Xanthine derivatives quantification in serum by capillary zone electrophoresis.

A capillary electrophoresis method was developed to quantify caffeine and theophylline, xanthine derivatives with bronchodilator activity. Buffer concentration, pH and applied voltage were optimized using a central composite design-face centred. Separation conditions were: silica capillary tube, 75 µm (i.d.) and 61 cm (total length); absorbance detection, 280 nm; borate buffer, 20 mM, pH 9.0; applied voltage, 25 kV and 1 psi injection/8 s. Validation was performed in blank serum following the International Conference Harmonization guidelines: resolution (peaks without overlapping), linear range (0.125-50 µg/mL; r(2) > 0.9999), limits of detection and quantification (10; 20 and 33; 66 ppb for caffeine and theophylline, respectively), intra- and inter-day precision (Relative standard deviation lower than 1.9%) and accuracy (98-101%). Migration times were <8 min. This method is simple, specific and suitable and reaches high label claims (98.7-100.4%) in pharmaceutical formulations analysis. Moreover, the method was applied to the monitoring of the analytes in serum of patients.

Rapid and sensitive determination of nicotine in formulations and biological fluid using micellar liquid chromatography with electrochemical detection.

Nicotine can be determined in pharmaceuticals and biological fluids by micellar liquid chromatography (MLC) using a C18 column, a mobile phase containing sodium dodecyl sulphate 0.15M-6% (v/v) pentanol-NaH(2)PO(4) 0.01 M (pH 6)-KCl 0.001 M, with electrochemical detection at 0.8 V. In the optimization step, the influence of the modifiers propanol, butanol and pentanol, and the voltage has been studied. With the proposed method the analysis time is below than 8 min, linearity better than 0.999, limits of detection and quantification (ng/ml) was 4 and 12 respectively, repeatability and intermediate precision below 1.8%, and all these parameters are adequate for the quantification of nicotine in chewing gum, dermal patches, tobacco and serum samples either by a pharmacologist, pathologist or toxicologist.