Paracetamol, caffeine and ibuprofen are found in over-the-counter pharmaceutical formulations. In this work, we propose two new methods for simultaneous determination of paracetamol, caffeine and ibuprofen in pharmaceutical formulations. One method is based on high-performance liquid chromatography with diode-array detection and the other on capillary electrophoresis with capacitively coupled contactless conductivity detection. The separation by high-performance liquid chromatography with diode-array detection was achieved on a C18 column (250×4.6 mm(2), 5 μm) with a gradient mobile phase comprising 20-100% acetonitrile in 40 mmol L(-1) phosphate buffer pH 7.0. The separation by capillary electrophoresis with capacitively coupled contactless conductivity detection was achieved on a fused-silica capillary (40 cm length, 50 μm i.d.) using 10 mmol L(-1) 3,4-dimethoxycinnamate and 10 mmol L(-1) β-alanine with pH adjustment to 10.4 with lithium hydroxide as background electrolyte. The determination of all three pharmaceuticals was carried out in 9.6 min by liquid chromatography and in 2.2 min by capillary electrophoresis. Detection limits for caffeine, paracetamol and ibuprofen were 4.4, 0.7, and 3.4 μmol L(-1) by liquid chromatography and 39, 32, and 49 μmol L(-1) by capillary electrophoresis, respectively. Recovery values for spiked samples were between 92-107% for both proposed methods.

Paracetamol is an active ingredient commonly found in pharmaceutical formulations in combination with one of the following compounds: codeine, orphenadrine, promethazine, scopolamine, and tramadol. In this work, we propose a unique analytical method for determination of these active ingredients in pharmaceutical samples. The method is based on capillary electrophoresis with capacitively coupled contactless conductivity detection. The separation was achieved on a fused silica capillary (50 cm total length, 40 cm effective length, and 50 μm id) using an optimized background electrolyte composed of 20 mmol/L β-alanine/4 mmol/L sodium chloride/4 μmol/L sodium hydroxide (pH 9.6). Each sample can be analyzed in a single run (≤2 min) and the limits of detection were 2.5, 0.62, 0.63, 2.5, 15, and 1.6 μmol/L for scopolamine, tramadol, orphenadrine, promethazine, codeine, and paracetamol, respectively. Recovery values for spiked samples were between 94 and 104%.

Levamisole is the most common adulterant found in cocaine samples and its electrochemical determination in cocaine seized samples is a challenge due to peak overlapping with cocaine. Herein, we propose a deconvolution procedure for levamisole determination in seized cocaine samples using screen‐printed carbon electrodes (SPE). Square‐wave voltammetry in 0.04 mol L−1 Britton Robinson buffered solution (pH 8.0) was selected in combination with optimized SWV parameters (f=8 s−1, a=10 mV and ΔEs=1 mV) to result in the best peak resolution to apply the deconvolution procedure. Deconvoluted responses of levamisole in the presence of cocaine were similar to untreated signals of standard levamisole solutions in absence of cocaine. A linear response was obtained in the range of 20–100 μmol L−1 (r=0.995). The results obtained for the analysis of a seized cocaine sample was statistically similar to that obtained by gas chromatography. Other adulterants found in cocaine street samples (paracetamol, glucose, phenacetin, caffeine, boric acid and lidocaine) did not affect the treated of voltammetric responses of levamisole. A pharmaceutical sample containing levamisole was also analyzed on SPEs and a recovery of 93±2 % was obtained (no deconvolution required for this sample), showing great applicability of SPEs for forensic and pharmaceutical analyses.

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