Magnesium in biological fluids

Al. Alcock, N., MacIntyre, I., and Radde, I., The determination of magnesium in biological fluids and tissues by flame spectrophotometry. J. Clin. Pathol. 13, 506-510 (1960). 

When the requirement is for many routine analyses of sodium and potassium, a simple filter fiame photometer burning a low temperature flame should be purchased. Many such models are on the market. On the other hand, if analysis for calcium and magnesium in biological fluids is also required, then only a fairly complex instrument with monochromator, photomultiplier, and high-temperature flame is satisfactory (Fig. 4). Compromise instruments between these two extremes lose the simplicity of the first type without gaining the versatility of the second. 

The determination of sodium and potassium in biological fluids and tissues is so widely practiced that no detailed discussion is necessary. A simple filter instrument with absorption or interference filters is perfectly adequate for most purposes. However, the determination of calcium and magnesium in biological fluids and tissues has proved more difficult and merits further discussion. 

Steinman, G. D. Process for measuring magnesium in biological fluids. US Patent 5397710, 1995 Chem. Abstr. 1995,122, 286071. 

Determination of Magnesium and Calcium in Biological Fluids and Tissues... 

Spec determination of magnesium by titan yellow in biological fluids... 

It may seem curious to make specific mention of this matter, but in a biological context, it is crucial. The nuclei of porphyrins and related systems are hydrophobic it appears to be generally desirable that the photosensitizer has some degree of intermediate polarity (i.e., amphiphilic properties Section 9.22.3) and the incorporation of a metal, such as zinc(II), which can take on an axial ligand (e.g., H20 in aqueous media, or RNH2 in a biological fluid), or magnesium(II), which can take on two, is expected to enhance solubility in hydroxylic solvents, and shift the... 

Clinical chemistry, particularly the determination of the biologically relevant electrolytes in physiological fluids, remains the key area of ISEs application [15], as billions of routine measurements with ISEs are performed each year all over the world [16], The concentration ranges for the most important physiological ions detectable in blood fluids with polymeric ISEs are shown in Table 4.1. Sensors for pH and for ionized calcium, potassium and sodium are approved by the International Federation of Clinical Chemistry (IFCC) and implemented into commercially available clinical analyzers [17], Moreover, magnesium, lithium, and chloride ions are also widely detected by corresponding ISEs in blood liquids, urine, hemodialysis solutions, and elsewhere. Sensors for the determination of physiologically relevant polyions (heparin and protamine), dissolved carbon dioxide, phosphates, and other blood analytes, intensively studied over the years, are on their way to replace less reliable and/or awkward analytical procedures for blood analysis (see below). 

Table 10.3 lists the approximate concentrations of various inorganic nutrients in the biological fluids. In most cases, the data refer to the total concentration of the ion, including free ion and ion complexed with organic compoxmds. The data for intracellular calcium and magnesium refer to the approximate concentration of the free, uncomplexed ions, A vital relationship revealed by the table is that Na levels are high in the plasma, and low in the cells, while K" levels are low in plasma, and high in cells. 

There are various methods that can be used to measure the biological availability of magnesium supplements these can involve in vitro or laboratory studies such as the rate of solubilization in rumen fluid or weak acid solution. This method of study is less time consuming and less costly than pursuing animal studies, although in vivo methods are preferred. 

X-Ray microanalysis can be used to quantitatively determine magnesium in microvolumes of biological fluids. The minimum detection limit is 0.05 mmol/liter for a 0.1 mL sample analyzed... 

Liu, C., Xin, Y., Tian, X. Chu, P. K. (2007) Degradation susceptibility of surgical magnesium alloy in artificial biological fluid containing albumin. J Mater Res, 22, 1806-814. 

Typical biological fluids include blood and blood serum, blood plasma, urine and saliva. Measurement of calcium in serum was the first analysis to which the technique of AAS was applied and is an obvious example of how FAAS is useful for biomedical analysis. Other specimens e.g. dialysis fluids, intestinal contents, total parenteral nutrition solutions, may be analysed on rare occasions. Elements present at a sufficiently high concentration are lithium and gold when used to treat depression and rheumatoid arthritis respectively, and calcium, magnesium, iron, copper and zinc. Sodium and potassium can be determined by FAAS but are more usually measured by flame atomic emission spectroscopy or with ion selective electrodes. Other elements are present in fluids at too low a concentration to be measured by conventional FAAS with pneumatic nebulization. With other fluids, e.g. seminal plasma, cerebrospinal fluid, analysis may just be possible for a very few elements. 

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