Measurement of calcium

Wachi and Jones (1991b) used a gas-liquid flat interface reactor as a semi-batch precipitation cell for the experimental measurement of calcium carbonate precipitation, as shown in Figure 8.15. 

Practical problems with hemi-equilibria can be avoided by allowing sufficient time for equilibrium to occur. However, there are some situations where this may not be possible. One is where the functional system desensitizes during the span of time required for equilibrium to be attained. Another is where the actual type of response being measured is transitory and where the only measurement of calcium transients where a spike of effect is the only response observed in the experimental system. 

Rizzuto, R., et al. (1995). Photoprotein-mediated measurement of calcium ion concentration in mitochondria of living cells. Method. Enzymol. 260 417-428. 

Shimomura, O., Musicki, B., and Kishi, Y. (1988). Semi-synthetic aequorin an improved tool for the measurement of calcium ion concentration. Biochem. J. 251 405 410. 

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... 

In 1964, Netrawali et al.66 described fluorescence measurements of calcium leucovorin in NaHC03 solution after paper chromatography and reaction with acidic orcinol. The gray-blue fluorescent species formed on the developed paper-gram was very sensitive for leucovorin, showing a detection limit of 0.1 yg. In the eluting solution, however, the required concentration increased to 0.5 pg. Recovery by this method was 100 15%, and results obtained from fluorescence were lower by 10 to 20% than those obtained by microbiological methods. 

In the studies on humans there appeared to be decreased calcium balances when 200 g or more of spinach per day was included in the diet. In two of the studies in which women were fed spinach, calcium intakes were below the Recommended Dietary Allowance of 800 mg/day (37). Some studies were conducted for short period of a week or less, which may not be sufficient time to adjust to a change in diet. From measurement of calcium excretion in urine after a test meal, it was shown that the calcium in oxalate-containing vegetables was less well-absorbed than that of milk or of vegetables not containing oxalic acid. However, this would not necessarily affect calcium balance, since the total amount of calcium in the diet would have to be considered. The effect of a combination of oxalic acid and fiber on calcium bioavailability should be further investigated. 

Most of the forementioned studies which examined the influence of various dietary fiber on the bioavailability of calcium by human subjects have depended upon the comparative measurements of calcium content of diets and calcium contents of stools and urine. As reviewed by Allen (3), calcium balance studies have distinct limitations relative to accuracy and precision. However, their ease of application and cost, laboratory equipment requirements, and real (or perceived) safety in comparison to available radioactive or stable isotope methods continue to make their use popular. In calcium balance studies, calcium absorption is assumed to be the difference between calcium excretion in the feces and calcium intake. Usually this is expressed as a percent of the calcium intake. This method assumes that all fecal calcium loss is unabsorbed dietary calcium which is, of course, untrue since appreciable amounts of calcium from the body are lost via the intestinal route through the biliary tract. Hence, calcium absorption by this method may underestimate absorption of dietary calcium but is useful for comparative purposes. It has been estimated that bile salts may contribute about 100 g calcium/day to the intestinal calcium contents. Bile salt calcium has been found to be more efficiently absorbed through the intestinal mucosa than is dietary calcium (20) but less so by other investigators (21). 

Gussone N, Eisenhauer A, Heuser A, Dietzel M, Bock B, Bohm E, Spero H, Lea D, Buma J, Nagler, TF (2003) Model for kinetic effects on calcium isotope fractionation (6 Ca) in inorganic aragonite and cultured planktonic foraminifera. Geochim Cosmochim Acta 67 1375-1382 Halicz L, Galy A, Belshaw NS, O Nions RK (1999) High precision measurement of calcium isotopes in carbonates and related materials by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). J Anal Atom Spectr 14 1835-1838... 

Mumallah, N.A.A. and Popiel, W.J. Calcium-selective electrode measurements of calcium molybdate solubilities in water, Anal Chem., 46(13) 2055-2056, 1974. 

Procedure (determination). Magnesium is determined by atomic absorption spectrophotometry (see Method 5.2, Measurement of calcium and magnesium by AAS ). 

Elemental composition Ca 95.41% H 4.79%. A measured amount of the solid is carefully treated with water and the volume of evolved hydrogen is measured using a manometer (Ig liberates 1.16 L H2 at NTP). The solution is then acidified with nitric acid and diluted for the measurement of calcium by AA or ICP spectrophotometry, or by a wet method (see Calcium). The hberat-ed hydrogen gas may be analyzed by GC using a TCD. Many packed and capillary GC columns are commercially available. 

Kramer, R. and Lagoni, H. 1969. Calcium selective electrode for the measurement of calcium ion activity in milk and milk products. Milchwissenschaft 24, 68-70 (German). 

Smith, J., Coronado, R., and Meissner, G. (1986). Single Channel Measurements of Calcium Release Channel from Skeletal Muscle Sarcoplasmic Reticulum. J. Gen. Physiol. 88 573-588. 

Various studies have evidenced strict structure-activity relationships within capsaicinoids, and the existence of these relationships provided a hint for the existence of a specific receptor [72]. On the other hand, different end-points have been used in the literature, and it is difficult to draw a consistent picture. In vivo assays such as pungency and ocular irritancy, functional assays such as the measurement of calcium currents in dorsal root ganglion neurons, and receptor assays such as the displacement of labeled RTX have been used. The relationship between the results of these assays is, at best, approximate [75]. 

Recent measurements of calcium and alkalinity in the ocean above the calcite saturation horizon (Milliman et ai, 1999 Chen, 2002) suggest dissolution in supersaturated waters. The proposed mechanisms are variations of the organic matter driven CaC03 dissolution mechanism. In these cases the authors suggest that microenvironments in falling particulate material (Milliman et al., 1999) or anerobic dissolution in sediments of the continental shelves and marginal seas (Chen, 2002) are locations of CaC03 dissolution. As the details and accuracy of measurements improve, thermodynamic and kinetic mechanisms required to interpret the results become more and more complex. 

Berelson W. M., Hammond D., and Cutter G. A. (1990) In situ measurements of calcium carbonate dissolution rates in deep-sea sediments. Geochim. Cosmochim. Acta 54, 3013-3020. 

The measurement of calcium absorption is of interest to those studying the availability of the calcium in various foods or supplements. The quantity and availability of food calcium are concerns in the prevention of osteoporosis. Calcium absorption is also of interest to those studying the interactions between different components of food and their influence on calcium absorption. Measurement of either fecal or urinary Ca can indicate the extent of absorption, but some fine-tuning is needed to yield an accurate picture, as described in what follows. The radioactive calcium can be supplied as calcium-45 or calcium-47. Where tire absorption of food Ca is of interest, ttie study can be run most accurately by using food containing naturally labeled calcium, that is, foods grown or animals raised in the presence of radioactive calcium. A less accurate picture can be attained by mixing radioactive calcium with the food, that is, with the plant or animal product. 

Primary hyperparathyroidism is diagnosed by laboratory studies. Hypercalcemia should be documented by measuring total calcium and serum albumin, or ideally free calcium, on more than one occasion before initiating further testing. Measurement of intact PTH (with concomitant measurement of calcium) is the most sensitive and specific test for parathyroid function and is central to the differential diagnosis of hypercalcemia. Serum l,25(OH)2D is usually in the upper half of the reference interval or increased in primary hyperparathyroidism, as PTH stimulates its production. By contrast, l,25(OH)2D (lilte PTH) is. low-normal or suppressed in nonparathyroid hypercalcemia, except in sarcoidosis, other granulomatous diseases, and certain... 

ISEs for the measurement of total calcium were introduced more recently than photometric methods. The specimen is acidified to convert protein-bound and complexed calcium to free calcium before measurement of calcium by ISE. Calcium ISEs are discussed later in this chapter. 

A common and important source of preanalytical error in the measurement of calcium is the increase in total, but not free, calcium concentration associated with tourniquet use and venous occlusion during sampling. Errors of 0.5 to 1.0 mg/dL (0.12 to 0.25 mmol/L) in total calcium may result because of the increase in protein-bound calcium caused by the efflux of water from the vascular compartment during stasis. Only small and clinically insignificant increases in free calcium have been reported with venous stasis. If a tourniquet is required, it should be applied just before sampling and released as soon as possible. 

Leary NO, Pembroke A, Duggan PF. Single stable reagent (Arsenazo III) for optically robust measurement of calcium in serum and plasma. Clin Chem 1992 38 904-8. 

Detection and Measurement of Calcium-Lowering Hormones 5.1. Bioassay Pboceduees... 

Moulin, P. and Roques, H., Zeta potential measurement of calcium carbonate, 7. Colloid Interf. Sci., 261, 115, 2003. 

Shimomura O, Musicki B, BCishi Y. Semi-synthetic aequorin an improved tool for the measurement of calcium ion concentration. Biochem. J. 1988 251, 405-410 Shimomura O, Musicki B, Kishi Y. Semi-synthetic aequorins with improved sensitivity to Ca " ions. Biochem. J. 1989 261 913-20 Shimomura O, Musicki B, Kishi Y, Inouye S. Light-emitting properties of recombinant semi-synthetic... 

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