Analytical Sciences

Simultaneous Determination of Paracetamol and Caffeine by Flow Injection-Solid Phase Spectrometry Using C₁₈ Silica Gel as a Sensing Support

P. ORTEGA-BARRALES, R. PADILLA-WEIGAND, and A. MOLINA-DÍAZ 

Department of Physical and Analytical Chemistry, Faculty of Experimental Sciences, University of Jaén, Paraje Las Lagunillas, E-23071 Jaén, Spain

A continuous and simple UV-photometric flow-through biparameter-sensing device has been developed for the simultaneous determination of paracetamol and caffeine at 275 nm. The sensor is based on temporary sequentiation in the arrival of the analytes to the sensing zone by on-line separation using C₁₈ bonded phase beads (the same as that used in the sensing zone) placed into a minicolumn just before the flow cell. The sample containing these compounds is injected into the carrier solution; paracetamol is determined first because it passes through the minicolumn, while caffeine is strongly retained in it. Then, caffeine is conveniently eluted from the precolumn and develops its transitory signal. Using 200 µl of a sample and deionized water as a carrier, the analytical signal showed a very good linearity in the ranges of 10 - 160 µg ml^-1 and 3.5 - 50 µg ml^-1 with detection limits of 0.75 and 0.56 µg ml^-1 for paracetamol and caffeine, respectively. If deionized water with the pH adjusted at 12 was used as a carrier solution, these parameters were 25 - 400 and 4 - 55 µg ml^-1 with 2.0 and 0.50 µg ml^-1 as the detection limits, respectively. The biparameter optosensor was satisfactorily applied to the simultaneous determination of these two analytes in pharmaceuticals.

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