Random-access sampler

The TRAACS 800+ shown in Fig. 2.18 consists of one or more analytical consoles, a random-access sampler and personal computer (PC). The analytical console is fitted with two peristaltic pumps which can each handle up to 10 pump tubes. The analytical manifolds are located above the pumps and utihze glass parts 1 mm in diameter, in order to keep reagent consumption low. Heating baths, UV digesters and dialysers can be built into the manifold. 

Even complex procedures can be automated, such as dialysis to clean up dirty samplers, solvent extraction, automatic distillation and on-hne UV digestion. Unhke the earlier AutoAnalyzer systems which use a purely step-wise autosampler, the TRAACS is fitted with a random-access sampler as standard. 

The random-access sampler can go to any sample cup position, any number of times, at any time during a run. This abihty to sample cups in any order and to return to sample cups more than once, allows system automation to be greatly extended. It saves time and work by allowing automatic re-run of sample(s) following off-scale peaks and also the automatic dilution and re-analysis of off-scale samples. The sampler also saves cup positions, allowing more samples and longer unattended runs. For example, one set of standards provides initial cahbration, drift correction, carry-over correction and periodic quality control. In addition, samples or standards can be sampled in repHcate form from a single cup. The random-access sampler can be controlled and either the operator or the computer can make the decision as to which cup the sampler must go to. 

This innovation generally involves modifications to the operation of the sampler and random access reagent selection, and can be implemented in both segmented and unsegmented flow analysers. For unsegmented flow analysis, the spectrophotometric determination of zinc and phosphate in soil extracts [368] is a good example. Zinc was determined only when phosphate was present at concentrations above a threshold level. The number of determinations required was reduced by 30%. Analogously, an expert flow system was proposed for the turbidimetric determination of chloride and sulphate in natural waters [369]. Both methods were implemented in the same manifold, and the need for sulphate determination was dependent on the chloride concentration determined. 

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