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In this work, an automated system for the study of the interaction of drugs with human serum albumin (HSA) was developed. The methodology was based on the quenching of the intrinsic fluorescence of HSA by binding of the drug to one of its binding sites. The fluorescence quenching assay was implemented in a sequential injection analysis (SIA) system and the optimized assay was applied to ionic liquids based on the association of non-steroidal anti-inflammatory drugs with choline (IL-API). In each cycle, 100 µL of HSA and 100 µL of IL-API (variable concentration) were aspirated at a flow rate of 1 mL min −1 and then sent through the reaction coil to the detector where the fluorescence intensity was measured. In the optimized conditions the effect of increasing concentrations of choline ketoprofenate and choline naproxenate (and respective starting materials: ketoprofen and naproxen) on the intrinsic fluorescence of HSA was studied and the dissociation constants ( K d ) were calculated by means of models of drug–protein binding in the equilibrium. The calculated K d showed that all the compounds bind strongly to HSA ( K d <100 µmol L −1 ) and that the use of the drugs in the IL format does not affect or can even improve their HSA binding. The obtained results were compared with those provided by a conventional batch assay and the relative errors were lower than 4.5%. The developed SIA methodology showed to be robust and exhibited good repeatability in all the assay conditions (rsd<6.5%). [ABSTRACT FROM AUTHOR]

Abstract: According to the current demands of environmentally friendly analytical chemistry and with a view to achieving lower reagent consumption with improved analytical performance, an automatic methodology composed of a photoreactor and fluorimetric detection (λ exc =287nm, λ em =378nm) was developed. To this end, a sequential injection analysis (SIA) system was developed for indomethacin determination using ultra-violet (UV) light which promotes an increase in the fluorescence of indomethacin. This increase in sensitivity makes it possible to apply this methodology to a dissolution test and to determine indomethacin in pharmaceutical formulations. The calibration graph for indomethacin was linear between 4.10×10−6 and 9.00×10−5 molL−1and the detection limit was 1.23×10−6 molL−1. The method was proven to be reproducible with a R.S.D.<5% and sampling rate of approximately 20 per hour. The potential effect of several compounds commonly used as excipients on analytical signals was studied and no interfering effect was observed. Statistical evaluation at the 95% confidence level showed good agreement between the results obtained for the pharmaceutical samples with both the SIA system and comparison batch procedures. [Copyright &y& Elsevier]

Abstract: This work reports the development of an automatic methodology based on the use of 1-anilinonaphthalene-8-sulfonate (ANS) as an interfacial fluorescent probe for detecting the hydrophobic environment shift around the probe, caused by the hydrolytic action of PLA2 on the liposomes. The implementation of this reaction in a sequential injection analysis (SIA) system along with the use of the mixing chambers permitted the evaluation of PLA2 activity and assessment of the inhibitory effect of the non-steroidal anti-inflammatory drugs (NSAIDs) on PLA2 activity. Several studies were performed with the aim of establishing the appropriate flow system configuration: the liposome substrate; PLA2 and ANS optimum concentrations and incubation times before and after the enzyme addition. Based on these studies, the optimum reaction conditions were selected. It was shown that PLA2 is effectively inhibited by the NSAIDs tested (meloxicam, tolmetin and ibuprofen) and by the α-lipoic acid, used as a positive control. Results obtained from the flow system are in agreement with those provided by the comparison batch procedures. The proposed methodology is in fact more efficient and rapid than the comparison batch experiments, enabling the exact timing of fluidic manipulations and precise control of the reaction conditions. [Copyright &y& Elsevier]