Solvents, analysis

Example The distance between two ends of a large, flexible molecule can provide information about its structural properties or its interaction with solvent. Analysis of an angle can reveal a hinged motion in a macromolecule. 

Pitch. For the solvent analysis of pitch, a number of methods have been proposed. The solvents may be used sequentially or a fresh sample may be used with each solvent. Either the least or the most powerflil solvent may be used first. The ratio of solvent to pitch or pitch fraction and the temperature and time of extraction vary. 

ASTM D 3271-93, Practice for Direct Injection of Solvent-reducible Paints into a Gas Chromatograph for Solvent Analysis, Annual Book of ASTM Standards, ASTM, West Conshohocken, PA (1998), Vol. 06.01. 

Elemental Analysis Titrimetric Analysis Solvent Analysis... 

Reaction conditions Cl2 AgSbF6 alkane molar ratio = 5 1 10, CH2C12 as solvent. Analysis by gas chromatography. 

Figure 6. Solvent analysis using a methyl silicone stationary phase.

In the few studies reporting on loading processes, specific analysis procedures have been developed in order to evaluate the course of the aminosilane deposition. Those include various in situ FTIR techniques as well as solvent analysis by various... 

After setting up a calibration curve (r = 0.996), unknown aminosilane concentrations in toluene solvent could be quantified. The total deposited amount of APTS was calculated from analysis of the residual amount of aminosilane in the solvent. Analysis was performed after two hours of reaction and consecutive filtration under ambient atmosphere. 150 /d aliquots of the salicylic aldehyde and the diethylether were added to 10 ml samples of the filtrate. Absorbance was measured one hour after the ether addition. The calculated loading value yields the total surface loading, including chemical and physical deposition, in the loading step. 

We fractionated CCB by a high vacuum distillation into several distillate fractions and undistlllable residue. The distillate fractions were subjected to a two-stage high temperature thermal process to convert them to aromatic pitches. The composition of the pitches produced was determined by a solvent analysis to define their suitability for synthetic carbon production. 

A number of important process parameters were investigated to find out their effect on pitch characteristics and yield of the toluene and quinoline insolubles. The pitches produced were characterized by solvent analysis, NMR, thermal, and elemental analysis. Insolubles in toluene, pyridine and quinoline were used because these fractions represent the fusable and infusable anisotropic liquid crystal fraction formed in the pitch. 

The CCB fractions were thermally-treated at 420°-450°C at atmospheric pressure in a nitrogen atmosphere and then vacuum stripped (0.5-1.Omm Hg) to remove the unreacted fractions. The pitch chemical structure was determined by NMR, and the pitch composition was determined by solvent analysis with toluene (at reflux) and quinoline (at 75°C). Toluene insolubles were determined because it represents a fusable pitch fraction with a 100% optical anisotropy on melting. 

There have been attempts to develop special methods for some elements which cause problems with solvent analysis when using the flame or furnace atomiser techniques. 

Cole, M. D., Occluded solvent analysis as a basis for heroin and cocaine sample differentiation . Forensic Sci. Rev., 10, 113-120 (1998). 

Table 8.7 Summary of common gas chromatographic detectors used in residual solvent analysis [97]...

API-related organic impurities usually involves high performance liquid chromatography (HPLC)-based analytical methods, with relatively non-specific detection techniques such as Ultraviolet/Visible (UV/Vis) Spectrophotometry. Residual solvents analysis usually involves gas chromatography (GC)-based analytical methods, again with relatively non-specific detection techniques such as flame ionization (FID). GC-based methods are most appropriate for volatile analytes such as residual solvents, whereas HPLC-based methods are more appropriate for the relatively non-volatile and polar API-related analytes. 

Dwivedi, A.M. Residual solvent analysis in pharmaceuticals. Int. J. Pharm. Excip. 2003, 33-37. 

Solvents analysis on separation possibility and enviromental effect... 

A countercurrent leaching system (Figure 32) is to treat lOkg/h of crushed sugar stalks with impurity-free water as the solvent. Analysis of the stalks is as follows ... 

The successful systems might be described by a class model based on pertinent descriptors of the substrates and the solvents. Analysis of the principal components model will then make it possible to determine in which respect the successful systems are similar to each other. Such an analysis may also furnish information on how to attain an optimum performance of the reaction. 

FIGURE I Example of a residual solvent analysis of a standard containing nine solvents at approximately 0.05 mg/mL. 

Fully protonated hexane (C6H14) has 14 protons in the spin system and Drobny9 reported the MQ spectra of //-hexane-terminal methyl groups) dissolved in a nematic solvent. Analysis of the 6Q and 7Q spectra of hexane-c/6, (6) was used to establish the relative signs of the dipolar couplings. The 6-quantum proton spectrum contains 36 transitions and the 7 quantum spectrum contains 4 transitions, as expected for an 8-proton spin system with C2h symmetry. The best fit of theoretically generated MQNMR spectra to the experimental spectra were obtained with a model where only the all-trans conformations of the alkane chain were appreciably populated. 

The preferred sample preparation method for residual solvent analysis of pharmaceuticals is direct injection of the dissolved sample (11,60). With this technique, the recovery is most reliable because there is no opportunity for recovery loss due to adsorption or entrapment. The other techniques involve a separation of the volatiles before the GC injection and there is a risk that the volatile will be trapped. Typical solvents for this analysis are water, dimethyl sulfoxide, benzyl alcohol, and dimethylformamide (11,12,61). The three latter solvents are chosen because they are higher-boiling than commonly used pharmaceutical solvents and thus elute after them and do not interfere with the analysis. Water offers the advantage that it contributes little interference with a flame ionization detector. 

---