Simultaneous determination of acetaminophen and tramadol by second derivative spectrophotometry

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 Delta lambda 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 urn, thus 308.0 nm was selected for A determination by graphic method. The determination ranges for A and T were 8.1x10(-7) - 51x10(-5) mol/L and 3.4x10(-1) - 5.0x10(-1) mol/L, respectively and call be determined with good precision and accuracy, without previous separation. A study of interferents, was carried out by using the excipients ZafinO 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.