Absorption scans

Physical Methods. Vitamins D2 and D exhibit uv absorption curves that have a maximum at 264 nm and an (absorbance) of 450—490 at 1% concentration (Table 8). The various isomers of vitamin D exhibit characteristically different uv absorption curves. Mixtures of the isomers are difficult to distinguish. However, when chromatographicaHy separated by hplc, the peaks can be identified by stop-flow techniques based on uv absorption scanning or by photodiodearray spectroscopy. The combination of elution time and characteristic uv absorption curves can be used to identify the isomers present in a sample of vitamin D. 

Fig. 1 Absorption scanning curve of the alizarin complexes of barium (1), strontium (2), calcium (3), magnesium (4) and beryllium cations (5). The amounts appUed were 2 pg in each case.

Note In the case of HPTLC plates the detection limit for the visual recognition of the violet = 530 nm) colored chromatogram zones was 20 ng per chromatogram zone. With the exception of the two tetrahydrosteroids the cor-ticosteriods could be detected on TLC plates with fluorescent indicators by reason of fluorescence quenching (Fig. 1 A). Figure 2 illustrates the absorption scans of the separations illustrated in Figures 1A and 1B. 

Fig. 1 Absorption scans of a range of dilutions of succinic acid [1].

Fig. 1 Absorption scan of a chromatogram with 10 pg ( ) per chromatogram zone of the carboxylic acids tartaric acid (1), malic acid (2), lactic acid (3), succinic acid (4), fumaric acid (5), stearic acid + front (6).

Fig. 1 Absorption scans of the pure substances (ca. 500 ng of each) cephaeline and emetine (A) and an extract of Ipecacuanhae Radix (B) cephaeline (1), emetine (2).

Fig. 1 Absorption scan of a chromatogram track (A) of a gentamycin standard (600 ng gentamycin C complex) and of an accompanying blank (B). Start (1), gentamycin Ci (2), gentamycin C2 and 2. (3), gentamycin Ci, (4), solvent front (5).

The absorption scans were made at a wavelength of 2 = 505 nm (Fig. 1). The limit of detection was 100 ng gentamycin C complex. The best conditions for fluorimetric determination (Fig. 2) were excitation at 2exc = 313nm and detection at 2fi > 390 nm. 

Fig. 1 Absorption scan of a chromatogram containing 200 ng dehydroascorbic acid per chromatogram zone.

Fig. 1 Absorption scan (A) and fluorescence scan (B) of a chromatogram track with 200 ng sugar per chromatogram zone raffmose (1), lactose (2) sucrose (3), glucose (4) and fructose...

Fig. 1 Absorption scan of a chromatogram track with 150 ng of each substance per chromatogram zone 1 = demeton-S-methylsulfone, 2 = dimethoate, 3a = transmevinphos,...

Fig. 2 Absorption scans of chromatograms with 50, 100 and 200 ng dibutyltin dichloride per chromatogram zone.

Fig. 1 (A) Chromatographic separation of sugars. Track 1 fructose, 2 sucrose, 3 glucose, 4 mixture of the substances in tracks 1-3, 5 mixture of substances in tracks 1-3 and 6, 6 Fructo-oligosaccharides, 7 1-kestose, 8 mixture of glucose, maltose, maltotriose and maltotetraose. (B) Absorption scan of track 5 with 200 ng each substance per chromatogram zone 1 = fructosyl-nystose, 2 = nystose, 3 = 1-kestose, 4 = fructose, 5 = sucrose, 6 = glucose.

Ames NP, Hartley RD, Akin DE. Distribution of aromatic compounds in coastal Bermudagrass cell walls using ultraviolet absorption scanning microdensitometry. Food Struct 1992 11 25-32. 

The time-dependent development of the initial absorption scans of the PVP transport in dextran, monitored at 237 nm, is shown in Fig. 8. The anomalous feature of these scans is that material which absorbs at 237 nm rapidly accumulates on the left-hand side of the boundary. This material appears to be evenly distributed in this region and would therefore not be detected by Schlieren optics. We have shown that accumulation of absorbing material on the LHS of the boundary is exactly balanced by the depletion of absorbing material on the RHS of the boundary. 

The Beckman XL software is installed in the computer controlling the instrument such that all the information associated with a set of scans from a run are stored in a folder designated by the date and time of the run. Export the folders containing the digitized information of the experimental absorption scans out of the controlling computer to a separate computer in which the latest version of DCDT+ (we use version 2.2.1) has been downloaded and installed. 

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