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 ophenanthroline (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 21 Fe II . In the analysis of a sample containing 2.3 mg l 21 Fe II (n = 10) a relative standard deviation of 1.7% has been obtained. The detection limit (3s) is 0.06 mg l 21 Fe II and the determination limit (10s) 0.2 mg l 21 Fe II . Determination of P is linear between 0.1 and 1 mg l 21 P and in the analysis of a sample containing 0.75 mg l 21 P (n = 10) a relative standard deviation of 4.1% has been obtained. The detection limit is 0.02 mg l 21 P and the determination limit 0.1 mg l 21 . 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.

Software

“…Especially prominent among the early software used with flow techniques was Flowtek, which was developed by van Staden and coworkers [1]; FIALab, which was devised by Ruzicka's group [2]; and DARRAY [3], which was developed by our research group. Some of these computer programs continue to be readily available and used at present as they greatly facilitate the implementation of flow techniques.…”

A review on sequential injection methods for water analysis

“…Among these, iron is the most determined metal in waters, if the two possible ionic forms are considered [49,59,71,74,83,103,127,[135][136][137]143,144,152]. This fact can be explained as iron determination can be fairly easy to obtain with spectrophotometric detection, due to well-known reactions.…”

“…That was the case of the work developed by Makchit et al [71]; the authors designed a homemade sequential injection system providing valuable information for "a do it yourself SI manifold". Other examples are described by Vieira et al [137] and Mas et al [135], involving different strategies of sampling and the use of sample as carrier stream.…”

“…Spectrophotometry was the most widely used method of detection, although there were also quite a few methods that involved electrochemical detection. Almost 20% each of the listed references, described the determination of nitrite [67,96,107,118,116,117,132,131,140,155] and phosphate [52,77,107,120,119,135,134,[140][141][142]. For monitoring aquatic media, it is important not only the determination of these anions individually, but also the ratio…”

Sequential injection analysis

“…Mas et al 186 demonstrated that the sample could be employed as the carrier stream, thus facilitating the use of inline standard additions for the successful determination of iron(II) and phosphorus in spiked waters. The only drawback with this idea was that the syringe pump required rinsing after each change of sample to avoid memory effects.…”