The success of TFA as a calibration technique lies in obtaining the optimum response factor matrix, which depends on a well designed calibration matrix as well as the composition of the sample and calibration solutions. In this study, the desirable calibration solution sets were those which indicated less correlation within the set, as shown by the calculated correlation coefficients. The discrepancy in the sample and calibration solutions was accounted for by implementing the generalized standard addition method, so that the responses of the sample and calibration solutions were measured under the same background interference conditions.

A scanning UV160U Shimadzu was used to obtain absorbances, while a Milton Roy HPLC was used to acquire chromatograms. TFA performed well, with the results from the HPLC agreeing within 2% for aspirin, 3% for salicylamide, and 8% for caffeine. The high disagreement for caffeine is understandable, if one realizes that the ratio of caffeine to aspirin is about 1:20 in the pain relievers.