Water-soluble UV filters

So, we can find fat-soluble and water-soluble UV filters. Thus, usually, lipsticks, oils, hydroalcoholic lotions and foundations (which have high fat content) are formulated with fat-soluble UV filters watery lotions and gels incorporate water-soluble UV filters and finally, creams, milks and microemulsions are formulated with both water- and fat-soluble UV filters, where both water- and fat-soluble UV filters r ain in the aqueous or fatty phase of the emulsion, respectively. 

Methods 1 and 2 for fat and water-soluble UV filters determination, respectively... 

Figure 3.1.5 An example of LC chromatograms showing the separation of (a) 12 fat-soluble and (b) 6 water-soluble UV filters. Only environmentally friendly solvents were used (adapted from Salvador and Chisvert, 2005b).

Properties White, odorless, microcrysalline powder. Mp 282C. Exhibits reddish fluorescence under filtered UV light. Undergoes phase change at 270-275C. Practically insoluble in water soluble in... 

Sunscreens, especially those with high sun protection factor (SPF), may contain considerable amounts of UV filters. E.g. for an SPF of 50, a UV filter content of 25% (w/w) can be necessary. Although this is achieved using a cocktail of several UV filters, the solubility of organic UV absorbers either in the oil or in the water phase of the emulsion should be at least about 10% as a rule of thumb. This is necessary, as the respective phase will be diluted upon emulsification, and the UV filter concentration in the final formulation will be correspondingly lower. 

The finishing of liquid detergents and cleansers typically employs short-chain alkylbenzene sulfonates such as toluene sulfonate or cumene sulfonate, which, because of their hydrotropic properties, ensure the solubility of other detergent components in an aqueous environment. Analysis of hydrotropic compounds is performed by ion-pair chromatography. The compounds are eluted in the order of increasing alkyl substitution. As demonstrated in Fig. 9-120, these compounds can be determined directly in the finished product without extensive sample preparation. The analyte samples are only diluted with de-ionized water and membrane filtered. As aromatic sulfonates may be detected both by their electrical conductivity and their UV absorption, the choice of suitable detection method mainly depends on the type of matrix. 

AU this has led to a great variety of UV filters being designed, with different solubility properties, since samples with different fat/water ratio content are available on the market. 

As is shown in Figure 3.1.1, some of these organic UV filters have a structure with an ionizable moiety, such as sulphonic ( SO3H) or carboxylate (COOH), which affords their solubility in water. 

Many research compounds are poorly soluble in water. When very lipophilic molecules precipitate in the donor wells, it is possible to filter the donor solution before the PAMPA sandwich is prepared. On occasion, the filtered donor solution contains such small amounts of the compound that determination of concentrations by UV spectrophotometry becomes impractical. One strategy to overcome the precipitation of the sample molecules in the donor wells is to add a cosolvent to the solutions (Section 7.4.4). It is a strategy of compromise and practicality. Although the cosolvent may solubilize the lipophilic solute molecule, the effect on transport may be subtle and not easy to predict. At least three mechanisms may cause Pe and membrane retention (%R) values to alter as a result of the cosolvent addition. To a varying extent, all three mechanisms may simultaneously contribute to the observed transport ... 

The supernatant concentration method uses small volumes of stock solution added to wells containing aqueous buffer in a microtiter filter plate of the type available from Millipore Inc. The solution is incubated for a given amount of time (typically in the range of 1-24 h depending on the requirements of the laboratory) and then filtered or centrifuged. The supernatant is analyzed by UV plate reader or HPLC and the concentration of dissolved species is calculated by reference to a calibration curve. This is often either a three- or a four-point curve prepared from serial dilutions of the stock solution using a solvent such as 80% v/v acetonitrile/water in which the compound is fully soluble. 

A three-cell apparatus (Vogel 724S) was used in electro-ultrafiltration [22]. The middle cell containing the material suspension had a stirrer and a water inflow. Each side of the middle cell was provided with a micropore filter attached to the platinum electrodes that separated the middle cell from the two outside chambers. These chambers had vacuum connections. Therefore, the ions accumulating at the respective electrodes were washed away by the continuous stream of the solution from the suspension in the middle cell to the eluate in the collecting tanks combined with the side chambers. A steady disequilibrium between the P on the materials and the respective soluble form in solution occurred and the materials were forced to replenish the P displaced away with the eluate. The concentration of P in the eluates was measured by UV-VIS spectrophotometry as phosphomolybdate [23]. 

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