Ion-pairing agents

Histones (from S4A mouse lymphoma). Purification used a macroprocess column, heptafluorobutyric acid as solubilising and ion-pairing agent and an acetonitrile gradient. [McCroskey et al. Anal Biochem 163 427 1987.]... 

Figure 2 Chromatogram of a polar (benzoic acid) compound with water acetoni-trile mobile phase. Chromatographic conditions — column 30 cm x 3.9 mm p-Bondapak C18 (10-pm particle size) mobile phase water acetonitrile (90 10) flow rate l.Oml/min column temperature ambient detector wavelength 254 nm. (A) No ion pairing agent. (B) With ammonium acetate as an ion pairing agent.

Therefore, the way to ensure reproducible adduct formation is to use mobile-phase additives (e.g. ammonium acetate or formate, formic, acetic or trifluoroacetic acid (in APCI), ammonium hydroxide, etc.). Their application in the mobile phase can be an effective way to improve the intensity of the MS signal and LC-MS signal correlation between matrix and standard samples. However, it is observed that some additives like trifluoroacetic acid or some ion-pairing agents (triethyl-amine) may play a role in ionisation suppression [3]. In addition, high concentrations of involatile buffers will cause precipitation on, and eventually blocking of, the MS entrance cone, leading to a fast decrease of sensitivity. For the in volatile NaAc buffer, it is advisable to maintain... 

The use of ion pairing agents, such as sodium benzenesulfonate, may be helpful in the analysis of complex mixtures of quaternary ammonium compounds, as they modify their retention times418. 

The analytes were well separated by the technique as demonstrated in Fig. 3.109. The limit of detection depended on the type of analytes, ranging from 0.2 /tg 1 to 2.6 lg/1. The limit of quantitation varied between 2 and 10 /tg/1. It was stated that the ion-pair LC-ESI-MS-MS technique using TrBA as the ion-pairing agent allows the separation of... 

When chromatographic resolution of species based on modifications located at the protein surface is desired, it may be advisable to use conditions that favor retention of native conformation.17 Here, the standard acidic conditions described in the preceding text may be inappropriate, and mobile phases buffered near neutrality may be required. Buffers based on ammonium acetate, ammonium bicarbonate, and triethylammonium phosphate may prove more useful in resolving polypeptide variants with differing posttranslational modifications, amino acid substitutions, or oxidation and deamidation products. The addition of more hydro-phobic ion-pairing agents may be needed to obtain polypeptide retention, and a variety of alkyl sulfonates and alkyl amines have been described for specific applications.17... 

Triethylamine (TEA) is a common additive used in RPLC, which can have two beneficial effects. It can serve as an ion-pairing agent to promote retention of anionic species, and it can suppress the interaction of basic solutes with residual silanols. In fact, it is most frequently used at concentrations of 5 to 25 mM to... 

Based on the theory, the separation of enantiomers requires a chiral additive to the CE separation buffer, while diastereomers can also be separated without the chiral selector. The majority of chiral CE separations are based on simple or chemically modified cyclodextrins. However, also other additives such as chiral crown ethers, linear oligo- and polysaccharides, macrocyclic antibiotics, chiral calixarenes, chiral ion-pairing agents, and chiral surfactants can be used. Eew non-chiral separation examples for the separation of diastereomers can be found. 

Ion-pair reverse phase HPLC. Aqueous samples confaining pyridoxine as infernal standard and 0.5% heptafluorobutyric acid as ion-pairing agent (IP) were injected in an RP-HPLC system with a Varian ODS-80TM column and eluted with 0.15% heptafluorobutyric acid in 24% methanol. Pyridinoline cross-link fluorescence was defecfed af Xgx 295 nm and Xem 400 nm (Bank ef al., 1997). 

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