REV . CHIM. (Bucureº ti) ♦ 59 ♦ Nr. 9 ♦ 2008 947 Potassium is the principal intercellular anion (98% of the potassium is intercellular and only 2% is intracellular), in the adult body is an average of 150 g potassium [2]. The potassium has many metabolic roles. Together with the sodium the hydro balance of the body is maintained. While the sodium favoring the retention of the water in the body the potassium is favoring the renal removal of the sodium [3]. The potassium has a role in the proteins and lipids metabolism, in harmonic synthesis has a role in the hepatic and muscular synthesis of the glycogen from the glucose, as well as in the muscular fiber synthesis. Potassium is necessary for the transmission of the excitation to the nerve endings of the effectors organs adjusting the neuron- muscular activity. At the same time the potassium is adjusting the cardiac rhythm. At the cardiac muscle level it has an antagonistic action in relation with the calcium; the potassium ions are accelerating the cardiac rhythm and the calcium ions are decelerating it. When it is in excess it can determine muscular paralysis, modification of respiratory and cardiac rhythm until the heart is stopping in the systole [4]. Calcium is the mineral element found in the biggest quantity in the human body (a kilo – a kilo and a half). Almost the whole calcium quantity from the body is fixed in the bones and teeth and the rest is distributed in the tissues and in the biological liquids. Reported to 100 g of tissue in the muscles are 70 g of calcium, in the nerves 15 g, in the cephalorachidian liquid 4, 5 g, and in the plasma between 9 and 10 mg of calcium [5]. The concentration of calcium in the blood is maintained between 9-11 %. The calcium has an important role in transmitting nervous impulses, being a tonic of the nervous system and strengthening the functional balance of it. In this way the muscular contraction is dependent on the presence of calcium, because the phenomenon which couples the nervous impulse to the actual muscular contraction is made only by the calcium ions. Together with the magnesium it is responsible for the health of the cardiovascular system. The calcium ions are stimulating the enzymatic equipment of the body. There are clinical situations, for example during cardiac surgery and intensive care, where knowledge of blood pH and K concentration ( pK + ) could warn the clinician of Multisensor for Clinical Analysis with Impact on Public Health Evaluation EUGENIA EFTIMIE TOTU 1 *, DANIELA MANUC 2 1 University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, Department of Analytical and Instrumental Analysis, 1-7 Polizu Str., 011061, Bucharest, Romania 2 University of Medicine and Pharmacy Carol Davila,Department of Public Health, 4 Eforie Str., 050037, Bucharest, Romania The objective of this paper was to study the suitability of multi gate ion sensitive field effect transistors (ISFETs) for clinical work with specific requirements in the public health evaluation. The obtained sensors were used in a flow cell assembly provided by Bellhouse Medical Products. As in our previous work [1], the sensors were intended for use in the analysis of biological fluids, where the concentrations of specific ions as sodium, potassium and calcium are of critical importance. The electrochemical characteristics for use in clinical chemistry were established. Keywords: public health evaluation, multi gate ISFET, ion selective membrane, ions of biological interest * email: eugenia_totu@yahoo.com impeding problems. Blood pH is an useful indicator of respiratory efficiency, and pK + levels could both change very rapidly, but presently known methods chemical analysis are not capable of monitoring these vital parameters continuously. The extracellular potassium concentration level (which could vary rapidly) affects both heart rate and contractility, and can be critical in some cases. Knowledge of the activities of other ions, such as calcium and bicarbonate, is also useful in the clinical assessment of patients, and knowledge of the simultaneous activities of a plurality of ions would be especially valuable as their concerted physiological action and interaction may permit more accurate diagnosis. In order to provide the clinician with this information, a number of novel microelectronic chemical sensors have been successfully developed for the measurement of pH, pK + , pCa 2+ , pNa + , pO 2 , and which are readily modified for the detection and measurement of other ionic species and chemical substances [6]. Lately it was possible to develop four-channel ChemFET devices, which could be successfully used for the on-line analysis of ions of biological interest in human blood [7]. A multiple function chemical transducer for this application would allow more precise computation of ionic activities because compensation could be made for imperfections in the selectivity of individual sensors by processing data from the transducers array in parallel. The measurement of ionic species in blood has traditionally been achieved by flame photometry, but the information provided by this technique relates to the total species concentration, and not the ionic activity. The latter is more appropriate for clinical diagnosis as the activity of a species is an index of its availability to participate in a chemical reaction, whereas the total concentration may not be related simply to ionic activity [1]. For example, plasma proteins bind significant amounts of electrolytes, particularly Ca 2+ which has a normal fasting venous plasma level of 2.4 mmol.L -1 , of which 1.2 mmol.L -1 is complex bound. In this important respect, electrochemical methods of ion analysis are preferable to the use of a flame photometer which gives the total calcium concentration. Furthermore, the flame photometer is large and expensive, and is not suited to use in the operating theatre or at the bedside.