ELSEVIER Analytica Chimica Acta 310 (1995) 447-452 ANALYTICA CHIMICA zyxwvutsrqpo ACM Multicommutation in flow analysis. Part 3. Spectrophotometric kinetic determination of creatinine in urine exploiting a novel zone sampling approach Albert0 N. Aratijo a, Jo& L.F. Costa Lima a, Boaventura F. Reis b3 *, Elias A.G. Zagatto b a Departamento de Q&mica Fisica, Faculdode de Farmcicia, Universidade do Porto, R. Anibal, Cunha s/n, 4050 Porto, Portugal b Centro de Energia Nuclear na Agricultura, Vniversidade de Go Paulo. Au. Centencirio 303, P.O. Box 96, 13400-970 Piracicaba SP, Brazil Received 26 August 1994; revised 8 February 1995; accepted 10 February 1995 Abstract Zone sampling performed on a single analytical channel and associated with the stopped-flow approach was proposed and applied to the spectrophotometric kinetic determination of creatinine in urine based on Jaff6’s reaction. The flow network comprised microcomputer controlled three-way solenoid valves. With multicommutation, the potentialities of zone sampling and stopped-flow were expanded, and the design of the flow set up was simplified. Influence of the main related parameters such as system configuration, reagent concentrations, temperature and timing were studied. The proposed system handled about 24 samples per hour. Baseline drift was not observed during extended operation periods (8 h). Sample pretreatment was not required. Results were reproducible (R.S.D. < 3%) and in agreement with those obtained in a batch procedure. Keywords: Flow injection; Spectrophotometry; Kinetic methods; Creatinine; Urine; Multicommutation 1. Introduction In flow systems with zone sampling, a selected aliquot of a dispersed sample is sampled and intro- duced into another carrier stream for further process- ing. The approach was conceived [l] to provide high degrees of sample dispersion in an efficient and controlled way. It was pointed out that sample dilu- tions as high as lo5 [2] could be attained and also * Corresponding author. other potentialities of the zone sampling process were demonstrated such as simultaneous determina- tions [3], wide range spectrophotometry [4], imple- mentation of the standard addition method [5], achievement of the concentration profile of a dis- persed sample [6], evaluation of elution efficiency of an ion exchange resin column [7], etc. However, flow networks with zone sampling are somewhat complex, involving at least two sample carrier streams and two injection ports, usually with solidary movement, e.g., switching at the same time [l-7]. High dispersion can also be accomplished by 0003-2670/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0003-2670(95)00102-6