UV transparency

In the absence of the acetate Chimassorb 944 does not elute. Also, the mobile phase used here is UV transparent down to at least 220 nm, which can aid in the detection of low UV-absorbing analites. 

The reason for such difficulties is the GPC mechanism itself. We do not separate by molar mass but by the size of the solvated molecules. Different solvation of chemical unlike molecules results in breaking the M sequence of the calibration curve this becomes visible especially in the low molar mass range. Sometimes such difficulties can be circumvented if a specific detector is used, e.g., if the sample absorbs in the ultraviolet (UV) range and the disturbing peaks are UV transparent. 

Recently, the detection of UV-transparent alkanemonosulfonates without ion pairing is made feasible by a light-scattering detector (LSD) [32]. The optimized selectivity for the separation of alkanemonosulfonates by chain length using LSD is shown in Fig. 15. The separation of the isomeric tetradecanemonosulfonates is exemplified in Fig. 16. 

Ganzler, K., Greve, K. S., Cohen, A. S., Karger, B. L., Guttman, A., and Cooke, N. C., High-performance capillary electrophoresis of SDS-protein complexes using UV-transparent polymer networks, Anal. Chem., 64, 2665, 1992. 

The pressurised dissolution/cooling procedure of Macko el al. [490], which uses a UV-transparent low-boiling point solvent, is fast and simple as no additional evaporation of the solvent, preconcentration or redissolution of the additive is necessary. Macko el al. [491] have given an extensive listing of HPLC analyses of aromatic antioxidants and UVAs which can be separated with n-heptane and n-hexane as the main component of the mobile phase. The method was also used for HPLC quantification of thioether antioxidants (Santonox R, Chimox 14 and Irganox PS 802) in MDPE [612],... 

The hindered secondary amines can be highly effective photostabilizers for various polymers (]+.,5.,.6) Various hindered amines have been shown to retard oxidation, but most share the common feature of being secondary or tertiary amines with the a-carbons fully substituted. The most widely exploited representatives of this class are based on 2,2,6,6-tetramethylpiperidine either in the form of relatively simple low molecular weight compounds, or more recently as backbone or pendant groups on quite high molecular weight additives ( i.,5.,6). The more successful commercial hindered amines contain two or more piperidine groups per molecule. Photo-protection by tetra-methylpiperidines (near UV transparent) must result from the interruption of one or more of the reactions 1 to 3. Relatively recent results from our own laboratories, and in the open literature will be outlined in this context. 

Most UV photodiodes have a sealed metal TO package with an entrance window made of glass or special UV-transmitting glass. A TO housing is extremely reliable but it often counts for a non-negligible part of the sensor costs. Cheaper housings that should be favored for consumer-product applications like in household appliances are hard to find. Full-plastic encapsulation requires a UV-transpar-... 

Fig. 5.45 A twlux PFD306B visible-blind UV photodiode based on polycrystalline Ti02. The chip with an active area of 2.9x5.4 mm2 is mounted on a TO-39 header. The sealed cap has an entrance window made from Schott s UV-transparent glass that transmits down to 240 nm.

Estimates of oCbiend using a rule-of-mixtures relationship are 3.0 X 102 and 7.2 X 103 cm lor 0.2 and 5.0% polyimide, respectively. This dependence of the optimum absorption coefficient (in terms of ablation rate), OVx on fluence is consistent with the observations of Chuang et al.6% for ablation of several UV-transparent (at 308 nm) polymers sensitized with low-molecular-weight dopants, e.g., PMMA doped with pyrene. For the pyrene-PMMA system, Chuang et al.6S reported maximum etch rates for 1.2 J/cm2 at a = 7 X 102 cm 1. It should not be expected that different dopant-matrix systems would yield the same optimum absorption coefficient for a given fluence level since the thermal properties for different polymers may vary significantly. 

Gel electrophoresis provides a simple method for separating complex protein mixtures. Because proteins are visualized using stains that may not be linearly incorporated in the gel, the intensity of the stained bands may be poorly correlated with the amount of protein. For this reason, gel electrophoresis is at best a semiquantitative technique capable of generating relative purity results. In CE, separations are commonly performed in free solution, i.e., in the absence of any support such as gel matrices. This allows the replacement of the capillary s content in between analyses and therefore the automation of the process. The use of UV-transparent fused-silica capillaries enables direct on-line optical detection of focused protein zones, eliminating the requirement for sample staining. The detection systems available to CE provide true quantitative capabilities. 

For ions that are UV transparent, detection is possible through the use of indirect detection. A wide variety of different eluent systems have been described in the literature. Eluents commonly used for indirect UV detection are similar to those used in non-suppressed conductivity detection phthalate and p-hydroxybenzoic acid along with other... 

Many chiral selectors have been developed for CE but CDs (natives and their derivatives) are by far the most widely used. In addition to their wide chiral discrimination abilities, CDs are usually well soluble in aqueous BGE, UV transparent, stable, environment friendly, easily available and relatively cheap, which makes them ideal candidates for CE. 

Convergent Bioscience has an interesting approach to detection in CE by using a CCD (charge-coupled device) camera to image the entire capillary (Figure 7). A UV-transparent capillary is needed and the entire capillary is excited with a xenon lamp. This is useful in cIEF... 

UV transparent (consider UV absorbing impurities) exception BGEs for indirect detection... 

One of the characteristics of many of these ions is that they are UV transparent, while most CE instruments are equipped with a UV detector. Eor this reason, a special technique called indirect UV detection is often applied. 

As shown in Figure 32, changes to the run buffer concentration can also affect migration time, resolution, and detector response (e.g., an increased background due to the use of non-UV transparent salt results in lower peak response and greater baseline drift). 

The azeotrope 70/30 MeCl2/HFIP Is an excellent solvent for PET and similar pol3nners, as well as for polystyrene. This combination, along with Its UV transparency, makes It an excellent GPC solvent. The Du Pont Product Information and Material Safety Data Sheet on HFIP should be consulted before using this system. 

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