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A method has been developed for the simultaneous determination of arsenic, antimony, bismuth, selenium and tellurium by generation of their gaseous hydrides and introduction of these hydrides into an inductively coupled plasma source where the atomic line emission from the elements is detected. The effect of different plasma-torch assemblies on the detection limits attainable has been studied and suitable compromise conditions have been established for the simultaneous generation of the hydrides of the analyte elements and their determination by optical ernission spectrometry in t h e plasma source. Dctection limits of 1 ng ml-1 or below for aqueous solutions of the elements studied have been obtained under the conditions employed to allow their determination in samples of interest in geochemistry.Keywovds A rsenic, antimony, bismuth, seleniunz and tellurium detevminat i o n ; geochemical samples ; hydride generatiox. ; inductively coupled plasma etnission spectrometry

Optoacoustic spectrometry can be employed to obtain data concerning the spectral absorption characteristics and thermal diffusivity of small solid samples. Theoretical expressions have been developed to relate the optical and thermal properties of such samples to the amplitude and phase of the signals observed in optoacoustic spectrometry when using dispersive and non-dispersive techniques. The validity of these expressions has been examined by using transparent and opaque materials with widely differing thermal diffusivities.

A simple single-beam spectrometer suitable for the study of optoacoustic spectra from small solid samples is described and the design of a suitable sample cell is reported. The performance characteristics of the spectrometer have been evaluated using different types of sample. A preliminary assessment of the predicted advantages of optoacoustic spectrometry over conventional techniques of ultravioletvisible absorption and reflectance spectrometry for solid samples has been made.

The construction of a pH sensor, having the configuration of a probe, is described. The probe utilises a plastic-fibre bundle at the end of which is fabricated a sensitive tip consisting of a styrenedivinylbenzene copolymer supporting an adsorbed colorimetric pH indicator, which is retained in position by a membrane of polytetrafluoroethylene (PTFE). Changes in pH in the vicinity of the sensitive tip cause a variation in the attenuation of specific reflected visible radiation bands. Initial results and performance specifications using bromothymol blue as the colorimetric indicator are presented.

In the simultaneous determination of arsenic, antimony, bismuth, selenium and tellurium by measurement of the atomic line emission from the elements in an inductively coupled plasma source after their introduction as the gaseous hydrides, two types of possible interferences were investigated. Mutual interferences between the analytes were found to be negligible under the operating conditions used. The presence of certain metal ions in solution resulted in low recoveries of some of the analytes, especially selenium ancl tellurium. However, this could be overcome by prior separation of the analytes by co-precipitation on lanthanum hydroxide.Keywords Arsenic, a n t i m o n y , bismuth, selenium a n d tellurium determination ; geocheniical saiq!des ; hydride generation ; inductively coupled plasma einission spectrometry ; interferences

The luminescence emission spectra of twenty-three polynuclear aromatic hydrocarbons (PAH) have been examined in n-alkane solvents at 77 K. The Shpol'skii effect, in which narrow-band (quasi-linear) emission spectra are obtained under these conditions when a monochromator of adequate resolving power is used, is shown to be readily observed for twelve of the compounds examined in these solvents. Quasi-linear emission spectra have also been obtained in tetrahydrofuran for some of the PAH compounds examined. These emission spectra provide for unambiguous qualitative identification of PAH compounds a t trace concentrations in solution; this effect is demonstrated by identification of the compounds present in an eight-component mixture of PAH compounds.Measurement of the low-temperature quasi-linear luminescence intensity can be applied quantitatively to the determination of these compounds provided that a standard additions procedure is employed in conjunction with the use of an internal standard to ensure sufficient accuracy and precision.

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