NEW APPROACH TO SEQUENTIAL INJECTION-ANALYSIS - USING THE SAMPLE AS CARRIER

A new way of implementing sequential injection analysis involving the use of the sample as a carrier is proposed. These systems are especial ly suitable for constructing continuous monitoring set-ups with no res trictions regarding the amount of sample which can be processed. A new standard addition methodology was used to calibrate the proposed syst em. The methodology was applied to the determination of Fe-Pi with o-p henanthroline (a reaction which involves a single reagent) and that of phosphorus by formation of a blue heteropolyacid (a reaction involvin g two reagents). The analysis rate is 8 min per sample (3 standard add itions). The manifold design together with an adequate programme of as piration-impulsion movements avoids the memory effects between samples . Determination of Fen is linear between 0.25 and 6 mg l(-1) Fen. In t he analysis of a sample containing 2.3 mg l(-1) Fe-Pi (n = 10) a relat ive standard deviation of 1.7% has been obtained. The detection limit (3s) is 0.06 mg l(-1) Fe-Pi and the determination limit (10s) 0.2 mg l (-1) Fen. Determination of P is linear between 0.1 and 1 mg l(-1) P an d in the analysis of a sample containing 0.75 mg l(-1) P (n = 10) a re lative standard deviation of 4.1% has been obtained. The detection lim it is 0.02 mg l(-1) P and the determination limit 0.1 mg l(-1). Both m ethods have been applied to the determination of Fe and P in spiked wa ters. The use of the methodology based on the standard addition has be en evaluated in the case of P determination in order to eliminate inte rferences of the multiplicative type.