Trifluoroacetic acid 286 INDEX

Transesterification, fatty acid analysis of lipids, 437, 439 Triacetin, lipase assays, 378 Triacylglycerol acylhydrolase, 371, 375, 378. See also Lipases Triacylglycerols, 432 Tributyrin, lipase assays, 378 Trichloroacetic acid (TCA) solubility index for protein hydrolysis, 152 in TBARS determination, 548-550 Trienes, conjugated, determination of, 515-517, 523-524, 526, 528 Trifluoroacetic acid (TFA), for determination of neutral sugars, 721-722, 724-725, 729-730... 

Substantial gradient shift due to absorbance or refractive index changes of the mobile phase during broad gradients. This is particularly serious for running MS-compatible trifluoroacetic acid (TFA) or formic acid gradient at low UV. 

Many cellulose derivatives form lyotropic liquid crystals in suitable solvents and several thermotropic cellulose derivatives have been reported (1-3) Cellulosic liquid crystalline systems reported prior to early 1982 have been tabulated (1). Since then, some new substituted cellulosic derivatives which form thermotropic cholesteric phases have been prepared (4), and much effort has been devoted to investigating the previously-reported systems. Anisotropic solutions of cellulose acetate and triacetate in tri-fluoroacetic acid have attracted the attention of several groups. Chiroptical properties (5,6), refractive index (7), phase boundaries (8), nuclear magnetic resonance spectra (9,10) and differential scanning calorimetry (11,12) have been reported for this system. However, trifluoroacetic acid causes degradation of cellulosic polymers this calls into question some of the physical measurements on these mesophases, because time is required for the mesophase solutions to achieve their equilibrium order. Mixtures of trifluoroacetic acid with chlorinated solvents have been employed to minimize this problem (13), and anisotropic solutions of cellulose acetate and triacetate in other solvents have been examined (14,15). The mesophase formed by (hydroxypropyl)cellulose (HPC) in water (16) is stable and easy to handle, and has thus attracted further attention (10,11,17-19), as has the thermotropic mesophase of HPC (20). Detailed studies of mesophase formation and chain rigidity for HPC in dimethyl acetamide (21) and for the benzoic acid ester of HPC in acetone and benzene (22) have been published. Anisotropic solutions of methylol cellulose in dimethyl sulfoxide (23) and of cellulose in dimethyl acetamide/ LiCl (24) were reported. Cellulose tricarbanilate in methyl ethyl ketone forms a liquid crystalline solution (25) with optical properties which are quite distinct from those of previously reported cholesteric cellulosic mesophases (26). 

Picomole (10 mol) Polyaromatic hydrocarbon Refractive index Reversed phase Sodium dodecyl sulfate Signal-to-noise ratio Solute retention time Void volume of system Triethylamine Trifluoroacetic acid Tetrahydrofuran Ultraviolet... 

Cationics of the structure alkylamidopropyl-A/-(2,3-dihydroxy)-A/A/-dimethyl-ammonium chloride have been analysed on a column (150 x4 mm i.d.) of micro-Bondapak CN with water/acetonitrile/THF (57 42 1 by volume) containing 0.1% trifluoroacetic acid as mobile phase and differential refractive index detection [32]. Quantification was by external standard and the method was applied to cosmetic products. 

The problem of the sense of the helix has also been attacked with the aid of optical rotation measurements in the following manner. Downie et al. (1957) investigated the optical rotation of copolymers of l- and D-leucine in benzene and in trifluoroacetic acid. In the latter solvent the copolymers exist as random coils, independent of the fraction of the L-form [designated as l/(d -f- l)]. Since the residue rotation (corrected for the dispersion of the refractive index) is a linear function of l/(d - - l), as shown in Fig. 96b, and is zero when l/(d + l) = 0.5, the observed rotation may be attributed to the excess of l- over n-residues. This conclusion is based on the assumption that the optical rotation of independent groups is additive, and is supported by the straight-line graphs obtained for a variety of solvents and randomly coiled polypeptides. The existence of the polypeptide in the randomly coiled form in trifluoroacetic acid is consistent with the absence of a contribution from any helical configuration. 

For acrylate polymers with higher levels of carboxylic acids, THF can be modified by the addition of acids such as acetic, phosphoric, or trifluoroacetic. Levels as high as 10% acetic acid are considered acceptable by most manufacturers for their styrene/DVB columns. If such a modified mobile phase is used, it may need to be premixed rather than generated using a dynamic mixing HPLC pump because on-line mixing often leads to much noisier baselines, particularly when using a refractive index detector. 

Pertrifluoroacetic acid, produced in situ from HP and trifluoroacetic anhydride, is an efficient reagent for B V oxidation of butanone to yield ethyl acetate. The possible mechanism of the oxidation of aliphatic ketones by pertrifluoroacetic acid is discussed. Several organic reactions, including BV oxidations, have been studied by using reactivity and selectivity indexes proposed in the DFT. The concepts of electrophilicity and nucleophilicity have been applied as reactivity descriptors. The local hardness has been applied as well as a selectivity descriptor. The reactivity and selectivity patterns have been studied for the reactants involved in these organic reactions. They have been ranked in theoretical scales, which are comparable with experimental results obtained from... 

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