Response surface modelling and kinetic studies for the experimental estimation of measurement uncertainty in derivatisation

Response surface modelling is proposed as an approach to the estimation of uncertainties associated with derivatisation, and is compared with a kineti c study. Fatty acid methyl ester formation is used to illustrate the approa ch, and kinetic data for acid-catalysed methylation and base-catalysed tran sesterification are presented. Kinetic effects did not lead to significant uncertainty contributions under normal conditions for base-catalysed transe sterification of triglycerides. Uncertainties for acid-catalysed methylatio n with BF3 approach significance, but could be reduced by extending reactio n times from 3 to 5 min. Non-linearity is a common feature of response surf ace models for derivatisation and compromised first-order estimates of unce rtainty; it was necessary to include higher order differential terms in the uncertainty estimate. Simulations were used to examine the general applica bility of the approach and to study the effects of poor precision and of ch ange of response surface model. It is concluded that reliable uncertainty e stimates are available only when the model is statistically significant, ro bust, representative of the underlying behaviour of the system, and forms a good fit to the data; arbitrary models are not generally suitable for unce rtainty estimation. Where statistically insignificant effects were included in models, they gave negligible uncertainty contributions.