Determination Of Calcium In Water Research Articles

Cyclic voltammetric determination of calcium in water in the presence of natural organic matter (humic acid) and Cu (II) at gold electrode's surface

Calcium and copper are essential for many physiological functions, including enzyme activation and reactive oxygen blockages. However, elevated levels of these metals (separately, synergetically or antagonistically) may result in disorders such as cancer, bone loss, and cardiovascular failure. Foods and water remain the major dietary sources of these metals. Thus, monitoring their levels in foods, water and drinks has become a matter of necessity. This paper reports for the first time the determination of calcium in water in the presence of humic acid (HA) and copper (II) ion (Cu2+) using cyclic voltammetry. The voltammogram displayed a large oxidative potential difference between the two metals (copper existed as a doublet low field while calcium showed a high field potential), enabling a reliable quantification. The detection limits (LODs) of calcium in the copper-free and copper-containing HA solutions are 6.91 × 10−4 and 2.89 × 10−3 mol/L, respectively, suggesting a potential for monitoring calcium in drinking water, soft drinks, wine and dairy products. Also, an LOD of 2.56 × 10−3 mol/L was obtained for Cu2+, implying the potential for simultaneous determination of both metals in aqueous fluids with high degree of reliability.

Pulsed flow chemistry. A new approach to the generation of concentration profiles in flow analysis

Pulsed flow chemistry (PFC) is described as a new approach to automated on-line analytical chemistry. In contrast to existing flow-based analytical chemistry methods, PFC is characterized by pulsed flow, turbulent mixing and low axial dispersion. The PFC system is fully computerized and all operations are under software control. Consequently, most flow analysis methods (e.g., flow injection, continuous flow, flow titration, etc.) can be selected with a simple click of the mouse. The system is easily miniaturized and portable which makes it particularly suited to field instrumentation. The system has been tested using several flow-based techniques including on-line titration for the determination of calcium in waters with potentiometric detection and a calcium ion sensor.

Usefulness of a ruggedness test in the validation of flow injection analysis systems

The usefulness of a ruggedness test to evaluate the influence of small variations in the parameters fixed in the assemblage of a flow injection analysis (FIA) system on its response is presented. The purpose of the tested system was the determination of calcium in water with increased sensitivity by differential potentiometry involving two identical calcium ion selective electrodes. Youden and Steiner's ruggedness test was found to be a useful technique to ascertain that the optimized system worked properly.

Determination of calcium in water, urine and pharmaceutical samples by sequential injection analysis

A sequential injection analysis system for the determination of calcium in water, urine and pharmaceutical samples is proposed. The method is based on the fast complexation reaction between cresolphthalein complexone and calcium with spectrophotometric detection. Baseline shift due to a background originating from coloured free reagent species, was eliminated by an optimised sequence of samples and reagents. The proposed system is fully computerised and is able to monitor calcium in samples at a frequency of 43 samples per hour with a relative standard deviation of < 1.4%. The calibration graph is linear between 0 and 20 mg l −1. The detection limit is 0.05 mg l −1.

Determination of calcium in waters, milk and wine by discontinuous-flow analysis

The flow-based analysis method, discontinuous-flow analysis (DFA), was used for the determination of total calcium in drinking water, milk and wine by titration with ethyleneglycoltetraacetic acid. The detector is a coated-wire calcium-selective electrode. The titration can be cycled continuously with a cycle time of about 1 min. This can be carried out with a single sample or with different samples using an autosampler. The method for waters and wine is simple, fast and highly reproducible. For milk, a back-titration method was used because of the complex matrix of the sample.

Determination of calcium in water by flow injection analysis — inductively coupled plasma (FIA-ICP) emission spectrometry

Using an 11 ml centrifugal type spray chamber, a rapid sample introduction rate of 320 injections per hour may be achieved when interfacing flow injection analysis and inductively coupled plasma emission spectrometric techniques. Calcium was determined in water samples with a relative standard deviation of better than 3.5% over the analytical range of 10 to 200 mg · l−1 Ca. Mean recovery was 97%.

Calcium-selective electrodes with pvc membranes and solid internal contacts

The response of calcium-selective electrodes based on PVC membranes has been investigated. The membrane, containing the calcium salt of di-n-octylphenylphosphoric acid, is in direct contact with the internal electrode made of silver, silver/silver chloride, or teflonized graphite. Evidence is given to support the hypothesis that the oxygen half-cell is responsible for the potential at the solid contact—membrane interface. Silver or teflonized graphite contacts provide better potential stability and analytical sensitivity than Ag/AgCl contacts. The electrodes can be used for determination of calcium in waters.

Direct potentiometric determination of calcium in waters with a constant complexation buffer

The effect of the composition of solutions in the direct potentiometric determination of total calcium content with an Orion calcium-selective electrode was investigated. In order to obtain accurate results for water samples, it is necessary to add ammonium buffer (0.02 M) to maintain constant pH, potassium nitrate (0.4 M) for constant ionic strength, iminodiacetic acid (0.02 M) for constant complexation of calcium, and acetylacetone (0.04 M) to mask magnesium. In the presence of the proposed Constant Complexation Buffer (CCB), the results are accurate to within a few percent in the range 20–800 mg Ca l -1.