The Chromatographic Method

The Chromato phic Method.— The chromatographic method for the determination of interaction virial coeflRcients is related to the gas-solubility 

The subscripts 1 and 2 refer respectively to the carrier gas and the solute. Km(l) is the partial molar volume of the solute in the stationary phase at infinite dilution. The quantity Ji is defined by 

An essential assumption in the derivation of equation (27) is that the carrier is insoluble in the stationary phase. 

The experiments utilize a chromatograph designed to operate at pressures up to about 2500 kPa. This requires that special provision be made for sample injection and detection.The ehoice of stationary phase is dictated primarily by the requirement for insolubility of the carrier gas, but it is also necessary that the stationary phase be a good solvent for the solute in order that adsorption of solute on the column packing be minimized.  

Retention volumes are determined at a variety of pressures and the term Bi2 — l m(l) is determined by least-squares analysis of the In fir vs. p curve. It is important in such an analysis to examine the effect of the p term on the error in the coefficient of the linear term. A check on the self-consistency of the method is the requirement that the intercept In F r be independent of the carrier gas.  

---

Without going into details of the chromatographic method, a SAR separation (asphaltenes having been eliminated) can be performed in a mixed column of silica followed by alumina. The saturated hydrocarbons are eluted by heptane, the aromatics by a 2 1 volume mixture of heptane and toluene, and the resins by a 1 1 1 mixture of dichloromethane, toluene and methanol. 

Table 4 lists the specifications set by Du Pont, the largest U.S. producer of DMF (4). Water in DMF is deterrnined either by Kad Fischer titration or by gas chromatography. The chromatographic method is more rehable at lower levels of water (<500 ppm) (4). DMF purity is deterrnined by gc. For specialized laboratory appHcations, conductivity measurements have been used as an indication of purity (27). DMF in water can be measured by refractive index, hydrolysis to DMA followed by titration of the Hberated amine, or, most conveniendy, by infrared analysis. A band at 1087 cm is used for the ir analysis. 

FIG. 22-87 Schematic illustration of the chromatographic methods most commonly used in downstream processing for protein recovery... 

In practice of chemical analysis of organic substances, for some classes of compounds measuring of summary concentration in re-count to one of representatives is used. In the case of need of information about the content of each component, the chromatographic methods are applicable. 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

Making use of the chromatographic methods mentioned above, two different acetyl esterases could be purified from AEI. These esterases were named PAE and FAE. A third esterase was purified from AEII and this esterase was named RGAE, since it appeared to be similar to the... 

In summary, these exploratory data suggest that the chromatographic method used could be a valuable tool for study of this polymerization reaction. Reasonable data were obtained for amount and composition of the copolymer. Formation of graft polymer and/or nitrile rich polymer was detected. More detailed chromatographic study of this batch polymerization could lead to a practical on-line monitoring method... 

The separation of different substances of a mixture is one of the most important matters of analytical and preparative chemistry. The most efficient among all the separation methods used in technology and analytical chemistry is the chromato-graphie one. As it is known, the chromatographic method is based on different... 

Wu, C. S., Senak, L., and Malawer, E. G., Size exclusion chromatography of poly(methyl vinyl ether-co-maleic anhydride) (PMVEMA). I. The chromatographic method, J. Liq.Chromatogr., 12, 2901, 1989. 

Principles and Characteristics Of the chromatographic methods discussed in Chapter 4 essentially only SEC and HPLC are used to some extent for the analysis of dissolutions containing both macromolecular and additive components. SPE is a useful device for working... 

The methylxanthines can be determined in foods and biological systems by the chromatographic methods of TLC, GC, HPLC, or CE. Ultraviolet spectroscopy following a separation procedure can also be used. More recently, immunoassay methods have been developed. There is no single best method the analyst must balance the features of each assay with the final requirements for data precision and reproducibility. 

Note that it is highly desirable that the identity of every sample is confirmed before analysis, and that samples are adequately pure for the measurement in question. In the pH-metric methods, the sensor is a pH electrode and cannot distinguish between analyte and impurity. In the methods that depend on UV absorbance, if a sample contains an impurity with stronger absorbance than the sample, then the calculation of results from experimental data is complicated. Combinatorial samples are by nature poorly characterized, and even in the chromatographic methods in which analyte and impurity will be separated, it may be difficult to assign the peaks unambiguously. It is therefore advisable to purify samples before they are submitted for analysis of log D and pKa. 

Once the chromatographic method is developed, the selectivity of the optimized separation is checked on at least three different lots of the selected stationary phase for the selected column to determine whether the stationary phase is suitable for use in a final method. 

Module 1, Determination of Chemical and Structural Information on the Sample. The task of Module 1 is to provide non-chromato-graphic data for analytes prior to specification of the chromatographic method. Data bases have been developed for pK values of organic molecules, isoelectric points of proteins, and fluorescence spectral properties of organic molecules. 

Conjunction of the chromatographic methods of component separation with methods of analysis of biological properties provides great opportunities in their analysis. This has made the search for bioactive substances easier and will aid the future development of new research methods. 

The chromatographic method of Moeller was chosen as the most convenient route to relatively large amounts of the partially resolved acetylacetonates. Two... 

The analytical parameters for GC-MS TIC analysis of organic acids listed in Table 3.1.7 represent a reasonable compromise between degree of separation and analytical time, resulting in the profile shown in Fig. 3.1.3. A faster run time, usually achieved by increasing the ramp rate (°C/min) of the chromatographic method, may... 

All of these compds were detected colori-merrically and more recently their presence was verified by the Chromatographic Method of Tswect, which is described under CHROMATOGRAPHY in Vol 3 of Encycl, pp C289-R to C298-L... 

---