“…Techniques applied to the analysis of pharmaceutical preparations include titrimetry (2), gravimetry (1), UV spectrophotometry (11), colorimetry (12)(13)(14), gas chromatography (15), and high pressure liquid chromatography (16). The colorimetric reaction (17) has been adapted for use in biological samples (18), but was not found to be specific for phentolamine. The HPLC analysis of phentolamine utilizes an ion-exchange column (16); however, the method is characterized by asymmetric peaks and poor resolution (R < 1.0).…”