Analytical sample preliminary treatment

The sample to be analysed does not require any particular sample pre-treatment. However, in the case of musts or cloudy wines, a preliminary clarification by centrifugation or filtration is recommended in order to prevent system blockage. Carbon dioxide levels exceeding 750mg/L should be reduced or eliminated before analysis to avoid degassing of the sample in the analytical circuit. 

Isotachophoresis may widely be applied to clinical analyses of urine, plasma, senun or tissues. Its main advantages include rapid and accurate determination of all charged molecules in a non-destructive way with minimum demands on the amount of the sample and on its preliminary treatment. In many cases, isotachophoresis can prospectively replace analytical procedures generally based at present on a combination of a suitable colorimetric and suitable chromatographic method. 

Preliminary treatment of a sample is sometimes necessary before it is in a suitable form for analysis by the chosen technique and method. This may involve a separation or concentration of the analytes or the removal of matrix components that would otherwise interfere with the analysis. 

TLC can be applied to the preliminary isolation of the compound under analysis from complex mixtures or to the purification of the products after a derivatization reaction. Several examples of TLC conditions for various substances and/or derivatives are given in Table 2.1. In all instances TLC must be carried out in such a way that it will contribute to the solution of a given analytical problem and that it should not become a source of difficulties and errors. As in the preceding instance, contamination of the sample with incidental impurities from the solvents used should be prevented. Chromatographic materials should also be tested for the presence of substances that could interfere with the compounds under analysis in the chromatogram. The quantitative recovery of individual zones from the layer for further treatment is obviously a prerequisite for reliable results. 

The increasing number of chemical analyses performed worldwide on marine Antarctic sediments for their contents in trace elements did demand the availability of at least one CRM of this kind. In order to foster the production of such a CRM, sediment was sampled in 1994 during the eighth Italian expedition in Antarctica. The sampling site was in Adelie Cove (74°46 Lat S 163°57 Long E), close to Terra Nova Bay where the Italian Base is situated. By means of a dredge, a mass of 100 kg was taken at a depth of 80 m and immediately frozen at -20°C in chemically decontaminated 2-1 polyethylene bottles. The whole mass, always kept at this temperature, was then delivered to ISS, where an aliquot of 10 kg was retained for preliminary analytical tests. The remaining mass of 90 kg was forwarded to the EC-JRC-IRMM laboratories for the treatment necessary to transform it into the candidate CRM (17-19). 

As can be seen in Figure 1, preliminary operations (sampling, sample pres ervation and treatment, subjection to separation techniques) involve intensive human participation and are time consuming (70 to 90% of the time devoted to the overall analytical process is expended on these operations) and the source of major random and systematic errors—which have a decisive influence on the quafity of the results. In addition, because of their variability, instrument manufacturers only undertake the automation/enhancement of preliminary operations in those instances where a wide market (e.g., clinical samples) is anticipated. 

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