**2.1.3 General procedure**

The FIA system used was simple as shown schematically in Fig.2. The sample solution was introduced into the reagent carrier solution by the Rhodyne injection valve. The complex (max=415 nm) was formed on passage of the reagent and iron (II) ion solution through the

Flow-Injection Spectrophotometric Analysis of Iron (II), Iron (III) and Total Iron 425

1986). A Fe(II)-Morin (1:2) complex was indicated by both methods. The reaction was very fast. Metal ions react with Morin in aqueous medium in the range pH: 2.0-7.0 forming coloured complexes with different stoichiometry. Absorption spectra's those correspond to solutions of 5x10-5 M of iron (II)-Morin complex was measured against a reagent blank and the average molar absorption coefficient of 6.82 x 104 L mol-1 cm-1 are shown in Fig. 3.

Fig. 3. Absorption spectras of iron (II)-Morin complex and Morin itself. (A) absorption spectra of iron (II)-Morin complex (5x 10-5 M) and (B) absorption spectra of the Morin in

As can be seen from the Fig. 3, the iron (II) Morin complex that has an absorbance maxima at 415 nm. At this wavelength, the Morin itself has no absorption while Morin complexes of all of the tested metal ions and the anions ( not shown) exhibited a negligible absorption.

In order to develop an FIA method based on the above phenomenon, the FIA setup shown in Fig.1 was used. In the FIA system, a complex was formed with an absorption spectrum that showed a maximum at 415 nm, which was in agreement with the value obtained in the

Various variables closely related to the iron determination were examined using the simple flow-injection analysis system with a fixed iron (II) concentration of 5 g L-1. The Morin concentration was varied from 1x10-6 M to 1x10-2 M. The peak height was found to increase with increasing Morin concentration up to 1x10-5 M and no noticeable increase was found at higher concentrations. Therefore, 1x10-5 M Morin was decided as colour developing

With the concentration of the Morin fixed 1x10-5 M, the pH of the carrier solution was varied from 2.0 to 7.0. The interference effect of the iron (III) were found to increase with increasing pH up to 4.5 and remain constant at higher pH. Also, the peak heights were found to increase with increasing pH up to 4.0, remain constant to 4.5 and decreased slightly above

**2.2.2 Optimisation of chemical variables and the FIA manifold** 

aqueous solution.

spectrophotometric study.

component of the carrier solution.

that.

mixing coil. A PTFE tubing (50 cm long) was attached before the flow-through detection cell as a mixing coil. The absorbance of the coloured complex was selectively monitored in the flow-through spectrophotometric cell at 415 nm. The transient signal was recorded as a peak, the height of which was proportional to the iron (II) concentration in the sample, and was used for all measurements. Five replicate injections per sample were made.

Fig. 2. Flow diagram of the FIA system used. R; reagent carrier solution (1x10-5 M Morin in ethanol: water (4:96 v/v) in 0.1 M HAc/Ac- buffer (pH:4.50)), P, Peristaltic pump, S; Rheodyne sample injection valve, RC; reaction coil (50 cm long, 0.5 mm i.d), D; spectrophotometric detector (*max* = 415 nm), W; waste, C; computer, P; printer.
