Multiresidue method using SPME for the determination of various pesticides with different volatility in confined atmospheres

An analytical method is described for assessing the vapour concentration of 11 pesticides (bioallethrin, chlorpyriphos methyl, folpet, malathion, procymidone, quintozene, chlorothalonil, fonofos, penconazole and trimethacarb) in confined atmospheres (e.g. a greenhouse after pesticide application). This study is a successful extension of a method previously developed by the authors for dichlorvos to much less volatile pesticides. Sampling was performed by using polydimethylsiloxane–solid phase micro-extraction (PDMS–SPME) fibres immersed in a 250-mL sampling flask through which air samples were dynamically pumped from the analysed atmosphere. After a 40-min sampling duration, samples were analysed by GC/MS.Calibration was performed from a vapour-saturated air sample. The linearity of the observed signal versus pesticide concentration in the vapour phase was proved from spiked liquid samples whose headspace concentrations were measured by using the proposed method. This procedure gave calibration curves with regression coefficients (R²) greater than 0.98, and the repeatability of these measurements was found with RSDs of 1.9–7.6%. As a field application test, this analysis procedure was used for the determination of gaseous procymidone concentrations as a function of time in the atmosphere of an experimental 8-m² and 20-m³ greenhouse. The pesticide was sprayed according to real cultivation conditions, and measurements were made for 80 h after application (8 measurements). The observed concentrations found ranged from 200 to 500 µg m^–3, thus indicating the level of contamination of the air breathed by people in such working conditions.Abbreviations GC/MS gas chromatography/mass spectrometry - SIM selective ion monitoring - FC43 perfluorotributylamine - RSD relative standard deviation - LOD limit of detection - LOQ limit of quantification     

Detection of ethanol in human body fluids by headspace solid-phase micro extraction (SPME)/capillary gas chromatography

Summary Ethanol has been found extractable from human whole blood and urine samples by headspace solid-phase micro extraction (SPME) with a Carbowax/divinylbenzene-coated fiber. After heating a vial containing the body fluid sample with ethanol, and isobutanol as internal standard (IS) at 70°C in the presence of (NH₄)₂SO₄, a Carbowax/divinylbenzene-coated SPME fiber was exposed in the headspace of the vial to allow adsorption of the compounds. The fiber needle was then injected into a middle-bore capillary gas chromatography (GC) port. The headspace SPME-GC gave intense peaks for both compounds; a small amount of background noises appeared, but did not interfere with the detection of the compounds. Recoveries of ethanol and IS were 0.049 and 0.026% for whole blood, respectively, and 0.054 and 0.085% for urine, respectively. The calibration curves for ethanol showed excellent linearity in the range of 80–5000 mg L^–1 for whole blood and 40–5000 mg L^–1 for urine; the detection limits for both samples were 20 and 10 mg L^–1, respectively. The data on actual determination of ethanol after the drinking of beer are also presented for two subjects.     

Amperometric method for on-line cyanide detection

An amperometric method for the detection of cyanide has been developed based on the anodic dissolution of gold in solutions containing cyanide. The method is characterized by a cyclic regeneration of the electrode surface. During the regeneration, the surface layers on the electrode are dissolved. By selection of suitable measuring potentials for the cyanide, linearity can be shown to exist between current and cyanide concentration over the concentration ranges from 0 to 10 mg/l and 10 to 100 mg/l. The lowest detection level is about 0.05 mg CN^–/l. Determinations in the concentration range investigated are possible at a measuring potential of E=270 mV. The method is suitable for detecting the end point during the decontamination of cyanide-containing sewage. The influence on the results of pH, temperature, flow rate, heavy metal content, type of decontamination agent and the presence of brighteners is discussed.     

Voltammetric evaluation of the electrode material on the oxidation of cyanide catalyzed by copper ions

The cyanide oxidation on vitreous carbon (VC), stainless steel 304 (SS 304) and titanium (Ti) was investigated through a voltammetric study of cyanide solutions also containing copper ions. Results showed that cyanide oxidation occurs by means of a catalytic mechanism involving adsorbed species as CN^–, Cu(CN)₄^3– or Cu(CN)₄^2– depending on the electrode material. It was observed that on VC, the adsorption of Cu(CN)₄^3– controlled the oxidation rate. Instead, for SS 304 and Ti, the adsorption of CN^– controlled the global process. However, in all cases, the adsorption of Cu(CN)₄^3– on the electrode surface was required for the catalytic oxidation of CN^–. Voltammetric experiments for solutions containing cyanide oxidation products, such as cyanogen (CN)₂ and cyanate (CNO^–), confirmed that the adsorbed species mentioned above controlled the catalytic oxidation of CN^– depending on the electrode material. A voltammetric identification of the oxidation products showed that cyanogen, (CN)₂ tended to adosorb on VC, while the formation of cyanate, CNO^– predominated on SS 304.     

Simple extraction of phencyclidine from human body fluids by headspace solid-phase microextraction (SPME)

Summary Phencyclidine (PCP) was found to be extractable by headspace solid-phase microextraction (SPME) from human whole blood and urine. Sample solutions were heated at 90°C in the presence of NaOH and K₂CO₃, and an SPME fiber was exposed in the headspace of a vial for 30 min. Immediately after withdrawal of the fiber, it was analyzed by gas chromatography with surface ionization detection (GC-SID). Recoveries of PCP were approximately 9.3–10.8% and 39.8–47.8% for whole blood and urine samples, respectively. The calibration curve for PCP showed good linearity in the range 2.5–100 ng mL^–1 whole blood and 0.5–100 ng mL^–1 urine. The detection limits were approximately 1.0 ng mL^–1 for whole blood and 0.25 ng mL^–1 for urine.     

Residue analysis of onions and other foodstuffs with a complex matrix using two-dimensional capillary-GC with three selective detectors

Summary A very fast determination of sulphate in ground and drinking water by inductively coupled plasma emission spectrometry (ICP/OES) is described. The 182.037 nm line was selected for the measurement of the total sulphur content, because this line is not disturbed by calcium, one of the main components in natural waters. The limit of determination (0.5 mg/l SO ₄ ^2– ) is low enough for most aquatic samples. With a two point calibration the linear working range is between 0.5 and 100 mg/l SO ₄ ^2– .     

Adsorptive accumulation voltammetry of copper(II) using complex formation reaction with salicylideneamino-2-thiophenol

Summary The cathodic stripping voltammetry of copper(II) was investigated with a method, based on the adsorptive accumulation of the Cu(II)-salicylideneamino-2-thiophenol (SATP) complex on a hanging mercury drop electrode. The copper(II)-SATP complex could be accumulated on the electrode at –0.20 V in 0.01 mol/l nitric acid. The reduction peak of the copper complex was observed by scanning the potential in a negative direction in the differential pulse mode. The calibration curve for copper was linear over the range 5×10^–9–1×10^–7 mol/l. This method was applied to determine copper(II) in GSJ (Geological Survey of Japan) standard rock reference materials.     

Synthesis and properties of podands with 4-antipyryliminomethine groups

Novel podands with 4-antipyryliminomethine groups on benzenes and various numbers of ethers are prepared. According to UV spectroscopy, these compounds form complexes with alkali, alkaline earth, and transition metals. Extraction of metal picrates demonstrated that the podands selectively form extractable complexes with these salts. A lead-selective electrode with an electrode function 22–24 mV/pPb is based on 1,8-bis[2-(4-antipyryliminomethine)phenoxy]-3,6-dioxaoctane. This enables 1·10^–6–1·10^–2 M Pb to be determined in the pH range 3.5–5.5. The electrode is highly selective for Pb in the presence of alkali and alkaline earth metals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2099–2102, September, 1990.     

Accumulation voltammetry of copper(II) at carbon-paste electrode containing salicylideneamino-2-thiophenol

Summary Accumulation voltammetry of copper(II) was investigated with a carbon-paste electrode containing salicylideneamino-2-thiophenol(SATP). Copper(II) was accumulated as the copper(II)-SATP complex on the electrode without an applied potential by immersing the electrode in 0.01 mol/l acetate buffer (pH 3.8) containing copper(II). The reduction peak of the copper(II)-SATP complex was observed at –0.12 V (vs. SCE) in 0.01 mol/l acetate buffer (pH 3.8) by scanning the potential in a negative direction. The calibration curve for copper(II) was linear in the range of 2×10^–9–1×10^–7 mol/l. Since the accumulation of copper(II) is based on a chemical reaction between copper(II) and SATP, copper(II) was selectively accumulated on the electrode. The presented method was applied to the determination of copper(II) in standard reference materials prepared by the National Institute for Environmental Studies.     

Stannous ion determination in99mTc radiopharmaceutical kits

Two simple and selective methods for determination of stannous ion in radiopharmaceutical kits are proposed. One of this permits the estimation of stannic ion. The first method unsed is a potentiometric titration of Sn²⁺ in HCl medium, using KIO₃ solution under nitrogen gas and a platinum redox electrode. The second method consists of a complexometric titration of tin (Sn²⁺ and Sn⁴⁺) using an EDTA standard solution at pH 5.5–5.6 without the use of nitrogen gas. The procedures employed indicate that both methods can be used for routine quantitative determination of tin in most labeled radiopharmaceuticals.     

Application of flow injection potentiometry to the determination of chloride in various matrices

Summary The preparation and performance of a tubular chloride ion selective electrode for flow injection potentiometry is presented. The influence of system parameters on sensitivity, detection limit, response time and sample throughput are investigated. It is shown that 60–200 samples can be processed per hour within the concentration range 0.1–10,000 mg/l. The precision is generally better than 1% r.s.d. over the entire range. Application of the proposed method to analysis of tap and mineral water, emission control of hydrogen chloride and the determination of chloride in pure silicon nitride is shown to give results very well comparable to other methods.

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Anwendung der Fließinjektions-Potentiometrie zur Bestimmung von Chlorid in verschiedenen Materialien

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

Voltammetric trace determination of ubiquinones at mercury electrodes

Summary Voltammetric methods were developed for the determination of ubiquinones on the basis of their adsorption and redox behaviour at mercury electrodes. Linear calibration plots were obtained in the concentration range between 10^–4 mol/l and 2.3·10^–5 mol/l from differential pulse voltammetric measurements under experimental conditions avoiding significant adsorption of the analyte. A remarkable decrease of the detection limit down to 10^–7 mol/l was achieved with the help of adsorptive accumulation of ubiquinone molecules at the mercury electrode followed by differential pulse detection. The resulting non-linear calibration plot was explained with a model, which takes into account both adsorption and diffusion of the analyte.     

Flow injection chemiluminescence determination of naftopidil based on potassium permanganate oxidation in the presence of formaldehyde or formic acid

A flow injection method is proposed for the determination of naftopidil based upon the oxidation by potassium permanganate in a sulfuric acid medium and sensitized by formaldehyde and formic acid. The optimum chemical conditions for the chemiluminescence emission were 0.25 mM potassium permanganate and 4.0 M sulfuric acid. Two manifolds were tested and instrumental parameters such as the length of the reactor, injection volume and flow rate were compared. When using the selected manifold in the presence of 0.4 M formaldehyde, naftopidil gives a second-order calibration graph over the concentration range 0.1–40.0 mg L^–1 with a detection limit calculated (as proposed by IUPAC) of 92.5 ng mL^–1 and a standard deviation of 0.12 mg mL^–1 for ten samples of 10.0 mg L^–1 naftopidil. In the presence of 1.15 M formic acid, naftopidil gives a second-order calibration graph over the concentration range 0.05–40.0 mg L^–1 with a detection limit of 14.2 ng mL^–1 and a standard deviation of 0.37 mg mL^–1 for ten samples of 10.0 mg L^–1 naftopidil. In both cases, the determination is free from interferences from common excipients such as sucrose, glucose, lactose, starch and citric acid.     

Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10^–8 to 1×10^–6 mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

All-Solid-State PVC Membrane Ag+-Selective Electrodes Based on Diaza-18-Crown-6 Compounds

Two diaza-crown ether compounds were synthesized and evaluated as Ag⁺-selective carriers in polyvinylchloride (PVC) membrane electrodes of solid-state type. The all-solid-state PVC membrane electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 exhibited a super-Nernstian response (75±10mV per decade) over the concentration range of 1×10^–1 to 7×10^–6M of Ag⁺ ion and a detection limit of 3×10^–6M, at a wide range of pH (pH 4–7). The response time of the electrode was fast (less than 10s), and it can be used for three months without any significant deviation in potential. The proposed all-solid-state PVC membrane electrodes revealed high selectivity toward Ag⁺ ion with respect to alkali, alkaline earth, heavy and transition metal ions. A flow-through cell of all-solid-state PVC membrane Ag⁺-selective electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 has also been prepared and applied for flow-injection analysis of Ag⁺ ion in solution.     

Spectrophotometric determination of anionic surfactants in tap and river waters with 1-(10-bromodecyl)-4-(4-aminonaphthylazo)-pyrimidinium bromide

Summary A new cationic dye, 1-(10-bromodecyl)-4-(4-aminonaphthylazo)-pyridinium bromide, was synthesized and evaluated as a new reagent for the determination of anionic surfactants. The reagent reacts with anionic surfactants, such as sodium dodecylsulphate and sodium dodecylbenzenesulphonate, to produce an ion associate in an aqueous medium. The colour change occurs simultaneously, and the colour development is very stable. This makes it possible to determine anionic surfactants directly by spectrophotometry without solvent extraction. The stoichiometric ratio of the ion associate was found to be 1:1 by the mole ratio method. The calibration graph was linear up to 2.5×10^–6 mol/l. The apparent molar absorptivity of the ion associate was 5.3×10⁴ l mol^–1 cm^–1 (at 595 nm). The relative standard deviation (n=10) for 1.2×10^–6 mol/l sodium dodecylsulphate was 4.9%. The proposed method was applied to the determination of anionic surfactants in tap and river waters.     

Kinetics and mechanism of ligand substitution reactions of NiL and Ni2L with cyanide ion (L = hexamethylenediaminetetraacetic acid)

Summary The kinetics and mechanism of reactions of cyanide ion with [NiL] and [Ni₂L] (L = hexamethylenediaminetetraacetic acid) have been studied spectrophotometrically at 25 ±0.1 °C, with pH=11.0±0.02, and I=0.1 M(NaClO₄). In both reactions the final product was [Ni(CN)₄]^2–. The order with respect to [CN^–] was found to be one over a wide range of cyanide ion concentrations for both the systems.In the Ni₂L-CN^– system, however, the reaction becomes zero order with respect to cyanide when [CN^–]<6×10^–4 M.     

Determination of morphine in process streams by sequential injection analysis with chemiluminescence detection

A procedure for the determination of morphine in process streams by sequential injection analysis based on the chemiluminescence reaction of morphine with acidic potassium permanganate in the presence of sodium hexametaphosphate is presented. The chemiluminescence emission has been monitored using an in-house detection system which consisted of a fibre optic flowthrough cell and a sensitive, low dark current, photomultiplier tube. The calibration graph (range 2 × 10^–8 to 1 × 10^–4 mol/l) was not linear over the entire range of concentration, with a polynomial equation of best fit of y = 1.0 × 10¹⁵ x³ – 2.2 × 10¹¹ x² + 1.3 × 10⁷ x – 8.3. The calibration function approximates linearity over the concentration range 2.5 × 10^–6 to 3.0 × 10^–5 mol/l where the slope of the log-log plot is 1.09 ± 0.16. The detection limit was estimated at about 10^–8 mol/l from the response of the lowest calibration standard (2.5 × 10^–8 mol/l) which gave a signal to noise ratio of 3 : 1. Although the structurally related codeine did not interfere significantly the results suggest that this method may be susceptible to matrix effects, dependent on the location of sampling from the process stream.     

A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques

A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10^–5–1.0×10^–1 M and 6.0×10^–6–1.0×10^–1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10^–6 and 6.0×10^–6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu²⁺ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu²⁺ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.     

Direct determination of benzylnitriles using the cyanide ion selective electrode

The response characteristics of the solid state cyanide ion selective electrode towards some benzylnitriles are investigated. In 10M KOH solution, the electrode exhibits nearly Nernstian response over the concentration range of 10^–2 to 10^–4 M of various substituted benzylnitriles with an anionic slope of 53–59 mV/concentration decade. The response time varies from 10 to 20 min depending on both the nature of the substituent group and the concentration of the nitrile compound. Direct potentiometric measurement of some nitrile compounds at the concentration level of 0.01 to 1 mg/ml shows an average recovery of 98.2% and a mean standard deviation of 2.3%. Many nitrogen functional groups do not interfere.