Quantifying uncertainty in quantitative TLC

The Eurachem/Citac Guide on measurement uncertainty establishes general rul es for evaluating and expressing measurement uncertainty across a broad spe ctrum of measurements and presents a spe;al calculation procedure called th e 'error-budget approach'. In this work the error-budget model has been tes ted using the quantitative HPTLC determination of sodium glutamate in a foo d product as an example. The TLC procedure was divided into stages, each of which was evaluated. The cause-and-effect diagram was constructed and poss ible sources of uncertainty were listed. We found that the dominant sources of uncertainty were sample preparation, chromatographic separation, second ary chromatography, stability of instrumentation, inhomogeneous illuminatio n, distribution of compound molecules in the stationary phase, and the rela tive position of spots and scanning slit, among others. The uncertainty est imated by means of the error-budget method was Less than one fifth of the v alue obtained from the validation study. The contribution from sources sele cted and processed according to the Citac guide is so small that it can be neglected.