Column loading range

Although evidence exists that concentration effects may be important with even acetylated lignins in THF, the effect of increasing column loadings from 1 to 2 mg seems unlikely as the cause of the variance in MW shown in Table I. This observation illustrates the more general problem in current SEC-based absolute MW measurement that of a limited concentration window for analysis. The limiting value for sample concentration appears to be near 1 mg per injection for HPSEC-DV, which is comparable to the 0.2-1 mg per injection range usable in HPSEC-LALLS (33). For studies... 

The subtraction curve in Fig. 3A (solid) is compared with that obtained by ramping the same column load twice with no probe, and then a third time after injecting the basic probe (dotted curve, Fig. 3B). The near congruence of the curves resulting from the first and third ramps demonstrates that acidic sites are part of the glass structure (silanols and silicates) and are not susceptible to desorption in this temperature range. 

The separation conditions are typically tested and planned with aqueous systems, and a relatively low on column loading. For the best quality spectra, the NMR stage requires the use of D2O, instead of H2O, which will lead to a different pH value. This different solvent system, and the fact that a different chromatographic system is used for the LC-NMR experiments and the development of the separation, will lead to differences in the observed chromatograms. In addition, the total on-column loading will be in the mg range if the... 

Pulsed sieve-plate columns have shown good efficiencies for frequencies between 60 and 150 strokes/min and amplitudes under 1 cm. In general, a plate spacing of 10 cm is considered most favorable. However, these columns operate well in only a limited load range and are also susceptible to fouling, particularly with sticky products. To some extent, the reduction in efficiency at underload can be compensated by changing the pulsation characteristics the load can also be artificially increased by recycling the raffinate. 

The suitability of a column for a particular use depends on various factors, such as stationary phase, solid support, column tubing material, inside diameter, percent liquid loading, and temperature. Columns may be prepared in various lengths and diameters depending on the particular objective. Preparative columns may range from 0.95 to 10 cm (3/8-4 ) in diameter or larger for the collection of quantities of individual... 

The waste water of all furfural plants contains some carboxylic acids, with acetic acid being the principal load, ranging from 1 to 5 percent by weight, as well as some furfural, in concentrations up to 600 ppm. The furfural concentration depends on the quality of the first distillation column, with good columns going down to 50 ppm. 

The throughput through these columns depends again on the density difference and the height of the back-up layer under the plates. The loading range is small. 

First method ca. 1 g intake (moisture of ca. 4%) was taken for analysis. NaCl/ H2O was added, the mixture was mechanically shaken and filtered at 0.2 pm. Recovery was evaluated with the spiked urban dust provided by SM T and was found to be (75 4)%. Derivatization was carried out with 4% NaBEt4 in acetic acid/acetate buffer, using He as carrier gas at 120 mLmin . The derivatized compounds were cryogenically trapped and separation was performed by GC (U-tube glass column of 0.5 m length and 3 nun internal diameter, filled with OV-101 as stationary phase loaded with 10% silica 80-100 mesh He was used as carrier gas at 120 mL min H2 was added as make-up gas at 30 mL min the column temperature ranged from ca. — 196 to 75 °C). Detection was by electrothermally heated QFAAS (T-tube) at 283.3 nm (detector temperature at 800 °C). Calibration was by standard additions, using MesPbCl as calibrant. 

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