Determination of Lead , Iron , Manganese and Zinc in Sea Water Samples by Atomic Absorption Spectrometry after Preconcentration with Chromosorb 105

A solid phase extraction procedure based a column technique for preconcentration of lead, iron, manganese and zinc from water samples was developed. The analyte ions as its diethyldithiocarbamate complex were retained on a column of Chromosorb 105 from buffered sample solution. Then they were eluted with acetone. The recoveries of lead, iron, manganese and zinc under the optimum working conditions were 100, 97, 100 and 100%, respectively. The relative standard deviations were less than 6%. The method presented was applied for the determination of lead, iron, zinc and manganese in sea water samples.

In this work, the exploration about the potential of Chromosorb 105 as sorbent for preconcentration of Pb, Fe, Mn and Zn as diethyldithiocarbamate complexes from aqueous solution has been made.Several parameters influencing the recoveries of analytes, including pH of sample, sample volume, eluent volume and effect of divers ions have been investigated in detail.An optimized procedure has been applied to the determination of trace metals in water samples.

Apparatus
Trace concentrations of metals were determined by FAAS using a Perkin Elmer Aanalyst 700 Model Atomic absorption spectrometer.The air-acetylene flame was adjusted according to the manufacturer's recommendations.A Hanna Instrument pH 211 microprocessor pH meter equipped with a combined glass calomel electrode was used for the pH adjustment.All solutions were delivered to pass through the glass column, having a stopcock and a porous disk was 10 cm long and 1.0 cm in diameter packed with Chromosorb 105.

Reagents and Solutions
All reagents were of analytical reagent grade unless stated otherwise and doubly distilled water was used through the experiments.Stock standard solution of 1000 mg L -1 metal ions was prepared by dissolving appropriate amount of nitrate salts in 1 % nitric acid.Chromosorb 105 was purchased from Phase Separation Inc., Norwalk, CT.The buffers used were phosphoric acid/dihydrogen-phosphate for pH 2, sodium acetate/acetic acid for pH 4 to 6 and ammonium hydroxide/ammonium chloride for pH 8 to 10.

Method Development
The column was dry-packed with 500 mg Chromosorb 105.A small amount of glass wool was placed on the disc to prevent the loss of the resin during sample loading.The bed height of resin bed was approximately 1.5 cm.It was washed successively with water, acetone and water, respectively.The column was preconditioned by passing blank solution prior to use.
After each use, the resin in the column was washed with large volumes of water and stored in water for the next experiment.
The performance of column method was tested with model solution before its application to the samples.100 mL of the model solution containing 20 µg Pb, 10 µg Fe, 10 µg Mn and 5µg Zn was buffered to desired pH. 3 mL of 0.05 % m/v NaDDTC solution was added to this solution.It was loaded to the top of the preconditioned column and gravitationally passed through at a flow rate of 2 mL min -1 .The column was washed with 5-10 mL of blank solution prepared with the corresponding buffer solution.Then, the retained metal ions were eluted with 10 mL of acetone.Acetone was evaporated to near dryness on a hot plate adjusted to ca. 30-40 o C and then cooled.The analytes in the effluent were determined by FAAS.

Analysis of Water Samples
The surface sea water samples were collected in pre-washed polyethylene bottles from a dirty region of Aliağa Bay.The bottles were cleaned with detergent, double distilled-deionized water, a dilute nitric acid and double distilled-deionized water, respectively.The samples were immediately filtered through a Millipore cellulose nitrate membrane having pore size 45 µm, acidified to pH 3 with hydrochloric acid and stored in precleaned polyethylene bottles.The samples were analyzed with the preconcentration procedure given above, within a week after their collections.For the analysis, the acidified sea water was firstly neutralized and then buffered to desired pH.The preconcentration procedure given above was submitted to these solutions.

Effects of pH
The effect of the pH on the retention of Pb, Fe, Mn and Zn as diethyldithiocarbamate complexes on the Chromosorb-105 resin column was studied by applying of the proposed procedure at different pH values (Fig. 1).The results indicate that the recoveries for Pb and Fe were found as 96% at pH 6, 97% at pH 4, respectively.The recoveries of both of Mn and Zn were found 100% at pH 9. Due to these results, the further studies were performed at pH 6 for Pb, at pH 4 for Fe and at pH 9 for both of Mn and Zn.

Influences of Eluent Type
To investigate the effect of elution solution, various eluents such as HNO 3 at the concentration range of 0.5, 1.0 and 1.5 mol L -1 and HCl at 0.5, 1.0 and 1.5 mol L -1 , acetone and 0.01 mol L -1 EDTA were tested.The results are shown in Table 1.As can be seen, the maximum recovery values were obtained with EDTA solution for Pb, pure acetone for Fe, Mn and Zn.Also the quantitative recovery for Pb was obtained with pure acetone.As being practical pure acetone was used for all elements as the eluent throughout the experiments.The volume of eluent was 10 mL.

Effect of Sample Volume
The effect of sample volume on the retention of metal ions was studied by varying the sample from 25 to 1500 mL.As can be seen in Fig. 2, the recoveries of Pb and Fe were quantitative until 1250 and 50 mL, respectively.But, the recoveries of Mn and Zn were quantitative until 250 mL.Although a high preconcentration factor (125) was obtained for Pb, it was 5 for Fe, and 25 for both Mn and Zn.From these results, the method could be applicable for the determination of Pb, Fe, Mn and Zn in environmental samples, such as sea water.

Precision of the method
The precision of the determination of lead, iron, manganese and zinc was evaluated under the optimum conditions mentioned above.For this purpose, five successive retention and elution cycles (with 20 µg Pb, 10 µg Fe, 10 µg Mn and 5µg Zn in 100 mL of solution) were performed.
It was found that the recovery of lead, iron, manganese and zinc were 100±4, 97±6, 100±3 and 100±4 at 95% confidence level, respectively.In conclusion, the precision of the method is very good, and the recovery of the analyte is quantitative (>95%).

Matrix Effects
The influence of interferences will come mainly from the major matrix ions in the water samples such as Na + , K + , Ca 2+ , Mg 2+ , HCO 3 and SO 4 2-on the preconcentration of Pb, Fe, Mn and Zn ions on Chromosorb 105 were investigated.To investigate the effect of matrix ions, 100 mL of solution containing 20 µg of each metal ions and coexisting the ion with varying concentrations was prepared.The recommended preconcentration and analytical procedure was applied to these solutions.It was found that the major matrix ions in the natural water samples show no obvious interference on the preconcentration with developed method of some trace metal ions (Table 3).The tolerable concentration for Na + was 10000, mg L -1 and that for K + , Ca 2+ , Mg 2+ , HCO 3 -and SO 4 2-was 1000 mg L -1 .

Capacity studies
The capacity study used was adapted from that recommended by Maquieira et al. [47].
The procedure has been given in Ref [8].
As shown in Table 4, the breakthrough capacities were found as 4.2, 8.0, 52.3 and 67.7 µmol g -1 for lead, iron, manganese and zinc, respectively.

Accuracy and Application
The developed method was applied to analysis of seawater samples.To estimate the accuracy of the procedure, different amounts of the investigated metal ions were spiked to 500 mL of seawater samples.The resulting solutions were submitted to preconcentration procedure.
Iron and zinc were determined by FAAS, on the other hand, lead and manganese were determined by GF-AAS.The recoveries of spiked analytes are given in Table 4.A good agreement was obtained between the added and measured analyte amounts in sea water.These results confirm the validity of the proposed method.

Fig. 1 .
Fig.1.The effect of pH on the recovery of metal-DDTC complexes

Fig. 2 .
Fig.2.The effect of volume of solution on the recovery of metal-DDTC complexes

Table 1 :
Influences of the various eluents on the desorption of metal-DDTC complexes *The mean of three replicates

Table 3 .
Precision of the method a Average of N determinations with 95% confidence level

Table 3 .
The influence of the foreign ions on the recovery of metal *The mean of three replicates

Table 4 .
Adsorption capacity *The mean of three replicates

Table 4 .
Determination of lead, iron, magnesium and zinc in sea water