Calcium, automatic determination

Thermogravimetry may be used to determine the composition of binary mixtures. If each component possesses a characteristic unique pyrolysis curve, then a resultant curve for the mixture will afford a basis for the determination of its composition. In such an automatic gravimetric determination the initial weight of the sample need not be known. A simple example is given by the automatic determination of a mixture of calcium and strontium as their carbonates. 

The most important applications of Ca " ISEs are in biomedical practice, especially in the determination of ionized calcium in serum. A pioneer work in this field was that by Moore [149] (see also [110,111]). At present the Ca ISE is used in the solvent polymeric version in a number of automatic devices for determining ionized calcium in serum, usually with periodic recalibration of the electrode and thermostatting to 37 °C. It should be noted that ISEs measure... 

F.R.P. Rocha, P.B. Martelli, R.M. Frizzarin, B.F. Reis, Automatic multicommutation flow system for wide range spectrophotometric calcium determination, Anal. Chim. Acta 366 (1998) 45. 

R.A.S. Lapa, J.L.F.C. Lima, J.L.M. Santos, Determination of calcium, magnesium, sodium and potassium in wines by FIA using an automatic zone sampling system, Food Chem. 55 (1996) 397. 

The major serum electrolytes—sodium, potassium, calcium, magnesium, chloride, and bicarbonate (CO2)—are fairly easy to determine. The metals are most readily determined by the use of fiame-spectrophotometiic or atomic absorption methods, although colorimetric methods exist for calcium and magnesium. Calcium and, less frequently, magnesium are also titrated with EDTA. Ion-selective electrodes are used for the routine analysis of sodium, potassium, and calcium. Bicarbonate is analyzed also by titration against standard acid (see Experiment 8) in addition to a manometric method. Chloride is widely determined by automatic coulometric titration with electrogenerated silver ion. 

In spectrophotometric methods which incorporate an on-line dialysis system, the acceptor streams are almost always connected to the detector after merging with the appropriate reagents. Dialysis is used mostly to remove interferents, such as suspended or colloidal materials, which interfere physically with the photometric detection but the technique is also often used to achieve different degrees of dilutions automatically. As an early example, Basson and van Staden [14] used an on-line dialyzer to achieve deproteination and dilution of serum samples in the determination of calcium by a cresolpthalein complexone FI photometric method. Owing to the dilution effects and the exclusion of potential interferents, interferences from Schlieren effects, such as those encountered in sorption separation systems (cf. Sec. 4.6.6) were not experienced in on-line dialysis spectrophotometric systems. 

Since the early days of analytical applications of ion-selective electrodes they have been used in clinical analysis. The progress in construction and miniaturisation of electrodes as well as contemporary development of computerised potentiometric apparatus have led to the production of automatic analyzers designed especially for clinical applications/ The high degree of response selectivity of the membrane sensors used today eliminates practically the mutual interaction of various blood, serum, plasma or urine components. Nevertheless when drugs or their metabolites are introduced into the body they in some cases may influence the electrode response and cause errors in estimation of the content of the ions present naturally, i.e., potassium, sodium, calcium and chloride. Such parasitic effects may be caused by the interaction of drugs with the electrode membrane. The aim of this study was to check whether some selected drugs can influence the determination of the above mentioned electrolyte ions in the serum. 

A specific-ion meter is capable of direct potentiometric determinations of electroactive species using pH, redox, or various ion-selective electrodes (i.e., chlorine, calcium, nitrate, ammonia/carbon dioxide, copper, and halides). Microprocessor control allows for instrument calculation of analyte levels by known additions, standard additions, or activity. An automatic temperature-compensation feature helps to reduce analytical errors. 

The relative standard deviation for measurements of the total alkaline earths in ocean waters is reported to be less than 0.1 % (Pate and Robinson, 1961 Culkin and Cox, 1966). In the case where an automatic titration system is applied, the author found a comparable coefficient of variation (c.v.) of 0.15 %. However, for water of lower salinity with an average magnesium content of 0.205 g/kg, a c.v. of only 0.65 % was measured by the author. Although the determination of the magnesium concentration is based on the difference between titrations, errors caused by the measurements of calcium and strontium can be neglected, when the analytical procedure described in Section 11.2.1 is used. 

Most elements in the periodic table have one, two, or even three isotopes that arc free from isobaric overlap. An exception is indium, which has two stable isotopes, " In and " In. The former overlaps with " Cd and the latter with " Sn. Mote often, an isobaric interference occurs with the most abundant and thus the most sensitive isotope. For example, the very large peak for Ar (see Figure ll-15b) overlaps the peak for the most abundant calcium isotope Ca (97%), making it necessary to use the second-most abundant isotope Ca (2.1%). As another example, the most abundant nickel isotope, Ni, suffers from an isobaric overlap by "Fe. This interference can be corrected by measuring the peak for Fc. From the natural-abundance ratio of the Fe isotope to that of Fe isotope, the contribution of Fe to the peak at m/z. 58 can be determined and the correction made. Because isobaric overlaps are exactly predictable from abundance tables, corrections for the problem can be carried out with appropriate software. Some current instruments arc capable of automatically making such corrections. 

Fig. 8. Titration curves obtained when titrating 20 ml of 0.0004 M EDTA with 0, 20, 40, 60, and 80 ml of Lab-trol added to the titrate. The curves are parallel and equally spaced, therefore the concentration of calcium can be estimated from the spacing, provided the titrant concentration is known. The linear portions of the curves provide a convenient guide in determining the control-pointer setting when the automatic-stop method is used to obtain more accurate results.

It was surprising, too, that the two dense castables had approximately 50% residual water after drying at 110°C, whereas the water amounts of LW products were determined between 20 and 30% only. This is interesting so far as with decreasing B.D. the cement contents increase automatically. Due to this, the amount of calcium aluminate hydrates must be logically higher in LW products. Nevertheless, it seems to be a fact that it is easier to dry products with more cement, respectively hydrates, if the pore sizes are big enough ... 

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