Chloroform, mobile phase

Tan et al. [615] successfully resolved the group VI (Cr(VI), W(VI), and Mo(VI)) metal-decacarbonyl (diphenylphosphinyl)alkane (ethyl to hexyl) bridge complexes on a mixed mode cyanopropyl/aminopropyl column (A = 254nm). A 97/3 hexane/chloroform mobile phase was used. Plots of Id versus alkyl bridge length were shown with the kf values varying fi-om 4 to 12. Individual k values were tabulated for all compound combinations. 

The effects of water levels in chloroform and 1,2-dichloroethane on solute retention is an important factor when using silica or alumina supports [745], Ethyl benzoate, dibutyl, diethyl, and dimethyl phthalate, and o- and p-nitroaniline were used as test solutes to monitor the magnitude of the effect of water level on retention. For example, k/ values for these solutes on the alumina support were initially between 1 (for dimethyl phthalate) and 8 (for p-nitroaniline) when water levels were <60 ppm in the chloroform mobile phase. When water levels reached approximately 150 ppm, all k values had fallen below 2. For water levels >300 ppm all k values = 1. This reemphasizes the critical need for water levels in nonaqueous NP separations to be strictly controlled. 

Microwave extraction realized at 120 °C for 30 min with Hexane -Acetone (3 2 V/V) as the extraction solvent was identified as the most effective extraction procedure for isolation of TPH from biotic matrices. The aim of this research is to develop a silica gel and alumina fractionation procedure for plant sample extraction. Column chromatography with two solvents (chloroform and hexane dichloromethane) as a mobile phase were used for clean-up of extract. In this research the efficiency of recovery received from chloroform as a mobile phase. 

With this mobile phase colour compounds and carotenoids separated with 15 ml of chloroform (first fraction) and the second fraction with 20ml chloroform contained total petroleum hydrocarbons. At the end Spectrofluorophotometry was employed for quantification of analytes. 

HPLC analysis of anatoxin-a was first carried out by Astrachan and Archer, " who extracted the toxin from Anabaenaflos-aquae using chloroform followed by hydrochloric acid. The HPLC analysis was carried out on an ODS column using hypochlorate-methanol. Other systems used since include acetic acid extraction and analysis on a reversed-phase C g column using methanol-water mobile phase, and extraction in water after ultrasonication and analysis on reversed-phase... 

Mobile Phase Chloroform Flow Rate 1.5mi/min Detector UV 254nm Temperature 25°C Pressure 2900 PSIG Sensitivity 0.2AUFS... 

Figure 13.21 shows the resolution of a dozen polymer additives at very high resolution using chloroform as the mobile phase. Tinuvin 622 will elute in pure chloroform whereas Chimassorb 944 and many other hindered amine light stabilizers (HALS) will not. With the addition of 1% triethyl amine to the chloroform, however, virtually all HALS will elute. 

Several other examples of modified mobile phases are given in Figs. 13.58 and 13.59 using 90/5/5 TEIF/MeOH/ACN and 95/5 chloroform/w-butylamine for the SEC analysis of poloxamer and nitrile-butadiene rubber samples, respectively. 

A detailed description of the versatility of multiple development techniques in one dimension has been given by Szabady and Nyiredy (18). These authors compared conventional TLC with unidimensional (UMD) and incremental (IMD) multiple development methods by chromatographing furocoumarin isomers on silica using chloroform as the monocomponent mobile phase. The development distance for all three methods was 70 mm, while the number of development steps for both of the "D techniques was five. Comparison of the effects of UMD and IMD on zone-centre separation and on chromatographic zone width reveals that UMD increases zone-centre separation more effectively in the lower Rf range, while IMD results in narrower spots (Figure 8.8). 

The alkanephosphonic acid dichlorides obtained by these methods are converted with amines, with all reactions carried out in solvents such as acetone, benzene, or diethyl ether at 10°C with triethylamine as HC1 captor. The conversion runs quantitatively followed by a purification with the help of column chromatography with chloroform/methanol in a ratio of 9 1 as mobile phase. The alkanephosphonic acid bisdiethanolamides could be obtained as pure substances with alkane residues of C8, C10, C12, and Ci4. The N-(2-hydroxyethane) alkanephosphonic acid 0,0-diethanolamide esters were also prepared in high purity. The obtained surfactants are generally stable up to 100°C. Only the alkanephosphonic acid bismonomethylamides are decomposed beneath this temperature forming cyclic compounds. 

However, consider the separation of solutes that are more polar than the aromatic hydrocarbons, for example mixtures of ethers or aliphatic esters. If it were attempted to separate a series of aliphatic esters on silica gel employing n-heptane as the mobile phase it would be found that the retention of the later eluting solutes was inordinately long. If a slightly stronger solvent, such as chloroform was used as an alternative to n-heptane, it would be found that the less polar esters... 

It is seen that at high concentrations (a) becomes unity and the surface is completely covered with the more strongly adsorbed solvent. The adsorption isotherm of chloroform on silica gel, determined by Scott and Kucera (5) is shown in figure 1. It is seen that the monolayer of chloroform collects on the surface continuously until the chloroform content of the mobile phase is about 50%. At this concentration the monolayer appears complete. Thus, between 0 and 50% chloroform in the n-heptane, the interactions between the solute and the chloroform in the mobile phase are continuously increasing. 

Concentration of Chloroform in n-Heptane %w/v In contrast, the interactions with the stationary phase are becoming weaker as the surface becomes covered with chloroform. Thus retention is reduced by both the increased interactions in the mobile phase and reduced interaction with the stationary phase. When the concentration of chloroform in the solvent mixture is in excess of 50%, then the interactive properties of the stationary phase no longer change as the surface is now covered with a mono-layer of chloroform. However, solute retention will continue to decrease due to the increased interactions of the solute with the higher concentrations of chloroform in the mobile phase. It is clear that even with this simple example the dependence of retention on solvent composition is quite complex. 

Solute Interactions with the Silica Gel Surface (Mobile Phase n-Heptane/Chloroform)... 

From a practical point of view the change in retention with solvent concentration will be greater at the lower concentrations of chloroform where interactions in both phases are being changed. At concentrations above 50%, however, interactions are only changing in the mobile phase and so the effect of solvent concentration on retention will be less significant. 

As a result of its highly polar character, silica gel is particularly useful in the separation of polarizable materials such as the aromatic hydrocarbons and polynuclear aromatics. It is also useful in the separation of weakly polar solute mixtures such as ethers, esters and in some cases, ketones. The mobile phases that are commonly employed with silica gel are the n-paraffins and mixtures of the n-paraffins with methylene dichloride or chloroform. It should be borne in mind that chloroform is opaque to UV light at 254 nm and thus, if a fixed wavelength UV detector is being used, methylene dichloride might be a better choice. Furthermore, chloroform is considered toxic and requires special methods of waste disposal. Silica gel is strongly deactivated with water and thus, to ensure stable retentive characteristics, the solvent used for the mobile phase should either be completely dry or have a controlled amount of water present. The level of water in the solvent that will have significant effect on solute retention is extremely small. The solubility of water in n-heptane is... 

Mobile phase Chloroform - 1-propanol - formic acid (50+10+5)... 

Mobile phase Chloroform - methanol - ammonia solution (32%) (204-164-10). 

Detection and resnlt The chromatogram was freed from mobile phase for 5 min in a stream of cold air, immersed twice in the dipping solution for 2 s and then dried for 5 min in a stream of cold air. In order to stabilize and enhance the fluorescence intensity it was then immersed twice for 2 s in a solution of Triton X-100 — chloroform (1+4), with the chromatogram being kept in the dark between and after these dipping processes. 

Mobile phase Chloroform — methanol — ammonia solution (32%) (20-1-16-1-10). 

---