Flow-injection spectrofluorimetric determination of ethylenethiourea

A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration graph was obtained between 0.1 and 2.0 μg mL^–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple. Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998     

FIA determination of pyruvate in serum based on direct chemiluminescence oxidation

Chemiluminescence was observed by mixing acidic potassium permanganate solution with pyruvate in the presence of quinine. A new simplified method for pyruvate determination based on this phenomenon was established. The chemiluminescence intensity is a linear function of the concentration of pyruvate in the range of 2 × 10^–6 to 1 × 10^–3 g/mL with a detection limit of 0.8 μg/mL and a relative standard deviation of less than 2.3%. The method has been successfully used to determine pyruvate in serum. Received: 3 April 1998 / Revised: 20 July 1998 / Accepted: 17 September 1998     

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     

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     

Determination of the pesticide Chlorpyrifos by cathodic adsorptive stripping voltammetry

The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP) were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working conditions for the determination of the compound were established. The peak current was linear over the concentration range 9.90 × 10^–8– 5.96 × 10^–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos in commercial formulations and treated waste water was carried out satisfactorily Received: 10 July 1997 / Revised: 1 April 1998 / Accepted: 6 April 1998     

FI spectrophotometric determination of Pd with DBOK-chlorophosphonazo

A flow injection method was developed for the determination of palladium, based on the reaction of palladium with DBOK-chlorophosphonazo with a detection limit of 0.07 μg/mL and a linear calibration range from 0.1 to 3.2 μg/mL of palladium. The reaction product has a maximum absorption at 630 nm. The method was applied to determine Pd²⁺ in catalysts and in anode mud samples. The relative error is less than 3% and the recovery of palladium is in the range 95% to 105% Received: 27 April 1998 / Revised: 24 August 1998 / Accepted: 26 August 1998     

FI spectrophotometric determination of Pd with DBOK-chlorophosphonazo

A flow injection method was developed for the determination of palladium, based on the reaction of palladium with DBOK-chlorophosphonazo with a detection limit of 0.07 μg/mL and a linear calibration range from 0.1 to 3.2 μg/mL of palladium. The reaction product has a maximum absorption at 630 nm. The method was applied to determine Pd²⁺ in catalysts and in anode mud samples. The relative error is less than 3% and the recovery of palladium is in the range 95% to 105% Received: 27 April 1998 / Revised: 24 August 1998 / Accepted: 26 August 1998     

Sampling and determination of hydrogen cyanide in cigarette smoke

A method for sampling and determination of hydrogen cyanide in cigarette smoke is described. Cigarette smoke is filtered through a glass fiber filter paper, and only gaseous compounds, such as hydrogen cyanide, are collected in a dilute sodium hydroxide solution. The cyanide is determined spectrophotometrically at 550 nm by the isonicotinic acid–pyrazolone method. Maximum absorbance is achieved within 10 min at room temperature, and remains constant for about 20 min. Beer’s law is obeyed in the range 0.04∼0.80 μg mL^–1 cyanide, with a molar absorptivity of 3.48 × 10⁴ L mol^–1 cm^–1. Received: 30 November 1998 / Revised: 21 April 1999 / Accepted: 30 April 1999     

Sampling and determination of hydrogen cyanide in cigarette smoke

A method for sampling and determination of hydrogen cyanide in cigarette smoke is described. Cigarette smoke is filtered through a glass fiber filter paper, and only gaseous compounds, such as hydrogen cyanide, are collected in a dilute sodium hydroxide solution. The cyanide is determined spectrophotometrically at 550 nm by the isonicotinic acid–pyrazolone method. Maximum absorbance is achieved within 10 min at room temperature, and remains constant for about 20 min. Beer’s law is obeyed in the range 0.04∼0.80 μg mL^–1 cyanide, with a molar absorptivity of 3.48 × 10⁴ L mol^–1 cm^–1. Received: 30 November 1998 / Revised: 21 April 1999 / Accepted: 30 April 1999     

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 chemiluminescence determination of isoniazid with electrogenerated hypochlorite

A flow-injection chemiluminescence method for the determination of isoniazid based on the sensitizing effect of isoniazid on the chemiluminescence generating luminol-hypochlorite reaction is described. The hypochlorite was electrogenerated on-line by constant current electrolysis, thus, eliminating instability of hypochlorite solution prepared from commercially available sodium hypochlorite. The calibration graph is linear in the range 1 × 10^–8 to 1 × 10^–6 g mL^–1, and the detection limit is 6 × 10^–9 g mL^–1. The relative standard deviation for determination of 5 × 10^–8 g mL^–1 is 2.8%. The proposed method has been successfully applied to the determination of isoniazid in pharmaceutical preparations. Reveived: 2 May 1998 / Revised: 27 July 1998 / Accepted: 7 August 1998     

Determination of ascorbic acid by use of a flow-through solid phase UV spectrophotometric system

A continuous flow-through solid phase spectrophotometric system was developed for the determination of ascorbic acid based on the measurement of its intrinsic absorbance in the UV region when retained on a 1 mm Sephadex QAE A-25 anion exchanger gel layer which is placed into an appropriate quartz flow-through cell, the absorbance exhibited by this solid phase being monitored at 267 nm. A monochannel manifold was used, the sample (300, 600 or 1000 μL) being injected into the carrier solution (acetate buffer). This solution also elutes the analyte after developing the analytical signal, and regenerates the resin layer which, therefore, remains ready for the next sample. The linear dynamic range and other analytical parameters vary according to the sample volume injected. Three calibration lines were established for 300, 600 and 1000 μL sample volume, which ranged from 1.0 to 20.0, 0.5 to 10.0 and 0.2 to 6.0 μg mL^–1, respectively. The detection limits were 0.04 (300 μL), 0.03 (600 μL) and 0.02 μg mL^–1 (1000 μL), the sampling rates 28, 24 and 21 h^–1, and the RSDs (n = 10) 0.87%, 1.08% and 0.90%, respectively. The amount of ascorbic acid in various samples (pharmaceuticals, sweets and urine) were successfully determined with this method. Received: 28 April 1998 / Revised: 3 June 1998 / Accepted: 30 June 1998     

Determination of ascorbic acid by use of a flow-through solid phase UV spectrophotometric system

A continuous flow-through solid phase spectrophotometric system was developed for the determination of ascorbic acid based on the measurement of its intrinsic absorbance in the UV region when retained on a 1 mm Sephadex QAE A-25 anion exchanger gel layer which is placed into an appropriate quartz flow-through cell, the absorbance exhibited by this solid phase being monitored at 267 nm. A monochannel manifold was used, the sample (300, 600 or 1000 μL) being injected into the carrier solution (acetate buffer). This solution also elutes the analyte after developing the analytical signal, and regenerates the resin layer which, therefore, remains ready for the next sample. The linear dynamic range and other analytical parameters vary according to the sample volume injected. Three calibration lines were established for 300, 600 and 1000 μL sample volume, which ranged from 1.0 to 20.0, 0.5 to 10.0 and 0.2 to 6.0 μg mL^–1, respectively. The detection limits were 0.04 (300 μL), 0.03 (600 μL) and 0.02 μg mL^–1 (1000 μL), the sampling rates 28, 24 and 21 h^–1, and the RSDs (n = 10) 0.87%, 1.08% and 0.90%, respectively. The amount of ascorbic acid in various samples (pharmaceuticals, sweets and urine) were successfully determined with this method. Received: 28 April 1998 / Revised: 3 June 1998 / Accepted: 30 June 1998     

Ultra-trace analysis of nitrite in food samples by flow injection with spectrophotometric detection

A flow injection system with spectrophotometric detection is proposed for the determination of low levels of nitrite based on its catalytic effect on the oxidation of gallocyanine by bromate in acidic media. Various analytical parameters such as acidity, reagent concentration, flow rate, sample size, time, temperature, and interfering species were studied. The calibration graph was linear for 0.020–0.500 μg/mL of nitrite. The method is successfully applied to food samples. Up to 30 ± 5 samples can be analyzed per hour. Received: 8 April 1998 / Revised: 3 June 1998 / Accepted: 31 July 1998     

Ultra-trace analysis of nitrite in food samples by flow injection with spectrophotometric detection

A flow injection system with spectrophotometric detection is proposed for the determination of low levels of nitrite based on its catalytic effect on the oxidation of gallocyanine by bromate in acidic media. Various analytical parameters such as acidity, reagent concentration, flow rate, sample size, time, temperature, and interfering species were studied. The calibration graph was linear for 0.020–0.500 μg/mL of nitrite. The method is successfully applied to food samples. Up to 30 ± 5 samples can be analyzed per hour. Received: 8 April 1998 / Revised: 3 June 1998 / Accepted: 31 July 1998     

In-situ concentration and determination of mercury by graphite furnace atomic absorption spectrometry with Pd-Rh as the chemical modifier

A method has been proposed for the determination of mercury by cold vapor generation graphite furnace atomic absorption spectrometry (CV-GFAAS) with Pd-Rh as coating and chemical modifier. The trapping efficiency for mercury with Pd-Rh was higher than with Pd alone. The characteristic mass of the method, which gives an integrated absorbance of 0.0044 s, was found to be 55 pg and the absolute detection limit (3 σ) of 37 pg was obtained with the proposed modifier. The method was successfully applied to the determination of mercury in standard reference water samples, wastewater samples and cosmetics with a recovery range of 95–104%. Received: 10 April 1998 / Revised: 20 August 1998 / Accepted: 23 September 1998     

In-situ concentration and determination of mercury by graphite furnace atomic absorption spectrometry with Pd-Rh as the chemical modifier

A method has been proposed for the determination of mercury by cold vapor generation graphite furnace atomic absorption spectrometry (CV-GFAAS) with Pd-Rh as coating and chemical modifier. The trapping efficiency for mercury with Pd-Rh was higher than with Pd alone. The characteristic mass of the method, which gives an integrated absorbance of 0.0044 s, was found to be 55 pg and the absolute detection limit (3 σ) of 37 pg was obtained with the proposed modifier. The method was successfully applied to the determination of mercury in standard reference water samples, wastewater samples and cosmetics with a recovery range of 95–104%. Received: 10 April 1998 / Revised: 20 August 1998 / Accepted: 23 September 1998     

End-point detection of the potentiometric titration of anionic polyelectrolytes using an anionic surfactant-selective plasticized poly (vinyl chloride) membrane electrode and an anionic surfactant as a marker ion

A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to dodecylbenzenesulfonate (DBS) ion is applied to the determination of anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) by potentiometric titration, using a poly (diallyldimethylammonium chloride) (Cat-floc) solution as a titrant. The end-point of the titration is detected as the potential jump of the plasticized PVC membrane electrode caused by decrease in the concentration of DBS ion added to the sample solution as a marker ion, due to the ion association reaction between the DBS ion and Cat-floc. The effects of the concentration of DBS ion, coexisting surfactants and electrolytes in the sample solution and pH of the sample on the degree of the potential jump at the end-point were examined. A linear relationship between the concentration of anionic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 2 × 10^–5 to 4 × 10^–4 N for PVSK, alginate, and carrageenan. Received: 30 April 1998 / Revised: 6 July 1998 / Accepted: 11 August 1998     

Electric and magnetic multipole integrals in STO basis sets: an analytical approach

A new method for the evaluation of one- and two-centre magnetic and electric multipole integrals for Slater-type functions is presented. The method is strictly analytical in that no approximations of any kind are involved. Two simple functions, ℐ₁ ^aug and ℐ₂ ^aug, are introduced, which employ only functions that are well known in electronic structure theory. With the use of augmentation exponents these functions apply to multipole integrals as well as other one-electron integrals, such as nuclear attraction integrals. The proposed method includes the analytic determination of derivatives of the integrals with respect to atomic displacements. Some illustrative test calculations are presented and compared to results from the literature. Received: 20 April 1998 / Accepted: 13 October 1998 / Published online: 1 February 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