SEC columns

Mass-Transfer Contact Section Where there is a strong possi-bihty that not all of the incoming vapors will be condensed in the pool, a direct-contact mass-transfer section is superimposed on the quench tank. This can be a baffle-tray section (as shown in Fig. 26-21) or a packed column sec tiou. 

Analogous to HPLC-HRGC, the combination of packed column SEC and capillary column GC can be used for the analysis of complex samples. The advantage of SEC/GC with respect to HPLC/GC is the absence of problems associated with the evaporation of the HPLC mobile phase prior to the GC analysis. 

Enantiomeric separations have proven to be one of the most successful applications of packed column SEC. Despite initial reluctance, many analysts now use SEC routinely for both analytical and preparative chiral separations. Additional studies of chiral recognition in SEC and continued improvements in instrumentation will ensure a prominent role for SEC in chiral separations methodology in the future. 

T. A. Berger, Paeked Column SEC, Royal Soeiety of Chemistry, Cambridge, 1995. 

Supercritical fluid chromatography (SEC) was first reported in 1962, and applications of the technique rapidly increased following the introduction of commercially available instrumentation in the early 1980s due to the ability to determine thermally labile compounds using detection systems more commonly employed with GC. However, few applications of SEC have been published with regard to the determination of triazines. Recently, a chemiluminescence nitrogen detector was used with packed-column SEC and a methanol-modified CO2 mobile phase for the determination of atrazine, simazine, and propazine. Pressure and mobile phase gradients were used to demonstrate the efficacy of fhe fechnique. 

Howard [772] has been amongst the first to show the usefulness of conventional SEC for polymer/additive systems. Coupek el al. [773] have also reported results with this technique in an early stage their work was limited to synthetic mixtures of additives. The use of open-column SEC in the analysis of plastics additives has been reported [774], Qualitative analysis of additives has been performed by stopped-flow SEC with IR detection [775]. Polypropylene oligomers were isolated from a PP/(Irganox 1010, Irgafos 168, DBS) matrix by dissolution (toluene)/precipitation (methanol) and Soxhlet... 

The choice of columns used for 2DLC is based upon experience with the sample and resolution required. The HPLC column descriptors of selectivity, resolution, peak capacity, sample capacity, degree of sample recovery, and speed of separation have been discussed previously (Unger et al., 2000). Columns with higher peak capacity and sample capacity (IEC, HIC, NPLC, and RPLC) are preferred in the first dimension, and higher speed columns (SEC and RPLC) are better in the second dimension. This is discussed in detail in Chapters 2 and 6. 

The separation and identification of two novel anthocyanins from red onion, Allium cepa, have also been reported. Scales of 2.37 kg red onion were cut and extracted twice with methanol containing 0.5 per cent TFA. The extract was filtered, extracted with ethyl acetate and the aqueous phase was further purified in an ion-exchange and an SEC column. SEC separation was performed in a Sephadex LH-20 column (100 X 5 cm i.d.) applying methanol-water-TFA (39.6 60 0.4, v/v) as the mobile phase at a flow rate of 2.5 ml/min. 

MESH equations. All of the equations used to describe the steady-state operation of a distillation column (Sec. 4.1.2). MESH stands for ... 

The flood-point and the maximum pressure drop criteria gave comparable tower diameters. The more conservative of the two criteria gives diameters of 5.50 and 6.12 for the top and bottom section of the tower, respectively. As the diameters for the top and bottom sections are not much different, it is attractive to use uniform column diameter. The decision of whether to make the top and bottom section diameters the same is based on the same criterion as for tray columns (Sec. 6.5.3). The preliminary column diameter is the larger for the two column sections, i.e., 6.12 ft. This diameter is normally rounded to the next nearest half foot, but in this example it is rounded only to the next nearest quarter foot. A diameter of 6.12 is far closer to 6 ft than to 6.5 ft. Column diameter is relatively small, and three excessive inches substantially increase the costs. The column is operated at high pressure, and high-pressure shells are expensive. Therefore, the preliminary column diameter is 6 ft 3 in. 

Berry, A.J., Ramsey, E.D., Newby, M., and Games, D.E. 1996. Applications of packed-column SEC using light-scattering detection. Journal of Chromatography Science, 34 245-53. 

Assuming the sample of incidents is representative, one out of two tray damage incidents can be prevented by avoiding excessive liquid level in the column (Sec. 13.2). Six out of seven incidents can be prevented by also preventing vacuum formation in sections of the column (Sec. 11.2, 11.7, 11.8, 12.6, 12.9, 12.11) and by adequate installation and inspection (Chap. 10). 

Several incidents have been reported where trays were lifted off their supports due to such slug (49, 107, 231, 296). The author is familiar with some additional similar experiences. Ellingsen s survey (107) suggests that over half the tray damage incidents in the chemical industry are caused by deep liquid levels in columns (Sec. 13.1). 

Sight glasses. These have been used to give visual indication of flooding (186). This technique is not commonly used in commercial columns (Sec. 5.7). 

Side products complicate column control. Each side product adds two control variables (side product lights and heavies concentrations), but only one manipulated stream (side product flow) to the column (Sec. 16.2). Only one of these two compositions can be controlled by the additional manipulated stream the other is either allowed to vary, or "rides on the nearest end-product composition. Alternatively, both lights and heavies content of the side product can be controlled, at the expense of letting the composition of one of the end products vary. Side drawoffs also escalate the potential for interaction among control loops. 

Differential pressure measurement is generally one of the least reliable measurements in a column (Sec. 5.4). Low pressure drops (e.g., packed towers) and density variations (e.g., vacuum towers) make a reliable measurement particularly difficult to achieve. 

Basic research work was performed to establish a method for the determination of PAHs and their hydroxylated degradation products, standard mixtures of hydroxy PAHs were determined qualitatively and quantitatively by APCI and ESI-LC-MS. Under S/N = 3 1 conditions detection limits of 0.3-50 (jg mL were obtained in APCI mode whereas ESI ionisation was less sensitive (cf 15.3.3.2 ESI, PAH) [304]. The whole spectram of PAHs determined according to EPA protocol were analysed in solid waste by APCI-LC-MS(-i-) and HPLC with fluorescence detection after Hquid-hquid extraction, however, determination was disturbed by methylated PAH [305]. A capillary column SEC was interfaced by APCI to an... 

Frequently crystals are well formed and melt sharply but have a colored impurity present. In many cases, if a solution containing the compound is boiled with a small quantity of activated charcoal, the colored impurity is adsorbed preferentially if this is unsuccessful, a pass of the solution through a short alumina column (Sec. 2.6.1) can be attempted. 

The GPDC chart abcissa is the flow parameter [Eq. (8.21)], the ratio of liquid kinetic energy to vapor kinetic energy. This parameter has been applied to tray columns (Sec. 6.2.3), but is far more suitable... 

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