High‐performance liquid chromatography coupled with graphite furnace atomic absorption spectroscopy (HPLCGF AA) gives element‐specific detection of environmental samples containing trace amounts of organotin or organolead species. The direct GF AA of organotin and organolead species is subject to errors arising primarily from loss of analyte prior to atomization, probably through the formation of refractory carbides and of compounds or complexes that are volatile at low temperatures. Examples abound in the literature of signal suppression in the GF AA of organometallic species in environmental samples, and several furnace tube modifications have been developed to overcome this suppression. Here, the analyte and a modifier are co‐pipetted into a conventional furnace tube, from either a solution of analyte or an HPLC effluent. Oxides of transition metals (e.g. chromium, manganese, or tungsten) are shown to enhance both tin and lead signals, whereas chlorides do not, suggesting the low‐temperature formation of relatively involatile metal oxides or volatile metal chlorides, respectively. In the absence of modifier, GF AA signal intensities decrease consecutively for equal quantities of mono‐, di‐, tri‐ and tetra‐butyltin species, but are nearly equal for the first three in the presence of complexing dichromate (Cr2O72−). The lesser signal increase for tetrabutyltin indicates a dissimilar low‐temperature complexation chemistry for the fully ligated neutral organometal to that for the ligated ions. similar results are demonstrated in post‐column addition of a matrix modifier to effluent containing either organotin or organolead species.

Disperse systems in which the crystallization process takes place within droplets of a defined diameter allow the formation of globule‐shaped crystals or agglomerates with narrow particle size distribution, provided that the mass transfer between individual emulsion droplets can be neglected. The crystallization can be initiated by evaporation of the solvent, by cooling, chemical reaction or addition of an antisolvent. For antisolvent crystallizations, a model has been developed in the present work.

A mathematical model for mass transfer and crystallisation in a disperse system is presented under consideration of the moving boundary. The equations describing crystal birth and growth are coupled with the equations for the counter-current mass transfer. Radial profiles of composition as a function of time are generated by numerical solution of the governing equations. By solving the population balance, the average size and also the size distribution of the crystals can be estimated as a f unction of crystallisation time, which is especially important for the precipitation of finely dispersed crystals

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