Ionized magnesium

The configurations of these elements show that a 3 5 electron is removed to ionize magnesium, whereas a 3 electron is removed to ionize aluminum or silicon. Screening makes the 3 S orbital significantly more stable than a 3 p orbital, and this difference in stability more than offsets the increase in nuclear charge in going from magnesium to aluminum. 

E. Murphy, Measurement of intracellular ionized magnesium, Miner. Electrolyte Metab. 19 (1993) 250-258. 

The development of a sensor for ionized magnesium turned out to be one of the most difficult challenges of recent years. Several carriers have been designed for this purpose but none have been satisfactory. The first report of a successful measurement of ionized magnesium in an automated clinical analyzer (Thermo, prev. KONE) was published only in 1990 [30]. The ionophore ETH 5520 was used as the active compound. Two other carriers have been used since then ETH 7025 (Roche, former AVL), and a derivative of 1,10-phenenthroline (Nova). All of the magnesium sensors are based on a plastic membrane. Numerical compensations of the influence of calcium ion and the ionic strength are used due to insufficient selectivity of the magnesium sensors. 

A growing interest in ionized magnesium measurements indicates that further improvements in the analytical properties of the Mg-ISSs, regarding the selectivity as well as the response time and lifetime, are needed, to facilitate wider clinical application of this method [31]. 

A procedure (Procedure 1) related to the measurement of ionized magnesium in human blood is given in the second part of this book. 

To characterize the analytical performance of the measurement system developed for the determination of ionized magnesium in human blood by the magnesium ion-selective electrode (Mg-ISE). 

Fig. 1.1. Microlyte 6/Microlyte Mg (by KONE/Thermo Fisher Scientific, Finland). The first electrolyte analyzer able to measure ionized magnesium, introduced commercially in 1992.

Special software was introduced into EEPROM of the Microlyte 6, thus it is called Microlyte Mg, to compensate for calcium interference, the influence of ionic strength and to compensate for liquid junction potential changes, known to influence the quantitative reports on ionized magnesium [3]. 

Using 150 pL of sample, a complete report containing the concentration of ionized magnesium, ionized calcium, sodium, potassium, chloride, pH and recalculated to pH — 7.40, the so-called pH-cor-rected ionized magnesium and calcium concentration can be obtained after a total measurement time of less than 2 min. The lifetime of the Mg-ISE is 2000 blood samples [4]. 

In our experiments, in the former matrices (Cal 1) the changes of reported ionized magnesium values were smaller than 1%, in the latter (Quality) a change from 0.43 to 0.47 (at +0.75mmol/L CaCl2) was observed. 

Measure ionized magnesium using selected controls on three instruments. Calculate standard deviation. Report the results as a mean value of four measurements and the results of our measurements are given in Table 1.3. 

With a linear range from 0.2 to 3.0mmol/L and within-run imprecision of better than 2% (at normal level), we conclude that the range of ionized magnesium concentrations encountered in serum or whole blood can be accurately and reliably measured. 

There is no simple algorithm that allows recalculating ionized magnesium into total magnesium, and vice versa. Ionized magnesium may be compared with results by other analytical methods, e.g. measurement by atomic absorption spectroscopy after ultrafiltration, only by employing the relevant recommendations [7]. 

The protocol presented reflects a real study that resulted in the introduction of the first commercial clinical analyzer measuring ionized magnesium in blood, i.e. Microlyte Mg [1-3]. 

Vannini SD, Mazzola BL, Rodoni L, Truttmann AC, Wermuth B, Bianchetti MG, Ferrari P. Permanently reduced plasma ionized magnesium among renal transplant recipients on cyclosporine. Transpl Int 1999 12(4) 244-9. 

Altura BT, DelFOrfano K, Yeh Q. A new ion selective electrode for ionized magnesium in whole blood, plasma and serum. Chn Chem 1991 37 948 (abstract). 

Cao Z, Tongate C, EHn RJ. Evaluation of AVL988/4 analyzer for measurement of ionized magnesium and ionized calcium. Scand J Clin Lab Invest 2001 61 389-94. 

Cecco SA, Hristova EN, Rehak NN, El in RJ. Clinically important intermethod differences for physiologically abnormal ionized magnesium results. Am J Clin Pathol 1997 108 564-9. 

Hristova EN, Cecco S, Niemeia JE, Rehak NN, Rlin RJ. Analyzer-dependent differences in results for ionized calcium, ionized magnesium, sodium and pH. Clin Chem 1995 41 1649-53. 

Huijgen HJ, Sanders R, Cecco SA, Rehak NN, Sanders GT, Elin RJ. Serum ionized magnesium comparison of results obtained with three instruments. Clin Chem Lab Med 1999 37 465-70. 

Marsoner HJ, Spichiger UE, Ritter C, Sachs C, Ghahramani M, Offenbacher H, et al. Measurement of ionized magnesium with neutral carrier ISE s progress and results with the AVL 988-4 magnesium analyzer. Scand J Clin Lab Invest 1994 54(Suppl. 217) 45-51. 

Ritter C, Ghahramani M, Marsoner HJ. More on the measurement of ionized magnesium in whole blood. Scand J Clin Lab Invest 1996 56(Suppl 224) 275-80. 

Sachs CH, Ritter CH, Puaud AC, Ghahramani M, Kindermans C, Marsoner H. Measurements of ionized magnesium in blood. Clin Chem 1991 37 945. 

Sanders GT, Huijgen HJ, Sanders R. Magnesium in disease a review with special emphasis on the serum ionized magnesium. Cfin Chem Lab Med 1999 37 1011-33. 

Shirey TL. Importance and interpretation of ionized magnesium (iMg) activity in acutely and chronically fil patients. Nova Biomedical, Waltham, Mass, 2001. 

Van Ingen HE, Huijgen HJ, Kok WT, Sanders TB. Analytical evaluation of Kone Microlyte determination of ionized magnesium. Clin Chem 1994 40 52-5. 

Wu C, Kenny M. Circulating total and ionized magnesium after ethanol ingestion. Clin Chem 1996 42 625-9. 

Muney virci-Delale O, Nacharaju VL, Altura BM, et al. Sex steroid hormones modulate serum ionized magnesium and calcium levels throughout the menstrual cycle in women. Eertil Steril 1998 69 958-962. 

Effective reaction rate constants for decomposition are given in Table 12.2. The temperature dependence corresponds to an activation energy of 16.7 kcal/mol. which must be an average for ihc various RMg X species present in the solution. This value is close to the dissoca-tion energy (23.4 kcal/mol) [20] calculated for a Mg—Mg bond in a singly 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... 

Rayana, M. C. et al. 2008. IFCC guideline for sampling, measuring and reporting ionized magnesium in plasma. Clinical Chemistry and Laboratory Medicine 46 21-26. 

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