HF liquid

Grevskott S, Sannaes BH, Dudukovic MP, Hjarbo KW, Svendsen HF. Liquid circulation, bubble-size distributions, and solids movement in two- and three-phase columns. Chem Eng Sci 1996 51 1703-1713. 

To simplify the above-mentioned MMLLE systems and, unlike the automated flowing MMLLE, the nonautomated, nonflowing design of MMLLE is simple to prepare manually and is an easy-to-use extraction procedure that is always done off-line prior to GC analysis. In this context, only a short piece of HF membrane is employed as an extraction device after the HF lumen and pores96 or only the pores97 have been filled with an appropriate organic solvent, the membrane is immediately immersed in the aqueous sample. The principle of this two-phase HF-MMLLE system is also called HF liquid-phase microextraction (HF-LPME) and will be briefly commented on in the next section. 

The procedure is normally carried out using a Teflon apparatus, and care is taken to eliminate any likelihood of exposure to HF liquid or vapors. Note HF is highly toxic. 

Haloaromatic compounds. Aryl chlorides are obtained by heating aryl chloroformates with AICI3 at 200°. For the preparation of the fluorides the chloroformates are treated with excess anhydrous HF (liquid-phase fluorination-decarboxylation). 

Gebhardt W, Schroder HF. Liquid chromatography-(tandem) mass spectrometry for the follow-up of the elimination of persistent pharmaceuticals during wastewater treatment applying biological wastewater treatment and advanced oxidation. J Chromatogr A 2007 1160 34-43. 

Typically, the vapor phase of hydrofluoric acid is used instead of HF liquid. HF vapor is known to strip native oxides during cleaning of silicon wafers [21] and was suggested for sacrificial oxide etching [22]. However, even using the vapor phase can be critical in terms of stiction, because a byproduct of the chemical reaction is water ... 

Fig. 5.3.9 Wafer-temperature window for vapor HF etching between stiction and too-slow etching [20] for constant temperature of the HF liquid (26=C)...

In practice, a difference of about 10 K between the temperature of the wafer and that of the concentrated HF liquid is recommended. To accelerate the reaction, the HF can be heated to around 50 °C. The wafer is placed a certain distance above the concentrated HF liquid and is exposed to the vapor phase formed (Fig. 5.3.10). 

Reprinted with permission. Copyright hf Liquid Nitrogen Proeeso-ing Corporation. 

---