UV TRANSMISSION

Although vitreous siUca is a simple, single-component glass, its properties can vary significantly, depending on thermal history, the type and concentration of defects, and impurities. Vitreous siUca can, however, be one of the purest commercially available glassy materials. In synthetic vitreous sihcas, for example, total metal contamination is typically measured ia the 50—100 ppb range. Even at such a low level of impurities, differences ia properties, such as uv-transmission, are observed for various siUcas. 

Fig. 7. Impiovements in uv transmission of atkoxide gel—silicas ( ) DYNASIL (.) 7940 Corning (-) GELSIL 1987 and ( ) GELSIL 1988,...

The UV transmission of Bisphenol-AF-derived poly(aryloxydiphenylsilane) shows a very sharp cut-off at about 285 nm (Figure 9.2). 

Figure 9.2. UV transmission of poly(aryloxydiphenylsilane) film obtained from Bisphenol AF and dianilinodiphenylsilane.

The methacrylate units incorporated in the polymer chain give excellent UV transmission, while the a-methylstyrene units provide good dry etch resistance and high thermal stability. 

Figure 9.4 UV transmission spectra obtained for PEN and PET bottle sidewalls O, PEN , PET...

A similar combination of ultrasound and photocatalysis has also been reported to destroy 2,4,6-trichlorophenol in aqueous solution [39]. An ultrasonic probe (22 kHz) with a uv light source (15 W) was used to examine the effect of changing such operating conditions as ultrasonic intensity, reaction temperature and uv transmission. The experiments involved using 2,4,6-trichlorophenol (100 ppm) and TiOj (0.1 g L ) and showed that the degradation rates increased with the temperature of the solution. The cumulative effect was more pronounced at lower ultrasonic intensities with little additional benefit derived at increased ultrasonic powers. 

The chip with dried spots was covered with a UV transmission filter, and then placed into UV crosslinking instrument. 

Surface-introduced photoreactive group, aryl diazirine, can generate carbenes by 365 nm UV exposure. However, gold-sulfiir bonds, which support photolinker on gold, can be easily broken by UV light below 300 nm. Therefore, UV transmission filter is essential in UV irradiation. 

Amorphous polymers characteristically possess excellent optical properties. Unlike all the other commercially available fluoropolymers, which are semicrystalline, Teflon AF is quite clear and has optical transmission greater than 90% throughout most of the UV, visible, and near-IR spectrum. A spectrum of a 2.77-mm-thick slab of AF-1600 is shown in Figure 2.5. Note the absence of any absorption peak. Thin films of Teflon AF have UV transmission greater Ilian 95% at 200 mm and are unaffected by radiation from UV lasers. The refractive indexes of Teflon AF copolymers are shown in Figure 2.6 and decrease with increasing FDD content. These are the lowest refractive indexes of any polymer family. It should be noted that the abscissa could also be labeled as glass transition temperature, Tg, since Tg is a function of the FDD content of the AF copolymer. Abbe numbers are low 92 and 113 for AF-1600 and AF-2400. 

In a few cases, analyses may be done on the process floor using a conventional scanning spectrophotometer and the usual laboratory cuvette or a specially made vial that fits into the sample cavity of the instrument. Cuvettes may be made from quartz (various grades depending upon UV transmission requirements), or from plastic (disposable) when UV wavelengths are not required for the measurements. In most cases these at-line analyzers have lower performance characteristics than dedicated laboratory instruments, but may be quite adequate for the task at hand. However, their use still requires manual sampling... 

The reproducibility of injection was demonstrated by repetitive injections (n=6) of a standard solution of corticosteroids at two different days. R.S.D. for retention times on day 1 and day 2 were 0.51 and 0.93, and for peak areas 2.49 and 1.78, respectively. The injection linearity in terms of analyte concentration and injection volume was also good (r > 0.998) [40]. Retention time and peak area reproducibility for corticosteroids extracted from urine was characterized by R.S.D. 2 and 7 % respectively [41]. Due to differences in UV transmission of the mobile phase, the baseline drifted with increasing acetonitrile concentration. 

Hoffmann, K., Kaspar, K., Gambichler, T., and Altmeyer, P., Change in ultraviolet (UV) transmission following the application of vaseline to non-irradiated and UVB-exposed split skin, Br. J. Dermatol., 143, 532, 2000. 

The High-Temperature and UV-Transmission Glasses. The last types of glass found in the laboratory are the quartz and UV-transmission glasses. From the many names that are used to describe this type of material, there may be confusion as to what to call it. It is often just called quartz, but this name can be deceiving because the term quartz could equally refer to the mineral quartz (which is a crystal) or amorphous silica (which is a glass). 

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