Calcium atomic absorption determination

Spencer and Sachs [29] determined particulate aluminium in seawater by atomic absorption spectrometry. The suspended matter was collected from seawater (at least 2 litres) on a 0.45 tm membrane filter, the filter was ashed, and the residue was heated to fumes with 2 ml concentrated hydrofluoric acid and one drop of concentrated sulfuric acid. This residue was dissolved in 2 ml 2 M hydrochloric acid and the solution was diluted to give an aluminium concentration in the range 5-50 pg/1. Atomic absorption determination was carried out with a nitrous oxide acetylene flame. The effects of calcium, iron, sodium, and sulfate alone and in combination on the aluminium absorption were studied. 

Schall192) recommended that the atomic absorption determination of magnesium, calcium, manganese, iron, and copper in fertilizers should be adopted as official, first action. 

Quigley, M. N. Determination of Calcium in Analgesic Tablets Using Atomic Absorption Spectrophotometry, ... 

Most potentiometric electrodes are selective for only the free, uncomplexed analyte and do not respond to complexed forms of the analyte. Solution conditions, therefore, must be carefully controlled if the purpose of the analysis is to determine the analyte s total concentration. On the other hand, this selectivity provides a significant advantage over other quantitative methods of analysis when it is necessary to determine the concentration of free ions. For example, calcium is present in urine both as free Ca + ions and as protein-bound Ca + ions. If a urine sample is analyzed by atomic absorption spectroscopy, the signal is proportional to the total concentration of Ca +, since both free and bound calcium are atomized. Analysis with a Ca + ISE, however, gives a signal that is a function of only free Ca + ions since the protein-bound ions cannot interact with the electrode s membrane. 

It must be pointed out that the atomic absorption system as used today, cannot accurately determine the calcium level of a solution. The reason for this is that results will vary depending upon the other elements present and the composition of the solution. Since it is impossible to duplicate every feature of the particular serum being analyzed, results have to be compared to standards which have been made up in serum dialysates. Such standards are available in the form of the Versatols where the calcium has been dialyzed out and then weighed back. This is distinct from substances such as Validate, which are used as controls and which values are re-sults of analysis. The variability of serum composition has significantly widened what is now considered the "normal range" for serum Ca assay when done by atomic absorption (37a). 

We have found that the use of serum standards for standardizing the instrument in the laboratory is useful. However, the serum standards cannot be used for urines. In urines, one runs into other problems and needs to use aqueous standards. Therefore, at present, while atomic absorption is the instrument of choice, there is much to be desired for the determination of calcium and magnesium in the routine laboratory of clinical chemistry. 

In patients on EDTA therapy, calcium cannot be determined by the Indirect colorimetric or fluorometrlc methods based on the chelation of a calcium - EDTA complex. However, In calcium determinations by atomic-absorption spectroscopy, the complexlng agent Is destroyed In the flame and the direct concentration of calcium can be determined. 

Calcium exists in the human body as Ca(II) protein-bound and free Ca (II) ions (Dilana et al. 1994). For total extracellular Ca in plasma, serum and urine a definitive isotope dilution-mass spectrometry (ID-MS) method exist. Free Ca(II) in plasma/serum can be determined with PISE, but no definitive and reference methods exist. For Ca in faeces, tissue and blood flame atomic absorption (FAAS) is used widely. 

Siong, T. E., Choo, K. W., and Shahid, S. M. (1989a). Determination of calcium in foods by the atomic absorption spectrophotometric and titrimetric method. Pertanika 12, 303-311. 

Atomic absorption spectrophotometry [165,166] has been used in the determination of calcium and magnesium in seawater. 

Several recent determinations of the alkali and alkaline earth metals in serum or urine have been reported. Barrett 29) determined potassium, sodium, and calcium in semm by diluting the samples with lanthanum chloride solution. Suttle and Field 3°) used atomic absorption spectroscopy to determine potassium and magnesium in sheep plasma. 

Jones and Isaac 16 ) compared atomic absorption spectroscopy and spark emission spectroscopy for the determination of several elements in plant tissue. By comparing results statistically using a t-test, no significant differences were found for calcium, manganese, iron, copper, zinc, and aluminium, but significant differences were found for potassium and magnesium at the 0.01 % level. Breck162) made a similar comparison study for 15 elements. 

Air-dry soil is mixed with 0.02 M calcium chloride solution (1 2 ratio, for instance, 10-g soil 20 mL 0.02 M CaCl2 solution) and mixed for 1 hour. The pH of the suspension can be measured directly. In addition, the solution can be filtered for the determination of aluminum or magnesium by atomic absorption spectroscopy (AAS) or inductively coupled plasma (ICP) spectroscopy (adapted from Reference 5). 

Phytate analysis of muffins, diet composites and stools was performed by a modification of the ferric ion precipitation method for HS-I (5) and by an ion exchange method for HS-II and -III (6). Calcium was determined by atomic absorption spectrophotometry. 

The present communication is concerned with calcium balance studies carried out during the Intake of a variety of dietary factors including minerals and protein as well as drugs. The studies were performed In adult males under strictly controlled conditions in the Metabolic Research Unit. The diet was kept constant throughout the relatively long term studies and complete collections of urine and stool were obtained. The composition of this diet was previously described (5). The diet and the excretions in urine and stool were analyzed for calcium throughout the studies. These data formed the basis of calcium balances which were determined for several weeks. Calcium was analyzed by atomic absorption spectroscopy (6). 

The atomic absorption characteristics of technetium have been investigated with a technetium hollow-cathode lamp as a spectral line source. The sensitivity for technetium in aqueous solution is 3.0 /ig/ml in a fuel-rich acetylene-air flame for the unresolved 2614.23-2615.87 A doublet under the optimum operating conditions. Only calcium, strontium, and barium cause severe technetium absorption suppression. Cationic interferences are eliminated by adding aluminum to the test solutions. The atomic absorption spectroscopy can be applied to the determination of technetium in uranium and its alloys and also successfully to the analysis of multicomponent samples. 

The concentration of calcium ions in solution can be determined using an atomic absorption spectrophotometer operating at a wavelength of 422-7 nm. The absorbance was measured for a range of known concentrations of calcium ions and the following calibration graph was drawn. 

Determination of calcium. The calcium content of the solutions was determined by atomic absorption spectrometry. To 100-pl samples, 3 ml of 1.56% La(N03)2 in 50 mM HCl was added. The atomic absorption was measured on a Perkin Elmer 372 atomic absorption spectrophotometer at 423 nm. 

The presence of calcium in horseradish peroxidase was demonstrated originally by Haschke and Friedhoff, working with the C and A (imspec-ified, but likely to have been predominantly A2) isoenzymes (209). HRP C and HRP A contain 2.0 0.13 and 1.4 0.19 moles calcium per mole enzyme, respectively, as determined by atomic absorption spectroscopy. Incubation in 6 M guanidinium hydrochloride and 10 mM EDTA for 4 hours at neutral pH and room temperature gave calcium-depleted enzymes with specific activities decreased by 40% and 15%, respectively. The thermal stability of calcium-depleted HRP C was also reduced compared to native enzyme. Reconstitution was successful only with calcium-depleted HRP C (209). It remains to be established whether this reflects true structural differences between the calcium binding sites of the two isoenz5unes, or is a consequence of the relatively harsh... 

WA water quality labs by atomic absorption and autoanalyzer techniques. Charge balance calculations Indicated that all dissolved species of significance were analyzed. Comparison of filtered and unflltered aliquots suggested that un-lonlzed species were not present In appreciable quantities. Sampling and analysis uncertainties were determined by the operation of two co-located samplers for 16 weeks. The calcium and sulfate data were corrected for the Influence of sea salt to aid In the separation of the factors. This correction was calculated from bulk sea water composition and the chloride concentration In rainwater (11). Non seasalt sulfate and calcium are termed "excess" and flagged by a ... 

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

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