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A method has been developed for the determination of benzthiazide, hydrochlorothiazide, and hydroflumethiazide in pharmaceuticals. The procedure is rapid and specific and employs established separation techniques. The active ingredient is eluted from a basic Celite column with an acetic acid-ether solvent and extracted from the organic phase into NaOH for the spectrophotometric determination.

Bendroflumethiazide and cyclothiazide are eluted from a sodium carbonate column with chloroform-acetic acid (98+2) and are measured directly by ultraviolet spectrophotometry. The method was collaboratively studied by 8 analysts. The average per cent recovery and standard deviations for simulated mixes of bendroflumethiazide and cyclothiazide were 99.61±0.94 and 98.85±3.28, respectively. For commercial preparations the respective values were 99.52±0.78 and 99.3±1.97. The method has been adopted as official first action for the determination of bendroflumethiazide.