Columns concentrator

A solution of 2-azido glycosyl nitrate 6 (2.5 mmol) and O-ethyl S-potassium dithiocarbonate 5 mmol) in acetonitrile (20 ml) was kept for 5 h at room temperature, diluted with dichloromethane (200ml), washed with water (30ml), dried (MgS04) and concentrated. Column chromatography of the residue (4 1 hexane-ethyl acetate, 0.3% triethylamine) gave the title compound in 97% yield. 

Technical Note No. 8, The Use of Concentrator Columns in Ion Chromatography, Dionex Corporation, Sunnyvale, CA, 1994. 

Carlson, et al (4) and C. Anderson, et al (5) have shown IC to be an excellent technique for low ppb analysis of water. Environmental applications for these analyses include determination of rain water composition and analysis of fuel cell effluents because ions in these solutions are often present in low ppb concentrations. Concentrator columns (3 x 50 mm) are used to accumulate sample ions to detectable quantities as large sample volumes are pumped through them. Samples may vary from 1 to 100... 

Figure 3. Trace analysis (ppb) of anions with a concentrator column...

B) paracetamol standard at about the same concentration. Column ODS 4.6 mm X 150 mm, mobile phase acetonitrile 0.05 M acetic acid (85 15) flow rate 1 ml/min. 

Figure 7. Optimal system configuration using AG4 guard column as the concentrator column. Five milliliters of Milli-Q water spiked with CI04" was loaded onto the concentrator column at varying concentrations of perchlorate. Eluent 0.5M 18-crown-6 and 5mM KOFI. Injection 5mL loaded onto concentrator column, flow rate 1.0 mL/min, temperature 20 °C [17].

To determine ions at mid pg/1 to mg/1 (ppb to ppm) levels with IC, a sample size of 10 to 50/pi is sufficient. To determine ions at lower levels, then a preconcentration or trace enrichment technique has t3rpically to be utilized [20]. With this method, the analytes of interest are preconcentrated on another column in order to "strip" ions from a measured sample volume. This process concentrates the desired species resulting in lower detection limits. However, preconcentration has several disadvantages, compared with a direct method, additional hardware is required. A concentrator column is used to preconcentrate the ions of interest, a sample pump is needed for loading sample, an additional valve is often required for switching the concentrator column in and out-of line with the analytical column and extra time is required for the preconcentration step. It was of interest to explore the development of a high-volume direct-injection IC method that would facilitate trace ion determinations without a separate preconcentration step. This would represent a significantly simpler and more reliable means of trace analysis. 

Quinaldic, trimesic, and stearic acids were derivatized with PNBDI to facilitate their chromatographic separation and UV detection (33). The procedure was as follows 125 /zL of PNBDI (2.6 mg) in dichloromethane was mixed with 200 /zL of concentrated column effluent in a 5-mL Reactivial and... 

D. SPLIT COLUMN PLUS AN ALDEHYDE CONCENTRATING COLUMN... 

Figure 2. Split column with a heads concentrating column...

Ethyl acetate is the major low-boiling impurity of heads fractions from continuous columns if bisulfites are absent in the distilling material. A heads fraction from a typical brandy column usually contains less than 1% of these volatile impurities, although the concentrated heads from an aldehyde-concentrating column may contain as much as 10-15% aldehydes. In either case, ethyl alcohol is the major component of the heads cut, and its recovery in usable form has been a troublesome processing problem. 

Figure 5.3-8. Details of the chum-turbulent flow regime of BSCR according to Inga [1], (db)0-gas bubble size at atmospheric conditions in the absence of solid particles, (d, )ps- bubble size at the operating pressure and catalyst concentration. Column height = 2.8 m, internal diameter = 0.316 m. P < 8 bars. Organic media, catalyst diameter < 100 pm.

These ratios are independent of concentration, column temperature, or retention time. 

Thiocamphor (see Section 2.8.2) (505 mg, 3 mmol) and 3-diazo-2,2,4,4-tetramethylpentane in THF (5 ml) were heated under N2 to reflux for 15h. The mixture was filtered and the solvent removed under reduced pressure. The crude episulfide was treated with n-Bu3P (3 ml, 12 mmol) and heated at 120°C for 15 h. The mixture was treated with Mel (3 ml, 48.2 mmol) in petroleum ether (30 ml) (very exothermic), stirred for 2h, filtered and concentrated. Column chromatography on silica gel (elution with petroleum ether) afforded the olefin in a 64% yield. 

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