Eluents salicylic acid

Fig. 42., Flota of the retention foctors of monoprotic acid versus the pH of the eluent, rhr iliilii wcrciohliiiiicil on l

Figure 4.37. Effect of eluent pH on selectivity in reverse-phase BPC. Column, 30 x 0.4cm, Bondapak-C, 10/jm mobile phase, 0.025M NaH2P04-Na2HP04 wiih 40%v methanol flowrate, 2ml/min temp., ambient detector, UV, 220nm, samples. 1—lOpg. (1) Salicylic acid (2) phenobarbitone (3) phcnacctin (4) nicotine ...

Electrochemical detectors can be used in the oxidative mode for a wide range of drugs, including cannabinoids, haloperidol, morphine, paracetamol, phenothiazines, salicylic acid, and tricyclic antidepressants. Operation in the reductive mode is more difficult as dissolved oxygen must be removed from the eluent (K. Bratin et al, J. liq. Chromat., 1981,, 1777-1795). Reductive applications include chloramphenicol and benzodiazepines. 

Fig. 3-30. Separation of various inorganic anions on a Nucleosil 10 Anion silica-based anion exchanger. - Eluent 0.025 mol/L sodium salicylate (pH 4.0 with salicylic acid) flow rate 1.5 mL/min detection refractive index injection volume 10 pL solute concentrations 1 to 2 g/L of the various anions.

The chromatogram shown in Fig. 3-66, obtained using nicotinic acid as the eluent, serves as an example of the variety of organic adds that can be used as eluents. Nicotinic acid is most suitable for the separation of monovalent anions. In contrast to other monocarboxylic adds, it is characterized by a good water solubility and a low equivalent conductance. In addition, its propensity to adsorb at the stationary phase is very low, which mostly prevents the formation of the usual system peak. However, divalent anions are strongly retained under these chromatographic conditions. For their fast separation, eluents based on salicylic add or trimesic add are more suitable. 

Although only monovalent anions are included in Table 6.8, similar effects are observed with some divalent anions. Salicylic acid will elute sulfate in 5.2 min and thiosulfate in 7.3 min under the conditions in Table 6.7. However, the weaker eluents such as succinic or nicotinic acid require an excessive amount of time to elute divalent anions. 

Another technique is vacancy spectroscopy. In this application, an eluent is used that absorbs uv or visible radiation. When the sample passes through the detector, less radiation is absorbed because of the vacancy. For example, the benzene ring in a mixture of 4 mM salicylic acid - (Tris) is measured at 254 nm. Alternately, the eluent for cations can be Ce and the decrease in the yellow color monitored in the visible region. 

Nivaud-Guemet, E. Guemet, M. Ivanovic, D. Medenica, M. Effect of eluent pH on the ionic and molecular forms of the non-steroidal anti-inflammatory agents in reversed-phase high-performance liquid chromatography. J.Liq.Chromatogr, 1994, 17, 2343-2357 [also aspirin, flufenamic acid, keta-zone, mefenamic acid, niflumic, niflumic acid, nixylic acid, oxyphenbutazone, phenacetin, salicylamide, salicylic acid, sulfinpyrazone]... 

Fig. 7.5. Effect of variation of the eluent pH upon elution volume. Chromatographic conditions column, pBondapak Cjg (10 pM) (300 mmX4 mm I.D.) mobile phase, eluent solutions (pH 3.0, 5.0, 7.0 and 9.0) were made up from 0.025 M NaH2P04 and/or 0.025 M Na2HP04 solutions plus 40% methanol (solutions were adjusted to final pH by the addition of 5% sodium hydroxide or phosphoric acid solution) detection, UV at 220 nm. , salicylic acid a, phenobarbitone a, phenacetin O, nicotine , methylamphetamine. Reproduced from Twitchett and Moffat (1975), with...

In 1973, ion-pair formation associated with phase transfer was used by Eksborg and Schill [3] to develop normal-phase ion-pair chromatography. A polar bare silica stationary phase was impregnated with an aqueous ionic solution. The eluent, a mixture of he mne, chloroform and pentanol, could separate various benzoic and salicylic acid derivatives. Karger [4] and Knox [5] used the normal phase mode with impregnated stationary phases to separate catecholamines by ion-pairing. 

The kind of counter ion of an ion-pair reagent is vitally important for selecting the appropriate detection method. If suppressed conductivity detection is applied, the ion-pair reagent is used in its hydroxide form. With direct conductivity detection, salicylate is perferred as the counter ion for tetraalkylammonium cations [19,20], since these salts exhibit a lower background conductance in aqueous solution. According to Wheals [21], eluents such as cetyltrimethylammonium bromide in combination with citric acid at pH 5.5 have proved suitable for UV-, RI-, and amperometric detection, as well as for direct conductivity detection. This example is an impressive illustration of the versatility of ion-pair chromatography. 

Several other organic acids have been used as eluents in anion chromatography. These include succinic, nicotinic, salicylic, fumaric and citric acid [14]. One objective was to find an eluent that is not adsorbed by the resin matrix and that attains equilibrium faster than benzoic acid. The following organic acids, listed in order of their increasing eluting power for sample anions, attain equilibrium fairly rapidly nicotinic, succinic, citric, fumaric, salicylic. 

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