Temperature elution

Figure 6. Graphs of Elution Temperature of (R) 4-Benzyl-2-oxazol-idinone against Program Rate for Three Different Initial Temperatures...

A partial solution to the problem of producing sharp peaks at low elution temperatures is to add a small amount of a higher-boiling co-solvent to the main solvent. As suggested by Grob and Muller (23, 24), butoxyethanol can be used as a suitable cosolvent for aqueous mixtures in such cases. 

Volatile analytes. As residue analysis is also trace analysis in the lower ppm (mg kg ) to ppb ( ug kg ) range, concentration steps usually involve evaporation of solvents (sometimes with traces of water present) to near dryness. The volatility of analytes can be deduced from their elution temperatures in GC, and thus whenever an analyte elutes from a nonpolar GC phase of film thickness <0.25 qm below approximately 150 °C, losses due to co-evaporation during concentration by the rotary evaporator or by a stream of nitrogen need to be avoided. 

The film thickness is calculated from the elution temperature of methyl dodecanoate (E j). However, quantitation of film thickness requires a calibration of elution temperature... 

Trying to determine which column is ideal for a specific analysis can be difficult with over 1000 different columns on the market [74]. A proper choice implies a definition of parameters such as column material, stationary phase (polarity), i.d., film thickness and column length. Guides to column selection are available [74,75]. The most important consideration is the stationary phase. When selecting an i.d., sample concentration and instrumentation must be considered. If the concentration of the sample exceeds the column s capacity, then loss of resolution, poor reproducibility and peak distortion will result. Film thickness has a direct effect on retention and the elution temperature for each sample compound. Longer columns provide more resolving probe, increase analysis times and cost. 

Fig. 21 Comonomer content vs. TREF elution temperature for an OBC and a blend of two random copolymers [46]...

Fig. 55. Gel-permeation chromatogram(GPC) of a microgel sample of Mw = 10X106 g/mol obtained in the anionic polymerization of EDMA in toluene. Microgel concentration = 1 g/L solvent = butyl acetate elution temperature = 70 °C is the weight-average molar mass of linear polystyrene used for comparison. [Reproduced from Ref. 256 with permission, Huthig Wepf Publ., Zug, Switzerland].

Figure 12.13 Typical effect of elution temperature on the SFC separation retention times increase with the temperature. 

The total time required for elution of the product from the zeolite was not studied systematically, but most of the recoverable metal was eluted in less than 5 min. Subsequent elution, even for days and with fresh solution, removed little of the remaining product. Thus, the recoverable portion of the product was eluted rapidly, while the nonrecoverable portion behaved similarly to the unreacted target material. Elution temperature had little effect between 25 and 90°C. 

Vapor pressure data are not available for the ionic and nonionic surfactants. Some alcohol ethoxylates have been analyzed by high temperature gas chromatography, but the fact that elution temperatures of the higher ethoxylated AEs are above 520 K on a SE 30 boiling point column (Stancher and Favretto, 1978) indicates that the vapor pressure of these compounds is comparatively low. This is consistent with the high boiling points of these compounds. In addition, since surfactants are rather water soluble, their Henry s law constants can be expected to be very low. Actually, no measured Henry s law constants are available. As a result, evaporation of surfactants can be expected to be negligible. 

Splitless injection reconcentration of the bands broadened in time requires either lowering of the column temperature at least 60-90°C below the elution temperature of the solutes of interest (cold trapping) or keeping of the column at least 20-25 °C below the solvent boiling point to create solvent effects. 

Chromatographic peaks attributable to the polydisperse surfactant Cm E were first recognised by using as internal standard a similar Cm E surfactant (the comparison of the elution temperature of the peaks is a doubtful criterion as elution temperatures vary with the age of the column) mixed (approximately 1 1 by mass) with a portion of residue solution. The values of n of the peaks pertaining to the distribution were then determined by introducing a mono-disperse C ., E an internal standard in another aliquot of the residue solution (1 10). 

During the second stage of the procedure, each pair of peaks is checked for sufficient resolution. If Rs< 1.5 (eqn.1.14), then depending on the elution temperature observed for the peak pair, either an isothermal segment may be inserted in the program, or the slope of a non-isothermal segment may be reduced. This procedure may be followed simultaneously for every ill-resolved pair of peaks. Therefore, few additional experiments are required. ... 

The oligonucleotide 5 AGACTCCGTCTC-TTTT 3 is an exact match to the HS subfamily except for the four T residues situated at the 3 end replacing the A residues normally occupying this position. Measured Td is the thermal elution temperature of the oligonucleotide (3 X SSPE) from different DNA sequences with exact complements to the first 12 nucleotides and to additional 3 AT pairs as listed. The 4 + 2 rule [R. B. Wallace, J. 

Fig. 5.18. Effect of polymerisation and elution temperature on the enantiomer separation factor (a) in the separation of D- and L-PA on L-PA imprinted polymers. Polymers were prepared by thermochemical initiation at either 60 or 40°C using AIBN or ABDV respectively as initiators. The samples consisted of ca. 20 nmol of each of D- and L-PA and BOC-L-PA as void marker. Flow rate 0.5 mL/min. Mobile phase MeCN/acetic acid 95/5 (v/v). The columns were thermostatted by immersing them in a circulating water bath at the indicated temperature. From O Shannessy et al. [8].

Chrom Q column by Gazdag et al.. Derivatization (silylation with N,0-bis(trimethylsilyl) trifluoroacetamide) was needed for those alkaloids containing free hydroxy groups and/or a carboxylic acid group (vincaminic and apovincaminic acids). In Table 17.6 the retention times and elution temperatures of the vinca alkaloids investigated - as such and as derivatives -are given. 

RETENTION TIMES AND ELUTION TEMPERATURES OF vinca ALKALOIDS20... 

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