A linear combination derivative spectrophotometric method is described. The method overcomes the problem of overlapping in derivative spectrophotometry and allows the maximum use of quantitative information. In addition, the method can be used to increase the selectivity, sensitivity and accuracy of the simultaneous analysis of multicomponent mixtures. The application of the method to the simultaneous determination of bongkrekic acid and toxoflavin, the toxic metabolites produced by Pseudomonas farinofermentans, is described.