Sodium error

The results obtained with ISEs have been compared several times with those of other methods. When the determination of calcium using the Orion SS-20 analyser was tested, it was found that the results in heparinized whole blood and serum were sufficiently precise and subject to negligible interference from K and Mg ([82]), but that it is necessary to correct for the sodium error, as the ionic strength is adjusted with a sodium salt [82], and that a systematic error appears in the presence of colloids and cells due to complexa-tion and variations in the liquid-junction potential [76]. Determination of sodium and potassium with ISEs is comparable with flame photometric estimation [39, 113, 116] or is even more precise [165], but the values obtained with ISEs in serum are somewhat higher than those from flame photometry and most others methods [3, 25, 27, 113, 116]. This phenomenon is called pseudohyponatremia. It is caused by the fact that the samples are not diluted in ISE measurement, whereas in other methods dilution occurs before and during the measurement. On dilution, part of the water in serum is replaced by lipids and partially soluble serum proteins in samples with abnormally increased level of lipids and/or proteins. 

Sodium error. When [H+] is very low and [Na+] is high, the electrode responds to Na+ and the apparent pH is lower than the true pH. This is called the sodium error or alkaline error (Figure 15-15). 

The Sodium Error Most glass combination electrodes are sensitive to Na+ as well as H+. The sodium error can become quite significant at high pH values, where 0.1 M Na+ may decrease the measured pH by 0.4 to 0.5 unit. Several things may be done to reduce the sodium error. Some commercial suppliers of electrodes provide a standard curve for sodium error correction. Newer electrodes that are virtually Na+ impermeable are now commercially available. If neither a standard curve nor a sodium-insensitive electrode is available, potassium salts may be substituted for sodium salts. 

To prepare the peptone medium, the components are dissolved in distilled water in the order listed, and the pH is adjusted to pH 7.0 with 4 N NaOH, using a pH electrode with a low sodium error. 

The potential at the external glass surface is developed as a result of ion-exchange reactions with the solution in which it is immersed. The glass structure must maintain anionic sites for the ion exchange. Silicon dioxide of greater than 50% by composition provides this characteristic. The stability, electrical conductivity, and sodium errors of an electrode are somewhat dependent on the ionic properties of other elements (modifier elements) in the glass. The ease with which ionic transfer between glass and solution can occur is the result of these components. 

Glass electrode calibration, 10 effect of light, 12 high alkalinity type, 10 limiting concentrations of solute, 14, 38 miniature, 23, 25 nature of. 10 sodium error, 9 temperature hysteresis, II, 12 titrations with, 15 zero drift, 10... 

The production of both an alcohol and the sodium salt of an acid might easily be confused with the hydrolysis products of an ester (in the above instance benzyl benzoate). Such an error would soon be discovered (e.g., by reference to the b.p. and other physical properties), but it would lead to an unnecessary expenditure of time and energy. The above example, however, emphasises the importance of conducting the class reactions of neutral oxygen-containing compounds in the proper order, viz., (1) aldehydes and ketones, (2) esters and anhydrides, (3) alcohols, and (4) ethers. 

Departures from the ideal behavior expressed by equation 7 usually are found in alkaline solutions containing alkaH metal ions in appreciable concentration, and often in solutions of strong acids. The supposition that the alkaline error is associated with the development of an imperfect response to alkaH metal ions is substantiated by the successhil design of cation-sensitive electrodes that are used to determine sodium, silver, and other monovalent cations (3). 

The molecular absoi ption spectra, registered at a lower temperature (e.g. 700 °C for iodide or chloride of potassium or sodium), enable one to find the absorbance ratio for any pair of wavelengths in the measurement range. These ratios can be used as a correction factor for analytical signal in atomic absoi ption analysis (at atomization temperatures above 2000 °C). The proposed method was tested by determination of beforehand known silicon and iron content in potassium chloride and sodium iodide respectively. The results ai e subject to random error only. 

The classification as a carcinogen need not apply to fibres with a length weighted geometric mean diameter less two standard errors greater than 6 pm Sodium dichromate Sodium dichromate dihydrate... 

The relative rate of reduction by lithium with respect to sodium was misquoted by me ii ref. 29 as 62.5 1. Eastham has criticized the accuracy of the original data and Krapchc and Bothner-By have agreed that their rate constants may have been in error. Thi figures cited above include lough corrections made in accord with Krapcho and Bothner-By estimates of the errors. 

A unit used small amounts of sodium sulfite and potassium sulfate. It was custom and practice to call these two chemicals simply sulfite and sulfate. During a busy period someone from another unit was asked to help and was told to prepare a batch of sulfate. The only sulfate he knew was aluminum sulfate, so he prepared a batch of it. Fortunately the error was spotted before the sulfate was used [13]. 

Tailing peaks or longer than expected elution volumes are sometimes caused by low solubility of the protein in the mobile phase. Using a trial-and-error process, select the proper pFf and ionic strength to address this problem. Detergents such as sodium dodecyl sulfate (SDS) are sometimes helpful but, because they change the conformation of many proteins and are difficult to remove from the column should be used only if other methods fail. 

Note. Under the above conditions of determination the following elements interfere in the amount specified when the amount of Mo is 10 fig (error greater than 3 per cent) V, 0.4 mg, yellow colour [interference prevented by washing extract with tin(II) chloride solution] Cr(VI), 2 mg, purple colour W( VI), 0.15 mg, yellow colour Co, 12 mg, slight green colour Cu, 5 mg Pb, 10 mg Ti(III), 30 mg (in presence of sodium fluoride). 

With 0.1M solutions, the ideal pH range for an indicator is limited to 45-9.5. Methyl orange will exist chiefly in the alkaline form when 99.8 mL of alkali have been added, and the titration error will be 0.2 per cent, which is negligibly small for most practical purposes it is therefore advisable to add sodium hydroxide solution until the indicator is present completely in the alkaline form. The titration error is also negligibly small with phenolphthalein. 

This reaction is subject to a number of errors (1) the hydriodic acid (from excess of iodide and acid) is readily oxidised by air, especially in the presence of chromium(III) salts, and (2) it is not instantaneous. It is accordingly best to pass a current of carbon dioxide through the reaction flask before and during the titration (a more convenient but less efficient method is to add some solid sodium hydrogencarbonate to the acid solution, and to keep the flask covered as much as possible), and to allow 5 minutes for its completion. 

In the presence of certain cations [sodium, potassium, lithium, calcium, aluminium, chromium, and iron(III)], co-precipitation of the sulphates of these metals occurs, and the results will accordingly be low. This error cannot be entirely avoided except by the removal of the interfering ions. Aluminium, chromium, and iron may be removed by precipitation, and the influence of the other ions, if present, is reduced by considerably diluting the solution and by digesting the precipitate (Section 11.5). It must be pointed out that the general method of re-precipitation, in order to obtain a purer precipitate, cannot be employed, because no simple solvent (other than concentrated sulphuric acid) is available in which the precipitate may be easily dissolved. 

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