New approach to sequential injection analysis: using the sample as carrier

Abstract

A new way of implementing sequential injection analysis involving the use of the sample as a carrier is proposed. These systems are especially suitable for constructing continuous monitoring set-ups with no restrictions regarding the amount of sample which can be processed. A new standard addition methodology was used to calibrate the proposed system. The methodology was applied to the determination of Fe^II with o- phenanthroline (a reaction which involves a single reagent) and that of phosphorus by formation of a blue heteropolyacid (a reaction involving two reagents). The analysis rate is 8 min per sample (3 standard additions). The manifold design together with an adequate programme of aspiration–impulsion movements avoids the memory effects between samples. Determination of Fe^II is linear between 0.25 and 6 mg l^–1 Fe^II. In the analysis of a sample containing 2.3 mg l^–1 Fe^II (n = 10) a relative standard deviation of 1.7% has been obtained. The detection limit (3s) is 0.06 mg l^–1 Fe^II and the determination limit (10s) 0.2 mg l^–1 Fe^II. Determination of P is linear between 0.1 and 1 mg l^–1 P and in the analysis of a sample containing 0.75 mg l^–1 P (n = 10) a relative standard deviation of 4.1% has been obtained. The detection limit is 0.02 mg l^–1 P and the determination limit 0.1 mg l^–1. Both methods have been applied to the determination of Fe and P in spiked waters. The use of the methodology based on the standard addition has been evaluated in the case of P determination in order to eliminate interferences of the multiplicative type.