Batch analysers with automatic sampling

This section deals with commercially available analytical processors designed for the analysis of a large number of samples containing one or several analytes in which the sampling system is a non-differentiated part of the system. They are characterized by their flexibility for adaptation to different needs in the determination of a large variety of analytes. Their sole limitations in this respect are the state of aggregation of the sample and the detection system to be used —photometric or spectrophotometric. 

In dealing with these analysers, a distinction wiil also be made according to whether the sample is transferred or not from its original position to the detection system. 

---

As all 30 samples are, apparently, measured in a simultaneous fashion, the system can be said to effect a parallel multi-determination —hence the generic name parallel fast analyser given by some workers to these instruments, which are even dealt with separately from batch analysers in automatic methods of analysis. However, such a difference is only apparent and, in fact, it is a typically discontinuous process, both because of the sequential measurement (with a single detector) and because there is a manual intermediate operation (the transport of the transfer disc from one module to the other). 

Fig. 1.3 Scheme of the different types of automatic analysers, classified according to the way In which sample transport Is effected. The examples Illustrate the determination of a single analyte In a liquid sample requiring dilution (0) and sequential addition of two reagents (Ri, R2) for the analytical reaction to develop, (a) Batch analyser, (b) Continuous analysers (SFA, segmented-flow FIA, flow-injection CCFA, completely continuous flow), (c) Robot station. Note that agitation is carried out by independent units in (a), is not required in (b) and is effected by a single unit in (c). (Adapted from [17] with permission of Ellis Horwood). 

In contrast to the two operations described above, the incorporation of the solid sample Into the analyser or Instrument Is comparatively easy to automate. Samplers with cups or vials holding each sample separately are relatively Inexpensive. In batch analysers, samples are treated and transferred separately continuous analysers, which are much commoner, involve Intermediate operations (dissolution, extraction, etc.) and do not have many automatic systems available for incorporation of solid samples. One such system Is the... 

Typically, all of the above routines employ interactive operator direction with subsequent execution. However, complete analysis routines are often predesigned and automatically executed to accommodate automatic sampling systems and batch analyses. 

In addition to the analysis of the thermal stability of the perchloric acid organic reaction media mixtures, a procedure was worked out to determine the fate of the perchloric acid by chlorine analysis of the batch, effluent streams, etc. Preliminary analyses on selected process samples showed no tendency for perchloric acid to concentrate in recycle material and therefore build up in the reactor. A total of less than 1% of the initial charge of perchloric acid (total chlorides calculated as perchloric acid) was found in the combined recovered acid-ester and olefin fractions. Less than 1 % of the initial charge of perchloric acid was found in the finished ester. The analytical method used was an oxygen bomb decomposition, followed by titration of chlorides with 0.0liV silver nitrate, using a recording automatic titrator. The eventual fate of the perchloric acid catalyst was... 

Common to all analytical procedures (manual, automatic, etc.) is the initial careful measurement of a volume of fluid (in clinical chemistry usually blood, serum, plasma, or urine) as well as volumes of standardizing solutions the accuracy and precision of this single operation are probably the factors that most affect the reliability of the whole procedure for any particular type of analysis. Several different sorts of error may be introduced at this stage the absolute volume of sample measured for each of a batch of replicate analyses may be incorrect the variation from one member of a batch to another in respect of the volume of sample taken may be outside the limits acceptable for the analysis and, when batches of specimens are analyzed, there may be cross-contamination of one specimen with material remaining in the system from the analysis of another specimen. 

Usually it can be defined in the LIMS whether the determined results are checked and compared automatically with the limits, which have been assigned before to a standard. In this case, the system is capable of making a proposal about how the sample or the entire batch could be evaluated. The modem LIMS supports a retrospective evaluation of data. It is possible to present the result of a specific test in a graph together with the results of former analyses. This function can be used for trend analyses — for example, for the rating of suppliers or for the observation of the trend of a specific test parameter. 

The different topics dealt with were chosen according to various criteria such as the degree of consolidation, scope of application and most promising trends. The monograph consists of four parts. The first, after dealing with the basic principles behind the automation of laboratory processes (Chapter 1) and the role of computers In this context (Chapter 2), describes automatic systems for sampling (Chapter 3) and sample treatment (Chapter 4). The second part discusses the principles and commonest components of the principal types of analysers, namely continuous (Chapters 5-7), batch (Chapter 8) and robotic (Chapter 9). The third part Is devoted to the automation of analytical Instrumentation spectroscopic (Chapter 10), electroanalytlcal (Chapter 11) and... 

---