Browse

You are looking at 91 - 100 of 33,786 items for :

  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All

A high-performance thin-layer chromatographic (HPTLC) method has been developed for determination of polyamines in beers. Beer samples, previously degassed, were derivatized with dansyl chloride and the dansyl derivatives were separated by HPTLC with silica gel as stationary phase and chloroform–triethylamine, 2 + 1 (v/v), containing 5% (m/v) polyoxyethylene-10-lauryl ether, as mobile phase. Quantitative analysis was achieved by in-situ fiberoptic-based fluorescence scanning. The compounds were determined over the range 0.5–85 ng, with relative standard deviations between 0.44–1.16% and detection limits in the range 0.28–0.39 ng. The simple preparation of the sample and the rapid microwave-assisted dansylation considerably reduce analysis time and effort.

Restricted access

The phytochemical fingerprint profile of ammoniacum gum (from Dorema ammoniacum) was defined by subjecting different extracts of the gum to qualitative and semi-quantitative analysis by high-performance thin-layer chromatography. The different compounds present in alcohol and n-hexane extracts of the gum and in its volatile oil were resolved by TLC and detected by densitometric scanning in the UV at λ = 254 and 366 nm, and by post-chromatographic derivatization. The resolved bands were evaluated for their spectral details, the relative concentrations were determined by densitometry, and band properties such as color, fluorescent or non-fluorescent nature, R F, and λmax were also recorded. Two commercial samples of ammoniacum gum were evaluated by comparison of their phytochemical fingerprint profiles with that of the genuine sample. The work has revealed the potential of this type of automated qualitative and semi-quantitative evaluation by HPTLC as an efficient tool for standardization, for testing the purity and authenticity of herbal drugs, and for quality-control purposes.

Restricted access

The aim of this study was to find suitable separation conditions for the rapid screening of indole derivatives in bacterial culture broths by planar chromatography with silica gel as the stationary phase. The mobile phase was optimized by the PRISMA method; thin-layer chromatography (TLC) was used in the pre-assays. Several mixtures of indole derivatives were used to achieve the necessary chromatographic separation. The combination acetic acid–ethyl acetate–toluene–n-hexane, 4 + 11 + 70 + 15 (v/v), was chosen for screening bacterial culture broths for indole-3-acetic acid (IAA) and other indole derivatives. This mobile phase was transferred, without modifications, to rotation planar chromatography (RPC) using the Extrachrom® prototype separation instrument. The results obtained by use of TLC and RPC were comparable in terms of separation efficiency, and found to be suitable for the intended purpose.

Restricted access

The reversed-phase thin-layer chromatographic behavior of 3d metal ions has been studied on silica gel GF254 layers impregnated with silicone fluid DC200, tri-aryl phosphate, and tri-n-butyl phosphate; mixtures of DMSO and HNO3 were used as mobile phases. The effect of silicone fluid DC200 and of the tri-aryl phosphate ion on the R F values of the metal ions is discussed. Mobile phases prepared from DMSO and 1 M HNO3 are most effective when the concentration of acid in the mixed mobile phase is between 0.10 and 0.70 M. The mechanism of migration is explained in terms of adsorption and complex formation. The effect of solvent composition on the migration behavior of the metal ions was also studied. Some binary and ternary separations were achieved.

Restricted access

Fumonisins were produced by six strains of Fusarium moniliforme and Fusarium proliferatum on inoculated rice culture. For study of fumonisins of the B series (B1, B2, B3, and B4) a quick and efficient two-step reversed-phase OPLC method was developed in which the first step serves for cleaning of the samples. Measurements were performed with the automatic OPLC instrument. Results showed that one isolate of F. moniliforme and one of F. proliferatum produced all the fumonisins investigated – the other isolates produced no fumonisins. This work is the first report of the separation of all the fumonisins of the B series by use of a planar layer liquid chromatographic technique.

Restricted access

The physicochemical properties of biogenic monoamines – their polarity, lability, and the trace amounts found in biological material – create great analytical difficulties in their identification and separation. The selective chromatographic separation of these amines is greatly facilitated by their derivatization. On the basis of theoretical assumptions 4-diisopropylaminodiazabenzene-4´-isothiocyanate (DIABITC) was synthesized and used to prepare the thiocarbamoyl derivatives of the amines. The colored derivatives were separated by TLC.

Restricted access
Restricted access

Quinolones, because of their hydrophilic (amphiionic) character, are strongly adsorbed by silica even from polar solvents. It has been shown that they can be chromatographed on thin layers of Diol-silica adsorbent by using solutions of di(2-ethylhexyl)ortho-phosphoric acid (HDEHP, an ion-pairing reagent) in polar solvents as mobile phases. Retention and selectivity in the adsorption–ion-association system can be controlled by adjusting the concentration of HDEHP (typically 5–10%, v/v) and changing the polar diluent. Both chromatograms and densitograms are presented.

Restricted access

Eighteen new agents have been used for visualizing eight esters of higher fatty acids after chromatography on silica gel, on a mixture of silica gel and kieselguhr, and on neutral aluminum oxide. Limits of detection (detectability, D), detectability index, and broadening index were determined for the esters investigated after use of the visualizing agents. For all the esters investigated the best detectability was obtained on the mixture of silica gel 60 and kieselguhr F254; it was worse on silica gel 60 F254 and worst on neutral aluminum oxide. Bromophenol blue was the best and most universal visualizing agent for all the esters investigated on all the chromatographic supports.

Restricted access