Etching acid, liquid

Cytochrome c Capillary etched with liquid crystals (cholesteryl or cyanopentoxy modified) 60 mM Citric acid and 50 mM P-alanine, pH 3.00 700 or 500 mm x 50 pm i.d 450 or 250 mm effective length, open tubular CEC... 

Capillary etched with liquid 60 mM Phosphoric acid and 700 mm x 50 pm i.d 450 mm effective... 

The solutions accumulate gradually dissolved material from the plastics and from time to time have to be discarded and replaced disposal presents environmental difficulties and for this reason efforts have been made to find alkaline rather than acidic liquids which are capable of etching satisfactorily but do not contain chromium. At the time of writing, unfortunately, development has not reached the stage at which the process based on chromic acid can be superseded for the entire range of substrates. 

Ultrasonic Atomization Nebulizers 1-5 (55kHz, 0.12 1/min) 30-60 (50 kHz) l-200[88] Medical spray. Humidification. Spray drying. Acid etching. Printing circuit. Combustion Very fine and uniform droplets, Low spray rates Incapable of handling high liquid flow rates... 

Several different analytical and ultra-micropreparative CEC approaches have been described for such peptide separations. For example, open tubular (OT-CEC) methods have been used 290-294 with etched fused silicas to increase the surface area with diols or octadecyl chains then bonded to the surface.1 With such OT-CEC systems, the peptide-ligand interactions of, for example, angiotensin I-III increased with increasing hydrophobicity of the bonded phase on the capillary wall. Porous layer open tubular (PLOT) capillaries coated with anionic polymers 295 or poly(aspartic acid) 296 have also been employed 297 to separate basic peptides on the inner wall of fused silica capillaries of 20 pm i.d. When the same eluent conditions were employed, superior performance was observed for these PLOT capillaries compared to the corresponding capillary zone electrophoresis (HP-CZE) separation. Peptide mixtures can be analyzed 298-300 with OT-CEC systems based on octyl-bonded fused silica capillaries that have been coated with (3-aminopropyl)trimethoxysilane (APS), as well as with pressurized CEC (pCEC) packed with particles of similar surface chemistry, to decrease the electrostatic interactions between the solute and the surface, coupled to a mass spectrometer (MS). In the pressurized flow version of electrochromatography, a pLC pump is also employed (Figure 26) to facilitate liquid flow, reduce bubble formation, and to fine-tune the selectivity of the separation of the peptide mixture. 

The hydrofluoric acid, however, attacks glass rapidly when tire action is exerted on a small surface, and much acid is employed. This property has been turned to account to etch glasB the acid is employed in a gaseous or liquid state, according to the occasion and the end proposed. The gaseous acid produces opaque traces the liquid acid transparent ones, Bnt the subject of etching on glass will be alluded to afterwards. 

Etching on Glass.—It has been statod at page 199, that hydrofluoric acid, either in the gasoone or liquid... 

The acid is rather feeble, but it reddens litmus,2 decomposes carbonates and neutralises alkalis with the formation of salts. The baser metals are also slowly attacked, and the liquid finds frequent use as an etching reagent in the metallographic examination of alloys.3... 

Hydrofluoric Acid. — Evaporate 10 cc. of hydrogen peroxide with a few drops of sodium hydroxide solution, transfer the concentrated liquid to a watch glass, evaporate to dryness on the latter, pour concentrated sulphuric acid over the residue, and allow the whole to stand two to three hours in a warm place. After washing off the glass, no etching should be visible. 

Most companies producing ICs today have been quite lax in the quality control of the liquid chemicals used in their processes. These chemicals include acids, bases, buffered etches, photoresists, and organic solvents. Essentially, the producers of ICs have left the quality control of these materials to the chemical manufacturers. Specifications for chemicals are set by SEMI (Semiconductor Equipment Manufacturers International) and are generally met by all chemical manufacturers. The level of metallic contaminations that can exist in U.S. chemicals ranges from 0.1 to 1 ppm. If the levels of metallic impurities were actually this high, U.S. manufacturers would not be able to produce integrated circuits. 

---