Semiaqueous solvent

Although not included in this discussion, these compositions may be formulated to be developed in what is known as a semiaqueous solvent [26], where an organic solvent, such as butanol, at levels between 5 and 20%, is present in the aqueous developer. Formulations developed in this manner have been shown to have resolution equivalent to the all-aqueous developers with, in some instances, superior adhesion to the substrate. 

Semiaqueous or Nonaqueous Solutions. Although the measurement of pH in mixed solvents (e.g., water/organic solvent) is not recommended, for a solution containing more than 5% water, the classical definition of a pH measurement may still apply. In nonaqueous solution, only relative pH values can be obtained. Measurements taken in nonaqueous or partly aqueous solutions require the electrode to be frequently rehydrated (i.e soaked in water or an acidic buffer). Between measurements and after use with a nonaqueous solvent (which is immiscible with water), the electrode should first be rinsed with a solvent, which is miscible with water as well as the analyte solvent, then rinsed with water. Another potential problem with this type of medium is the risk of precipitation of the KC1 electrolyte in the junction between the reference electrode and the measuring solution. To minimize this problem, the reference electrolyte and the sample solution should be matched for mobility and solubility. For example, LiCl in ethanol or LiCl in acetic acid are often used as the reference electrode electrolyte for nonaqueous measurements. 

All of the fat-soluble vitamins, including provitamin carotenoids, exhibit some form of electrochemical activity. Both amperometry and coulometry have been applied to electrochemical detection. In amperometric detectors, only a small proportion (usually <20%) of the electroactive solute is reduced or oxidized at the surface of a glassy carbon or similar nonporous electrode in coulometric detectors, the solute is completely reduced or oxidized within the pores of a graphite electrode. The operation of an electrochemical detector requires a semiaqueous or alcoholic mobile phase to support the electrolyte needed to conduct a current. This restricts its use to reverse-phase HPLC (but not NARP) unless the electrolyte is added postcolumn. Electrochemical detection is incompatible with NARP chromatography, because the mobile phase is insufficiently polar to dissolve the electrolyte. A stringent requirement for electrochemical detection is that the solvent delivery system be virtually pulse-free. 

The removal of triglycerides from the food sample by saponification provides the opportunity to utilize reversed-phase chromatography. The unsaponifiable matter is conventionally extracted into a solvent [e.g., diethyl ether/petroleum ether (50 50) or hexane] that is incompatible with a semiaqueous mobile phase. It then becomes necessary to evaporate the unsaponifiable extract to dryness and to dissolve the residue in a small volume of methanol (if methanol is the organic component of the mobile phase). For the analysis of breakfast cereals, margarine, and butter, Egberg et al. (153) avoided the time-consuming extraction of the unsaponifiable matter and the evaporation step by acidifying the unsaponifiable matter with acetic acid in acetonitrile to precipitate the soaps. An aliquot of the filtered extract could then be injected, after dilution with water, onto an ODS column eluted with a compatible mobile phase (65% acetonitrile in water). 

Ni et al. (2002) studied the stability of SarCNU (NSC 364432) in water, ethanol, propylene glycol (PG), Capmul PG, and DMSO, as well as their combinations over the temperature range of 25-660. The two cosolvents are an 80% PG 20% ethanol mixture (PE), and a semiaqueous vehicle (WPE) containing 50% water 40% PG 10% ethanol. The degradation mechanism in all the studied solvents is the same, and the stabilization by these vehicles follows the order of Capmul PG > Ethanol > PE > PE > PG > WPE > water, which is in agreement with their decreasing polarities. 

A series of semi-aqueous solutions of the samples, containing 3-60% (w/w) methanol were titrated. From these titrations, the ps a values (the apparent ionization constants in methanol-water solvent) were obtained, and the Yasuda-Shedlovsky procedure was applied to estimate the aqueous pKg values (Avdeef, et ah, Anal. Chem., 65, 42-49 (1993)). The four-parameter procedure was used for electrode standardization in both aqueous and semiaqueous solutions."... 

Axarel 46/ Petroferm Semiaqueous defluxer mixed aliphatic hydrocarbons, diisobutyl dibasic acid ester mixture, and alkyloxy polyethylene oxyethanol High performance solvent cleaning for batch or in-line process N/A 2.8 N/A 96 <0.1... 

Since the use of solvent such as 1-1 trichloroethane is being banned, semiaqueous-developable permanent dry film resist has been developed by Hitachi Chemical to withstand the plating condition as previously described and is used extensively in Japan. 

The codisposal of trace metals (e.g. Co), synthetic chelates (e.g. ethylenediaminetetraacetic acid, H(4) EDTA) and water-miscible organic solvents has occurred at some contamination sites. The reactions of Co(II)-EDTA with a redox reactive naturally occurring solid, goethite, in aqueous and semiaqueous (methanol-water, acetone-water) suspensions was studied. UV-visible spectroscopy indicated that goethite catalysed oxidation of Co(II)-EDTA to Co(III)-EDTA by dissolved O2. These reactions have important implications on the fate of the redox-sensitive metal in complex, mixed waste environments. 

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