Micellar electrokinetic chromatography (MEKC) was examined for the separation and determination of Mo(VI), Cr(VI), Ni(II), Pd(II), and Co(III) as diethyl dithiocarbamate (DDTC) chelates. The separation was achieved from fused silica capillary (52 cm × 75
Capillary electrophoresis (CE) is coming up as an alternative analytical technique for the elemental analysis in parallel with liquid chromatography [
Sodium diethyl dithiocarbamates (Na-DDTC) (Fluka, Switzerland), nickel(II) chloride, cobalt(II) acetate, palladium(II) chloride, ammonium molybdate(VI), and potassium bicarbonate (E-Merck, Germany) were used. The chemical methanol (RDH, Germany), acetonitrile, and chloroform (E-Merck, Germany) were used. Guaranteed reagent grade hydrochloric acid (37%), potassium chloride, acetic acid, sodium acetate, ammonium acetate, sodium tetraborate, boric acid, sodium bicarbonate, sodium carbonate, ammonium chloride, and ammonia solution were form E-Merck, Germany. Buffer solution pH 1–10 at unit interval was prepared from the following; hydrochloric acid-potassium chloride (pH 1-2), acetic acid-sodium acetate (3–6), ammonium acetate (pH 7) boric acid-sodium tetraborate (8–9.5), sodium bicarbonate-sodium carbonate (pH 9), and ammonium chloride-ammonium solution (pH10). The pH measurements were performed with an Orian 420A pH meter with combined glass electrode and reference interval electrode (Orian Inc. Boston, USA). The spectrophotometric study was carried out with double beam Perkin Elmer 35 spectrophotometer (Perkin Elmer, Singapore) with 1 cm quartz cuvettes. The spectrophotometer was controlled by the computer with software. The determination of nickel, cobalt, and molybdenum was carried out with Perkin Elmer AA 800 (Perkin Elmer, Singapore); atomic absorption spectrometer with standard burner head and an air-acetylene flame under the conditions recommended was determined in quadruplet (
The solution (1-2 mL) containing Mo(VI) (1.6–30.0
Three samples of hydrogenated vegetable oil (Ghee) were collected from local market (Hyderabad, Pakistan); (1) Pak Ghee (Pakistan oil mills (Pvt) Karachi), (2) Naz Ghee (Tallu oil Mills, Hyderabad, Pakistan), (3) unbranded Ghee. Sample (20 gm each) was transferred to separate conical flak and was added nitric acid (1 M) (30 mL). The contents were shaken on the mechanical shaker for 1 hour. The layers were allowed to separate and aqueous layer was collected. The aqueous layer was concentrated to 5 mL and final volume was adjusted to 10 mL. The solution (0.5 mL) was processed as analytical procedure after adjustment of the pH to 5. The amount of nickel was evaluated from external calibration curves based on linear regression equation,
Potato and Almond samples collected from local market (Jamshoro, Pakistan) were properly washed and outer skin peeled off. The remaining mass was cut into small pieces, and 40 g of potato and 20 g of Almond was burned in the furnace at 700°C and 650°C, respectively, for 10 hours. The ash of each sample was treated separately with 5 mL of H2SO4 (0.1 M). The content was mixed well and filtered with Whatman 9 filter paper. The pH of each solution was adjusted to 5 and final volume was made up to 10 and 15 mL, respectively, for potato and almond samples. The solution 1 mL was processed as analytical procedure. The amount of molybdenum was calculated from external calibration curves.
Cobalmine injection (1 mL) (Merck, Marker (Pvt.) Ltd, Germany) or 4 tablet of Neurobion (Merck, Marker (Pvt.) Ltd, Germany) were weighed and grinded to powder and each added 5 mL of aqua regia (HCl-HNO3 3 : 1 v/v). The contents were heated gently to near dryness. The residue was dissolved in distilled water and filtered. The pH of the solution was adjusted to 5, and final volume was made up to 20 mL. The solution (1 mL) was taken and analyzed following analytical procedure.
The samples for the analysis of nickel, molybdenum, and cobalt were also analyzed by standard addition. The solutions 0.5 mL in duplicate were taken from the prepared solution after acid extraction of nickel from Ghee. A solution was added nickel 10
DDTC is reported to react with a number of metal ions to form complexes extractable in organic solvents [
DDTC metal chelates indicate less solution stability in acidic medium [
Effect of pH on the mobility of metal complexes with respect to neutral marker acetone.
Variation in migration velocity with concentration of borate buffer.
The impact of the concentration of CTAB and the effect of the ratio of buffer and surfactant on the separation of metal chalets was examined. A significant improvement in the separation and electrophoretic mobility of Pd(II), Ni(II), and Co(III) was observed with cationic surfactant CTAB, particularly at higher concentration. However, at the higher concentration of CTAB current inside the capillary was developed, which again affected the separation. In order to avoid this effect, volume of added CTAB (thus the concentration) was varied from 1 mL to 5 mL at an interval of 1 mL. The electrophoretic mobility of the metal chelates remained nearly constant (Figure
Variation in mobility with volume of surfactant under optimized conditions.
The solvent systems were examined, but no significant improvement in the separation was observed. An improvement in the separation was observed when n-butanol in methanol used. The percentage of n-butanol in methanol was varied between 1 to 7% at an interval of 1%. However, a better separation was obtained using 1% n-butanol in methanol (Figure
The effect of the amount of organic modifier on the migration velocity of metal complexes, with respect to acetone.
The applied voltage affects the retention factor as well as the environment developed inside the capillary by creating the joule heating effects. The use of cationic surfactant reversed the direction of EOF, and negative voltage was applied to induce the migration of analyte towards the selection window. The effect of applied voltage was investigated within −5 kV to −20 kV at an interval of −2 kV. An acceptable separation between all the five metal chelates and reagent was observed within −10 kV to −15 kV, and −10 kV was selected owing to better separation with lower applied voltage. A final separation of all five metal complexes along with reagent is presented in Figure
Electropherogram of five metal ions obtained using 25 mM borate buffer of pH 9.1 containing CTAB (30%, 100 mM) and organic modifier (butanol) in ratio of (70 : 30 : 5 v/v/v). Conditions: capillary, fused silica 52 cm (effective length 40 cm), i.d. 75 mm, applied voltage −10 kV at reverse polarity, hydrostatic injection 4 sec. UV-VIS detection at 225 nm, capillary temp, 25°C.
Linear calibration curves for simultaneous determination were drawn by recording average peak height (
Quantitative MEKC Data of DEDTC metal chelates.
Metal ions | Calibration range | Limit of quantitation | Limit of detection (LOD) | Linear regression | |
---|---|---|---|---|---|
Co(II) | 0.5–4.0 | 0.0501 | 0.0167 | 0.9979 | |
Cr(VI) | 0.25–2.0 | 0.025 | 0.0083 | 0.9997 | |
Ni(II) | 0.4–12.0 | 0.04 | 0.0133 | 0.9985 | |
Mo(VI) | 0.16–3.0 | 0.016 | 0.005 | 0.9989 | |
Pd(II) | 2–10.0 | 0.2 | 0.067 | 0.9991 |
Vegetable oils hydrogenated using Ni as catalyst was analyzed for the contents of Ni, after extraction of nickel in nitric acid. The amounts found were 3.66–4.18
The determination of amount of Mo(VI) in potato and almond samples.
Sample | Metal ion | Amount found by CE | Amount found by St.Add | Amount found by AA | C.V |
---|---|---|---|---|---|
Potato | Mo(VI) | 0.293 | 0.32 | 0.25 | 3.9% |
Almond | Mo(VI) | 0.7025 | 0.72 | 0.67 | 1.02% |
Amount of Ni(II) present in hydrogenated Ghee samples.
S. No. | Sample | Metal Ion | Amount found by CE | Amount found by AA | Relative deviation % |
---|---|---|---|---|---|
1 | Pak Ghee | Ni(II) | 4.185 (4.1) | 3.742 (2.1) | 4.5% |
2 | Naz Ghee | Ni(II) | 3.658 (2.6) | 2.900 (1.7) | 3.51% |
3 | Without name | Ni(II) | 3.88 (1.7) | 4.923 (1.2) | 4.06% |
Determination of Co(II) in pharmaceutical preparations.
S. NO | Sample | Metal ion | Amount found by CE (RSD%) | Amount prescribed | C.V |
---|---|---|---|---|---|
1 | Neurobion tablet | Co(II) | 3.8 | 4.4 | 2.9% |
2 | Cobalmine injection | Co(II) | 43.3 | 44.0 | 1.02% |
(a) Electropherogram of Ni a in Naz oil sample, b spiked with Ni(II) standard Under optimized conditions (b) Electropherogram of Ni (a) pak oil sample (b) spiked with Ni(II) Under optimized conditions.
(a) Electropherogram of Co a in Cobalmine injection b spiked with Co 20 ppm. (b) Cobalt in Neurobion injection (b) spiked with 10 pmm standard Under optimized conditions.
Electropherogram of (a) potato sample (b) spiked with standard Mo solution under standard operating condition.
A simple and sensitive MEKC method has been described for the determination of Mo(VI), Cr(VI), Pd(II), Ni(II), and Co(III). The separation was obtained within migration time within 12 minutes with LODs within 0.005–0.0176
All the authors of the paper declare that they do not have a direct financial relation with any commercial identity mentioned in the paper that might lead to a conflict of interests for any of the authors.