Reagent purification

Purified water is used to prepare reagents. This is normally prepared using a preliminary clean-up stage using deionization, reverse osmosis or distillation of tap water, followed by a second, high-quality, deionization or distillation (see Section 12.1.5). 

Acids and ammonia used for sample acidification and pH neutralization are purified by sub-boiling distillation using a quartz condenser, or isothermal distillation as described in Section 12.1.5. 

Borate pH buffer. A solution is prepared containing 1 mol/L boric acid and 0.35 mol/L ammonia. This buffer gives a pH of 8.35 when diluted 100-fold in seawater. Boric acid may precipitate if the pH of this solution is too low, in which case the ammonia concentration has to be increased. Contaminating metal ions can be removed from this buffer by adsorption on Mn02 which is removed by filtration. Thereto Mn02 suspension is added to a final concentration of 50-100//mol/L the mixture is equilibrated for several hours and then filtered over a 0.45 pm filter. 

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Reaction water, 68 Reactive diluents, 221 Reagents, purification of, 440 Recycled PET products, applications of, 531-532... 

The chemical change in the Fricke dosimeter is the oxidation of ferrous ions in acidic aerated solutions. It is prepared from a -1 mM solution of ferrous or fer-roammonium sulfate with 1 mM NaCl in air-saturated 0.4 M H2S04. Addition of the chloride inhibits the oxidation of ferrous ions by organic impurities, so that elaborate reagent purification is not necessary. Nevertheless, the use of redistilled water is recommended for each extensive use. Absorption due to the ferric ion is monitored at its peak -304-305 nm. The dose in the solution is calculated from the formula... 

This equation is in agreement with the experimentally found dependence of the reaction rate on amine concentration. The decrease of the order of the reaction kinetics with respect to amine concentration in the presence of hydroxyl-containing impurities is partially due to the catalytic mechanism when a hydroxyl-containing compound, whose acidity is far higher than that of amine, acts as a proton donor. It should be stressed that, with the usual technique of reagent purification and cleaning of the reaction vessels, the moisture content in the reaction mixture is still rather high, and the order of the reaction kinetics with respect to aniline concentration considerably differs from two. 

Purffication. Lucidol material contains 76-90% of active reagent. Purification has been accomplished by fractionation - and by refluxing in an azeotrope separator until homogeneous and then distillation. Kochi and Mocadlo vacuum distilled Lucidol material several times and obtained a product of greater than 99% purity. Bartlett and McBride extracted Borden material with cold 15% aqueous potassium hydroxide, followed by neutralization with solid ammonium chloride and vacuum distillation (98.4% pure). 

Since the sensitivity of the method is often limited by the high blank values caused by the presence of traces of ammonia in the reagents, purification of the reagents by distilling ammonia from their alkaline solutions may be necessary. 

See also Analytical Reagents Purification. Arsenic. Atomic Absorption Spectrometry Electrotfiermal. Atomic Mass Spectrometry Inductively Coupled Plasma. Dioxins. Elemental Speciation Oven/iew. Endocrine Disrupting Chemicals. Geochemistry Sediment. Humic and Fulvic Compounds. Isotope Dilution Analysis. Mass... 

See also-. Analytical Reagents Purification. Distillation. Extraction Solvent Extraction Multistage Countercurrent Distribution. Liquid Chromatography Principles Mobile Phase Selection Normal Phase. 

Figure 6.9 Experimental setup of the trifluor-omethylation reaction with Ruppert s reagent. Purification by various scavenger resins in flow PS-benzaldehyde (PS-CHO) for residual Ruppert s reagent, QuadraPure-SA (QP-SA ...

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