Silica controlled distance method

As Newton recognized, this short range of action of molecular forces has made the force measurement extremely difficult. Only in the past few years or so has it been possible to make the necessary measurements at the nanometer level to prove these ideas. Two problems have been overcome. The first one was the measurement technique. Optical methods, such as multiple beam interferometry and laser optical levers, have been developed to measure atomic distances. Piezoelectric actuators were invented to control nanomovements. The second issue was surface smoothness. Smooth surfaces of oxides such as mica, silica ot alumina have been found. Also tiny smooth probes have been made on a large scale by electronic wafer fabrication routes. Tbese new techniques have allowed a new and proper definition of molecular adhesion. 

For the control of penicillin V fermentations (10), the following HPTLC method was used Chromatography was carried out on silica gel HPTLC plates (Merck) with the solvent toluene/ethyl acetate/acetic acid (40 40 20) along a distance of 5 cm. After drying, scanning was done at 268 nm. The Revalues for 4-hydroxy-penicillin V, penicillin V, and phenoxyacetic acid were 0.34,0.50, and 0.60, respectively. The concentration was about 1 mg/ml each, the spotting volume 250 nl, the coefficient of variation 1.5-3.0%, for low concentrations (4-OH-penicillin V) 6.6% (see Fig. I). 

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