Calcium determination Subject

Magnesium, like calcium, is subject to the effect of anions, although to a lesser degree. The most serious interference derives from refractory acidic oxides formed in the flame from a number of elements, particularly aluminum and silicon. The effect of phosphate and sulfate is much less marked than with calcium (Fig. 17), hut if aluminum or silicon is also present in the solutions, magnesium depression is much more severe than with either of these interfering agents alone. These interferences can be overcome by the addition of strontium, lanthanum, or calcium. Leithe and Hofer (L4, L5) showed that magnesium could be determined... 

Calcium retention is dependent on two factors, absorption and excretion. Normal subjects have been observed to have apparent calcium absorptions of 23 (sd = 12) to 27 (sd = 17) percent of the calcium from normal diets (21,22). For 20 women aged 55 to 65 consuming 629 (se = 92) milligrams dietary calcium daily, the apparent absorption was 32.1 (se = 1.9) percent (23). An apparent calcium absorption of 29.5 percent (n = 130) may be calculated from data published by Heaney et al. (15). Apparent absorption values from 29 to 42 percent may be calculated from data published by Linkswiler (24,25). However, much lower apparent absorption values of 6 to 15 percent may also be calculated from data published from the same laboratory (26). Although there is considerable variability in the apparent absorption values determined from many studies, a conservative value of 25 percent seems realistic for normal people consuming typical diets. 

Strategies for determining calcium bioavailability The term bioavailability implies that fraction of a nutrient, drug or toxicant that is utilized relative to the amount consumed. Calcium is fed to the test subject in amounts below what the subject will utilize. This ensures that all of the calcium provided can be absorbed and metabolized. Then, that fraction... 

A very important ligand (or chelating agent) for titrimetric analysis is the ethylenediaminetetraacetate (EDTA) ligand. It is especially useful in reacting with calcium and magnesium ions in hard water such that water hardness can be determined. The next section is devoted to this subject. 

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 ... 

The results obtained with ISEs have been compared several times with those of other methods. When the determination of calcium using the Orion SS-20 analyser was tested, it was found that the results in heparinized whole blood and serum were sufficiently precise and subject to negligible interference from K and Mg ([82]), but that it is necessary to correct for the sodium error, as the ionic strength is adjusted with a sodium salt [82], and that a systematic error appears in the presence of colloids and cells due to complexa-tion and variations in the liquid-junction potential [76]. Determination of sodium and potassium with ISEs is comparable with flame photometric estimation [39, 113, 116] or is even more precise [165], but the values obtained with ISEs in serum are somewhat higher than those from flame photometry and most others methods [3, 25, 27, 113, 116]. This phenomenon is called pseudohyponatremia. It is caused by the fact that the samples are not diluted in ISE measurement, whereas in other methods dilution occurs before and during the measurement. On dilution, part of the water in serum is replaced by lipids and partially soluble serum proteins in samples with abnormally increased level of lipids and/or proteins. 

Having the glucoside, we could now determine its concentration in the leaves. Extract samples of varying sizes were subjected to calcium hydroxide treatment, acidification, extraction, and glc quantitation. The amounts of parasorbic acid obtained from the samples are shown in Figure 1 to be proportional to sample size. 

Other methods that have been used in determination of the amount of moisture in coke include (1) extraction of coke using anhydrous methanol and the addition of calcium hydride with coal constituents (CaH2) from which the amount of released heat is measured, and (2) extraction of coke using anhydrous dioxan and measurement of the refractive index of the solution to determine its water content. Application of these methods to coal may be subject to error because of (1) interaction of the coal (in contrast to coke) with the calcium hydride, leading to chemical errors, and (2) the influence of extractable constituents on the refractive index of the dioxan. 

The grape spirits permitted are subjected to rigorous quality standards, performed by the laboratories and tasters panel of the IVDP. Turbidity, color, aroma, and taste are evaluated. Ethyl carbamate, total higher alcohols, acetaldehyde, ethyl acetate, methanol, 2-butanol, 1-buta-nol, allylic acid, and cyanidric acid concentrations are analyzed calcium, copper, and iron contents determined and the alcohol content, total acidity, and density assessed. All must be below designated limits (Regulamento n° 84/2010). 

Treatment of tardive dyskinesia is often unsatisfactory, especially in severe cases. A large number of treatments have been proposed (SEDA-20,40), including antiparkinsonian drugs, benzodiazepines, baclofen, hormones, calcium channel blockers, valproate, propranolol, opiates, cyproheptadine, tryptophan, lithium, manganese, niacin, botulinum toxin, ECT, dietary control, and biofeedback training. In an open study, 20 patients (mean age 65 years) with severe unresponsive tardive dyskinesia (mean duration 44 months, mean exposure 52 months) were treated with tetrabenazine (mean dose 58 mg/day) (310). The mean score on the AIMS motor subset, determined from videotapes, improved by 54%. Sedation was the only subjective complaint. 

Since we did not find adverse effects on zinc balance by the higher fiber diet containing spinach until the fourth week of study 3, balance studies should be carried out for longer periods of time to determine if negative zinc balances persist. Perhaps in the earlier studies on effects of spinach on calcium balance of human subjects, more definitive effects would have been noted if the spinach had been fed along with a higher fiber diet. Length of study period is also a likely factor, as some of the studies were carried out for less than 2 weeks. 

Besides the effect of dietary calcium level, the amount of iron, and perhaps the level of other metals, may affect zinc bioavailability. Solomons and Jacob (13) have shown in human subjects that increasing the iron/zinc ratio from 0 1 to 3 1 in solutions containing 25 mg of zinc and corresponding amounts of iron as ferrous sulfate produced a progressive decrease in the plasma zinc response. They further reported that the chemical form of iron was an important determinant of the interaction. Solomons (14) extensively reviewed both inhibitory factors and enhancers of zinc bioavailability found in foods. 

Several zinc absorption studies, using oral doses of ZnCl2 were carried out. 65zq plasma levels were determined serially on the day of the oral administration of the zn tracer. Urinary and fecal 65zn excretions were determined for approximately 15 days. The subjects studied were fully ambulatory males who were In good nutritional state. They were normal according to all clinical and laboratory criteria. Including the serum levels of zinc, calcium, and phosphorus. The effect of three Intake levels of calcium on the zinc balance was studied, namely, of 200, 900,... 

The nutrient balance technique, whether used for measuring N balance, calcium balance, or balance of other nutrients, is not particularly accurate. Inaccuracies are introduced with feeding. It may not always be possible to measure exactly how much food is consumed by the animal or human subject. Inaccuracies are introduced in collecting the excreta, especially as collections must be made over the course of many days. An important source of error is the fact that the value for N balance is determined by subtraction, that is, subtracting the amount excreted from that consumed. The values for balance, whether positive or negative, are often small compared to the values for the amount of nutrient consumed. 

For current densities at or above 0.2mA/cm, the sensation associated with transdermal iontophoresis is determined by the type of ion being delivered into the skin. When human subjects compared the sensation experienced during iontophoresis of different salt solutions applied to the right and left forearms, delivery of calcium caused less sensation than delivery of phosphate, magnesium, and zinc, which caused less sensation than delivery of chloride, acetate, citrate, and sulfate, which in turn caused less sensation than delivery of lithium, potassium, and sodium. In general, multivalent ions were found to cause less sensation than monovalent ions. ... 

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