Sodium background

Lithium in blood was determined by Kimura et al.[4 ] by FI liquid-liquid extraction with proton-dissociable chromogenic 14-crown-4 derivatives as the extraction-spectrophotometric reagent. Lithium may be determined selectively in blood under a high sodium background of 130-160 mM, after extraction of the lithium complex into chloroform. The method also features a low sample consumption of 20 pi and high sample throughput of 100 h ... 

Note Phosphoric acid [8] and hydrochloric acid [6, 9] have both been suggested in the literature as substitutes for phthalic acid. The addition of sodium dithionite [9] is also occasionally mentioned and sometimes no additives are employed [10]. The alternative reagents offer no advantages over the phthalic acid containing reagent since they usually cause more background coloration. The limits of detection are about 0.1 —0.5 pg per chromatogram zone [5]. 

Note If the spray solution or a nonbasic dipping solution is employed for detection then it is advisable to spray afterwards with a 10% aqueous solution of sodium carbonate or a 2% solution of borax in ethanol — water (1 + 1). It is often possible to achieve the required basicity by placing the chromatogram in a twin-trough chamber one of whose troughs contains 5 ml 25% ammonia. This is not suitable for the Chiralplate (Macherey-Nagel) because in this case the plate background acquires a dark violet coloration. 

Note Rhodamine B is a universal reagent that can be used on silica gel, talc, starch [5] and cellulose layers, just as on urea [1] or silver nitrate-impregnated [7] phases. Liquid paraffin-impregnated silica gel and RP layers are less suitable, since the background to the chromatographic zones is also intensely colored. It is often possible to increase the detection sensitivity by placing the plate in an atmosphere of ammonia after it has been sprayed or dipped, alternatively it can be oversprayed with sodium or potassium hydroxide solution. 

Note The background can be decolorized by spraying afterwards with 5% aqueous ammonia solution and/or 5 — 10% sodium thiosulfate in 50% aqueous ethanol [2, 3]. The sodium hydroxide may be replaced by potassium hydroxide in dipping solution 11 [4]. 

Tantalum powder is produced by reduction of potassium heptafluoro-tantalate, K2TaF7, dissolved in a molten mixture of alkali halides. The reduction is performed at high temperatures using molten sodium. The process and product performance are very sensitive to the melt composition. There is no doubt that effective process control and development of powders with improved properties require an understanding of the complex fluoride chemistry of the melts. For instance, it is very important to take into account that changes both in the concentration of potassium heptafluorotantalate and in the composition of the background melt (molten alkali halides) can initiate cardinal changes in the complex structure of the melt itself. 

In IC this problem of electrolyte background is overcome by means of eluant suppression. Thus in the above example of sodium and potassium analysis, if the effluent from the separating column is passed through a strong base anion exchange resin in the hydroxide form (suppressor column) the following two processes occur ... 

Indirect UV absorbance detection in capillary zone electrophoresis has been used to analyze sodium alcohol sulfates. Excellent reproducibility was obtained when veronal buffer was used as UV-absorbing background electrolyte [302],... 

Thiols, thioethers, disulfides Sodium metaperiodate + benzidine Substances with divalent sulfur yield white chromatogram zones on a blue background. [36]... 

Note Alternatively 1% solutions of starch, iodine and sodium azide may be sprayed successively onto the chromatogram in that order [4, 9], Other orders of application are also referred to in the literature [1, 2, 17] and sometimes the starch is also worked into the layer so that it is not necessary to spray with it [11, 12]. Sometimes the treatment of the chromatograms with starch solution is omitted [5,6,14] in such cases colorless chromatogram zones appear on a brown layer background. 

After drying in a stream of cold air coumaphos (hRj 30-35) appeared as an intense red chromatogram zone on a colorless background, while parathion methyl (hRj 40-45), fenitrothion (h/ f 45-50) and parathion ethyl (hRf 60-65) yielded yellow zones as they did with sodium hydroxide alone (. v.). The detection limit for coumaphos was 10 ng per chromatogram zone. 

Note It is occasionally recommended that sodium acetate be added to the reagent [2]. Thiophosphate insecticides with a simple P—S bond yield yellow chromatogram zones and those with a P=S double bond yield brown ones on a light brown background [10]. Further treatment of the stained chromatogram with iodine vapors increases the detection sensitivity [7] more than does spraying afterwards with caustic soda solution, which is also occasionally recommended [16, 17, 20, 21]. 

At the end of this period the solution was removed from the condenser while still hot and titrated immediately with 0.002500 N sodium thiosulfate before any appreciable oxygen could be absorbed and oxidize iodide ion to triiodide ion. The disappearance of the yellow color of triiodide ion against a white background was used for the end point. These solutions usually had a slight brown tint at the end point, which was assumed to be organic matter distilled over from the soil. Accordingly, the blank was usually titrated first and its final color was used as a standard end point color for the other three solutions run with it. 

To establish the well drainage boundaries and fluid flow patterns within the TFSA-waterflood pilot, an interwell chemical tracer study was conducted. Sodium thiocyanate was selected as the tracer on the basis of its low adsorption characteristics on reservoir rocks (36-38), its low and constant background concentration (0.9 mg/kg) in produced fluids and its ease and accuracy of analysis(39). On July 8, 1986, 500 lb (227 kg) of sodium thiocyanate dissolved in 500 gal (1.89 m3> of injection brine (76700 mg/kg of thiocyanate ion) were injected into Well TU-120. For the next five months, samples of produced fluids were obtained three times per week from each production well. The thiocyanate concentration in the produced brine samples were analyzed in duplicate by the standard ferric nitrate method(39) and in all cases, the precision of the thiocyanate determinations were within 0.3 mg/kg. The concentration of the ion in the produced brine returned to background levels when the sampling and analysis was concluded. 

Taylor and Jarman [1] observed SL spectra in the range of 280-740 nm from 2 M NaCl solutions saturated with argon, krypton and xenon sonicated at frequencies of 16 and 500 kHz. The spectra showed a continuum background with bands at about 310 nm and a peak of sodium D line, which exhibited appreciable asymmetric broadening, as shown in Fig. 13.2. The bands around 310 nm result from the A2L+ — X2n transition of OH radicals. The OH bands are quenched in salt solutions compared with those in water, which suggests the energy transfer reaction... 

Valproic acid has been determined in human serum using capillary electrophoresis and indirect laser induced fluorescence detection [26], The extract is injected at 75 mbar for 0.05 min onto a capillary column (74.4 cm x 50 pm i.d., effective length 56.2 cm). The optimized buffer 2.5 mM borate/phosphate of pH 8.4 with 6 pL fluorescein to generate the background signal. Separation was carried out at 30 kV and indirect fluorescence detection was achieved at 488/529 nm. A linear calibration was found in the range 4.5 144 pg/mL (0 = 0.9947) and detection and quantitation limits were 0.9 and 3.0 pg/mL. Polonski et al. [27] described a capillary isotache-phoresis method for sodium valproate in blood. The sample was injected into a column of an EKI 02 instrument for separation. The instrument incorporated a conductimetric detector. The mobile phase was 0.01 M histidine containing 0.1% methylhydroxycellulose at pH 5.5. The detection limit was 2 pg/mL. 

Particular cases are potassium selective potentiometric sensors based on cobalt [41] and nickel [38, 42] hexacyanoferrates. As mentioned, these hexacyanoferrates possess quite satisfactory redox activity with sodium as counter-cation [18]. According to the two possible mechanisms of such redox activity (either sodium ions penetrate the lattice or charge compensation occurs due to entrapment of anions) there is no thermodynamic background for selectivity of these sensors. In these cases electroactive films seem to operate as smart materials similar to conductive polymers in electronic noses. 

---