A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm × 75 μm I.D.) filled with a borate buffer (50 mmol L^–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved is 2 × 10^–6 mol L^–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions. Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998     

Flow injection spectrofluorimetric determination of iron(III) in water using salicylic acid

A simple and fast flow injection fluorescence quenching method for the determination of iron in water has been developed. Fluorimetric determination is based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The carrier solution used was 2 × 10⁻⁶ mol L⁻¹ salicylic acid in 0.1 mol L⁻¹ NH₄⁺/NH₃ buffer solution at pH 8.5. Linear calibration was obtained for 5–100 μg L⁻¹ iron(III) and the relative standard deviation was 1.25 % (n = 5) for a 20 μL injection volume iron(III). The limit of detection was 0.3 μg L⁻¹ and the sampling rate was 60 h⁻¹. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters).     

Spectrofluorometric determination of hesperidin by manual and flow-injection methods

A reliable and highly sensitive method for the determination of hesperidin is described. It involves the formation of a highly fluorescent complex between hesperidin and aluminium (III) in a micellar medium. There is a linear relationship between fluorescence intensity (λ_em = 496 nm, λ_ex = 391 nm) and hesperidin concentration over the range 5 × 10^–7– 2 × 10^–5 mol L^–1. The detection limit is 79 μg L^–1. The method can easily be adapted to a flow system using a three-channel manifold, the peak height being proportional to the hesperidin concentration over the range 1 × 10^–6– 1 × 10^–4 mol L^–1. Manual and flow-injection procedures have been successfully applied to the determination of hesperidin in orange peel and orange juice. Received: 21 October 1998 / Revised: 16 December 1998 / Accepted: 25 December 1998     

Optosensing of hydrochloric acid based on the fluorescence quenching of a flavone copolymer

An optical fiber sensor for the continuous determination of hydrochloric acid is presented. It is based on the fluorescence quenching of a flavone containing copolymer membrane by hydrochloric acid. The quenching efficiency is greatly enhanced in the presence of Fe(III). This enhancement is attributed to the primary inner filter effect, as well as the formation of a complex between the 4′-N,N-dimethylaminoflavone group in the copolymer and the Fe(III) species extracted from hydrochloric acid solution. The optical response is linear and reversible for 0.10–6.00 mol L^–1 HCl with a response time of the order of a second. The standard deviations for repeated alternative measurements of 0.20 and 2.00 mol L^–1 hydrochloric acid are 0.32% and 0.46% (n = 10), respectively, indicating a good reproducibility. Because of the covalently bonding of the dye to polymer, the sensor exhibits also a good stability. Selectivity has also been evaluated for some potential interferents. The sensor in conjunction with a flow-injection system can be used for on-line determination of hydrochloric acid. Received: 15 January 1998 / Revised: 14 April 1998 / Accepted: 18 April 1998     

Flow injection atomic absorption spectrometric determination of iodide using an on-line preconcentration technique

A continuous flow atomic absorption spectrometric system was used to develop an efficient on-line preconcentration-elution procedure for the determination of iodide traces. Chromium (VI) is introduced into the flow system and is reduced to chromium (III) in acid medium proportionally to the iodide present in the sample. The Cr(III) reduced by iodide is retained on a minicolumn packed with a poly(aminophosphonic acid) chelating resin, while unreduced Cr(VI) is not retained. Reduced Cr(III) is preconcentrated by passing the sample containing iodide through the system during 3 min, and is then eluted with 0.5 mol L^–1 hydrochloric acid and determined by flame atomic absorption spectrometry (FAAS). The detection limit (3σ) obtained is 2.5 μg L^–1. Other ions typically present in waters do not interfere. The proposed method allows the determination of iodide in the range 6–220 μg L^–1 with a relative standard deviation of 2.7% at a rate of 17 samples h^–1. The method has been applied to the determination of iodide in tap and sea waters. Received: 16 September 1999 / Revised: 15 November 1999 / Accepted: 19 November 1999     

Flow injection-solid phase spectrofluorimetric determination of pyridoxine in presence of group B-vitamins

A flow-through optosensor has been prepared for the sensitive and selective determination of pyridoxine (vitamin B₆) in aqueous solutions. The sensor was developed in conjunction with a monochannel flow-injection analysis system with fluorimetric detection using Sephadex SP-C25 resin as an active sorbent substrate. This method of determination is carried out without any derivatization. The wavelengths of excitation and emission were 295 and 385 nm, respectively. When a HCl (10^–3 mol L^–1) / NaCl (3 × 10^–2 mol L^–1) solution is used as carrier solution, the sensor responds linearly in the measuring range of 5–200, 10–400 and 50–1800 ng mL^–1 with detection limits of 0.33, 0.67, and 5.70 ng mL^–1 for 2000, 1000 and 200 μL of sample volume, respectively. The relative standard deviation for ten independent determinations is less than 0.75% for 0.2 and 1.0 mL of sample volumes used, and 1.31% for 2.0 mL of sample volume used. The method was satisfactorily applied to the determination of vitamin B₆ in pharmaceutical preparations. Received: 4 June 1998 / Revised: 16 July 1998 / Accepted: 6 August 1998     

Electrochemical Study of 4-Nitrophenol at a Modified Carbon Paste Electrode

 A zeolite-modified carbon paste electrode (CPE) has been used for the determination of 4-nitrophenol by differential pulse voltammetry (DPV). The electrochemical reduction of 4-nitrophenol at −1.0 V is carried out in a Britton-Robinson medium at pH 3.5. The cyclic voltammetric (CV) behaviour has been investigated to study the nature of the process. Studies on the effect of pH were carried out over the pH range 2–9 with the Britton-Robinson buffer solution, and the influence of pH on peak height and peak potential was analyzed. A linear relationship between peak intensity and concentration is obtained in the range 0.2–10 mg L⁻¹, with a detection limit of 0.04 mg L⁻¹; a relative standard deviation of 1.5% for a 5 mg L⁻¹ 4-nitrophenol concentration and a relative error of 2.6% were also obtained (n=11). Received March 3, 1998. Revision December 10, 1998.     

Determination of biogenic amines in fermented beverages and vinegars by pre-column derivatization withpara-nitrobenzyloxycarbonyl chloride (PNZ-Cl) and reversed-phase LC

Summary The reagentp-nitrobenzyloxycarbonyl chloride (PNZ-CI) was used for pre-column derivatization of biogenic amines (BAs) at ambient temperature followed by reversed-phase, liquid-chromatographic separation of the derivatives. Optimized derivatization of samples was achieved within 10 min in borate buffer by adding PNZ-Cl in acetonitrile (MeCN). Excess reagent was scavenged by subsequent addition of glycine in water. For LC a Superspher^? RP-18e column and gradient elution using a ternary gradient system containing sodium acetabe buffer (pH 6.1), sodium acetate buffer (pH 4.3) and MeCN, were used. The PNZ-derivatives were quantified by their UV-absorption at 265 nm. Detection limits of BAs were approximately 62–1000 μg L⁻¹ (injected amounts: 53–850 pg) at a signal-to-noise ratio of 3:1. The coefficients of determination were 0.9906–0.9992. Diaminohexane was used as internal standard. Recoveries of BAs ranged from 78–93% depending on the food matrix. This method was applied to the quantitative determination of 2-phenylethylamine, tryptamine, serotonin, putrescine, histamine, cadaverine, tyramine, spermidine, and spermine, in beer, wine, vinegars, and lactic fermented cabbage juice. Parts of the results were presented at the 35th Congress of the “Deutsche Gesellschaft für Ern?hrung”, Kiel, 19^th–20^th March 1998, and the “Regionaltagung der Lebensmittelchemiker”, Giessen, 9^th–10^th March 1998     

Amperometric method for the determination of myoglobin based on the electrochemical reduction on the glassy carbon electrode

An irreversible reduction peak of oxymyoglobin (MbO₂) was observed on the bare glassy carbon electrode (GCE) in acetate buffer solution under atmospheric conditions. It is the reduction of bonded oxygen in Mb, but not the heme Fe(III)/Fe(II) redox couple that underwent electrochemical reaction on the electrode. The peak current achieved a maximum value in acetate buffer solution of pH 4.0. The peak potential was pH dependent, suggesting that the proton was involved in the electrochemical reaction. Furthermore, the peak current was linearly related to the concentration of myoglobin in the range of 2.5 × 10^–8∼ 1.0 × 10^–6 mol · L^–1 with a detection limit of 5 × 10^–9 mol · L^–1. Received: 20 March 1998 / Revised: 24 June 1998 / Accepted: 1 July 1998     

Automated continuous monitoring of drug dissolution process using a flow injection on-line dialysis sampling – solvent extraction separation spectrophotometric system

Inductively coupled plasma optical emission spectrometry (ICP-OES) was used for the element-specific determination of water-soluble organosilicon species separated by high-performance liquid chromatography (HPLC). Leachates from different waste deposit sites were investigated. The polydimethylsiloxane (PDMS) degradation product dimethylsilanediol (DMSD) could be detected in almost all samples in the low mg L^–1 range, and it was furthermore possible to determine trimethylsilanol (TMSOL) in some leachate samples in the μg L^–1 range. TMSOL was additionally analyzed by a method established before (LT-GC/ICP-OES). This study proved the occurrence of silanol compounds in leachates from locations were silicone material is deposited. Received: 10 July 1998 / Revised: 2 November 1998 / Accepted: 5 November 1998     

Simple and Selective Spectrophotometric Method for the Determination of Iron (III) and Total Iron Content, Based on the Reaction of Fe(III) with 1,2-Dihydroxy-3,4-Diketocyclo-Butene (Squaric Acid)

 Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of the colored product is 3.95×10³ L·mol⁻¹·cm⁻¹, at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5–20 mgL⁻¹, with a detection limit of 0.3 mgL⁻¹ and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL⁻¹ standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using the FAAS technique, were found to be in satisfactory agreement. Author for correspondence: University of Ioannina, Department of Chemistry, Laboratory of Analytical Chemistry, Ioannina 451 10, Greece. E-mail: panavelt@cc.uoi.gr Received July 27, 2002; accepted December 20, 2002 Published online April 11, 2003     

Group separation of trace rare-earth elements by countercurrent chromatography for their determination in high-purity calcium chloride

A method has been developed for the separation of the entire group of rare-earth elements from high-purity calcium chloride by countercurrent chromatography, and subsequent determination of the elements by ICP– MS. A solution of diphenyl[dibutylcarbamoylmethyl]phosphine oxide in chloroform (0.5 mol L^–1) has been chosen as reagent for the extraction and preconcentration of trace rare-earth elements from aqueous 5% CaCl2 solution, 3 mol L^–1 in HNO3 and 0.1 mol L^–1 in HClO4. The analytes are back-extracted into a small volume of water and the aqueous eluate is subjected to ICP–MS measurements. The performance characteristics of the procedure developed have been checked by use of the standard addition technique and a real CaCl2 sample (Merck product) has been analyzed. The results obtained demonstrate the applicability of countercurrent chromatography to the determination of ultratrace elements. Received: 6 December 2000 / Revised: 27 February 2001 / Accepted: 6 March 2001