Free Ionized Magnesium

Magnesium is taken up into cells until the normal intracellular ionized magnesium concentration is achieved. Intracellular magnesium losses occur, when bound magnesium is released (ATP breakdown, acidosis) leading to an increased intracellular free magnesium concentration, which is normalized... 

The method was designed for the determination of ionized (free) magnesium (iMg2"1") together with other major electrolytes (Na+, K+, Cl and Ca2+) and pH in blood serum, plasma or whole blood in the environment of the commercially available Microlyte 6 analyzer supplied by Thermo Fisher Scientific, Finland (previously KONE Instruments, Finland) [1-3]. 

O. Dolgounitcheva et al., Ab initio electron propagator calculations on the ionization energies of free base porphyrin, magnesium porphyrin and zinc porphyrin. J. Phys. Chem. 109, 11596-11601 (2005)... 

The usefulness of soaps is limited by their tendency to precipitate out of solution in hard water. Hard water is water that is acidic or that contains ions of calcium, magnesium, or iron. In acidic water (such as the acid rain of environmental concern), soap molecules are protonated to the free fatty acids. Without the ionized carboxylate group, the fatty acid floats to the top as a greasy acid scum precipitate. 

Only chemical interferences were observed sodium and potassium ionized in the air-acetylene flame, and aluminum ionized in the nitrous oxide-acetylene flame magnesium and calcium exhibited evidence of interference by both phosphorus and aluminum. All the other elements were found to be interference-free. The addition of 1000 ppm of cesium as an ionization suppressor effectively removed the ionization interference in the sodium and potassium solutions. Similarly, 1000 ppm of lanthanum removed the interference due to phosphorus and aluminum in the magnesium and calcium solutions and suppressed the ionization of aluminum. 

Fig. 4.9 Energies of free cations and of ionic compounds as a function of the oxidation state of the cation. Top Lines represent the ionization energy necessary to form the +1. +2, +3, and + 4 cations of sodium, magnesium, and aluminum. Note that although the ionization energy increases most sharply when a noble gas configuration is broken, isolated cations are always less stable in Itiifher oxidation states. Bottom Lines represent the sum of ionization energy and ionic bonding energy for hypothetical molecules MX, MXj, MXj, and MX in which the interatomic distance, r, has been arbitrarily set at 200 pm. Note that the most stable compounds (identified by arrows) arc NaX, MgXj, and AlXj. (All of the.se molecules will be stabilized additionally to a small extent by the electron affinity of X.)...

Plasma contains 1.6-2.3 mg/dL (0.7-1.0 mmol/L) of magnesium, 20-25% of which is protein bound. As with Ca +, the unbound (ionized) portion of plasma magnesium is the biologically active fraction. Intracellular Mg + concentration is about 10 mmol/L, mostly bound to organelles. The intracellular concentration of free Mg " " is 0.025-0.5 mmol/L. 

Ionized calcium and total calcium measurements are both performed with PVC-type electrodes. Membranes based on lipophilic alkyl phosphates with phosphonate plasticizers have only marginal selectivity over magnesium but have been used in the past to determine ionized calcium (i.e., free calcium) in undiluted blood samples (M8). Interference from protons at low pHs prevents such membranes from being employed for total calcium determinations on samples diluted with acid. Use of ionophore ETH 1001 (see Fig. 2) overcomes any concerns about selectivity, whether from magnesium or pH, and is now the neutral carrier system most often utilized within analyzers to detect ionized or total calcium. 

Eriochrome Black T is a typical indicator. It contains three ionizable protons, so we will represent it by Hsin. This indicator can be used for the titration of Mg + with EDTA. A small amount of indicator is added to the sample solution, and it forms a red complex with pait. pf the Mg " the color of the uncomplexed indicator is blue. As soon as all the free Mg. is titrated, the EDTA displaces the iudicator from the magnesium, causing a change in the color from red to blue ... 

Magnesium concentration can be determined in physiological samples such as serum and urine by FAAS, FAES, and UV-visible spectrophotometry. Urine must be acidified (pH 1.0) by hydrochloric acid to release magnesium from salts of the sediment. Recently, potentiometry has become available for the measurement of ionized (free) magnesium in serum and blood. 

Potentiometry ISEs for the determination of ionized (free) magnesium are now available. They use membranes with neutral ion carriers (e.g., modified ETH 5220), which, however, lack specificity with respect to calciiun. Therefore, magnesium and calcium must be measured simultaneously in the same analytical portion (with different electrodes) and magnesium concentration is calculated from this. 

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