Hydrazine determination in allopurinol using derivatization and SPE for sample preparation

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Hydrazine is a useful building block in the synthesis of organic pharmaceuticals but it is highly toxic so its determination at low ppm range is required.

In this work, hydrazine was determined in allopurinol active pharmaceutical ingredient (API) sample at 2.5 ppm level by using derivatization and solid phase extraction (SPE) followed by reversed phase liquid chromatography (RPLC).

Hydrazine does not contain chromophore part and is not retained in RPLC thus derivatization was necessary for its determination. Benzaldehyde was found to be the most appropriate derivatization reagent so the analyzed solute was benzaldehyde azine, which had adequate UV absorption and could be retained in RPLC. The derivatization reaction was performed in 0.2 M NaOH solution/MeOH = 50/50 (v/v) mixture, which is a proper solvent for allopurinol, too.

Because of the low detection limit, 50 mg sample had to be dissolved in 5 mL solvent. This is a very concentrated solution therefore column overload is expected. Using a C18 SPE for sample preparation allowed to get rid of the huge amount of allopurinol. As allopurinol has a more polar character than benzaldehyde azine, it was easy to wash out from the SPE phase. The benzaldehyde azine can be eluted with a strong solvent and then the eluted sample can be analyzed by RPLC. Limit test validation of the liquid chromatographic method has been performed as well.

This complex but not complicated analysis can be used for the accurate determination of hydrazine in allopurinol API. Furthermore it is applicable for other APIs which are more polar than benzaldehyde azine and soluble in high concentration in the aqueous solvent.

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