Simultaneous multiple injection in monosegmented flow analysis

A flow approach for simultaneous multiple injection (SMI) in monosegmented flow analysis (MSFA) is described. In this approach, the sample and the reagent (or other solution, such as a diluting fluid) are simultaneously injected into the reaction coil of a monosegmented flow analyser. The monosegment is homogenised while it is carried towards the detector. The sample dilution procedure is not based on a gradient concentration pattern and dilution factors up to 150 were obtained by using hydrodynamic sampling. The system was applied to perform sample dilution in the determination of glucose in blood plasma. The results showed good correlation with those obtained by the Clinical Hospital of UNICAMP. The SMI approach was also applied to add reagent to the sample in nitrite determination in natural water, providing a methodology that has a sampling frequency of 72 h(-1), a relative standard deviation of <2%, at 60 mu g l(-1) N-NO2-, a linear response range up to 260 mu g l(-1) and a 3 s limit of detection of 5 mu g l(-1) N-NO2-. Thus, the sensitivity is close to that of the manual reference method. Recovery tests carried out with sea water samples also showed that MSFA overcomes the Schlieren effect, without needing any special procedure. (C) 1998 Published by Elsevier Science B.V. All rights reserved.