An enzymatic method for determining magnesium

Abstract

Magnesium deficiency in the human body (hypomagnesemia) is a phenomenon typical of almost all countries of the present-day world, including the industrialized countries. Hypomagnesemia is most often due to low dietary magnesium; however, stress, high levels of physical activity, hypodynamia, alcohol abuse, hormonal contraception, etc., may also be responsible for the development of magnesium deficiency [1]. To diagnose the states of magnesium deficiency, the concentration of magnesium in human blood plasma and cells is usually determined by atomic emission spectrometry (AES) with flame ionization [2], inductively coupled plasma AES [3], atomic absorption spectrometry (AAS) with flame [4] or electrothermal [5] atomization, and spectrophotometry with the use of organic reagents (Magon is most frequently used) [6].Recent medical studies have demonstrated that the possibility of magnesium deficiency cannot also be excluded at a normal concentration (16-30 µ g/mL) in blood plasma and cells [7][8][9]. The diagnosis of magnesium depletion (particularly in diabetic patients or postoperative heart patients) can be reliably performed only with the use of a magnesium loading test, i.e., by administering magnesium-containing drugs to patients [8,9]. Substitution therapy is primarily empirical in the cases of latent magnesium deficiency or the impossibility of determining the total magnesium content of the human body.Thus, the analysis of a single biosubstrate (blood) is insufficient for the correct evaluation of the magnesium content of the human body and for the correction of its deficiency with the use of an appropriate magnesiumcontaining drug. The determination of magnesium in daily urine gives additional information on the level of patient's health and provides an opportunity to develop an appropriate course of treatment. The normal magnesium content of urine from adult humans is 100-300 mg/day [10,11]. Under the conditions of magnesium deficiency, the daily excretion of magnesium can be lower than 25 mg/day (0.5 mmol/day).In clinical laboratories, urine magnesium is determined by chelatometric titration [11], AAS with flame and electrothermal atomization [12,13], and spectrophotometry with the use of Xylidyl Blue [14,15] or Magon [8]. Currently available procedures for the determination of magnesium in urine are accurate and inexpensive but insufficiently sensitive (chelatometry), simple but insufficiently accurate (spectrophotometry), or require the use of expensive instrumentation and the removal of spectral interferences (AAS). Moreover, procedures for the simple and reliable determination of magnesium in urine at a low concentration level (ng/mL) were not described in the literature. Consequently, the development of highly sensitive and selective (in particular, enzymatic) procedures for the determination of magnesium is of particular current interest for the accurate evaluation of the magnesium content of biological systems and the subsequent therapy. The use of enzymes of different origins, such as alkaline phosp...

Enzymatic methods of analysis: Novel approaches and applications

“…39 The activating effect of Mg II on the alkaline phos phatase from chicken intestine underlies the selective en zymatic procedure for its determination in the concentra tion range of 0.6-6 ng mL -1 (s r = 0.04 for the concentra tion с l ).…”