Determination Of Alkaline Earth Metal Ions Research Articles

Underwater determination of calcium and strontium ions in oilfield produced water by laser-induced breakdown spectroscopy (LIBS).

Laser-induced breakdown spectroscopy (LIBS) was applied to the determination of scaling ions in oilfield-produced water employing underwater measurements. Initially, the stability of plasma was verified using four different optical setups and expansion of the laser beam, and a combination of an achromatic lens with a meniscus lens were necessary to stabilize the plasma. Preliminary experiments demonstrated that only the determinations of Ca(II) and Sr(II) ions were feasible while the signal for the Mg(II) ion was absent and the sensitivity for Ba(II) was very low. The laser pulse repetition rate was evaluated and rates of 10 and 20 Hz provided a more stable breakdown in water compared to repetition rates of 2 to 7 Hz, besides imparting higher intense signals. The increase in salinity showed a small matrix effect, decreasing the sensitivities of the calibration curves by 8-13% when standard solutions with a salinity of 30‰ were used instead of water. Under optimized conditions with a laser pulse energy of 31 mJ, gate delay of 300 ns, gate width of 5.0 μs, repetition rate of 10 Hz, and accumulation of 500 laser shots, a linear range from 25 to 150 mg L-1 was obtained, with limits of detection of 0.58 and 0.85 mg L-1 for Ca(II) and Sr(II), respectively. The underwater determination of scaling ions in produced water by LIBS provided results that do not significantly differ from those obtained by inductively coupled plasma atomic emission spectroscopy (ICP OES) at a confidence level of 95%, with relative errors of up to 5.2%. These results demonstrate the potential of underwater LIBS measurements as an analytical tool for the determination of alkaline-earth metal ions in produced water, which can help the oil industry to overcome the problems related to scale formation.

Application of atmospheric pressure discharges with a liquid cathode for determination of alkaline-earth metal ions in aqueous solutions

The concentrations alkaline-earth metal ions in water solutions were determined by the method of emission actinometry of atmospheric pressure discharge plasma with a liquid cathode. The rubidium atoms were the actinometer component in plasma, whose cations with a known concentration were added to the analyzed solution. The solutions of magnesium, calcium, barium with concentrations of 10−6-10−4 gl−1 were analyzed. It is established that the addition of electrolytes in the solution influence on the emission intensity of the metal atom lines. However, the use of the ratio of the intensities of the radiation of the analyzed components and the component-actinometer can improve the accuracy of the analysis. The water hardness factor of the tap water was determined using this method.

Separation and Determination of Alkaline-Earth Metal Ions as UV-Absorbing Chelates with EDTA by Capillary Electrophoresis. Determination of Calcium and Magnesium in Water and Serum Samples

Capillary electrophoresis of alkaline-earth metal ions was examined with a UV-absorbing chelating agent. The metal1 chelates separated in a capillary were measured by on-column UV-absorptive detection. When ethylenediamine-tetraacetic acid (EDTA) was used as an chelating agent in a carrier solution (pH 9.2), the order of the migration time (t(m)) of metal ions was as follows: Ba(2+)<Sr(2+)<Ca(2+)<Mg(2+) (Be(2+) could not be detected). These four ions were separated within 16min using a capillary (50μm i.d.) of 75-cm effective length (L(D)) at an applied voltage of 30kV, and calcium and magnesium ions were separated within 4min using a 25-cm capillary at an applied voltage of 20kV. By using a 50-cm or 25-cm capillary, Ca(2+) and Mg(2+) in river, tap and underground water samples were determined; the detection limits of metal ions were about .10(-5)M (1M=mol dm(-3)), and the relative standard deviations for the determination of around 10(-4)M of the metal ions were less than 2.0%. The method was also applied to the determination of Ca(2+) and Mg(2+) in a standard serum sample.

Application of modified normal pulse polarography and its differential mode to alkaline-earth metal ions in acid solutions

The simultaneous determination of alkaline-earth metal ions in acid solution was studied by modified normal pulse polarography. Well-defined waves were recorded for calcium, strontium and barium, but no limiting current was found for magnesium, because of its very negative reduction potential. The differential mode of this method gives peak-type polarograms and is useful for the simultaneous determination of species for which the half-wave potentials lie close together. The interference of dissolved oxygen was eliminated by the use of tetramethylammonium chloride as a supporting electrolyte.