A practical guide for developing and pre-validation of analytical methods

4 A practical guide for developing and pre-validation of analytical methods 

In the following, a practical guide for a step-by-step procedure is presented to establish a validated method of analysis both for determination of a specific migrant in a food simulant and the residual concentration in a plastic. This procedure was first developed and then applied in a European project (Franz and Rijk 1997) and found to be very practical. It should be considered as a recommendation based on the great practical experience of the analysts involved. 

Basically, two types of method must be taken into account  

Generally, the method to be developed should allow quantitative analysis of the analyte at the required restriction limit in all the official food simulants, including substitutes or alternatives and/or in the polymer, respectively. That means that for very low SML values which are assumed to be in the range of the detection limit, the aim should be to obtain a detection limit equal to or even lower than the restriction criterion. For other, higher SML and QM values, the aim should be to obtain a detection limit at least ten times below the legal or self-defined restriction criterion. It should also kept in mind that the method description should provide the relevant intra-lab-oratory precision data (at the required SML/QM value) according to ISO 5725 -(ISO 1994). 

The most suitable analytical methodology should be selected based on the required performance characteristics. A sound literature search is always of great help with respect to known methods for the respective analyte and matrices. In most cases the search results will not directly provide the method wanted but will allow the most likely successful analytical approach to be set up. In this context, pre-considerations should address the most appropriate sample work-up procedure as well as the suitable analytical separation and detection system. The question of direct analysis of the analyte or a derivate formed after chemical reaction should be clarified. And finally, some thoughts should already be given to the question of chemical stability of the analyte in the given matrices under the applied conditions. 

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