Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Liquid chromatography normal-phase

Normal-phase liquid chromatography (NP-HPLC), as the name implies, is the original version of HPLC. Nowadays it is not often used, only when results obtained with reverse-phase LC prove unsatisfactory. It is discussed first for didactic reasons. [Pg.80]

In NP-HPLC the stationary phase is more polar than the mobile phase and the interaction between analyte and column has predominantly polar character (hydrogen bonding, tt-tt or dipole-dipole interactions, etc.). The most commonly used NP stationary phase is silica gel ([Si02]j [HjOJ, ). Alter colunm preparation the surface of silica gel consists mainly of hydroxyl groups bound to silica atoms as shown in Fig. 7. [Pg.81]

These hydroxyl groups are often called silanol groups. These predominantly bind analytes by polar interactions. Other stationary phases are also used, such as aluminum oxide or chemically modified silica gel. In the latter case usually amino, diol, nitro, or cyano group containing chemicals are reacted with the free silanol groups to modify their binding properties. [Pg.81]

Mobile phases in NP-HPLC are mostly apolar solvents (or solvent mixtures) such as -hexane, n-heptane, dichloromethane, dichloroethane, diethyl ether, methyl acetate, ethyl acetate, acetone, isopropanol, ethanol, or methanol. In NP-HLPC more polar solvents represent higher solvent strength and these elute compounds faster from the column. The typical order of solvent strength is hydrocarbons ethers esters alcohols acids amines (going from weak to strong). [Pg.81]

The biggest problem in using NP-HPLC is its dramatic sensitivity to water. Even water traces (in the mobile phase or from the sample) may bind to the column, deteriorate its performance, and cause irreproducibility. In addition, particular care must be taken to ensure accurate pH, as in NP-HPLC, retention is very sensitive to the charge state of the analyte. Owing to these practical problems NP-HPLC is relatively rarely used. Its main application fields are separation of polyaromatic hydrocarbons, sterols, vitamins, chlorophylls, ceramides, and other Upid extracts. [Pg.81]

In normal-phase liquid chromatography the stationary phase is a polar adsorbent and the mobile phase is generally a mixture of non-aqueous solvents. [Pg.44]

1 Retention mechanisms and mobile phase ects in normal-phase liquid chromatography [Pg.44]

Both the solvent-interaction model (Scott and Kucera, 1979) and the solvent-competition model (Snyder, 1968, 1983) have been used to describe the effects of mobile-phase composition on retention in normal-phase liquid chromatography. The solvent interaction model on the one hand provides a convenient mathematical model for describing the relationship between retention and mobile phase composition. The solvent competition model on the other hand provides a more complete, quantitative description of the relative strengths of adsorbents and organic solvents used in normal-phase chromatography. [Pg.44]

1 Solvent interaction model for normal-phase liquid chromatography. The solvent-interaction model of Scott and co-workers (Scott and Kucera, 1979) assumes that the analyte partitions between the bulk mobile phase and a layer of solvent absorbed onto the stationary phase. The quantitative description of the relationship between retention and the composition of the mobile phase in the solvent-interaction model requires the definition of the void volume corrected retention volume (V), which is related to the retention volume (F ) and the void volume (Fq) by [Pg.45]

If we assume that the volume of stationary phase, Vg, volume of adsorbed liquid. Fa, then replacing Fj by Fa and substituting into equation (3.2) gives [Pg.45]

Leak from injector Poor flow rate due to surfactant Poor detection due to surfactant Unsuitable column Unsuitable counter-ion [Pg.82]

Unsuitable cone, organic modifier Too high cone, buffer Unsuitable pH Unstable flow rate Unstable temperature Non-equilibrated column Too diluted cone, buffer [Pg.82]

Check sensitivity of detector adjust cone, sample soln. [Pg.82]

Usually UV absorption of eluent is high because of counter-ion and buffer. Select suitable wavelength or change detector [Pg.82]


On-line coupling of normal-phase liquid chromatography (NPLC) and gas chromatography is today a well developed and robust procedure and has been regularly applied to environmental analysis. When a fraction of the NPLC sample is introduced in to the GC unit, a large-volume interface (LVI) is needed but, due to the volatility of the organic solvent used in NPLC, this does not present such a great problem. [Pg.361]

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. [Pg.362]

The most common approaches to sulfonylurea determinations involve high-performance liquid chromatography (HPLC). The earliest reported methods utilized normal-phase liquid chromatography (LC) with photoconductivity detection this type of detector demonstrated undesirably long equilibration times and is no longer... [Pg.400]

Okamoto, M., Kakamu, H., Nobuhara, K. and Ishii, D., Effect of silver-modified silica on retention and selectivity in normal-phase liquid chromatography,. Chromatogr. A, 722, 81, 1996. [Pg.50]

The mechanism of reversed phase chromatography can be understood by contrast with normal phase chromatography. Normal phase liquid chromatography (NPLC) is usually performed on a polar silica stationary phase with a nonpolar mobile phase, while reversed phase chromatography is performed on a nonpolar stationary phase with a polar mobile phase. In RPLC, solute retention is mainly due to hydrophobic interactions between the solutes and the nonpolar hydrocarbon stationary surface. The nonpolar... [Pg.142]

NP-HPLC, NPLC Normal-phase liquid chromatography... [Pg.758]

One column can be used for different types of liquid chromatography by changing the eluent components. As an example, a column packed with octadecyl-bonded silica gel has been used for size-exclusion liquid chromatography with tetrahydrofuran (THF), normal-phase liquid chromatography with n-hexane, and reversed-phase liquid chromatography with aqueous acetonitrile. Examples of the chromatograms are shown in Figure 1.4. [Pg.5]

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. [Pg.84]

Example 2 Chromatography of nitroaniline isomers. The elution order of the nitroaniline isomers was ortho, meta, and para in normal-phase liquid chromatography using H-butanol-w-hexane mixtures as the eluent, when the stationary phase material was either silica gel, alumina, an ion-exchanger, polystyrene gel, or octadecyl-bonded silica gel. The results indicate that the separation of these compounds can be performed on a range of different types of stationary phase materials if the correct eluent is selected. The best separation will be achieved by the right combination of stationary phase material and eluent.68... [Pg.84]

Figure 4.19 Solvent strength of combination of n-pentane and more polar solvents in normal-phase liquid chromatography using alumina. Symbols. A, methyl acetate, 0> acetone, , chloroform, and O, benzene. Figure 4.19 Solvent strength of combination of n-pentane and more polar solvents in normal-phase liquid chromatography using alumina. Symbols. A, methyl acetate, 0> acetone, , chloroform, and O, benzene.
The elution order of phthalic esters is related to the carbon chain length. The longer the chain length, the shorter the retention time in normal-phase liquid chromatography, and the elution order is reversed in reversed-phase liquid... [Pg.89]

To increase Vs, the chromatographer can increase the surface area of the stationary phase materials in normal-phase liquid chromatography, increase the stationary phase volume in reversed-phase or partition liquid chromatography, or increase the ion-exchange capacity in ion-exchange liquid chromatography. In general, if the internal diameter of a column is constant, the retention time... [Pg.99]

The qualitative analysis of retention behaviour in liquid chromatography has now become possible. Quantitative retention-prediction is, however, still difficult the prediction of retention time and the optimization of separation conditions based on physicochemical properties have not yet been completely successful. One reason is the lack of an ideal stationary phase material. The stationary phase material has to be stable as part of an instrument, and this is very difficult to achieve in normal-phase liquid chromatography because the moisture in organic solvents ages the silica gel. [Pg.131]

Perrin, C., Vu, V.A., Maftouh, M., Massart, D.L., Vander Heyden, Y. Screening approach for chiral separation of pharmaceuticals Part I. Normal-phase liquid chromatography. J. Chromatogr. A 2002, 947, 69-83. [Pg.210]

Caude, M. J. and lardy. A., Normal-phase liquid chromatography, in Handbook of HPLC, Katz, E., Eksteen, R., Schoenmakers, R, and Miller, N. (Eds.), Marcel Dekker, New York, 1998, pp. 325-363. [Pg.94]

Solvents selected were similar to the solvents that Glajch et al. [35] used for Normal Phase Liquid Chromatography. Methyl tert- butyl ether (a proton acceptor) was selected instead of ethyl ether, since the former one is less volatile. The other two selected solvents were methylene chloride (dipole interactions) and chloroform (proton donor). These three solvents meet all practical requirements. The polarity P [21] of the solvents is 2.5, 3.1 and 4.1, respectively. The solvents were used in pure form no supporting solvent was used. [Pg.285]


See other pages where Liquid chromatography normal-phase is mentioned: [Pg.94]    [Pg.318]    [Pg.813]    [Pg.969]    [Pg.328]    [Pg.100]    [Pg.133]    [Pg.429]    [Pg.635]    [Pg.7]    [Pg.44]    [Pg.65]    [Pg.81]    [Pg.81]    [Pg.81]    [Pg.84]    [Pg.85]    [Pg.87]    [Pg.88]    [Pg.90]    [Pg.99]    [Pg.133]    [Pg.192]    [Pg.207]    [Pg.251]   
See also in sourсe #XX -- [ Pg.31 , Pg.34 ]




SEARCH



High-performance liquid chromatography normal phase

High-performance liquid chromatography normal/reversed phase modes

High-pressure liquid chromatography normal phase

Normal Phase Ion-pair Partition Liquid Chromatography

Normal liquids

Normal phase

Normal phase liquid chromatography NPLC)

Normal-phase chromatography

Normal-phase high pressure liquid chromatography , solvent

Normal-phase liquid chromatography chromatograms

Normal-phase liquid chromatography compositional analysis

Normal-phase liquid chromatography cyano column

Normal-phase liquid chromatography separations

Normal-phase liquid chromatography silica column

Normal-phase micro-liquid chromatography

Normalized liquid chromatography

Phases chromatography

Phases liquid chromatography

Retention in Normal-Phase Liquid Chromatography

© 2024 chempedia.info