High speed liquid chromatography for in-process control of rifabutin

A fast HPLC method has been developed for simultaneous determination of rifabutin and its synthesis precursors. The analytes are separated in 1.8 min by means of a Kromasil 100 C₁₈ column (50 mm × 2.1 mm i.d., 3.5 μm) at 30 °C. The mobile phase (A: 5 mM KH₂PO₄ adjusted to pH 6.5 with KOH; B: acetonitrile) was pumped at a flow rate of 0.4 ml min⁻¹ according to the fast gradient mode: 0 min, 58% B; 0-0.4 min, 95% B. Detection was by ultraviolet absorbance at 275 nm. The method was validated in accordance with the International Conference on Harmonisation (ICH) guidelines and good accuracy, intermediate precision (≤4.6%) and linearity in the range 5-50 mg l⁻¹ were observed for all compounds. This method is sensitive (limits of detection ranged between 0.1 and 0.3 mg l⁻¹) and selective to quantify rifabutin and its synthesis precursors and could be used for in-process control.     

Extractive-spectrophotometric determination of trace amounts of potassium with cryptand 2.2.2 and methyl orange

A spectrophotometric study on the extraction of potassium into chloroform as an ion pair, formed between the cryptand 2.2.2-potassium complex and the highly colored methyl orange counterion, is described. Optimum conditions for extraction are established (potassium recovery 100.2 ± 3.5%) and a new spectrophotometric determination of trace amounts of potassium is proposed (linear working range: 0.3–3.5 ppm of K⁺; apparent molar absorptivity: 2.2 × 10⁴ liters · mol⁻¹ · cm⁻¹; precision, in terms of relative standard deviation: 1.9%). The actual possibilities of predicting relevant analytical performance characteristics (i.e., sensitivity, selectivity, and precision) of these methods in the light of known complexing ability of cryptands in aqueous phase are discussed. The results obtained in this study are compared with those previously obtained using crown ethers as ligands.