THE GENERALIZED STANDARD ADDITION METHOD IN A CLOSED-LOOP FLOW SYSTEM

Abstract

A new approach using flow-injection configuration is proposed as an alternative to apply the generalized standard addition method. The flow system contains a calibrated closed loop in which a spectrophotometric flow-cell is placed. The sample is entrapped into the closed loop by a suitable valve and it is allowed repetitive passages through the flow-cell; the addition of the standard solutions is made through an additional sample valve with a relatively small sample volume. After the addition, transient signals are obtained due to the repetitive passage of the added standard through the detector until it is completely dispersed into the sample by a mixing chamber. The proposed method resembles the manual, conventional procedure; a very small volume of standard solution is added to a relatively large volume of sample in such a way that the matrix of the latter is not significantly modified. Mathematical derivations that relate the concentration of the sample with that of the standard and the number of additions are performed with the analysis of the pH indicator methylorange. The analysis of iron in milk shows that good reproducibility is obtained using only one standard and one addition.

Keywords:

• Flow-injection analysis
• Standard addition
• Closed-loop
• Mixing chamber
• Spectrophotometric flow-cell

ACKNOWLEDGMENTS

We would like to thank the Universidad Simón Bolívar, Caracas, Venezuela, for financial support.