Modifier basic

Patel et al. [40] found that moismre and the pH of the micro-environment influenced degradation the most. They identified the best diluent for tablet manufacture as being dibasic calcium phosphate, with a basic modifier (sodium carbonate, sodium bicarbonate or magnesium oxide). The authors indicated that the degradation pathways observed were deiodination, deamination and decarboxylation. The data are shown in Table 2.4. 

Cyclotol 75% RDX + 25% TNT Basically modified Composition with a higher RDX content for better performance. Used as a high VOD castable main explosive and also considered as a substitute for PBX-9404... 

Chapter 2 by J. Kim, Y.H. Choi and K.-P. Yoo is a fascinating review of the supercritical fluid extraction of alkaloids. This technique using basic modifiers, provides an alternative method for the extraction of alkaloids. 

Azo dyes with relatively low molecular masses and one to three sulfonic acid groups serve as acid azo dyes for dyeing and printing wool, polyamide, silk, and basic-modified acrylics and for dyeing leather, fur, paper, and food. The main area of application is the dyeing of wool and polyamide. 

For pharmaceutical compounds, LC-MS has found extremely wide acceptance due to the low-level detection that can be achieved, in addition to the selectivity and specificity that are attained by using HPLC in conjunction with MS detection. LC-MS is also convenient because of its compatibility with reversed-phase HPLC mobile phases. Volatile mobile phase additives such as trifluoroacetic acid, formic acid, and ammonium hydroxide are very common and can be utilized not only to aid in the chromatographic separation but also to influence the ionization state of the molecule (i.e., acid modifiers to protonate [M + H]+1, and basic modifiers to deprotonate [M — H] ). This requirement may require a modification of the potency method if phosphate was utilized however, it is not viewed as a major drawback. 

Basic Modifiers pH Shift. Basic mobile-phase modifiers such as... 

NH4TNH3 ( pH 9) and BUNH3VBUNH2 (wpH 10) show a decrease in their pK values with increasing organic content [74]. These basic modifiers have an average pH decrease on the order of -0.05 to -0.1 pH units per 10 v/v% acetonitrile. The minimum of the pH values as a function of acetonitrile composition for basic modifiers is reached at approximately 30-50 v/v% MeCN. Upon further increase in MeCN concentration the pH of the basic modifier will increase. For example, ammonium/ammonia basic modifier pH values in acetonitrile/water mixtures are 0% MeCN 9.29, 10% MeCN 9.27, 20% MeCN 9.21, 30% MeCN 9.17, 40% MeCN 9.19, 50% MeCN 9.21, 60% MeCN 9.34 [64]. For BUNH37BUNH2 (wpH 10), basic modifier pH values in acetonitrile/water mixtures are 0% MeCN 10.00, 20% MeCN 9.78, 40% MeCN 9.65,60% MeCN 9.79 [64]. For basic modifiers a decrease in pH is also observed with increase of methanol content on the order of 0.1 pH units per 10 v/v% methanol. 

The surface of the silica may be dynamically coated with transition metals, and the selectivities observed can be attributed to the complexes between the metal ions and the analyte species [56], The use of silver-impregnated silica (adsorption of salts of transition metals on the silica surface) has been used for the analysis of saturated and unsaturated fatty acid methyl esters (FAME) and triacylglycerols (TAG) [57], The retention of the unsaturated FAME and TAG can be attributed to the stability of the complex that is formed between the K electrons of the carbon-carbon double bonds and the silver ions. The predominant interaction for saturated analytes is with the polar silanol groups. The secondary interactions are those of the silver ions with the unpaired electrons of the carbonyl oxygens of the analytes. The amount of silver adsorbed onto the silica and the pH (employment of acidic or basic modifiers) have been determined to have an effect on the retention and resolution of certain acidic and basic compounds and fatty acids [58]. 

Also, because of the weakly acidic sllanol groups present in silica gel, basic modifiers, such as ammonia, diethyl amine and triethyl amine, have often been added to the solvent systems used in TLC-analysis of alkaloids to avoid tailing caused by chemisorption (see Fig. 

However, under basic conditions the stability of silica gel is poor18. Depending on the nature of the organic solvents used 1n combination with the basic modifier, the silica gel is dissolved at various rates. This limits the applicability of silica gel as stationary phase in the HPLC analysis of alkaloids. For certain solvent systems the column life can... 

Chan et al.11 preferred cyclohexylamine as the basic modifier in the analysis of drugs of abuse on pellicular silica gel or aluminium oxide columns. Volatile amines were less suited, because the solvent composition changed with time, and secondary and tertiary amines absorbed UV-light at 254 nm. 

Caude et al. 6,48 used ethylamine as the basic modifier in a solvent system of ethyl acetate - methanol - water in order to analyze some opium alkaloids in pharmaceutical... 

Most problems can be solved on silica gel as the stationary phase. If either some specific selectivities or the addition of a basic modifier is required, amino modified silica gel (90 10 v/v) often brings the solution. 

Finally, contamination of sample spectra can also occur by cross-contamination during sample preparation and by carryover of residual analyte from a sample analyzed earlier in the run.172 173 Essentially, any component of the assay that is reused for each sample or batch of samples can be a source of cross-contamination or carryover. These include, for example, evaporators, pipettors, automated liquid handlers, recycled sample vials, and LC and GC autosamplers. Care needs to be taken in the selection of appropriate wash solvents that will readily solubilize the sample and analytes. This will usually be a combination of high percentage of organic solvents that may include a volatile acidic or basic modifier (e.g., formic acid or aqueous ammonia). Failure to properly wash all sample components from a chromatographic column can result in late eluting components appearing in the next, or later, analytical runs. 

GC-MS the modifier identity is more important than modifier concentration for enhancing extraction efficiencies of PAHs and PCBs however, the concentration influences over high molecular weight PAHs recoveries PCBs best modifiers acidic/basic modifiers including methanol, acetic acid and aniline low molecular weight PAHs best modifiers aniline, acetic acid, acetonitrile, methanol/toluene, hexane and diethylamine high molecular weight PAHs best modifiers toluene, diethylamine and methylene chloride Determination Online SFE-LC-UV extraction recovery 237... 

Selectivity effects are determined by mobile phase interactions between the stationary phase and the solute. Those mobile phases containing proton donors will interact with basic solutes. Conversely, mobile phases containing proton donor acceptors will interact strongly with acidic solvents. Where excessive interactions occur between the solute and the mobile phase, peak tailing can result. However, the inclusion of a basic modifier (triethylamine) can overcome such strong interactions and thereby improve peak shape. 

M - H] ions form when ammonia, a basic modifier, is used. 

According to ISO 31000 2009 it is basically modifying the risk. (However, note that controls may be any process, policy, device, practice or other action which modify risk, and that controls may not always exert the intended or assumed modifying effect.)... 

Method development in SFC is significantly easier, since only one mobile phase (CO2) with a few modifiers (methanol, ethanol, isopropanol, acetonitrile) instead of a multitude of solvent mixtures has to be tested. If the first experiments do not show at least a partial resolution, it is recommended that one should switch to another CSP. To optimize SFC separations, the amount of the modifier can be varied between 5 and 25%, as well as varying its nature. As in HPLC, acidic and basic modifiers can be used. Pressure changes have a greater influence on retention than on selectivity. 

Matos, E. Perez-Mayoral, E. Soriano, A. Zukal, R.M. Martin-Aranda, A.J. Lopez-Peinado, I. Fonseca, J. Cejka, Experimental and theoretical study of pyrazole N-alkylation catalyzed by basic modified molecular sieves, Chem. Eng. J. 161 (2010) 377-383. 

---