Acetone concentration in the mobile

Figure 2. Rf values of penicillins vs. acetone concentration in the mobile phase...

In any chromatographic analysis the method of detection is determined by the nature of the analyte and the mobile phase used must not interfere with this system. The use of ultraviolet absorption detection systems is very common but the solvents used must not absorb significantly at the wavelength used. For instance, absorption at 280 nm is frequently used to detect protein but some solvents, e.g. acetone, absorb at this wavelength. Similarly the use of concentration gradients in the mobile phase may present problems with refractive index and electrochemical detection systems. 

The RP-TLC behaviour of some common food dyes was investigated in detail. The chemical structure of dyes are listed in Fig. 3.2. Measurements were carried out on RP-18 silica plates using aqueous ammonium sulphate (0.1 0.5 1.0 M), ethanol and acetone in various volume ratios. Developments were performed at room temperature (22 2°C) in chambers previously saturated with the vapours of the mobile phase. It was found that the presence of dissociable anorganic salt modifies markedly the RP retention behaviour of dyes. The retention of dyes generally decreases with increasing concentration of the organic modifier in the mobile phase. It was further concluded that RP-TLC can be successfully used for the separation of this class of synthetic food dyes [81]. 

An increase in the polarity of the mobile phase produced by increasing the amount of acetone in the mobile phase resulted in a decrease in resolution within the polar and nonpolar dimers. On the other hand, a decrease in the polarity of the mobile phase by increasing the amount of acetonitrile resulted in the insolubility of the samples at concentrations required for refractive index detection (20-40 mg/ml), thus limiting the use of the mobile phase of polarity less than that of system II. 

Steroids. The same kind of results were obtained with steroids (15). However, to obtain suitable migrations, it was necessary to use higher concentrations of acetone or methanol in the mobile phase. Plots of Rm values of testosterone esters vs. acetone or methanol concentration in the... 

Self-Test M4.1B Inorganic cations can be separated by liquid chromatography according to their ability to form complexes with chloride ions. For the separation, the stationary phase is saturated with water and the mobile phase is a solution of HCI in acetone. The relative solubilities of the following chlorides in concentrated hydrochloric acid are CuCl2 > CoCl2 > NiCl2. What is the order of elution of these compounds ... 

Because of their complementary character, TLC and HPLC can be used simultaneously for the easier solution of complicated separation problems. Thus, the determination of cap-saicinoids in fruit of hot pepper Capsicum annuum L. by spectrophotometry, TLC and HPLC has been reported. Samples were homogenized with acetone followed by a homogenization with acetone-petroleum ether 1 1 v/v until the tissue was nearly white. The extract was filtered and the acetone was washed out by small amounts (0.01 ml) of water. The ether phase was dried with anhydrous NajSC and concentrated in vacuum at 30°C. The extract was separated on silica TLC plates using a petroleum ether-acetate-methanol (75 20 5) mobile phase. The capsaicinoids were scraped off the layer and further analysed by HPLC. The Rp values of carotenoids and capsaicinoids are listed in Table 2.2. It was stated that the method can be employed for the measurement of carotenoids in hot peppers [19]. 

Normal-phase HPLC has also found application in the analysis of pigments in marine sediments and water-column particulate matter. Sediments were extracted twice with methanol and twice with dichloromethane. The combined extracts were washed with water, concentrated under vacuum and redissolved in acetone. Nomal-phase separation was performed with gradient elution solvents A and B being hexane-N,N-disopropylethylamine (99.5 0.5, v/v) and hexane-2-propanol (60 40, v/v), respectively. Gradient conditions were 100 per cent A, in 0 min 50 per cent A, in 10 min 0 per cent A in 15 min isocratic, 20 min. Preparative RP-HPLC was carried out in an ODS column (100 X 4.6 mm i.d. particle size 3 jum). Solvent A was methanol-aqueous 0.5 N ammonium acetate (75 25, v/v), solvent B methanol-acetone (20 80, v/v). The gradient was as follows 0 min, 60 per cent A 40 per cent A over 2 min 0 per cent A over 28 min isocratic, 30 min. The same column and mobile phase components were applied for the analytical separation of solutes. The chemical structure and retention time of the major pigments are compiled in Table 2.96. 

The blend of poly(bisphenol A carbonate)-(poly(caprolactone) PC-PCL is particularly unusual in that both polymers are capable of crystallization and FT-IR has been used to study the state of order in these blends as a function of the method of preparation 254,255). In this case, PCL is a macromolecular plasticizer for PC. The PCL becomes progressively less crystalline as the concentration of PC increases. PC is amorphous if the blend is cast from methylene chloride but semicrystalline if cast from tetrahydrofuran. When PC in the pure form is exposed to acetone, it will not crystallize, but in the blend, exposure of acetone causes the PC to crystallize which emphasizes the additional mobility of the PC in the blend. 

Sometimes, the use of high-concentration buffers in the reversed-phase mode decreases column life and efficiency. Therefore, the use of an alternative mobile phase (i.e., normal phase) is an advantage in chiral resolution with these buffers. The most commonly used solvents in the normal phase mode are hexane, cyclohexane, and heptane. However, dichloromethane, acetone, propanol, ethyl-acetate, ethanol, and chloroform also have been used as mobile phase solvents. Hargitai and Okamoto [110] used hexane-2-propanol (in different ratios) as the mobile phase in the chiral resolution of several drugs. These authors also studied... 

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