Chromatography HPLC mobile phase

Degasser for high-performance liquid chromatography (HPLC) mobile phase... 

Table 5.4.11 High-performance liquid chromatography (HPLC) mobile phase gradient composition (adapted from [31])...

The great versatility of HPLC lies in the fact that the stability of the chemically bonded stationary phases used in partition chromatography allows the use of a wide range of liquids as a mobile phase without the stationary phase being lost or destroyed. This means that there is less need for a large number of different stationary phases as is the case in gas chromatography. The mobile phase must be available in a pure form and usually requires degassing before use. The choice of mobile phase (Table 3.6) is influenced by several factors. 

Our initial attempts to separate the Cj and Dj isomers of 5 (G = 1) used octadecyl polysiloxane (ODS) as high performance liquid chromatography (HPLC) stationary phase and mixtures of acetonitrile/HjO or methanol/HjO as mobile phases. Under these classical reverse-phase conditions, the resulting efficiencies were extremely poor because of the low solubility of 5 (G = 1) in both mobile phases. By contrast, mixed mobile phases which contained acetonitrile (ACN) with some percentages of a cosolvent such as tetrahydrofuran (THF) substantially improved... 

Normal phase (NP) separations are comparatively rarely used in environmental analysis. Again, the reasons lie in the range of analytes amenable to this mode of separation, and in the limited compatibility of typical normal phase HPLC (NP-HPLC) mobile phases with mass spectrometric detection (this also applies to IC). Not only for this reason has interest recently grown in hydrophilic-lipophilic interaction chromatography (HILIC), which represents a viable alternative to the separation of very polar compounds with mobile phases that have a much better compatibility with MS detection, for example, acetonitrile/water with a low water content, typically below 10%, 32 Nonetheless, NP chromato-graphy retains its important role in sample preparation, particularly for the cleanup of complex environmental samples. In the off-line approach, fractions are collected and the relevant one is injected into the reversed phase HPLC (RP-HPLC) system, often after solvent exchange. 

Figure 3.20. Analysis of carboxylic acids and alcohols by reversed phase HPLC, with indirect UV detection, (a) Carboxylic acids. Chromatography conditions mobile phase, 3 X 10 4 M l-phenethyl-2-picolinium in acetate buffer (pH 4.6) column, ju-Bondapak phenyl detection, indirect UV absorbance at 254 nm. Peaks 1, acetic acid 2, propionic acid 3, butyric acid 4, valeric acid 5, caproic acid S, system peak, (b) Aliphatic alcohols. Chromatography conditions mobile phase, 4 x 10 4 M nicotinamide in water column. Ultrasphere ODS detection, indirect UV absorbance at 268 nm. Peaks 1, methanol 2, propylene glycol 3, ethanol 4, 2-propanol 5, 1-propanol 6, system peak 7, 2-butanol 8, 2-methyl-l-propanol 9, 1-butanol. (Redrawn from Refs. 23 and 24 with permission.)...

Figure 7 Liquid chromatography inductively coupled plasma mass spectrometry (LC-ICP-MS) chromatogram of a standard mixture of organolead and inorganic lead compounds (Pb2+, TML, and TEL) using reversed-phase HPLC. Mobile phase, 0.1 M ammonium acetate, and 0.1 M acetic acid at pH 4.6, 30% ethanol. Flow rate 1 mL/min. (From Ref. 26.)...

Chromatography The derivatives can be analysed by several techniques. Liquid chromatography was used to separate acetylated products following extraction from aqueous solutions with chloroform, evaporation of the solvent and dissolution of the residue in the HPLC mobile phase. Separations were achieved by ODS reversed phase liquid chromatography using acetonitrile/ water as the eluent or with hexane/ethanol (19 1) on normal phase columns (Develosil 60). 

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