Subboiling distillation

Element Subboiling Quartz Still, Doubly Distilled-Water Feed Doubly Distilled in Quartz, Distilled Water Feed" Deionized, Monobed, Polyethylene Apparatus, Distilled-Water Feed" Distilled Two-Stage Commercial Metal Still, City Water Feed," Recirculating Ultrapure System, Metal" Single-Pass Deionization of Tap Water" Deionization, Carbon Absorption, Deionization, Membrane Filtration ... 

Subboiling distillation circumvents both of these problems and is considered a simple and effective technique for removing metallic or cationic impurities (Figure 7.2). In subboiling distillation, infrared heaters vaporize liquid from the surface without boiling. The vapor is condensed on a tapered cold finger, and the distillate is collected in a suitable container. 

Subboiling distillation also is an effective technique for the purification of nitric, hydrochloric, hydrofluoric, perchloric, and sulfuric acids. Typical analyses indicate a 100-fold reduction in the level of metallic impurities.73 While this method is extremely efficient for the removal of metal ions, it offers litde purification from impurities with high vapor pressures, such as organic matter and many of the anions. 

Ultrahigh-purity acetic acid, ammonia solutions, and mineral acids prepared by double subboiling distillation, having ng per kg impurity levels, are available commercially for use in the most demanding trace analyses. 

The most successful method for purifying volatile acids, ammonia solutions, and solvents, and which is operated on a small commercial scale, is that of subboiling distillation. The apparatus is constructed from quartz or, for hydrofluoric acid, of polytetra-fluoroethylene (PTFE), and infrared radiators vaporize the surface of the liquid without bringing it to the boil. The vapor is condensed on a tapered cold-finger condenser and the liquid is collected in a suitable container, itself constructed from quartz or PTFE. Apparatus is available that will deliver 20 or more liters per still per day. 

In a conventional laboratory, Adeloju and Bond [42] observed considerable variations when periodically measuring voltammetrically standard solutions of cobalt, nickel, copper, zinc, selenium, and lead owing to the variability of airborne contamination. They stress that the adoption of a blank substraction approach is no more than a futile exercise because of the variability of the analytical blank levels with time. Boutron [43] assessed the effect of air purity on the analysis of a standard solution containing 10 ng/mL of iron. When samples were prepared in an ordinary laboratory environment, values of 20.6 ng/mL were observed Finally, Gretzinger et al. [44] filled carefully cleaned quartz beakers (cross-section, 16 cm volume 20 mL) with 10 mL of 1 M HCl, prepared by subboiling (or nonebullient) distillation [45], deposited them uncovered in an ordinary laboratory on different days, and measured the iron level in the HCl solution. The weather was found to play an important role as a rule, when it is raining the air is essentially more pure than when it is dry. On one dry day, the amount of iron in the 10 mL of 1 M HCl over a periode of 6 hr was up approximately 20 ng, on another up to more than 30 ng. 

Figure 2. Quartz apparatus for purifying acids or water by subboiling distillation (with permission from Kiirner, Ro-senheiiti/Oberbayem. Germany) this device is also available in PFA for the subboiling distillation of hydrofluoric acid (with permission from Berghof Maassen. Eningen u. A Germany)...

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