Use as mobile phases

The influence of NH., and CO, on the chromatographic behaviour of benzoic acid and its derivatives (o-, m-, p-hydroxybenzoic, nitrobenzoic, aminobenzoic, chlorobenzoic acids) was studied. The work was carried out by means of upgoing TLC on Sorbfil plates. Isopropanol- and ethyl acetate-containing water-organic eluents were used as mobile phases in the absence or presence of gaseous modifiers in the MP. The novel modification of TLC has been found to separate benzoic acids with different values of their dissociation constants more effectively than water-organic mobile phases. 

Involatile inorganic buffers, when used as mobile-phase additives, are the prime canse of blocking of the pinhole. The situation can be alleviated either by replacing them by a more volatile alternative, such as ammonium acetate, or by nsing post-colnmn extraction to separate the analytes from the buffer, with the analytes, dissolved in an appropriate organic solvent, being introduced into the mass spectrometer. 

The mobile phase is always freshly made up. This is done by mk-ing the three mobile phase components in a separating funnel and shaking vigorously several times the top phase is used as mobile phase. 

M tris-HCl buffer solution (pH 7.94) was used as mobile phase. The peak separation obtained with a three column set (G 3000 PW + 2 G5000 PW) is comparable to the peak separation obtained in the present study for the molecular weight range, 120,000 to 3.6 X 10. Peak broadening appeared to be appreciable although no calculations of single-species variance were done. 

The separation can be optimized by the alteration of the mobile phase composition. The more the polarity of solutes, the less the content of water of mobile phase must be. If water-alcohol mixmre is used as mobile phase, the resolution can be improved by using alcohol witli different chain lengths and different water proportions. 

The sample is dissolved in the eluent used as mobile phase. 

Marnela et al. [57] used an amino acid analyzer using fluorescence detection to determine penicillamine in urine. Urine is analyzed on a Kontron Chromakon 500 amino acid analyzer containing a column (20 cm x 3.2 mm) of AS70 resin in the Li (I) form. Buffers containing LiOH, citric acid, methanol, HC1, and Brij 35 at pH 2.60, 3.20, and 3.60 are used as mobile phases (0.4 mL/h). The fluorescence reagent is prepared by the method of Benson and Hare. Detection is at 450 nm (excitation at 350 nm). The analyte response is linear from 0.025 to 10 mM, with a limit of detection of 25 pM. 

Volatile substrates were again reacted in the gas-phase, and selectivities equal to those from the homogeneous phase reactions were obtained. For less volatile substrates supercritical CO2 was used as mobile phase and the substrates were added via a stepwise injection. For styrene a small drop in selectivity was observed compared to the... 

The important column parameter t0 can be measured in various ways. In most cases, the center of the first band or baseline disturbance, following sample injection, denotes t0. If there is any doubt on the position of t0, a weaker solvent (or other unretained compound) can be injected as sample, and its tR value will equal t0. A weaker solvent provides larger k values and stronger sample retention than the solvent used as mobile phase (see Table 15.1 for a list of solvents according to strength). 

In supercritical fluid chromatography, fluids above their critical point are used as mobile phases. This chapter discusses the principles of operation, mobile phase considerations, parameters that can be adjusted in method development as well as an overview of instrumentation required and a few pertinent examples from current literature. Not everything can be illustrated, but the advantages of this diverse technology will be highlighted. 

The impurities of H-acid (65), an intermediate for various synthetic dyes, include Koch s acid (66), omega acid (67), chromotropic acid (68) etc. They were determined by RP-HPLC-UVD at X 235 nm, using as mobile phase a 0.3 M aqueous solution of sodium sulfate184. 

THE TWO- AND THREE-STEP GRADIENT PROGRAMMES USED FOR THE ANALYSIS OF EXTRACTS FROM VACCINIUMMYRTILLUS L. AND VACCINIUM V1TIS-IDAEA L. MIXTURE OF TOLUENE, HEXANE, ETHYL ACETATE, AND METHANOL WERE USED AS MOBILE PHASES... 

Measurements were realized in an ODS (250 x 4.6 mm i.d.) and in an octylsilica column (150 x 4.6 mm i. d.) at 29°C. Particle size of both stationary phases was 5 /jm. Various mixtures of water-methanol and water-ACN were used as mobile phases containing phosphate buffers of different pH. Flow rate and detection wavelength also depended on the chemical character of the analytes. Chromatographic profiles illustrating the effect of electrochemical treatment on the dyes are depicted in Fig. 3.87. 

SO far. Methanol or hexane-propanol mixtures are usually used as mobile phase. Tetrahydrofuran and chloroform are excluded since they dissolve the polymer. Snch chiral phases are commercially available from Daicel nnder the names Chiralpak OT(-I-) and OP( + ). 

In the reversed-phase mode, mixtures of aqueous buffer and acetonitrile are commonly used as mobile phase. Other modifiers are possible, but as shown in Figure 6, acetonitrile often produces the best separations and peak shapes. Several studies have shown the fundamental importance of keeping the chiral analytes neutral when working with polysaccharide stationary phases in the reversed-phase mode. ° ° Therefore, acidic compounds are preferably analyzed at low pFI while basic compounds will be analyzed either in basic media or at low pH in the presence of a chaotropic salt such as sodium perchlorate (NaC104) or potassium hexa-fluorophosphate Some illustrations of the effect of the addi-... 

The hydroperoxides of various phospholipids, such as phosphatidylcholine (PC— OOH, 155), phosphatidylserine (PS—OOH), phosphatidylethanolamine (PE—OOH), phos-phatidylinositol (PI—OOH) and cardiolipin (CL—OOH), can be determined by HPLC-ELD on a polar LC—NH2 column, using as mobile phase a MeOH//-PrOH/40 mM aqueous NaH2P04 mixture (61 30 9 by volume). ELD is by the hanging Hg drop electrode method set at —150 mV vs. SCSE. The relative mobility for the given chromatographic system is shown in equation 68, which is almost a reversal of the order shown in equation 63 for HPTLC. The LOD varies from about 0.5 to 1.0 pmol, depending on the class of phospholipid hydroperoxide . ... 

For obvious reasons CDs (and other dextrins) are potentially good chiral selectors for chromatography on the one hand they can be used as mobile phase additives (CMPA) in TLC45, HPLC46 and CE47 49 and on the other they can be covalently bonded onto solid supports50,51 and silica gei 52- 54 xhis approach can be extended to the preparative resolution of enantiomers41,55,56. 

Table 3.1—Eluotropic force and viscosity of solvents used as mobile phases. The eluant strength of the mobile phase can be adjusted by mixing different solvents together.

Carbendazim and thiophanate-methyl were determined in cabbage and onions (5,44). Au-tors et al. (44) used the cation-exchange technique for the HPLC determination. The preservatives were detected at 275 nm, and tetramethylammonium nitrate in nitric acid was used as mobile phase recoveries were 75% at a level of 0.08 mg/kg, when the determination limit of the method was 0.02 mg/kg. 

After benzoylation, it was possible to analyze together the food substances of varying chemical structures, such as alcohols, esters of 4-hydroxybenzoic acid, phenolic antioxidants, saccharides, and sugar alcohols. The method allowed the determination of these substances in different matrices by the same analytical procedure, using the same cleanup. The preservatives were separated on an RP-18 column. Acetonitrile-water (50 35) or acetonitrile-water-butylmethyl ether (110 35 40) were used as mobile phases. Detection was UV at 230 nm (71). 

Benzimidazole carbamates are usually analyzed by HPLC. Different stationary phases have been assayed, and alkyl-bonded-silica-based phases have generally been considered the most useful separation mode, although polymer-based columns performed better in separating benzimidazole fungicides (20). Buffered water and methanol (124,20) or acetonitrile (125) have been used as mobile phases. 

Unlike post-column derivatization, no restrictions are imposed by the solvent system used as mobile phase. The reaction conditions can therefore be chosen freely. 

Sometimes, the use of high-concentration buffers in the reversed-phase mode decreases column life and efficiency. Therefore, the use of an alternative mobile phase (i.e., normal phase) is an advantage in chiral resolution with these buffers. The most commonly used solvents in the normal phase mode are hexane, cyclohexane, and heptane. However, dichloromethane, acetone, propanol, ethyl-acetate, ethanol, and chloroform also have been used as mobile phase solvents. Hargitai and Okamoto [110] used hexane-2-propanol (in different ratios) as the mobile phase in the chiral resolution of several drugs. These authors also studied... 

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