Plasma electrolyte determination

N. Etxebarria, R. Antolin, G. Borge, T. Posada and J. C. Raposo, Optimisation of flow-injection-hydride generation inductively coupled plasma spectrometric determination of selenium in electrolytic manganese, Talanta, 65(5), 2005, 1209-1214. 

Plasma consists of water, electrolytes, metabolites, nutrients, proteins, and hormones. The water and electrolyte composition of plasma is practically the same as that of ail extracellular fluids. Laboratory determinations of levels of Na, K+, Ca, CL, HC03, PaC02, and of blood pH are important in the management of many patients. 

Electrolytes and other plasma components with low molecular weights enter the primary urine by ultrafiltration (right). Most of these substances are recovered by energy-depen-dent resorption (see p. 322). The extent of the resorption determines the amount that ultimately reaches the final urine and is excreted. The illustration does not take into account the zoning of transport processes in the kidney (physiology textbooks may be referred to for further details). 

There are numerous substances that are administered intravenously and have a direct effect on biochemical analysis. Obviously, glucose or electrolyte concentrations will be spuriously elevated if the specimen is taken from the same vein into which these substances are being administered. The presence of sulfobromophthalein dye (BSP) in serum or plasma will interfere with protein determined by the biuret method. The... 

Instruments are offered in the market for clinical determination of electrolytes in blood, plasma or serum. One of them, for example, carries out simultaneous determinations of Na, K, Ca, Mg, hematocrit and pH. The cations are of the free type (see Section m.A) and are measured with specific ion-selective electrodes. In complex matrices such as blood or its derived fractions the concentration of free Ca and Mg is affected by the pH of the solution, for example, a slight change of pH will produce or neutralize anionic sites in the proteins, binding or releasing these cations furthermore, the response of the Mg-selective electrode is also affected by the concentration of free Ca(II). The correction... 

The regional poison centers certified by the American Association of Poison Control have reported 55 cases of metformin ingestion by children (128). Unintentional ingestion of 1700 mg of metformin did not pose health risks. In 21 children tested for blood glucose, lactate, or electrolytes, there was no evidence of lactic acidosis. Plasma metformin concentrations were not determined. 

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]. 

J. P. Gramond and F. Guyon, Separation and determination of warfarin enantiomers in human plasma samples by capillary zone electrophoresis using a methylated /3-cyclodextrin-containing electrolyte, J. Chromatogr., 615 36 (1993). 

A. Alimonti, F. Petmcci, C. Dominici, S. Caroli, Determination of Pt in biological samples by inductively coupled plasma atomic emission spectrometry (ICP-AES) with electrothermal vaporization (ETV), J. Trace Elem. Electrolytes Health Dis., 1 (1987), 79D83. 

Animals are placed in appropriately-sized metabolism cages for an appropriate period of time to allow collection of an adequate volume of urine (for large animals only a few hours may be needed for rodents, 12-24 hours might be required). To preserve the quality of the urine specimens, the collection vial must have a small neck (to prevent evaporation of water) and it should be surrounded by wet ice or frozen cold packs to ensure the urine is maintained at 4 °C for the duration of the collection period (Emeigh Hart and Kinter 2005). At the end of the collection period a blood sample is obtained under appropriate anesthesia (note the use of C02 will falsely elevate plasma potassium levels and render the method inaccurate) for determination of electrolyte and creatinine levels. 

Plasma and urine electrolytes and creatinine are determined by standard methods (Durst and Siggard-... 

Most doctors use the plasma concentrations of creatinine, urea and electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease. Protein and amino acid catabolism results in the production of ammonia, which in turn is converted via the urea cycle into urea, which is then excreted via the kidneys. Creatinine is a breakdown product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). Creatinine is mainly filtered by the kidney, though a small amount is actively secreted. There is little to no tubular reabsorption of creatinine. If the filtering of the kidney is deficient, blood levels rise. 

The determination of renal function in anesthetized animals provides specific information on the effects of chemicals on glomerular filtration rate and renal blood flow. In addition, the ability of the kidney to reabsorb or secrete electrolytes may be determined by fractional clearance of Na+, K+, HCO3, Cl, and so on. Fractional clearance involves comparison of electrolyte clearance to the clearance of a substance such as inulin, which is removed from plasma by glomerular filtration. Thus, fractional clearance takes glomerular filtration rate into account, allowing comparisons of electrolyte transport between treated and control animals even if renal hemodynamics have changed. Nephron function may be assessed by free water clearance, representing the ability of the kidney to remove almost all Na+ from urine. 

Renal function is an indication of the physiological state of the kidney glomerular filtration rate (GFR) describes the flow rate of Altered fluid through the kidney, while creatinine clearance rate (Ccr) is the volume of blood plasma that is cleared of creatinine per unit time, and is a useful measure for approximating the GFR. Most clinical tests use the plasma concentrations of the waste substances of creatinine and urea, as well as electrolytes, to determine renal function. The nephron is the functional unit of the kidney (Figure 10.1) it consists of two parts ... 

E2. Ellis, D. J., Hartley, T. F., and Dawson, J. B., The use of electrolytic separation for the determination of copper in plasma by atomic absorption spectroscopy. Proc. Congr. Int. Speclrom. Absorption Fluorescence At., 3rd, Paris, 1971 in press (1972). 

EN86 Boeyckens, A., Schots, J., Vandenplas, H., Senesael, F., Goedhuys, W. and Gorus, F.K. (1992). Ektachem slides for direct potentiometric determination of sodium in plasma Effect of natremia, blood pH, and type of electrolyte reference fluid on concordance with flame photometry and other potentiometric methods. Clin. Chem. 38, 114-118. 

Effects of the test substance on renal parameters should be assessed. For example, urinary volume, specific gravity, osmolality, pH, fluid/electrolyte balance, proteins, cytology, and blood chemistry determinations such as blood urea nitrogen, creatinine, and plasma proteins can be used. 

Serum, heparinized plasma, whole blood, sweat, urine, feces, or gastrointestinal fluids may be assayed for Nah Timed collections of urine, feces, or gastrointestinal fluids are preferred to allow comparison of values with reference intervals and to determine rates of electrolyte loss. Serum, plasma, and urine may be stored at 2 C to 4 C or frozen. Erythrocytes contain only one tenth of the Na" present in plasma, so hemolysis does not cause significant errors in serum or plasma Na values. Lipemic samples should be ultracen-trifuged and the infranatant analyzed unless a direct ISE is used. 

Determination of plasma and urine osmolality can be useful in the assessment of electrolyte and acid-base disorders. Comparison of plasma and urine osmolalities can determine the appropriateness and status of water regulation by the kidneys in settings of severe electrolyte disturbances, as might occur in diabetes insipidus or the syndrome of inappropriate antidiuretic hormone (SIADH) (see Chapters 45 and 50). The major osmotic substances in normal plasma are Ha, Cr, glucose, and urea thus expected plasma osmolality can be calculated from the following empirical equation ... 

The 9mOsmol/kg added to the above equation represents the contribution of other osmoticaUy active substances in plasma, such as K", Ca " ", and proteins, and 1.86 is two times the osmotic coefficient of Na, reflecting the contributions of both Na and CT. The reference interval for plasma osmolality is 275 to 300mOsmol/kg. Comparison of measured osmolality with calculated osmolality can help identify the presence of an osmolal gap, which can be important in determining the presence of exogenous osmotic substances. Comparison of calculated and measured osmolalities can also confirm or rule out suspected pseudohyponatremia caused by the previously discussed electrolyte exclusion effect. 

Alterations of HCOj and CO2 dissolved in plasma are characteristic of acid-base imbalance. Its value has most significance in the context of other electrolyte values and with blood gases and pH values. The full clinical significance of the determination of total CO2 wiU become apparent in the following discussion of acid-base physiology. 

Abnormalities of acid-base status of the blood are always accompanied by characteristic changes in electrolyte concentrations in the plasma, especially in metabolic acid-base disorders. Hydrogen ions cannot accumulate without concomitant accumulation of anions, such as CL or lactate, or without exchange for cations, such as or NaL Consequently, electrolyte composition of blood serum or plasma is often determined along with measurements of blood gases and pH and to assess acid-base disturbances. 

Diagnosis of renal problems, xanthinuria, and toxemia of pregnancy via determination of the ratio of hypoxanthine to xanthine in plasma is facilitated by the use of biosensors. Xanthine oxidase immobilized on aminopropyl-CPG (controlled pore glass) activated with glutaraldehyde oxidizes hypoxanthine first to xanthine and then to uric acid. Use of an IMER with biosensors for hypoxanthine, xanthine, and uric acid provides the necessary data. Pre- or postcolumn enzymatic reactions catalyzed by creatinine deiminase, urease, alkaline phosphatase, ATPase, inorganic pyrophosphatase, or arylsufatase facilitate analysis of uremic toxins (simultaneous detection of electrolytes, serum urea, uric acid, creatinine, and methylguanidine). 

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