Photoionisation detection

Gas chromatography and high-performance liquid chromatography with NP detection [326-328], photoionisation detection and mass spectrometric detection [329-332] have all been used in general surveys of pesticides in insecticides in soils. 

Cutter et al. [763] have described a method for the simultaneous determination of inorganic arsenic and antimony species in non saline waters using selective hydride generation with gas chromatography-photoionisation detection. 

These workers showed that dissolved arsenic and antimony in natural waters can exist in die trivalent and pentavalent oxidation states, and the biochemical and geochemical reactivities of these elements are dependent upon their chemical forms. They developed a method for the simultaneous determination of arsenic (III)+antimony (III+V)+ antimony (III+V) that uses selective hydride generation, liquid nitrogen cooled trapping, and gas chromatography-photoionisation detection. The detection limit for arsenic is lOpmol L 1 while that for antimony is 3.3pmol L 1 precision (as relative standard deviation) for both elements is better than 3%. 

Clark Al, McIntyre AE, Lester JN, et al. 1984. A comparison of photoionisation detection gas chromatography with a Tenax GC sampling tube procedure for the measurement of aromatic hydrocarbons in ambient air. J Environ Anal Chem 17 315-326. 

Vien S. H. and Fry R. C. (1988) Ultrasensitive simultaneous determination of arsenic, selenium, tin and antimony in aqueous solution by hydride generation gas chromatography with photoionisation detection, Anal Chem 60 465-472. 

An ion mobility spectrometer consists of a sample-introduction device a drift tube where ionisation and separation of ions takes place and a detector. Ionisation sources of choice include radioactive sources (e.g. a 63Ni foil), photoionisation methods, corona-spray ionisation, flame ionisation and corona discharge. The most common detection method used to measure the... 

ESI operating in the negative ion (NI) mode has been the interface most widely used for the analysis of anionic perfluorinated surfactants. In addition, ESI has also been optimised for the determination of neutral compounds such as the sulphonamides PFOSA, Et-PFOSA and t-Bu-PFOS. The use of atmospheric pressure photoionisation (APPI) has been explored in few works [78-80]. Takino et al. [78] found as the main advantage of this technology, the absence of matrix effects, but the limits of detection were considerably higher than those obtained by LC-ESI-MS/MS. 

Undoubtedly, mass spectrometric detection has a substantial role to play in condensed-phase chromatographic analyses of toxic impurities. As in GC/MS, it can be highly sensitive, although this is probably more analyte-specific than in GC/MS. Selectivity can be gained by SIM on single quadrupoles or, if necessary, SRM on MS/MS instruments. What must be considered is the appropriate ionisation mode to be used in LC/MS. Most modern instruments use atmospheric pressure ionisation sources, including electrospray ionisation (ESI), atmospheric pressure chemical ionisation (APCI) and more recently atmospheric pressure photoionisation (APPI). 

Hippier, M., and J. Pfab, Detection and Probing of Nitric Oxide (NO) by Two-Colour Laser Photoionisation (REMPI) Spectroscopy on the A <- X Transition, Chem. Phys. Lett., 243, 500-505 (1995). 

Vien and Fry [762] have reported a gas chromatographic determination of arsenic, selenium, tin and antimony in natural waters. The gaseous hydrides are generated, concentrated on a cold trap, and then injected into the gas chromatograph with the use of drying agents or carbon dioxide scrubbing. A specially conditioned Tenax column suppresses unwanted byproduct elution and separates the volatile hydrides at room temperature. A photoionisation detector was used and the authors reported a detection limit as low as 0.001 pg L ... 

These additives are essentially high boiling point liquids and so the most appropriate technique to use is liquid chromatography (LC-MS). A range of synthetic plasticisers such as phthalates, adipates, mellitates and sebacates can be detected using the atmospheric pressure chemical ionisation (APCl) mode. Process oils are hydrocarbon mineral oils and require either the atmospheric pressure photoionisation (APPl) head (which can ionise nonpolar species) or, where the oil contains sufficient aromatic character, the use of in-line UV or fluorescence detectors. A fluorescence detector is particularly sensitive in the detection of polyaromatic hydrocarbon (PAH) compounds in such oils. 

On the experimental side, the coupling of crossed molecular beam techniciues with sophisticated detection techniques (Laser Induced Fluorescence, CARS or REMPI spectroscopy, Rydberg tagging photoionisation using synchrotron radiation or U lasers) has improved considerably the detailed study of chemicid reactivity. It is now possible to prepare reactants in a well defined state and to analyze the reaction products at a fixed scattering angle for a. collision at a well defined kinetic energy [1]. 

In physical and theoretical methods there has been a notable increase in the use of recently developed techniques - most of which have trendy acronyms. Thus DRAMA P NMR has been used to determine internuclear P-P distance in a phosphine sulfide 4,8-residue substituted decapeptide, and XANES has been applied to structural studies of phosphine selenides. In the mass spectral field MALDI-TOF has been found to be better than FAB for the determination of the mass spectra of nucleotide triphosphates, LA-FTICR has been used to study tris(cyanoethyl)phosphine and metaphosphates have been detected for the first time by laser photoionisation MS. ERMS was shown to be a powerful technique for the analysis of structurally similar organophosphate insecticides (OPs) and trace quantities of OPs can be determined by Cl using water as the ionising agent. 

Babin F. J. and Gagne J. M. (1992) Hollow cathode discharge (HCD) dark space diagnostics with laser photoionisation and galvanic detection,... 

The Voyager GC from Photovac Inc. has a miniaturised electron capture /photoionisation dual detection system. It has three columns built in and an isothermal oven for fast analysis of up to 40 volatile organic compounds (VOCs). There are preconfigured assays for environmental, petrochemical and other applications. It has a refillable gas cylinder. The rechargeable batteries enable eight hours of use in the field but it can also operate from AC or DC power. It weighs 6.8kg. 

Non-chemical derivatisation has been employed for the detection of photoionisable species. The effluent is passed through a quartz tube where it is irradiated with ultraviolet light and the photoionised products passed to the conductivity detector [64,65]. Krull has reported the detection of the active components, typically organonitro derivatives, of a large number of explosives and drugs by in situ LC decomposition [66]. 

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