https://doi.org/10.1155/2019/1467631
“A series of complexing adsorbents is prepared by coating silica particles with linear polyhexamethylene guanidinium (PHMG) chloride followed by saturation with a number of sulphonated nitrosonaphthols reagents electrostatically retained by positively charged polymer layer. PHMG coated silica is hydrolytically stable even during treatment with 6 M HCl heated up to 50 °C. The adsorption of 1-nitroso-2-naphthol-3,6-disulfonic acid (nitroso-R-salt), 2-nitroso-1-naphthol-4-sulfonic acid (nitroso-N-salt), and 2-nitroso-1-naphthol-3,6-disulfonic acid (nitroso-K-salt) on PHMG modified silica was studied. The effective immobilisation of sulphonated nitrosonaphthols was achieved in the range of pH of 3 – 8, while the adsorption of the monosulphonated reagent (nitroso-N-salt) is twice as high as the disulphonated analogues (nitroso-R-salt and nitroso-K-salt). The adsorption of Cu(II), Fe(III), Co(II), Ni(II), Al(III), Zn(II), Pb(II), Mn(II), and Cr(III) on prepared complexing adsorbents under static and dynamic conditions was studied as a function of time, pH, sample volume, and presence of interfering ions. Metal ions can be desorbed by using 1 M HCl or 1 M HNO3. The preconcentration factors of metals under optimized conditions are varied from 20 to 80. The developed method was used for the preconcentration of trace metals from natural waters followed by ICP-OES determination. The sub-ppb limits of detection of metals are achieved.”
”
2.1. Reagents
All reagents used in this work had analytical grade. Standard stock solutions of Cu(II), Fe(III), Co(II), Ni(II), Al(III), Zn(II), Pb(II), Mn(II), and Cr(III) (100 mg L−1) were prepared by dissolving the corresponding salts in 1 mol L−1 nitric acid and further diluted in double distilled deionized water on daily basis. 1 M HNO3, 1 M NaOH, 0.1 M acetate–acetic acid buffer (pH 4.0 – 6.3), 0.5 M ammonia–ammonium acetate buffer (pH 6.5 – 7.0), and 0.1 M ammonia–ammonium chloride buffer (pH 8.0 – 8.5) were used for pH adjustments. The silica gel Silokhrom S-120 (Reakhim, Stavropol, Russia) having particle size 0.1 – 0.2 mm, specific surface area of ~120 m2g−1, and pores of average diameter 45 nm was used as a matrix for the preparation of adsorbents. Polyhexamethylene guanidine chloride (PHMG, 95% pure) was supplied by the Institute of Eco-Technological Problems (Moscow, Russia). 1-Nitroso-2-naphthol-3,6-disulfonic acid (nitroso-R-salt, NRS), 2-nitroso-1-naphthol-4-sulfonic acid (nitroso-N-salt, NNS), and 2-nitroso-1-naphthol-3,6-disulfonic acid (nitroso-K-salt, NKS) were obtained from Sigma-Aldrich (St. Louis, MO, USA).
2.2. Equipment
ICP-OES spectrometer Optima 5300DV (Perkin-Elmer) with a cross-flow nebulizer and a Ryton Scott chamber was used for the detection of metal ions. Elemental measurements were made in axial view mode using wavelengths and operating parameters recommended for the spectrometer, which are presented in Table 1.
The pH values were adjusted using a Seven Easy S20 digital pH meter (Mettler-Toledo, Switzerland) calibrated using four standard buffer solutions of pH 1.65, 4.01, 7.00, and 9.18. UV-Vis spectra were recorded with Cary 100 spectrophotometer (Varian, Australia). A MasterflexL/S peristaltic pump (Thermo Fisher Scientific, USA) was used for pumping solutions through a glass minicolumn (30 x 3 mm I.D.) containing 0.1 g of the sorbent.
Thermogravimetric analysis (TGA) of prepared adsorbents was performed with STA 449 C analyser (Netzsch, Germany) coupled to FTIR spectrometer Nicolet 380 via TGA/FT-IR interface (Thermo Scientific, USA). This instrument can be used for differential scanning calorimetry, thermogravimetry, and analysis of the released gas phase. FTIR spectra are used for measurement of absorbance of gases released from the sample heated in platinum crucible in the temperature range from 30 to 760°С.
Semiempirical method PM3 of computational chemistry software GAMESS was used for the calculation of geometry of the molecules. Molecular parameters are calculated for the most stable conformational forms using geometric parameters and van der Waals atomic radii.
“