Simultaneous determination of metal ions as complexes of pentamethylene dithiocarbamate in Indus river water, Pakistan

1 Introduction

Determination of trace metals in water (Wattoo et al., 2006, 2004; Arain et al., 2001, 2002; Wang and Lee, 1997) is often made possible by the addition of complexing agent and analyzing the sample by spectrophotometry or by liquid chromatography. Most separation methods in use are based on the formation of metal dithiocarbamate especially ammonium pyrrolidine dithiocarbamate and sodium diethyl dithiocarbamate as ligands to stabilize high oxidation states which allow monitoring of the oxidation rather than the reduction of metal dithiocarbamate complex formed in situ in the liquid chromatographic system (Bond and Wallace, 1981, 1982). Sodium diethyl dithiocarbamate has been used as a derivatizing reagent for gas chromatography as well as liquid chromatography (Arain et al., 2001; Bond and Wallace, 1982; Cardwell et al., 1976) using electrochemical and spectrophotometric detections (Bond and Wallace, 1983).

Mostly chromatographic separations of metal dithiocarbamates were achived using normal phase chromatography with UV–Visible spectrophotometric detection (Liška et al., 1979; Moriyasu and Hashimoto, 1978; Brooks et al., 1967; Jan and Young, 1978; Danielsson et al., 1978; Sturgeon et al., 1980). Babu and Naidu (1991) reported the use of pentamethylene dithiocarbamate for the complexation, solvent extraction and AAS determination of Fe, Ni, Cr and Mn from water. Asolkar et al. (1992) used the same reagent for the determination of Cd²⁺, Cu²⁺, Fe³⁺ and Pb²⁺ on thin layer chromatography. Arain et al. (2002) separated the series of six metal ions as chelates of pentamethylene dithiocarbamate by capillary gas chromatography (CGC) and high performance liquid chromatography (HPLC); see Fig. 1.

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Figure 1

Structural diagram of PMDTC–metal complex.

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In the present work, we have investigated the determination of Fe³⁺, Cr³⁺, Mn²⁺, Cu²⁺, Ni²⁺, Co²⁺ ions from fresh water samples collected from river Indus at Ghulam Muhammad barrage. The metal contents were preconcentrated as complexes of pentamethylene dithiocarbamte, extracted in organic solvent and simultaneously determined by HPLC. The seasonal variations in the metal contents of river Indus water were also evaluated.

2 Experimental

3 Results and discussion

The reagent reacts with iron, chromium, manganese, copper, nickel and cobalt to form color complexes (Arain et al., 2002; Ramana et al., 1991; Kubáň et al., 2005). Maximum color development occurs in neutral to slightly acidic media. The metal chelates are easily extractable in chloroform. The reagent was examined for preconcentration, extraction and simultaneously determination of Fe³⁺, Cr³⁺, Mn²⁺, Cu²⁺, Ni²⁺ and Co²⁺. Metal pentamethylene dithiocarbamate chelates (Fig. 1) were separated as reported (Arain et al., 2002) on HPLC column (150 × 4.6 mm. id, 5 μm). HPLC was calibrated with six standards and extraction efficiency was evaluated by adding 250 ml distilled water. The instrument was recalibrated after five samples; it was observed that percentage recovery was 94–100% with a coefficient of variation (C.V) up to 3.9%.

This method was applied for the determination of metal ions in water samples collected from Indus river and were examined quantitatively from April to March (n = 12). The percentage recovery (Table 1) of each of the metal ions was examined using analytical procedure and the average recovery (n = 5) was observed within 92–99% with coefficient of variation within 1.2–3.9%. The average concentration of Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺ observed were 78, 61, 542, 23, 14.2 and 42.6 μg/L, respectively as shown in (Table 2). The concentration of metal ions exhibited the Fe³⁺ > Cr³⁺ > Mn²⁺ > Cu²⁺ > Ni²⁺ > Co²⁺, decreasing sequence.

The total metal ions concentration fluctuated between 2.12 and 960 μg/L at Ghulam Muhammad barrage and 4.6–1383 μg/L at Kotri SITE area. The seasonal variation of metal ions (Fig. 2) was uniform and depended upon water flow. High flow occurs in summer, when snow melts extensively and dominant monsoon rains augment many fold. Metal contents were diluted in peak flow season June to September and concentration level was high in winter due to the shortage of water especially during December to February (Fig. 2). Fig. 2 also indicates maximum concentration of metal ions in the month of January and minimum in the July, which is due the water discharge in river Indus. The results also indicate highest concentration of iron through out the study.

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Figure 2

Seasonal variation of metal ions.

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4 Conclusion

This method have been used for the determination of chromium, manganese, iron, cobalt, nickel and copper ion as pentamethylene dithiocarbamate chelates in Indus river water and effluent water samples (after mixing industrial effluents from SITE area) and good correlation was observed with that of atomic absorption spectrometry. The metal ions contents were observed in a safe limit but concentration of iron and copper contents were slightly on the higher side. This is might be due to the extraction from sediments at acidic pH adjusted for the preservation of water samples.