**2.2 Results and discussion**

### **2.2.1 Spectrophotometric studies of the Morin-metal complexes**

The reaction mechanism of the present method was as reported earlier (Busev A.I., et al. 1981). Job's method of continuous variation and the molar ratio method were applied to ascertain the stoichiometric composition of the complex (MacCarthy P. and Zachary D.H.,

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

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.

Sea, river and industrial water samples collected in Nalgene plastics were acidified by adding 1 mL of hydrochloric acid (0.1 M) per 100 mL of sample solution behind filtration over 0.45 m Millipore Filter (Millford, MA). After filtration, 20 L of water samples were injected directly into the FIA system for the determination of iron (II). Total iron was determined by reducing of all forms of iron to iron (II) in the procedure described (van

A 0.10 g sample of the certified metal alloy (Zn/Al/Cu 43XZ3F) was dissolved in 12 mL of concentrated HCl+HNO3 (3:1 v/v) in 100 mL beaker. The mixture was heated on a hot plate nearly to dryness; 5 mL HNO3 was added to complete dissolution and diluted to 100 mL with deionized water. The solution was filtered and transferred quantitatively to 1000 mL volumetric flask and made up to volume with deionized water. 9 mL of this solution was treated with 1 mL of sodium azide (2.5 % w/v) for iron (III) reduction. After the reduction step, 20 L of this solution was used for the determination of total iron (van Staden J.F. and

Metal ore samples (0.10 g) were powdered ( 500 mesh) and prepared as in the procedure

The reaction mechanism of the present method was as reported earlier (Busev A.I., et al. 1981). Job's method of continuous variation and the molar ratio method were applied to ascertain the stoichiometric composition of the complex (MacCarthy P. and Zachary D.H.,

described above. All analyses were performed with the least possible delay.

**2.2.1 Spectrophotometric studies of the Morin-metal complexes** 

**2.1.4 Sample preparation procedures** 

Kluever L.G. 1998).

**2.2 Results and discussion** 

Staden J.F. and Kluever L.G. 1998; Asan A., et al. 2003).

was used for all measurements. Five replicate injections per sample were made.

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 aqueous solution.

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 spectrophotometric study.

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

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 component of the carrier solution.

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 that.

Flow-Injection Spectrophotometric Analysis of Iron (II), Iron (III) and Total Iron 427

It is apparent from the Table 1 that the proposed method can tolerate all of the interfering species tested in satisfactory amounts and it is therefore adequately selective for the

The FIA method was applied to the determination of iron (II) and total iron in water samples and ore samples. In order to evaluate the accuracy of the proposed method, the determination of total iron in a standard reference material (Zn/Al/Cu 43XZ3F) and metal alloy sample was carried out. The analytical results obtained by the proposed method are in

good agreement with the certified values as is shown in Table 2.

Alloy (1) 8.23(0.12) 8.58 Alloy (2) 16.15(0.16) 16.62 Std Zn/Al/Cu 43XZ3 F 0.083(0.02) 0.085

are in good agreement with each other as shown in Table 3.

(1) Samples were collected at Samsun, Turkey.

(3) Calibration curve method. (4) Standard addition method.

a pre-concentration process.

Sample Total Fe(1) (%) Certified Fe (%)

Table 2. Total iron content of iron alloys and standard reference material

Values in parenthesis are the relative standard deviations for n=5 with confidence level of 95 %.

Samples(1) Iron (II)(2) (g L-1) Total iron (2) (g L-1)

 Found(3) Found(4) Found(3) Found(4) AAS Kurtun river water 38.33(0.24) 38.55(0.12) 42.33(0.02) 42.91(0.18) 43.65(0.17) Seaport sea water 68.84(0.32) 68.65(0.24) 85.13(0.12) 85.75(0.06) 86.12(0.12) Baruthane sea water 47.51(0.18) 47.62(0.14) 57.24(0.04) 57.65(0.15) 58.97(0.24) Organized industry water 78.84(0.22) 78.65(0.18) 78.13(0.14) 98.75(0.07) 99.12(0.10)

(2) Values in parenthesis are the relative standard deviations for n=5 with confidence level of 95 %.

Atomic absorption measurements taken in water samples were also given for comparison in Table 3. The analytical value of total iron in water is slightly in good agreement with that obtained by the AAS method. The results obtained show that the proposed method can be applied in the determination of iron (II) and total iron content in the water samples without

Table 3. Determination of iron (II) and total iron in river and sea water samples

For the application of the proposed FIA method to river and sea water samples collected from different sources were analyzed by using both calibration curve and standard addition methods. The values obtained from the calibration curve and the standard addition methods

determination of Fe (II) and total iron.

**2.2.5 Applications** 

The pH of the reagent carrier was however adjusted to 4.5 to obtain maximum peak height and minimum iron (III) interference in the analysis. In order to proceed with the final system design, the effect of sample volume, mixing coil length and flow-rate were studied using Morin at fixed concentration of 2.5x10-4 M and pH 4.5.

The sample volume was varied from 5-50 L. The peak height was decreased by decreasing sample size, and the peaks were broadened with increasing sample size due to sample zone dispersion. A sample injection volume of 20 L was selected as a compromise between sensitivity and sample throughput rate.

The mixing coil (RC) was examined by using PTFE tubing's (0,5 mm i.d.) at different lengths ranging between 10 and 150 cm. The peak height was increased with increasing mixing coil length from 10-50 cm. The peak height was decreased for lower concentrations and broadened for higher concentrations at longer coil lengths. A mixing coil length 50 cm was decided convenient for better peak height and shape.

The flow-rate was varied from 0.2 to 2 mL min-1. The peak height decreased by increasing flow-rate, probably the extent of reaction decreased. A flow-rate of 0.8 mL min-1 was selected as a compromise between sample throughput rate and sensitivity.
