Propylparaben separation

H3PO4 / 40 % acetonitrile at a flow rate of 1 mL/min. was used, and UV detection at 210 nm was used. The method was used for the separation of benzoic acid, methylparaben, ethylparaben, propylparaben, saccharin, sorbic acids, and /7-hydroxybenzoic acid. 

Separately add and dissolve the following ingredients in alcohol methylparaben, propylparaben, and anise oil. 

Fig. 10.5. Separation of parabens with the poly(TBAAm-co-AMPS)-coated column. Conditions column, 750 mm x 25 pm i.d. (600 mm effective length) mobile phase, 20% acetonitrile (v/v) in 50 mMTris-HCl buffer field strength, 400 V/cm injection, 12 kV for 3 s at the side of the anode detection wavelength, 254 nm. Peak identification 1, methylparaben 2, ethylparaben 3, propylparaben 4, butylparaben 5, amylparaben. Reproduced with permission from Sawada and Jinno [11].

The vital importance of size and shape as compared with absolute molecular weight is emphasized by another pair of exceptions on the calibration curve in Figure 5-37—aspirin and propylparaben. These two compounds have essentially identical molecular weights (180.2 and 180.1, respectively), but are easily separated by SMGPC. From the structures, it can be deduced that propylparaben acts as a larger molecule in solution than does aspirin. This is probably due to a solvent effect where the THF hydrogen-bonds to the polar groups in propylparaben. Thus, propylparaben should elute before aspirin, and as shown on the calibration curve, it does. 

Other components, is rendered sterile separately, asep-tically weighed, and incorporated in preparing a final product that meets the sterility requirement. This is done because of difficulty in terminal product sterilization, such as lack of penetration of steam into the ointment base and instability of components owing to high dry heating. Antimicrobial preservatives such as methylparaben (0.05%) and propylparaben (0.01%) and its combinations phenylmercuric acetate (0.0008%), chlorobutanol (0.5%),and benzalkonium chloride (0.008%) are used as needed. 

Figure 4.10. Waters EmPower screen showing a contour map, a chromatogram at 270nm showing the separation of nitrobenzene and propylparaben. Spectra of these two components are shown in the right-hand panel annotated with their respective maximum absorbance wavelengths.

In a separate steam jacketed tank, add Polawax, cetostearyl alcohol, acetylated lanolin, oil-neutral vegetable triglycerides mixture, and propylparaben, and carefully melt at 70°C. 

Minoxidil and tretinoin were extracted from cosmetic formulations and separated from methyl-, ethyl-, and propylparabens on a cyanopropyl column (A = 283 nm and 367 nm). A 30-min 10/90 ->-70/30 acetonitrile/water (10 mM NaC104 to pH 3 with HCIO4) gradient was used. Calibration curves were generated for 1-500 pg/mL samples. Detection limits of 5ng were reported [1540]. 

The same authors also reported the use of the system coupling an ultrashort C18 monolithic column with a FIA scheme for the determination of three antioxidants (pro-pylgallate, butylhydroxyanisole, and butylhydroxytoluene) (Garcia-Jimenez et al., 2009) and four preservatives (methylparaben, ethylparaben, propylparaben, and butylparaben) (Garcia-Jimenez et al., 2010) at pgmL"i level. The proposed approach, able to separate the analytes in only 85 or 150 s, respectively, was satisfactorily validated for the determination of the selected analytes in commercial food and cosmetics samples without any prior derivatization reaction. 

A flow injection system coupled to a monolithic column has been described for the simultaneous determination of antioxidants (PG and BHA), sweeteners (potassium acesulfame, sodium saccharin, and aspartame), and preservatives (methylparaben, eth-ylparaben, propylparaben, and butylparaben), using photometric detection [56]. The monolithic column used as separation system was a 5 mm commercial precolumn of silica Cjg. The mixture was separated in only 400 s with resolution factors greater than 1.1 in all cases. Detection was accomplished by means of a DAD at the respective wavelength of each compound. The detection limit obtained for PG was 0.02 pg/mL. The method was applied to the analysis of food and cosmetic samples and the results were compared with those obtained using a conventional LC method. 

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