Cobalt(III) Tetramethylenedithiocarbamate as a New Flotation Collector for Preconcentration and Separation of Lead Determinated by Zeeman ETAAS - Enimiteva et al. page 05


Selection of Surfactant

To select the most suitable surfactant for separation of lead ions, different foaming reagents were tested by flotation of a series of standard solutions under conditions previously determined as optimal. The cationic surfactant (BTC), as well as non-ionic surfactant (TX-100) foam very well, but no flotation occurred. The anionic surfactants floated with different recovery efficiencies. NaDDS and NaOL were the most successful surfactants for lead flotation with Co(TMDTC)3 (Table 2). Several anionic surfactants (NaDDS, NaOL, NaPL and NaST) and the pair of NaDDS /NaOL were also used. The detergent NaDDS shows the highest recovery rate of lead ions by flotation (98.44 %) and therefore was selected as a reagent for this method (Table 2).

table_02

Influence of Ionic Strength and Induction Time

The ionic strength (Ic) of the floating reaction mixture must be Ic = 0.02 mol/L regulated by saturated solution of KNO3. That value was chosen from previous work (Čundeva & Stafilov, 1997; Čundeva et al., 2000; Pavlovska et al., 2001; Stafilov et al., 2001; Pavlovska et al., 2000; Bundalevska et al., 2005; Zajkova Paneva et al., 2005; Paneva et al., 2007; Čundeva et al., 2007).
The induction time (τ) is the time necessary for the incorporation of metal traces in the collector precipitate. For this procedure by Co(TMDTC)3 performed at pH 6.0, the optimal induction time was 15 min.

Detection Limit

To determine the standard deviation of the method ten blanks were floated by the recommended procedure and then the concentration of lead was determined by Zeeman ETAAS. The limit of detection (LOD) of the method was estimated as three values of the standard deviation (s) of the blank. The precision of the method was expressed by means of the relative standard deviation (sr).
The standard deviation (s) of ETAAS method for lead was 0.59 mg/L, the detection limits 0.18 mg/L, while the relative standard deviation 1.55 %.

Application of the Method

The developed method was successfully applied for Pb flotation preconcentration for natural water samples. For those purposes four samples in two series of fresh and tap waters from Strumica (the city tap water and fountains Kalinka, Topuska and Sofilari) were analysed by ETAAS.



Each water sample (0.5 L) was preserved by acidification with a few milliliters of nitric acid (pH<3). The proposed procedure with Co(TMDTC)3 was applied. After flotation lead was 20-fold concentrated and determined with ETAAS using calibration curves and the methods of standards additions (Table 3). The recovery value (98.44 %) shows that the preconcentration and separation of lead by the recommended procedure is satisfactory.

table_03

As for confirmation, this method was verified by determination of lead in the surface water reference materials SPS-SW1 Batch 107 (Spectra pure Standards AS) and LGC-6019 River Thames Water (LGC Standards). Before the application of the method with the reference standard materials they were diluted 10 times. The data in Table 4 shows that the results of the reference materials analysis agreed well with the certified values (Student’s t-test, 95 %).
table_04