title: Caffeine monitoring in biological fluids by solid surface fluorescence using membranes modified with nanotubes.
abstract: BACKGROUND
  In this work, a new methodology based upon enhancement of rhodamine B fluorescent signal is proposed for the quantification of caffeine traces.
  
  
  METHODS
  Membrane filters treated with multiple wall carbon nanotubes were employed as solid support for determination step by solid surface fluorescence.
  
  
  RESULTS
  Experimental variables that influence the preconcentration step and fluorimetric sensitivity have been optimized using uni-variation assays, presenting linearity from 1.1 to 9.7×10(3) μg/l, with a correlation coefficient of 0.99. At optimal conditions, a limit of detection of 0.3 μg/l and a limit of quantification of 1.1 μg/l were obtained. The method showed good sensitivity and adequate selectivity and was satisfactorily applied to the determination of trace amounts of caffeine in urine, plasma and serum belonging to subjects with different sex, ages and habit of caffeine intake.
  
  
  CONCLUSIONS
  Chemofiltration step eliminated the highly fluorescent matrix, thus enabling and allowing CF quantification, in the presence of other methylxanthines. The proposed methodology represents an innovative application of the solid surface fluorescence using membrane filters modified with MWCNTs.
authors.affiliation: Instituto de Química de San Luis (INQUISAL-CONICET), Chacabuco y Pedernera, 5700 San Luis, Argentina.
authors.forename: María Carolina
authors.initials: MC
authors.lastname: Talio
authors.forename: Magdalena
authors.initials: M
authors.lastname: Alesso
authors.forename: Mariano
authors.initials: M
authors.lastname: Acosta
authors.forename: María Gimena
authors.initials: MG
authors.lastname: Acosta
authors.forename: Marta O
authors.initials: MO
authors.lastname: Luconi
authors.forename: Liliana P
authors.initials: LP
authors.lastname: Fernández
mesh_terms: D002110:Caffeine / Q000097:blood* / Q000652:urine*; D002138:Calibration; D005260:Female; D005374:Filtration / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008567:Membranes, Artificial; D037742:Nanotubes, Carbon / Q000737:chemistry*; D009757:Nylons; D015203:Reproducibility of Results; D012235:Rhodamines / Q000032:analysis; D012680:Sensitivity and Specificity; D052616:Solid Phase Extraction; D013050:Spectrometry, Fluorescence
chemical_list: D008567:Membranes, Artificial; D037742:Nanotubes, Carbon; D009757:Nylons; D012235:Rhodamines; D002110:Caffeine; C029773:rhodamine B
keywords: Biological fluids; Caffeine monitoring; Carbon nanotubes; Chemofiltration; Nylon membranes; Solid surface fluorescence