**2.2.5 Applications**

426 Macro to Nano Spectroscopy

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

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

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

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

The developed analytical method was validated by evaluating the linear dynamic range, precision, accurate, limit of detection (LOD) and limit of quantification (LOQ) as well as by applying the standard addition technique. Under the optimized experimental conditions, a linear calibration graph was obtained for 0.01-120 mg L-1 iron (II) under the optimum conditions with a regression coefficient of 0.9914. The relative standard deviation for the determination of 5 g L-1 iron (II). was 0.85 % for 10 replicate injections. The limit of detection (blank signal plus three times the standard deviation of the blank) was 0.4 g L-1.

The interference effects of many cations and anions on the determination of 5 g L-1 iron (II)

Over 50000 Cr(III), Al(III), Cd(II), Mn(II), K(I), Na(I), Ag(I), Ca(II), Mg(II),

In the table, the tolerable concentration of each diverse ion was taken as a highest concentration causing an error of ± 3 %. Most of the ions examined did not interfere with the determination of iron (II). The major interference was iron (III) at the amounts of 200 g L-1.

Table 1. Effect of foreign ions on the determination of 5 μg L-1 of iron (II) in solution

NH4+, SCN-, tartrate, oxalate, citrate, thio-urea

Ba(II), Hg(II), CN-, NO3-, NO2-, SO42-, CO32-, Cl-, Br-, PO43-,

selected as a compromise between sample throughput rate and sensitivity.

The sample throughput of the proposed method was almost 60 sample h-1.

using Morin at fixed concentration of 2.5x10-4 M and pH 4.5.

decided convenient for better peak height and shape.

**2.2.3 Calibration, accuracy and precision** 

were examined. The results summarized in Table 1.

Tolerance limit (μg L-1) Foreign ion

Over 200 Fe (III)

**2.2.4 Interference studies** 

sensitivity and sample throughput rate.

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.


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

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

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


(1) Samples were collected at Samsun, Turkey.

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

(3) Calibration curve method.

(4) Standard addition method.

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

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 a pre-concentration process.

Flow-Injection Spectrophotometric Analysis of Iron (II), Iron (III) and Total Iron 429

All reagents used were of analytical reagent grade and the solutions were prepared with double distilled and deionized water. The reagent diphenylamine-4- sulfonic acid sodium salt (DPA-4-SA) was provided by Merck. The chemical formula of the DPA-4-SA is shown in Fig. 4. Standard iron(III) (1 mg mL*−*1) and iron(II) (5 mg mL*−*1) solutions were prepared by dissolving FeCl3 6H2O and FeCl2 4H2O in 0.05 M nitric acid and standardized by titration with EDTA. The stock solution of DPA-4-SA (1*×*10*−*2 M) was prepared by dissolving the diphenylamine-4-sulfonic acid sodium salt in deionized water. All stock solutions were stored in polyethylene containers. All polyethylene containers and glassware used for aqueous solutions containing metallic cations were cleaned with (1+1) nitric acid while the rest were cleaned with 3 % Decon 90, all were rinsed with deionized water before use. The working standard solutions were prepared by appropriate dilution immediately before use. Interference studies were carried out using chloride or nitrate salts of the metal cations, and sodium or potassium salts of anions. All solutions were degassed before use using a sonicator (LC 30). A certified metal alloy sample consisting of 0.085 % Fe (Zn/Al/Cu

The pH measurements were carried out using a Jenway 3040 Model digital pH-meter consisting of a contained glass pH electrode. UV-Visible spectra of the DPA-4-SA reagent and metal-DPA-4-SA complexes were taken with a Unicam spectrophotometer (GBC Cintra 20, Australia). A peristaltic pump (ISMATEC; IPC, Switzerland) was used to propel the samples and reagent solutions. Samples were injected into the carrier stream by a 7125 model stainless steel high-pressure Rheodyne injection valve provided with a 20 μL injection loop. Absorbance of the colored complex formed in the flow system was measured using a UV-visible spectrophotometer equipped with a flowthrough micro cell (Spectra SYSTEM UV 3000 HR, Thermo Separation Products, USA), and connected to a computer (IPX Spectra SYSTEM SN 4000) incorporated with a PC 1000 software program. The reaction coil was made of PTFE tubing (1 m, 0.5 mm, i.d.). A UNICAM 929 model (Shimadzu AA-68006) flame atomic absorption spectrophotometer with deuterium- lamp background correction was used for the determination of iron in reference to the FIA method. The measuring conditions were as follows: UNICAM hollow cathode lamp, 10 cm 1-slot burner, airacetylene flame (fuel gas flowrate 1.50 L min*−*1), 0.2 nm spectral bandwidth, and 7 mm burner height. The wavelength and

The manifold of the flow-injection system was similar to that proposed in our previous study (Asan et al., 2003). The peristaltic pump was used for propelling the reagent carrier solution at a flow-rate of 1 mL min*−*1. Samples were injected into the reagent carrier solution, soon load the reaction coil. The reaction zone containing the complex was moving towards the flow-through spectrophotometric detector cell in which the presence of iron(III)-DPA-4- SA complex was selectively monitored, and the absorbance of the complex at 410 nm was

Sea and river water samples collected in Nalgene plastics were acidified by adding 1 mL of nitric acid (0.1 M) per 100 mL of sample solution after filtration over a 0.45 μm Millipore

**3.1 Experimental** 

**3.1.1 Reagents, chemicals, equipment** 

43XZ3F) was provided by MBH Analytical Ltd. (UK).

the lamp current of iron were 248 nm and 5 mA, respectively.

**3.1.2 Preparation of water samples and certified metal alloy solution** 

continuously recorded.
