Gas chromatography with pulsed flame photometric detection multiresidue method for organophosphate pesticide and metabolite residues at the parts-per-billion level in representatives commodities of fruits and vegetable crop groups.

A gas chromatographic method with a pulsed flame photometric detector (P-FPD) is presented for the analysis of 28 parent organophosphate (OP) pesticides and their OP metabolites. A total of 57 organophosphates were analyzed in 10 representative fruit and vegetable crop groups. The method is based on a judicious selection of known procedures from FDA sources such as the Pesticide Analytical Manual and Laboratory Information Bulletins, combined in a manner to recover the OPs and their metabolite(s) at the part-per-billion (ppb) level. The method uses an acetone extraction with either miniaturized Hydromatrix column partitioning or alternately a miniaturized methylene dichloride liquid-liquid partitioning, followed by solid-phase extraction (SPE) cleanup with graphitized carbon black (GCB) and PSA cartridges. Determination of residues is by programmed temperature capillary column gas chromatography fitted with a P-FPD set in the phosphorus mode. The method is designed so that a set of samples can be prepared in 1 working day for overnight instrumental analysis. The recovery data indicates that a daily column-cutting procedure used in combination with the SPE extract cleanup effectively reduces matrix enhancement at the ppb level for many organophosphates. The OPs most susceptible to elevated recoveries around or greater than 150%, based on peak area calculations, were trichlorfon, phosmet, and the metabolites of dimethoate, fenamiphos, fenthion, and phorate.     

Determination of sulphur compounds in beer using headspace solid-phase microextraction and gas chromatographic analysis with pulsed flame photometric detection

A simple and sensitive method for the analysis of volatile and semi-volatile sulphur compounds in beer at trace levels was developed using headspace solid-phase microextraction (SPME) and gas chromatography with pulsed flame photometric detection. Different SPME fibres were tested and a Carboxen-polydimethylsiloxane coated fibre was found to be the most appropriate. The adsorption and desorption conditions were optimised. The effect of ethanol concentration in the sample on the extraction of analytes was examined. A 60 m non-polar capillary column preceded by a 10 m length of a polar column was found to be capable of separating a wide range of C1-C6 sulphur compounds. The pulsed flame photometric detector enabled increased sensitivity to be obtained over previous methods, such as dynamic headspace followed by conventional flame photometric detection or sulphur chemiluminescent detection, with high sulphur selectivity. Two sulphur compounds, 2-methyl-1-butanethiol and 3-methylthiophene, were identified in beer for the first time.     

A Dual-Channel Flame Photometric Detector with a Seperate Combustion Chamber

A new version of the dual-channel flame photometric detector is described for compounds containing phosphorus and sulphur. The sample is mixed with hydrogen before introduction into the detector. The burner is formed as a specific combustion chamber, which is separated from the emission chamber of the detector. Interference signals in the P-channel, caused by sulphur-containing compounds (crosstalk signals) are damped electrically. Thus the selectivity to hydrocarbons is increased by a factor of up to 10⁷, crosstalk signals are reduced by a factor of 10³ and flame stability is guaranteed (there are no flame-outs caused by amounts of up to 50 μl of liquid samples).     

Selective chemiluminescence detection of sulfur-containing compounds coupled with nitrogen—phosphorus detection for gas chromatography

A new sulfur and nitrogen—phosphorus detector for gas chromatography is described. The detector is an integrated thermionic ionization— chemiluminescence device permitting simultaneous detection of sulfur-containing and nitrogen- or phosphorus-containing compounds. This new flameless detector utilizes a heated rubidium-doped ceramic bead in a thermionic ionization chamber to produce sulfur monoxide from sulfur compounds. The SO is mixed with O₃ and the resulting chemiluminescence is monitored with a photomultiplier tube, providing sulfur-selective detection. The thermionic ionization detector signal serves as an independent second response channel, affording simultaneous selective and sensitive nitrogen—phosphorus detection. Two chromatograms are obtained, one in which selectivity is exhibited for nitrogen and phosphorus compounds, and the other for sulfur compounds present in the sample.     

Electrocatalysis of Chemical Warfare Agent Sulfur Mustard in Room Temperature Ionic Liquid

Room temperature ionic liquids (RTILs) have the potential for being ideal alternatives for organic solvents in chemical warfare agent (CWA) electrochemical reactions. In this paper, electrocatalysis of CWA sulfur mustard (SM) was achieved by exploring the potential advantage of RTIL methyltrioctylammonium bis (trifluoromethylsulfonyl) imide and further this methodology was used for the detection of CWA. The hydrophobicity of this RTIL offers the opportunity to use this methodology in field condition without environmental humidity effect. The diffusion coefficient calculated for SM in RTIL was 0.196×10⁻⁹ cm²/s. The electrochemical parameters deduced from cyclic voltammetry such as electron transfer coefficient (α), electron transfer number (n) and heterogenous rate constant were estimated 0.11, 2 and 4.41 s⁻¹, respectively. The electrocatalytic activity of the RTIL toward the electrochemical reduction and oxidation of CWA is evidenced, showing the potential of this novel approach for the oxidation of other toxic CWAs. The new RTIL based strategy provides an opportunity to develop field deployable detection of CWA and could provide a new paradigm shift in CWA detection approach, addressing the escalating threat of CWA.     

Organic fuelled flames in selective ionization detectors for chromatography

Summary The selectivities of two flame-based ionization detectors identified as a Remote FID (RFID) and a Flame Thermionic Ionization Detector (FTID) have been improved by introducing methane as a fuel for the flame. Both the RFID and FTID feature a detector struture in which the ionization polarizer and collector are located several centimeters downstream of an oxygen-rich flame, rather than immediately adjacent to the flame as in a flame ionization detector. The RFID detects long-lived negative ions produced in the flame by the combustion of lead, tin, phosphorus, or silicon compounds. The FTID re-ionizes and detects neutral electronegative products generated by combustion of nitrogen, halogen, or phosphorus compounds. An organic-fuelled RFID can detect 1 pg Pb (Sn, P)/sec with a selectivity of the order of 10⁶ versus hydrocarbons. An organic fuelled FTID is applicable to detection of compounds at nanogram and higher levels. FTID selectivity for PCB compounds in a transformer oil matrix is of the order of 10⁵1. The improved selectivity achieved by using an organic-fuelled flame is also applicable to the detection of phospholipid and other non-volatile N, P, or Cl compounds using an FID/FTID detector accessory for a TLC/FID analyser.     

Performance and application of controlled temperature-gradient lamps in atomic absorption spectrometry

An improved design of controlled temperature-gradient lamp (CTGL) is suitable for arsenic, cadmium, phosphorus, potassium, rubidium, selenium, sodium, sulphur and zinc. Intensity and linewidth measurements indicate that the CTGL is significantly more intense than an electrodeless discharge lamp (EDL) at the same linewidth. CTGL's also compare favourably with EDL's when used as light sources for a.a.s. Arsenic and selenium can be determined at very low concentrations (ng ml^-1) by the hydride generation technique. Sulphur and phosphorus can be detected in the vacuum ultra-violet region using nitrogen-separated flames; the limits of detection are 13 and 10 μg ml^-1, respectively.     

Detection of aqueous phase chemical warfare agent degradation products by negative mode ion mobility time-of-flight mass spectrometry [IM(tof)MS]

The use of negative ion monitoring mode with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass spectrometer [IM(tof)MS] to detect chemical warfare agent (CWA) degradation products from aqueous phase samples has been determined. Aqueous phase sampling used a traditional electrospray ionization (ESI) source for sample introduction and ionization. Certified reference materials (CRM) of CWA degradation products for the detection of Schedule 1, 2, or 3 toxic chemicals or their precursors as defined by the chemical warfare convention (CWC) treaty verification were used in this study. A mixture of six G-series nerve related CWA degradation products (EMPA, IMPA, EHEP, IHEP, CHMPA, and PMPA) and their related collision induced dissociation (CID) fragment ions (MPA and EPA) were found in each case to be clearly resolved and detected using the IM(tof)MS instrument in negative ion monitoring mode. Corresponding ions, masses, drift times, K(o) values, and signal intensities for each of the CWA degradation products are reported.     

Developments in the application of gas chromatography with atomic emission (plus mass spectrometric) detection

Capillary gas chromatography with atomic emission detection is a highly element-selective and sensitive detection technique for many non-metal as well as metallic elements. A 3-5 order of magnitude element/carbon selectivity, compound-independent calibration and the possibility to calculate (partial) molecular formulae are some of the attractive features of the technique. In the present review, the emphasis is on real-life applications for non-metals such as sulphur, phosphorus, nitrogen and the halogens, and on the potential of combined atomic emission/mass spectrometric detection.     

Evaluation and comparison of selective gas chromatographic detectors for the analysis of pesticide residues

Summary A series of studies is described on the evaluation and comparison of some selective gas chromatographic detectors used in pesticide residue analysis. A detailed study of the optimization and response characteristics of the CsBr and RbCl three-electrode alkali flame ionization detector for N and P compounds, the Coulson electrolytic conductivity detector in the nitrogen, sulphur and pyrolytic modes of operation and the sulphur phosphorus emission detector, a type of flame photometric detector, was carried out to obtain maximum sensitivity and reliability for the analysis of pesticide residues in various biological substrates. It was observed that the alkali flame and electrolytic conductivity detector responses to nitrogen compounds were of the same order, while the electrolytic conductivity detector was more sensitive than the flame photometric detector to sulphur compounds. Also, attempts were made to correlate the responses from these different detector systems using the insecticide chlorpyrifos which contains P, S, Cl and N atoms. The use of chlorpyrifos as an evaluation standard in verifying the acceptable performance of these types of detectors is recommended.Chemistry and Biology Research Institute Contribution No 901     

Determination of inorganic arsenic species in aqueous samples by ion-exclusion chromatography with electro-chemical detection

Arsenic(III) and -(V) were separated by ion-exclusion chromatography, using 0.01 M orthophosphoric acid eluent. Both forms of arsenic can be monitored by UV detection at 200 nm, but sensitivity is poor. Amperometric detection with a platinum-wire electrode at an applied potential of + 1.00 V allows arsenic(III) to be determined down to 0.012 μM. Detector response was shown to be linear to 1.00 μM, at which concentration, ten replicate injections of arsenic(III) gave a relative standard deviation of 1.3%.In an application of the chromatographic procedure with amperometric detection to analysis of bottled mineral waters, arsenic(III) was measured by direct injection, and total inorganic arsenic was determined as arsenic(III) after reduction of arsenic(V) by sulphur dioxide     

the microwave-excited emissive detector in gas-phase chromatography-I Some studies with sulphur compounds

An examination is made of the characteristics of a microwave-excited emissive detector and its potential use in the gas chromatography of sulphur compounds. The column was operated slightly above atmospheric pressure (ca. 105 kN m (2)) and the microwave detector at a convenient reduced pressure (e.g., 13-40 mbar). It is concluded that the most sensitive and specific wavelengths for analytical purposes are not necessarily the same for all the sulphur compounds examined, viz. carbon disulphide, thiophen, thioglycollic acid, dimethylsulphoxide and sulphur dioxide. The spectra obtained for each compound with argon or helium as carrier gas were characterized and only the atomic lines due to sulphur at 190.0 and 191.5 nm, the CS system with a bandhead around 257.6 nm and the C(2) bandhead at 516 nm were shown to be common to the organic compounds (except CS for thioglycollic acid). Carbon disulphide was the most easily fragmented and gave a limit of detection of 0.2 ng of sulphur at 257.6 nm even with the low luminosity monochromator used. Thioglycollic acid was the least easily fragmented compound.     

The use of a piezoelectric crystal to determine sulphur dioxide in gases

This work describes the detection of sulphur dioxide with a piezoelectric crystal, at a resonance frequency of 9 MHz, covered with an active coating containing trioctylmethylammonium dichromate which irreversibly bonds sulphur dioxide in an oxidation-reduction reaction. The decrease in the vibration frequency of the crystal is directly proportional to the mass of sulphur dioxide bonded. The detector works on the basis of integration of the decrease in the frequency over a given time interval (at least 10 min), resulting in a high measuring sensitivity. The calibration curve is linear for sulphur dioxide concentrations from a few to 500 microg/m(3). Partial exhaustion of the capacity of the active coating, occurring after prolonged use, appears as nonlinearity of the detector concentration response. This nonlinearity can be compensated by a simple mathematical correction that permits the lifetime of the active coating to be lengthened by several orders of magnitude.     

Dialkyltin salts as extractants in methods for the determination of arsenic and phosphorus

Dialkyltin salts are suitable as extractants for various oxygen-containing anions. They are particulary powerful for the extraction of arsenate and phosphate ions, but are also useful for liquid-liquid extraction of anions of dibasic acids. It is shown that the high extraction power of these dialkyltin complexes can be explained by formation of innersphere complexes with the extracted anions. A method is proposed for the separation of arsenic, phosphorus and silicon using dialkyltin salts. Applications to the extraction-spectrophotometric determination of phosphorus and arsenic in vanadium and steel, and to extraction/atomic absorption determinations of arsenic and phosphorus in metals and alloys are surveyed. The use of the dialkyltin salts for the neutron activation determination of arsenic and as active components in membranes of ion-selective electrodes for phosphorus(V) and arsenic(V) is demonstrated.     

预富集装置在QCM传感器检测芥子气中的运用

在化学战剂的诸种检测方法中, 质量型微传感器以其响应快速、使用简便等优点成为一种理想的检测手段. 但是这种传感器的使用往往受到检出限的限制, 对于低浓度的毒剂不能及时报警. 预富集技术的运用可以提高微传感器的检测限. 本文研制了一种预富集装置并对其进行了初步测试. 芥子气通过此预富集装置之后在QCM(石英晶体微天平)传感器上的检出限可以达到0.1 mg/m3.     

Electrochemical Sensing of Chemical Warfare Agent Based on Hybrid Material Silver‐aminosilane Graphene Oxide

The threat from chemical warfare agents (CWAs) imparts an alarming call for the global community not limited to human being but also extends as unprecedented environmental threat, hence, timely detection and degradation in the event of CWAs attack is very crucial. Herein, we describe a hybrid material of 3‐aminopropyltriethoxysilane (APTES) modified graphene oxide (GO) on glassy carbon (GC) electrode along with electrodeposited silver nanodendrimers (AgNDs) for the electrochemical detection and degradation of CWA sulphur mustard (HD). The AgNDs/APTES‐GO hybrid material was characterized by SEM, EDX, BET, TGA, Raman, UV‐Vis, XPS and XRD techniques. The AgNDs/APTES‐GO modified GC electrode was also characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Electrochemical studies indicated presence of electrocatalysis owing to the synergistic effect of AgNDs and GO for sensing CWA HD via reductive dehalogenation. The AgNDs/APTES‐GO modified GC electrode exhibited linearity for CWA HD from 5.3 μM to 42.4 μM. Constant potential electrolysis was performed with modified electrode and degradation products were analysed using GC‐MS, highlighting the great potential of graphene based hybrid material. This new strategy provides an opportunity for the development of “detect and destroy” system for the CWAs and other environmental toxic pollutant, which could help in mitigation of on‐ site events for first responders.     

Wet ashing of coal with perchloric acid mixed with periodic acid for the determination of sulphur and certain other constituents

A method is described for the determination of sulphur and some other inorganic constituents of coal. Organic matter is destroyed by wet combustion with perchloric acid and periodic acid. The method is rapid and efficient. Silica and sulphur are determined gravimetrically, iron, aluminium, vanadium, titanium, phosphorus, and arsenic spectrophotometrically, and calcium and magnesium volumetrically. No loss occurred by volatilisation. The complete analysis scheme devised was applied to a bituminous coal of Iowa origin.     

Reaction of Tricoordinate Phosphorus Compounds with Pseudohalogens. Scope and Mechanism

Abstract

The selectivity of sulphur, selenium and oxygen removal from pseudohalogens: phosphorus disulphides 1 and 2, diselenides 3 and oxophosphoranesulphenyl chlorides 4 has been investigated. A mechanistic rationalization is proposed to account for sulphur (selenium)/oxygen extrusion variation as a function of substrates structure and reaction conditions.     

Determination of arsenite, arsenate and monomethylarsonic acid in aqueous samples by gas chromatography of their 2,3-dimercaptopropanol (bal) complexes

Procedures are described for the determination of arsenite, arsenate and monomethylarsonic acid in aqueous samples. The arsenicals (after reduction of arsenic to the tervalent state) readily react with 2,3-dimercaptopropanol (BAL) to yield their BAL complexes. The products are extracted with benzene and introduced into a gas Chromatograph equipped with a flame-photometric detector for sulphur. One aliquot of sample is treated with stannous chloride solution and potassium iodide solution to reduce arsenate and monomethylarsonic acid, then BAL is added and the complexes are extracted with benzene. The extract is analysed for total inorganic As plus monomethylarsonic acid. Magnesia mixture and phosphate solution are added to another aliquot to remove arsenate by co-precipitation with magnesium ammonium phosphate. The precipitate is filtered off and arsenite determined in the filtrate. The detection limits are 0.02 ng of As for arsenate and arsenite and 0.04 ng of As for monomethylarsonic acid.     

Determination of arsenic at a gold-plated carbon paste electrode using constant current stripping analysis

A new stripping method for the determination of arsenic in water samples with a gold film-plated carbon paste electrode has been developed for the use in constant current stripping analysis (CCSA). In the novelized procedure, differentiation between As(III) and chemically pre-reduced As(V), the effect of Cu(II) on the response of arsenic, and the stability of sample solutions were studied in detail. Compared to the voltammetric approach, the method utilizing CCSA offers a more rapid procedure with improved analytical characteristics such as reproducibility, selectivity over the Cu(II) ions, or lower detection limit (3 ppb for As(III) and 0.5 ppb for As(V), respectively). The possibilities of the optimized method are demonstrated by determinations of As(III), As(V), and total arsenic in samples of polluted river water.