Dissolution molar solution preparation

Fe S 0.1 M Na2S solution was mixed with S (3 1 molar ratio) at 180°C. After complete dissolution of S, the solution was mixed at 140°C with 0.4 M Fe(NH4)2(SO4)2 (both solutions prepared with fresh boiled water to minimize concentration of oxygen) in a specially designed reactor and aged for 30 min. The mixture was then quenched, hltered, and dried under a nitrogen atmosphere. 

An initial solution was prepared by dissolving metallic niobium powder in 40% hydrofluoric acid. The dissolution was performed at elevated temperature with the addition of a small amount of nitric acid, HN03, to accelerate the process. The completeness of niobium oxidation was verified by UV absorption spectroscopy [21]. The prepared solution was evaporated to obtain a small amount of precipitate, which was separated from the solution by filtration. A saturated solution, containing Nb - 7.01 mol/1, HF - 42.63 mol/1, and corresponding to a molar ratio F Nb = 6.08, was prepared by the above method. The density of the solution at ambient temperature was p = 2.0 g/cc. Concentrations needed for the measurements were obtained by diluting the saturated solution with water or hydrofluoric acid. 

Several problems arise in the preparation of solutions in nonaqueous solvents. The large thermal coefficient of expansion of many solvents necessitates the use of weight methods to establish concentrations, with subsequent calculation of molarities from weight concentrations. Also, solutions must be prepared and maintained under strictly anhydrous conditions during the course of the experiment. Further, since the preparation of quantities of highly pure solvent is difficult, the use of minimum amounts is desirable. Finally, salts sometimes dissolve very slowly in certain solvents, which makes efficient stirring to hasten dissolution important. 

Then a known concentration of each analyte is prepared. The absorbance of these solutions are measured at each of the two wavelengths. Solving the two simultaneous equations, two equations for c and C2 are obtained. Then the known values of individual concentrations and calculated values of the four molar extinction coefficients are substituted in the derived equations to arrive at the unknown concentrations of the two components in the mixture. Multicomponent analysis is normally used in the dissolution testing of tablets. Standard hardware and software components for multicomponent dissolution testing based on compendial method are available from instrument manufacturers. 

Based on the known heats of formation for NaOH(aq), NaCl(aq), NaBr(aq), Nal(aq), and ZrCUCcr), the author studied the heats of formation of ZrBr4(cr), Zrl4(cr). He used two independent methods the dissolution of the Zr-halides in excess NaOH solutions and dissolution in H2O. Molar ratios of Zr-halide to the aqueous medium were always 1/1500. Corrections of the measured heats of reactions for Hf contents of 1.7% in Zr phases were determined but were found to be within the error of the method. The solid Zr halide samples were prepared by halogenation of metals (X = Br, I) or carbides (X = Cl). The Zr/X ratio in these phases was not analysed for X = (Br, I), but literature data were invoked to show that the ratio is A. For the iodide, the Zr content in the solid was analysed to be within 0.05% of the theoretical value of IZ. 

Solution concentrations of 0.5% are usually prepared in vials or dissolution vessels and injection of 1-5 mg of polymer are loaded onto the column in analytical TREF. The more sensitive detectors should be used to allow for the lowest concentration possible in order to reduce co-crystallization and entrapment effects. Polyolefin homopolymers, which elute in a narrow temperature range, may often result in column plugging, especially if they have large molar mass in those cases, a lower concentration of sample should be used for injections. 

The solid inclusion complexes were obtained as precipitates from aqueous solutions of ethyl trans-cinnamate and a- and B-cyclodextrins in 80 and 95% yields, respectively. The ester in the complexes was determined by NMR in deuterodimethyl sulfoxide, and the molar ratios of the ester to the cyclodextrins were observed as 0.5 for the a-cyclodextrin complex and 1,0 for the 3-cyclodextrin complex. The X-ray diffraction patterns of these complexes showed that they were highly crystalline as shown in Figure 1, and could not be described with those of the ester and the cyclodextrin the precipitates should have different crystal structures from those of the guest and the hosts. These inclusion complexes have been prepared, and their dissolution and thermal behavior were examined by Uekama, et al. [9], Hursthouse, et al. determined [10] the crystal structure of 3-cyclodextrin complex with ethyl trans-cinnamate and showed that the complex was composed of 1 mole of the guest and 1 mole of the host. 

In the preparation of the BCD complex of simazine, a mixture of 5.00 g (24.8 mmol) of technical grade simazine and 30.4 g (24.8 mmol) of BCD in 500 ml of water was heated at 100 C for 11 days. There was no significant dissolution of the simazine. Fifty ml of 1,4-dioxane was added as a co-solvent, and die mixture heated at 100 °C for 2 days, yielding a clear solution. After cooling to room temperature 392 mg of white precipitate (unreacted simazine) was isolated after refrigeration of the filtrate at 4 tT for 5 days, 12.99 g of unreacted BCD came out of solution. Removal of solvent from ti remaining solution followed by vacuum drying provided 22.12 g of BCD complex, mp 150-162 °C. Elementary analysis CTable I) of the material indicated a 2 1 5 simazine/BCD/HjO molar ratio (24.8% simazine). 

Example Assuming a typical MALDI matrix with an Mr of about 200 g mol dissolution at 10 mg ml in a suitable solvent yields a matrix solution that is 0.05 M in concentration, which is equal to 5 x 10 mol pl An average peptide of Mr around 2000 g moL dissolved at 0.01 mg mT results in 5 x 10 mol pl (5 pmol pl ). Mixing the matrix with the analyte solution 1 1 (vA ) results in a molar matrix-to-analyte ratio of 10,000 1 for preparation on a target. Pipetting 1 pi of this mixture per spot onto a MALDI target corresponds to 2.5 pmol of sample per spot (Fig. 11.11). In fact, MALDI-TOF-MS of peptides can be extended to 1/lOOOth of this amount, and thus, may routinely deliver useful spectra down to a few fmol of peptide per spot, which is equal to a molar matrix-to-analyte ratio of 10,000,000 1. 

Highly-polymerized deoxyribonucleic acid, (DNA), from calf-thymus, was purchased from Sigma Chem. Co. and used as received. Stock solutions of DNA were prepared by dissolution overnight in 5 mM phosphate pH 7 buffer and were stored at 4°C in the dark for short periods only. Concentrations of DNA per nucleotide phosphate were determined by absorption spectroscopy using a molar extinction coefficient of 6,600 M cm at 260 nm [4]. N,N -Dimethyl-2,7-diazapyrenium dlchloride (DAP " ") was prepared and purified according to the method of HUnig et al. [5] whereas ethidium bromide (EB ) was purchased from Sigma Chem. Co. and used as received. 

Sample preparation. Samples were synthesized using an alkaline silicate solution and three metakaolins (namely Mkl, Mk2 and Mk3). The alkaline silicate solution was obtained by the dissolution of KOH pellets (85.2 % purity) and amorphous silica (99.9 % purity) in water at room temperature. Syntheses were performed by mixing the alkaline silicate solution and metakaolins. The samples were named Ml, M2 and M3. Other samples were realized with addition of ammonium molybdate (10 and 20% molar) to the alkaline solution before metakaolin. These samples were named Ml-20, M2-10, M2-20 and M3-20. 

As already described in the previous sections, the classical approach for preparation of polymeric nano-size aggregates from amphiphilic block copolymers by self-assembly in a selective solvent involves several steps. The first step is synthesis of an amphiphilic copolymer with a narrow molar mass distribution, followed by purification and characterization. Then, the self-assembly is performed by adding a non-solvent of one block into dilute copolymer solution or by direct dissolution of the copolymer in a selective solvent. Usually, the copolymer concentration varies between 1 and 10 g (0.1-1 wt%). 

---