Sodium determination

Na Influx Studies. Na influx was monitored according to the procedure of Owen and Villereal (34), with some modifications. Cells were seeded onto 60-mm culture dishes, grown, and serum starved as described for the assays above. The cells were washed with incubation media and incubated in 3 ml of the appropriate agent at 37 C. After incubation the cells were rapidly washed in ice cold 0.1 mM MgCL and extracted with 5% TCA/0.5% KNO3 for sodium determination or 0.2% SDS for protein determination. Sodium concentration was measured using a Varian Model 275 Atomic Absorption Spectrophotometer. Protein was determined fluorimetrically. 

Hi) Radiation buffer for sodium determination Prepare a saturated solution with reagent-grade CaCl2, KC1, MgCl2, in that order. 

Ionophoresis of the buffer salts. When considering evaporation (Section 1.1.1.1) mention was made of sodium determination in eluates of the strip after the run. Measurements of potential on the strip have confirmed the presence of salt zones (unpublished and P21). When current is applied, the sodium peak due to evaporation moves partially toward the cathode and diminishes at the same time. A second new and unexpected sodium peak appears near the anode (Fig. 16). Determinations of both sodium and barbiturate proved the presence of both ions together on the same spot (P8). Experiments with sodium barbiturate as anodic electrolyte and potassium barbiturate as cathodic electrolyte proved that it is an accumulation of the cation leaving the anodic buffer vessel which causes this new and unexpected peak (Fig. 17). The reason appears to lie in the unequal mobilities of the two ions which tend to occupy a zone from which the faster ion (sodium) needs the same time to reach the cathode as the slower ion (barbiturate) needs to reach the anode (G26, P7). It is, of course, necessary that one anion be discharged at the same moment as one cation. 

Flame AAS may also be used for sodium determination, although this offers... 

Although ionization of sodium is negligible and potassium small in an air—propane flame, some ionization is experienced in the recommended hotter air—acetylene flame. Ionization should be suppressed by the incorporation of excess potassium or cesium (for sodium determinations) or excess sodium or cesium (for potassium determinations), at concentrations of 1000/igml-1 or greater, in the form of chlorides or nitrates, in both sample and standard solutions. Cesium is the more effective but more expensive ionization suppressant. Extent of ionization is inversely related to analyte concentration with errors due to incomplete suppression thus being greater at low concentrations. As it is difficult to obtain alkali metal salts free from traces of other alkali metals, possible contamination must be considered, especially at low analyte levels. Use of a branched capillary for introduction of ionization buffer has been advocated for flame spectrometry to... 

Diverging results have been reported on the influence of triglycerides concentration on sodium determination in some cases, disturbance was seen already from 800 mg/dl onwards, whereas other researchers observed interference only from 3 000 mg/ dl onwards (E39, E83, E105, E266, E304). 

E335 Geary, T.D., O Leary, T.D. and van Brunt, N. (1987). Improved sodium determination on the Kodak Ektachem systems as reflected by the decreased effect of bicarbonate. Ann. Clin. Biochem. 24, Suppl. 2, 56. 

CsCl Suprapur from Merck was used for matrix modifier preparation for sodium determination by flame atomic emission analysis. 

All measurements were performed with the program GIRAF and with the previous ones without shutdown of the instrument at the same analytical conditions (according to Perkin-Elmer cookbook ) by the same analyst with the same reference materials applied as calibration and test solutions. The matrix modifier for lead determination by graphite furnace analysis was used separately from the reference materials, i.e. was not mixed with them. The matrix modifier for sodium determination by flame atomic emission analysis was introduced in all corresponding solutions (the blank and the reference materials for the calibration and test). Three replicates of all measurements were made. 

Construct a spreadsheet to determine the intensity ratio of sodium to lithium and plot this versus the ppm sodium. Also plot the sodium intensity versus ppm sodium. Determine the concentration of the unknown and its standard deviation. 

The serum sodium concentration and fluid status should be monitored every 2 to 3 hours over the first 24 hours of admission in patients with symptomatic hypernatremia to permit appropriate adjustment in the rate of infusion of hypotonic fluids. After symptoms resolve and the serum sodium is less than 148 mEq/L, serum sodium determinations every 6 to 12 hours and fluid status assessment every 8 to 24 hours are generally sufficient to follow the course of therapy. 

If the amount of sample is limited, as it may very well be for a patient s semm, a one-point standard addition technique may be used. The technique is outlined for a sodium determination in semm by flame AES. The emission intensity from the sample is measured, and then a known concentration of Na is added, again without significantly... 

Adding an excess of a more easily ionized element to all standards and samples eliminates ionization interference. This addition creates a large number of free electrons in the flame. The free electrons are captured by the analyte ions, converting them back to atoms. The result is to suppress the ionization of the analyte. Elements often added as ionization suppressants are potassium, rubidium, and cesium. For example, in the AAS determination of sodium, it is common to add a large excess of potassium to all samples and standards. Potassium is more easily ionized than sodium. The potassium ionizes preferentially and the free electrons from the ionization of potassium suppress the ionization of sodium. The detection limit of the sodium determination thereby decreases. The ionization suppression agent, also called an ionization buffer, must be added to all samples, standards, and blanks at the same concentration for accurate results. An example of the use of ionization suppression is shown in Fig. 6.20. Absorbance at a barium resonance line (atomic absorption) and absorbance at a barium ion line (by barium ions in the flame) are plotted as a function of potassium added to the solution. As the potassium concentration increases, barium ionization is suppressed the barium stays as barium atoms. This results in increased atomic absorption at the resonance line and a corresponding decrease in absorbance at the ion line. The trends in absorbance at the atom and ion lines very clearly show that barium ion formation is suppressed by the addition of 1000 ppm of the more easily ionized potassium. 

Typical composition of commercial-grade sodium determined by standard methods of analysis is given in Table 5.1, where 1 ppm=10" °. 

The instructions given in the section on sodium determination by flame photometry (3.3.2.1) should be applied analogously. 

Since the concentrations of potassium ions are generally lower than those of sodium ions, and since the calibration curve approaches an ideal straight line, the results are more accurate than those of sodium determination. For this reason, twin determination from two different measured volumes is sufficient. 

Flame atomic emission spectrometry Basic information on FAES is presented elsewhere in this encyclopedia. Sodium measurements are performed at 590 nm with the use of a propane flame (1925°C). Physiological samples for sodium determination are highly diluted before measurement. The diluent and the calibrator solution contain the same concentration of lithium ions so as to balance flame instability by a concomitant measurement of lithium in the reference beam (the so-called lithium guideHne). At the same time, lithium ions inhibit the ionization of sodium atoms. This procedure cannot be used in the case of therapy with lithium salts. That is why some authors prefer the concomitant measurement of caesium to that of lithium. Dilution adjusts the viscosity of the sample to that of the calibrator solution to produce identical aspiration rate and drop size on nebulization. As other electrolytes interfere with sodium measurement, their concentration in the caH-brator solution must be similar to their concentration in the sample. For the measurement of sodium in urine, calibrator solutions different from those for serum measurement are needed as the electrolyte concentrations in urine samples are quite different from those in serum and their relations are very variable. As the concentration of the electrolytes in serum is rather constant, calibrator solutions for serum measurements can fulfill their function better than those for urine in other words, urine determinations are usually less accurate. FAES proved to be sufficiently reliable to be used as the basic principle of the sodium reference measurement procedure. In routine use, however, FAES is less accurate. Its application is given up by most clinical laboratories in favor of potentiometric measurements... 

Potentiometry For sodium determinations by potentiometry, a glass electrode is usually used, but ion-carrier or ion-exchange membranes are also feasible for the ISE. A silver/silver chloride or a calomel electrode is used as the reference electrode. 

The first detector to be used for SFA was a photometer, and photometric determinations still form the vast majority of current methods. Other detectors in common use are UV spectrophotometers, used primarily for pharmaceutical compovmds and for bitterness in beer flame photometers, for potassium and sodium determination fluorimeters, used primarily for measuring low levels of determinants in the presence of interferences, such as the determination of histamine in blood, and vitamins in food extracts and ion-selective electrode and pH detectors. In principle, almost any detector with flow-through capability can be used with SFA systems, and determinations based on densitometry, thermometry, and luminescence have been published, among others. 

TABLE 2. Interference of Coexistent Elements for the Sodium Determination Using Flame Photometry... 

TABLE 3. Tolerable Selectivity Factors for Extra- and Intracellular Sodium Determination (1% Error) in Presence of Interfering Ions J and Selectivity Factors of Available Na -Selective Electrodes... 

Evaluation Procedure. All the data were examined and evaluated by using the method described by Cohen-Adad (13). Only experimentally obtained data were evaluated. Data obtained from smoothing equations or by extrapolation were excluded from consideration. The data calculated on the basis of sodium determination (1) and the 298 K values reported by others (3, 4) are clearly incorrect and were not included. Some data (4) were reported as mol dm d and could not be used here because no density information was given and the values could not be recalculated in terms of mole fraction. All the other data are consistent with each other and were evaluated together. 

Table 11.12 Interlaboratory variation of flame photometric sodium determinations in polyolefins (sodium content, ppm) ...

Table 1.13 Comparison of sodium determination in polyolefins by neturon activation analysis, emission spectrography and flame photometry (sodium ppm) ...

The amount of energy emitted also depends upon the (i) temperature and (U) composition of the flame. It is therefore very necessary that the two flame variables must be maintained constant and that standard solutions be used to calibrate the stem. The need to maintain flame composition constant also dictates which element should be determined first. Thus, sodium which gives a very high background emission is measured first and the quemtity of sodium determined is added to all the standards. Certain elements, such as the alkali met s, enhance the emission of other elements. On the other hand, some substances like alumlnate emd silicate cause a decrease in emission of other elements. To relieve this deleterious effect certain other elements known as the releasing agents (strontium or lanthanum) must be added. 

---