In this work is proposed, a simple experiment for the simultaneous determination of losartan (L) and hydrochlorothiazide (H) in synthetic and real samples by derivative spectrophotometry technique. For the students it is relevant to know this technique for simultaneous determinations of drugs, allowing that the students recognize that this technique is simple, rapid and applicable to quality control. This experimental work, it is proposed in order to being applied to undergraduates into laboratories of analytical chemistry. Furthermore, it is given the integration of the theoretical knowledge with the experimental work; this correlation is of interest for the students.

A rapid method for the simultaneous determination of acetaminophen (A) and tramadol (T) by second derivative spectrophotometric has been developed. From a solvent effect studies and the spectral behaviours of A and T, ethanol was selected as solvent. For a Δλ value of 210 nm a smoothing factor of 8,000 and scale factor of 1,000,000 were selected, because in these conditions the signal/noise ratio was favoured in order to avoid error. In these conditions also it is possible the simultaneous determination of A/T in a molar relation of 17/1 contained in pharmaceutical formulations. At 285.7 nm the second derivative value is T concentration dependent, corresponding to zero-crossing point of A. On the other hand, T does not absorb between 296.0 to 400.0 nm, thus 308.0 nm was selected for A determination by graphic method. The determination ranges for A and T were 8.1x10-7 - 5 1x10-5 mol/L and 3.4 x10-7 - 5.0 x10-5 mol/L, respectively and can be determined with good precision and accuracy, without previous separation. A study of interferents, was carried out by using the excipients Zafin® tablet. The recoveries were 97.4 ± 2.0% and 100.6 ± 1.7% for A and T, respectively. This tablet containing both drugs was assayed using the methods developed, showing a good accuracy and precision.