Heptafluorobutyric acid reagent

Reagent 3 anhydrous n-heptafluorobutyric acid Solvent 1 benzene... 

Increased retention of the analytes can also be achieved by addition of various ion-pair reagents in the mobile phase Tetrabutylammonium cations have typically been used as counter ions, at around pH 6.5, to increase retention and improve the selectivity in the analysis of monobasic penicillins (105, 123). Alkyl-sulfonic acids have been also used to improve the separation of -lactams bearing an amine function in their side chain or having a neutral side chain. Heptanesul-fonic acid (80, 103), decanesulfonic acid (87, 93, 106), dodecanesulfonic acid (77, 107-110), or mixtures of octanesulfonic and dodecanesulfonic acids (73, 75, 78, 79) constitute the principal alkylsulfonic acids used in -lactam analysis. In some applications, heptafluorobutyric acid (74, 76) or sodium thiosulfate (90, 112, 115, 116, 121, 122) has also been used as an ion-pairing reagent. 

If polar sequences or short phosphopeptides fail to bind to the stationary phase upon loading, the acetonitrile content of the eluent could be reduced to 3%. A further decrease is not possible for standard Ci8-columns, as the stationary phase could collapse reducing the loading capacity and the reproducibility. Instead, TFA could be replaced by the more hydrophobic ion-pair reagent HFBA (heptafluorobutyric acid), or a stationary phase with a special coating compatible with pure aqueous eluents could be used (e.g., Aqua-column from Phenomenex). 

For HPLC-MS/MS assays, the mobile phase is an important consideration. For reversed-phase HPLC systems (the most common), mobile phase A is water plus one or more modifiers while mobile phase B is usually either acetonitrile or methanol with one or more modifiers. Modifiers have to be volatile for HPLC-MS/MS assays. Typical modifiers are acetic acid, formic acid, and ammonium acetate. Formic acid is so popular that it is now available as a premixed HPLC solvent (0.1% in water or acetonitrile). Most other modifiers are not recommended. Triethylamine (TEA) and trifluoroacetic acid (TFA) are a problem as they are known to cause ion-suppression problems. For some special HPLC-MS/MS assays that need ion-pairing reagents, hexylamine and heptafluorobutyric acid have been found to be successful [51-53], Gao et al. [54] recently evaluated a series of ion-pairing reagents in terms of their suitability for an HPLC-MS/MS assay. 

Figure 7.12. We make a peptide iadder You need a 100-)il glass tube, a heating block, two vacuum pumps, and two solvent traps one for trimethylamine/trifluoroethanol (coupling buffer) and TFEITC and one for heptafluorobutyric acid (cleaving reagent). Aerial oxygen does not interfere, and nitrogen gassing is unnecessary.

A. Frolov and R. Hoffmann, Separation of Amadori peptides from their unmodified analogs by ion-pairing RP-HPLC with heptafluorobutyric acid as ion-pair reagent. Anal. Bioanal. Chem., 392 (2008) 1209-1214. 

Examples of applications of derivatization reagents include diazomethane for acids and phenols acetic anhydride for phenols heptafluorobutyric acid for anilines and phenols. 

For the library samples that contain very polar by-products, excess reagents, or impurities, an ion-pair reagent may be added to the mobile phase to improve retention of the polar components on the reversed-phase HPLC column. For small polar basic components such as amines, 0.1-1% of heptafluorobutyric acid can be added into the mobile phase containing acetonitrile or methanol in water. For small polar acidic components such as carboxylic acids, 5-20 mM of tetrabutyl-ammonium dihydrogenphosphate can be added into the mobile phase containing acetonitrile or methanol in 50 mM phosphate buffer (pH 7.4). 

The extracted THC-COOH is transferred completely into Nil glass vials. As derivatization agents 50 pL pentafluoropropanol and 80 pL heptafluorobutyric acid anhydride are added and the reaction mixture is heated to 65 C for 20 min in the crimp-closed vial. The remaining derivatization reagents are then completely evaporated and the remainder is carefully transferred to conical autosampler microvials (ND 8, 1.1 mL) using a microliter syringe and toluene as solvent, so that an end volume of 200 pL is achieved for the injection of 1 pL aliquots of the derivatized extract. 

Derivatization Reagents 50 pL pentafluoropropanol 80 pL heptafluorobutyric acid anhydride... 

An alternative approach for the analysis of blood samples from the same group of Iranian mustard gas victims has been described (50). As mustard gas alkylates amino acids in hemoglobin, adducts will be formed, which remain in the bloodstream for some time. Selective cleavage of the alkylated N-terminal valine of the a-chain of hemoglobin was carried out by using the modified Edman reagent pentafluorophenyl isothiocyanate. After derivatiza-tion of the adduct-derived pentafluorophenylthio-hydantoin with heptafluorobutyric anhydride, the... 

Lanthanide shift reagents are hard Lewis acids and normally do not react with alkenes. But Eu(fod)3 in combination with silver heptafluorobutyrate [46] alters the spectrum of alkenes by a type of interaction shown in Fig. 10.19. 

Derivatization Most amino acids are nonvolatile and must be derivatized prior to separation by GC. Amino acids are both esterified and acylated to produce N(0,S)-acylamino acid esters, with the most common being (N(0,5)-trifluoroacetyl- -butylesters. Other alcohols of low relative molecular mass have also been employed for the esterification including methanol, propanol, isopropyl alcohol, butanol, or isobutyl alcohol. Several different acylating reagents have been explored as well, including acetic anhydride, trifluoroacetic anhydride, penta-fluoroproprione anhydride, or heptafluorobutyric anhydride. 

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