Water residual, determination

In some cases the chemical method given by Karl-Fischer titration can also be applied for residual water determination. This method is based on oxidizing methyl sulfite with iodine into colorless iodide and methyl sulfate. The reaction only takes place when free water is available in the system. 

The hydrolysis by alkali is illustrated by the following experimental details for benzamido. Place 3 g. of benzamide and 50 ml. of 10 per cent, sodium hydroxide solution in a 150 ml. conical or round-bottomed flask equipped with a reflux condenser. Boil the mixture gently for 30 minutes ammonia is freely evolved. Detach the condenser and continue the boiling in the open flask for 3-4 minutes to expel the residual ammonia. Cool the solution in ice, and add concentrated hydrochloric acid until the mixture is strongly acidic benzoic acid separates immediately. Leave the mixture in ice until cold, filter at the pump, wash with a little cold water and drain well. RecrystaUise the benzoic acid from hot water. Determine the m.p., and confirm its identity by a mixed m.p. test. 

The mixture is kept for 3 hours at 105°C after the oxide addition is complete. By this time, the pressure should become constant. The mixture is then cooled to 50°C and discharged into a nitrogen-filled botde. The catalyst is removed by absorbent (magnesium siUcate) treatment followed by filtration or solvent extraction with hexane. In the laboratory, solvent extraction is convenient and effective, since polyethers with a molecular weight above about 700 are insoluble in water. Equal volumes of polyether, water, and hexane are combined and shaken in a separatory funnel. The top layer (polyether and hexane) is stripped free of hexane and residual water. The hydroxyl number, water, unsaturation value, and residual catalyst are determined by standard titration methods. 

Only particular solvents are suitable for certain purposes. The choice depending, for instance, on their residual water content or their acid-base nature if Rf values are to be reproduced [1, 2]. Halogen-containing solvents may not be employed for the determination of chlorinated pesticides. Similar considerations apply to PAH analyses. Pro analyst grades are no longer adequate for these purposes. It is true that it would be possible to manufacture universally pure solvents that were adequate for all analytical purposes, but they would then be too expensive for the final user [3, 4]. 

On an industrial scale PCI3 is sprayed into steam at 190 and the product sparged of residual water and HCl using nitrogen at 165. Phosphorous acid forms colourless, deliquescent crystals, mp 70. T, in which the structural units shown form four essentially linear H bonds (O - H 155-I60pm) which. stabilize a complex 3D network. The molecular dimensions were determined by low-temperature single-crystal neutron diffraction at 15K.f - ... 

Figure 8. Image and diffraction pattern from an (100) epitaxial. specimen of gold prepared in an unbaked UHV evaporator by depo.sition onto KOI and then transfer onto amorphous carbon. Here water vapour was the dominant residual gas (determined by mass spectrometry). The particles are square pyramidal single crystals.

The direct aqueous injection and LC/MS/MS muiti-residue method determines aiachior, acetochior, metoiachior and their soii metaboiites in water sampies. The accuracy of the anaiyticai method is estimated based on the recovery of known concentrations of each metaboiite fortified into controi water sampies that are then carried through the anaiyticai procedure. The method was vaiidated over the range 0.25-20 qg kg for aii components and is presented in Section 7. 

Residues of isoxaflutole, RPA 202248 and RPA 203328 are extracted from surface water or groundwater on to an RP-102 resin solid-phase extraction (SPE) cartridge, then eluted with an acetonitrile-methanol solvent mixture. Residues are determined by liquid chromatography/tandem mass spectrometry (LC/MS/MS) on a Cg column. Quantitation of results is based on a comparison of the ratio of analyte response to isotopically labeled internal standard response versus analyte response to internal standard response for calibration standards. 

All copolymers were prepared by solution polymerization, under adiabatic conditions, giving at least 99.9% conversions. The polymer gels were granulated and then dried at 90 °C to a residual water content of 10 to 12%. The active polymer content of each sample was calculated from the initial weight of the comonomers and the weight of the dried gel. Hydrolysis of the polymers was determined by conductometric titration to be less than 0.2% of the acrylamide charge. The molecular weight of the polymers was 8-10 million as determined by intrinsic viscosity measurements. 

Polyurethane networks were prepared from polyoxypropylene (POP) triols(Union Carbide Niax Polyols) after removal of water by azeotropic distillation with benzene. For Niax LHT 240, the number-average molecular weight determined by VPO was 710 and the number-average functionality fn, calculated from Mjj and the content of OH groupSj determined by using excess phenyl isocyanate and titration of unreacted phenyl isocyanate with dibutylamine, was 2.78 the content of residual water was 0.02 wt.-%. For the Niax LG-56, 1 =2630, fn=2.78, and the content of H2O was 0.02wt.-%. The triols were reacted with recrystallized 4,4"-diphenylmethane diisocyanate in the presence of 0.002 wt.-% dibutyltin dilaurate under exclusion of moisture at 80 C for 7 days. The molar ratio r0H = [OH]/ [NCO] varied between 1.0 and 1.8. For dry samples, the stress-strain dependences were measured at 60 C in nitrogen atmosphere. The relaxation was sufficiently fast and no extrapolation to infinite time was necessary. 

Wong [8] reported that the losses of chlorine are not related to the formation of iodate by the oxidation of iodide by hypobromite. The presence of iodate in seawater may cause significant uncertainty in the determination of small quantities of residual chlorine in water. Determinations of residual chlorine at the 0.01 mg/1 level are of questionable significance. 

Nail, St. L., Johnson, W. Methodology for in-process determination of residual water in freeze-dried products. Developments in Biological Standardization, Vol. 74, p. 137-152. Acting Editors Joan C. May, F. Brown, S. Karger AG, CH-4009 Basel (Switzerland), 1992... 

Studies with the freeze dried DPPC liposomes in trehalose solution showed, that not Tg )f the amorphous sugar is the critical temperature during storage, but the bilayer transition emperature Tm. for the lyposomes determines the short term stability of the formulation. With trehalose as lyoprotectant and a low residual water content, Tm proved to be 10 to 30 °C below the onset of T . 30 min heating above Tm but well below T% decreased the retention of CF after rehydration. Tm< after the heating was reduced from 40 to 80 °C to below 25 °C. 

We have examined very carefully reaction mixtures of (I) in methylene dichloride with perchloric acid. Under our best anhydrous conditions, when the reaction mixtures were neutralised with anhydrous triethylamine, the concentration of hydroxyl groups was between 2 x 10"3 and 10"2 M, which corresponds to between 2 and 5% of the perchloric acid concentration [18]. These small concentrations of hydroxyl groups are difficult to determine accurately, and they probably correspond to the residual water concentration. Thus this line of evidence favours the Keele mechanism. 

Protonation by residual water in the solvent is the rate-determining step in the... 

Fig. 4.7. The first-order rate constant as a function of the initiator concentration for the polymerisation of styrene in nitrobenzene by various salts for details see text and the table below. The pumping time, /p, determines the concentration of residual water which neutralises some of the initiator. In this instance the impurity acts as an inhibitor , in contrast to the examples in Figs. 4.5 and 4.6...

Finally, highly reactive salts such as triphenylmethyl hexachloroantimonate provide very convenient scavenging agents for the removal of the last traces of nucleophilic impurities in polymerisation solvents. Penczek (35) has taken this further in developing a spectroscopic technique for the determination of trace quantities of residual water by reaction of the latter with known concentrations of triphenylmethyl salts, according to the following equilibria ... 

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