Stationary phases polyester

Gas chromatographic analysis, using an HMDS-treated Chromo-sorb W column with 7% Craig polyester as the stationary phase, indicated the product to have a purity of 97%. The 3% impurity is most probably the isomeric 1-methylcyclohexene. 

Restricted access phases are another approach to exploiting the differences in characteristics of analytes. Large analytes are excluded from an internal surface on which an adsorptive stationary phase is present. A herbicide analysis for Metsulfuron methyl, Bentazone, Bromoxynil, methylchlorophenoxy acid, and Mecoprop in the presence of humic acid was performed on restricted access reversed phase media.52 The cytostatic compound epirubicin and its metabolites were separated from plasma using a Pinkerton GFF II column.53 Gradient separations of polymers on reversed phase and on normal phase represent an alternative to gel permeation chromatography. Polyesters of noncrystalline materials were separated on a variety of such phases.54... 

Many substances can serve as the stationary phase for gas chromatographic separations of methyl esters in most cases polyester, polyether, or silicone greases are used. Percival (18) has investigated the composition of polyesters by methanolysis with sodium methyl oxide. The dimethyl esters of the dicarboxylic acids present in the composition and free glycols are formed and subsequently are separated at temperatures between 110° and 180° C. on a column of GE silicone SF-96 and Fluoropak 80. It should be possible to adapt this method to the analysis of polyesters used as plasticizers. 

Tail reducers are polar substances added in small quantities along with the stationary phase, and are used most frequently with nonpolar phases. Phosphoric acid is used with polyesters(7) for analysis of fatty acids and has been found effective for... 

In analysis of polar compounds, tailing is minimized if the stationary phase is similar in composition to the types of sample being analyzed. For example, alcohols with carbowax, esters with polyesters, and amines with tetraethylenepentamine. If these phases do not give the desired separation, it may be advisable to add them to another phase as a tail reducer. 

One of the most common problems associated with deterioration of columns is the presence of water and/or oxygen in the carrier gas. This is more common with nitrogen than with helium. Stationary phases such as polyesters, FFAP, SP-1000, and carbowax depolymer-ize rapidly with 100 ppm of water in the carrier gas columns may be satisfactory the first day and destroyed the next. If this is occurring, peaks for polar compounds will begin to tail and this will become progressively worse. It is not necessary to have a fancy device to remove the water, but it should have the capacity to remove large quantities of water. 

Columns prepared with polymeric stationary phases such as Carbowax, polyesters, or polyphenyl ethers, should be conditioned at a temperature at which the column will be used. These stationary phases contain polymers of varying molecular weight and the conditioning helps to remove the more volatile portions. 

The GC separation of esters and the selection of the stationary phase represent problems of varying degrees of complexity in individual cases. An acceptable separation can usually be obtained on different polyester stationary phases (EGA, butanediol succinate polyester, EGS, etc.), Carbowax-type phases, OV-17, OV-225 and SE-30. Non-selective and non-specific stationary phases are preferred. The supports should not be acidic, and they are sometimes modified by silanization. In particular instances, when other groups are also derivatized prior to the analysis the selection of the stationary phase may be very difficult. These problems are discussed for individual types of compounds in Chapter 5. 

Problems with the selection of the stationary phase for the GC of acyl derivatives are similar to those associated with the GC of esters. In simple separations silicone and polyester phases are satisfactory but more complicated separations require special phases, low coatings, mixed phases, etc. Individual cases are discussed for specific types of compounds in Chapter 5. 

TFA-methyl esters are very volatile. Their retention times on polyester stationary phases are up to six times shorter and on silicone stationary phases up to three times shorter than those of the corresponding acetyl methyl esters. A high volatility can also result in losses of the derivatives during their preparation, and therefore esterification with diazomethane is not recommended as mere evaporation of ethereal solution can cause significant losses of the derivatives of Ala, Val, Gly and Leu. If evaporation of the... 

A number of packings with different stationary phases have been tested for the GC separation of TFA-butyl esters of amino acids. Polyester stationary phases, e.g., 1%... 

The selection of a stationary phase suitable for the GC analysis of all amino acids seemed to be the main problem hindering the wider use of these derivatives, which were always applied to a limited number of amino acids only. For the separation of TFA-amyl esters about 100 stationary phases have been tested, most of which were rejected owing to the decomposition of the acyl derivatives of hydroxyl and thiol groups that proceeds on some stationary phases with Tyr, Ser, Hypro, Thr and CysH. The application of 25% DECS led to the elution of only eight derivatives of amino acids out of thirteen that were analysed [225], The polyester PEGA and the silicones QF-1 and MS-710 [197,227, 228] were reported as the most suitable liquid stationary phases. For the analysis of... 

GC was performed on a polyester stationary phase (10% of neopentyl glycol sebacate or Carbowax 20M) at 170°C. The method was applied to a mixture of aldopentoses, aldo-hexoses and aldoheptoses in biological material. 

A stationary phase possessing medium polarity between the above two, e.g., organic silicone polyester composed of ethylene glycol succinate combined with cyanoethyl silicone, is recommended as the most suitable [437]. 

Aldonitrile acetates of sugars have been applied to their GC analysis in different polysaccharides [442] on LAC-4R-886 polyester stationary phase (190°C)and to the analysis of polyols and aldoses in urine and crystalline lenses [444] on a capillary column of borosilicate glass (60 m X0.3 mm l.D.) coated with SE-30 containing a dispersion of Silanox 101 (temperature programming at l°C/min from 150°C). These derivatives were very stable and a uniform product was formed from every individual substrate. 

On a column coated with 5% of LAC-4R-886 polyester stationary phase, a single large... 

Partition Chromatography. Unlike the other types of chromatography discussed thus far, this type is usually used for analytical (rather than preparative) applications. In addition, this type of chromatography is often performed in a thin-layer (rather than a column) format. The stationary phase in partition chromatography is usually a glass plate (rigid) or polyester sheet (flexible) coated with a very thin layer of the desired adsorbent. For most applications, the adsorbent is a cellulose, silica, polyamine, or aluminum oxide-based matrix. In... 

Fig. 22. LC-CC chromatogram of an aliphatic polyester, stationary phase Tessek silica gel, eluent acetone/hexane 51 49 (v/v) (from [121] with permission)...

Capillary and packed (GC) columns are of value in the analysis of complex mixtures of lipids. The best capillary column length will depend on the complexity of the material injected, however, 30-m columns are often employed. In packed columns, many types of stationary phases are available for lipid separation, and these include silicone and alkylated or cyanogenated derivatives, polyesters, polyglycol, and carboranes. It is also common to derivatize the fatty-acid side chains to the corresponding methyl esters by reaction in BF3/ methanol prior to chromatographic analysis to achieve more distinct and uniform separations. 

A variety of compounds have been used as the stationary phase in GLC, These include methyl silicone polymers, substituted silicone polymers, and silicone polyesters (Table 6-1). These materials are coated or chemically bonded onto the surface of the support particles or onto the walls of the column. Although more expensive, bonded materials are preferable because of their stability. 

To have a reasonable residence time in the column, an analyte must show some degree of compatibility (solubility) with the stationary phase. Here, the principle of like dissolves like applies, where like refers to the polarities of the analyte and the immobilized liquid. Polarity is the electrical field effect in the immediate vicinity of a molecule and is measured by the dipole moment of the species. Polar stationary phases contain functional groups such as —CN, —CO, and —OH. Hydrocarbon-type stationary phases and dialkyl siloxanes are nonpolar, whereas polyester phases are highly polar. Polar analytes include alcohols, acids, and amines solutes of medium polarity include ethers, ketones, and aldehydes. Samrated hydrocarbons are nonpolar. Generally, the polarity of the stationary phase should match that of the sample components. When the match is good, the order of elution is determined by the boiling point of the eluents. 

Figure 15.13 Analysis of synthetic polymers, using new and aged polyester fabric (after Swiss Federal Laboratories for Materials Testing and Research, St. Galien). Conditions sample, polyethylene terephthalate dissolved in hexafluoroisopropa-nol columns,fourcolumns25cm x 7 mm i.d. stationary phases, HibarLiChrogel PS 1, PS 20, PS 400, and PS 4000 in series, 10[im mobile phase, Imlrnin" chloroform-hexafluoroisopropanol (98 2) temperature, 35 °C UV detector, 254 nm.

Using this (LI) preparation procedure, Stefanovic and Walker (SO) studied the effect of stationary phase-support ratio on the gas-chromatographic separation of trifluoroacetylamino acid butyl esters using ethylene glycol adipate polyester columns. They found that, for certain amino acids, the elution pattern was a function of the amount of liquid phase on the column packing. When 0.5% ethylene glycol adipate was used, sharp well-defined peaks were obtained and all the amino acids listed in Table 6 except cysteine and methionine were completely sepa-... 

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