Calcium concentration determination

The effect of the three major cations. Nab Kb and Mg b is offset by their inclusion in calibrators at normal serum concentrations. An automated diluter is recommended because the imprecision (expressed as the coefficient of variation [CV]) for measurements of total calcium should be less than 1.5% and preferably less than 1%. A serum-based calibrator with calcium concentration determined by ID-MS is available commercially. 

Comparison of results for the first and last entries in Table 7 (AOS 2024 and IOS 2024) was for samples for which the hydrophobe linearity, hydrophobe carbon number, and relative disulfonate content were held nearly constant. The major differences in these surfactants were possible differences in the relative locations of the double bond and the sulfonate group in the alkenesulfonate and in the relative locations of the hydroxy group and the sulfonate group in the hydroxyalkanesulfonate. Analyses to determine these are quite difficult. At calcium ion concentrations below 100-250 ppm, AOS 2024 appeared to be more salt-tolerant than linear IOS 2024. At higher calcium concentrations, the calcium ion tolerance of the two surfactants was similar. 

Another mechanism to maintain CO when contractility is low is to increase heart rate. This is achieved through sympathetic nervous system (SNS) activation and the agonist effect of norepinephrine on P-adrenergic receptors in the heart. Sympathetic activation also enhances contractility by increasing cytosolic calcium concentrations. SV is relatively fixed in HF, thus HR becomes the major determinant of CO. Although this mechanism increases CO acutely, the chronotropic and inotropic responses to sympathetic activation increase myocardial oxygen demand, worsen underlying ischemia, contribute to proarrhythmia, and further impair both systolic and diastolic function. 

Calcium-selective electrodes have long been in use for the estimation of calcium concentrations - early applications included their use in complexometric titrations, especially of calcium in the presence of magnesium (42). Subsequently they have found use in a variety of systems, particularly for determining stability constants. Examples include determinations for ligands such as chloride, nitrate, acetate, and malonate (mal) (43), several diazacrown ethers (44,45), and methyl aldofuranosides (46). Other applications have included the estimation of Ca2+ levels in blood plasma (47) and in human hair (where the results compared satisfactorily with those from neutron activation analysis) (48). Ion-selective electrodes based on carboxylic polyether ionophores are mentioned in Section IV.B below. Though calcium-selective electrodes are convenient they are not particularly sensitive, and have slow response times. 

As light emission from aequorin is dependent on Ca2+, the protein has been widely employed for determination of this ion. In particular, the protein was used in the past in the highly sensitive measurement of intracellular calcium concentration in several kind of cells [16]. More recently immobilized aequorin was used to develop an optical biosensor for measurement of calcium ions in complex... 

Savory et al. 3S) measured calcium and magnesium directly in protein-free filtrates of serum or urine. Baker et al. 36) found that both trichloroacetic acid and hydrochloric acid suppress calcium absorption and that uniform acid content is therefore required for the determination of calcium. Okuda and Sasamoto37) determined calcium by adjusting solution conditions to 20 — 50 % methanol and 650 mg % lanthanum serum is diluted 21-fold and urine is diluted 10—21 fold to bring the calcium concentration into the optimum range of 1 to 0.5 mg %. 

A very important advantage of the relative bioavailability assay is that experimental parameters may be selected which are easily quantitated. Thus, Tso et al. (11) determined the relationship between dietary calcium concentration (X, g/kg) and... 

Dissolved Concentrations of Calcium and SO2 Species. The equilibrium dissolved concentrations of total calcium and SO2 (sulfite plus bisulfite) species are important because comparison of these equilibrium concentrations with actual measured values determines the degree of gypsum saturation, and hence the potential for gypsum scale formation in the scrubber. As a first approximation, the fraction gypsum saturation of a scrubber liquor, having specified pH and specified concentrations of magnesium and chloride, is proportional to the measured calcium concentration, and inversely proportional to the measured S02 concentration. 

Gypsum Saturation from Measurements of Dissolved SOg. Use of measurements of dissolved calcium to determine gypsum saturation is relatively easy from a computational standpoint use of measurements of dissolved SO2 is more difficult. However, wet chemical analyses for calcium are frequently subject to interference by high concentrations of magnesium. For installations where a quick and reliable analysis for calcium is not available, the use of dissolved SO2 is preferred, and the following correlation applies ... 

R. B. Alexander, E. S. Bolton, S. Koenig, G. M. Jones, S. L. Topalian, C. H. June, and S. A. Rosenberg, Detection of antigen specific T lymphocytes by determination of intracellular calcium concentration using flow cytometry, J. Immunol. Methods 148, 131-141 (1992). 

To determine the rate of dissolution of hemlhydrate crystals, the same vessel was used as for the crystallization study. The vessel was filled with the sulphate-rich solution (zero Initial calcium concentration). An amount of sieved hemlhydrate seed crystals, about 10% In excess of that required to saturate the solution, was added. At very short time Intervals, samples were taken using a similar procedure to that for the gypsum growth Investigation. Samples were separated Into crystals for size analysis (with a 190pm orifice) and crystal content and solutions for analysis. Further details are given by Mukhopadhyay (17). 

To be able to interpret these results and to correct for the lower calcium concentrations at high sulfate and phosphate concentrations, the partition coefficients D have been determined. These values follow from the slopes of the curves in figure 7. For 5.5 and 6.0 M HjPO a D of about 1.5 10" is obtained. A similar D-value for both acid concentrations should indeed be obtained, when the activity coefficients of the ions in solution is not strongly affected by the acid concentration. The D-value for 6.5 M H PO lies somewhat higher. This could e.g. be caused by a higher activity coefficient of cadmium compared to calcium at this acid concentration. The thermodynamic D-value cannot be determined by increasing the residence time, because a residence time of 2400 seconds already caused anhydrite formation. 

Serum calcium or serum ionized calcium concentrations (ionized calcium concentrations are preferable to determine free and bound calcium, especially with concurrent low serum albumin)... 

The determinants of calcium sensitivity, ie, the curve relating the shortening of cardiac myofibrils to the cytoplasmic calcium concentration, are incompletely understood, but several types of drugs can be shown to affect calcium sensitivity in vitro. Levosimendan is the most recent example of a drug that increases calcium sensitivity (it may also inhibit phosphodiesterase) and reduces symptoms in models of heart failure. 

Conditioning of the manganese oxide suspension with each cation was conducted in a thermostatted cell (25° 0.05°C.) described previously (13). Analyses of residual lithium, potassium, sodium, calcium, and barium were obtained by standard flame photometry techniques on a Beckman DU-2 spectrophotometer with flame attachment. Analyses of copper, nickel, and cobalt were conducted on a Sargent Model XR recording polarograph. Samples for analysis were removed upon equilibration of the system, the solid centrifuged off and analytical concentrations determined from calibration curves. In contrast to Morgan and Stumm (10) who report fairly rapid equilibration, final attainment of equilibrium at constant pH, for example, upon addition of metal ions was often very slow, in some cases of the order of several hours. 

The authors suggested that this was the first report of exogenous calcitonin causing hypercalcemia. There were several unknowns in this case, including the calcium concentration before treatment and the concentration of PTHrp, which would have helped to determine the cause of the hypercalcemia. Calcitonin is usually associated with a reduction in calcium concentration rather than a rise. The authors postulated that calcitonin could alter PTHrp concentrations, with different effects depending on cell type. They also provided evidence of hypercalcemia caused by calcitonin in non-human models (14). 

Hou (1992) used a simple screening test to determine whether acid and direct dyes precipitate at calcium concentrations typical of hard waters of the SE Piedmont region of the U.S. Of the 52 dyes tested, only three direct dyes (Direct Black 19, Direct Black 22, and Direct Blue 75) and seven acid dyes (Acid Red 88, Acid Red 114, Acid Red 151, Acid Brown 14, Acid Black 24, Acid Orange 8, and Acid Blue 113) precipitated. Although the Ca salts of acid and direct dyes were thought to be the most likely metal salts to precipitate after dye discharge to natural waters, the precipitation is not likely to occur unless dye concentrations exceed 0.02 to 0.6 mg/L, a level far greater than reported concentrations of dyes in surface waters. 

The value of mH+ is determined by the previously described technique from this equation along with the other carbonic acid system components. The calcium concentration is calculated from the relation given in equation 2.10. 

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