Carbon nanotubes membrane for caffeine determination in biological fluids

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The use of nylon membranes modified with carbon nanotubes (CNTs) for the determination of caffeine in biological fluids has been proposed by researchers from San Luis University at Argentina (1). The proposed configuration is based on the retention of the analyte into the modified membrane and its in-surface determination by means of solid surface fluorescence (SSF). Although caffeine is not a fluorescent molecule, this methodology takes advantage of the interaction between caffeine and Rhodamine B which produces an enhancement of the native fluorescence of this dye.
 
(a) Rhodamine B   (b) Caffeine
Modified membranes are easily fabricated by impregnation of the bare membranes with a solution that contains Rhodamine B, activated CNTs and hexadecyltrimethylammonium bromide (HTAB), the latter being a cationic surfactant employed for CNTs dispersion. After a drying step the membranes are ready to isolate caffeine from biological samples. The extraction procedure makes use of a flow systems that delivers 10 mL of the sample or standard solution through the membrane. As a consequence of the extraction, the selectivity of the determination is enhanced reducing the interference of other methylxanthines like theobromine or theophylline as well as reducing the sample matrix effect on the final determination. Moreover, the effective retention of the analyte and the in-surface SSF measurement, not being necessary an elution step, improves the sensitivity providing limits of detection as low as 0.3 µg/L. The optimized method has been applied to the analysis of biological samples, comprising urine, plasma and serum. The excellent relative recoveries, close to 100%, and good precision values make this alternative very promising. Moreover, the approach seems to be versatile and easily applicable to other analytical problems.

We suggest the original article to our readers. In the manuscript you will find the optimization of the main variables that affect to the extraction performance and a discussion about the basis of the method and an interesting interfering study.

Reference:

(1) Caffeine monitoring in biological fluids by solid surface fluorescence using membranes modified with nanotubes. Link to the article

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