Thin-layer chromatography recovery plate

Subsequently the alkenylglycerols can be reacted with acetic acid anhydride-pyridine, usually a 1 5 (v/v) mixture, in a sealed tube. The tube is heated at 70-80°C for 45 min and then cooled to room temperature, and the seal is carefully broken. The contents are diluted with an equal volume of water and extracted with n-hexane. Two separate extractions with n-hexane should allow complete recovery of the alkenylglycerol diacetates. The combined hexane extracts are washed with water until neutral and then dried over anhydrous Na2S04. The purity of the preparation can be determined by thin-layer chromatography on silica gel G in a solvent system of petroleum ether-diethyl ether-acetic acid (80 20 1, v/v). Again two separate plates can be run, one for spraying with TNS and the other for charring with sulfonic acid (plus heat). 

Catalytic synthesis of l-ethyl>6-fluoro-l,4-dihydro-4-oxo-7-(l-piperazinyl)-quinoline-3-carboxylic acid ethyl ester (Norfloxacin ethyl ester) (15a). To a dry 15 mL recovery flask equipped with a reflux condenser was added 13 (150 mg, 0.5 mmole), (R)-binap (10 mg, 0.017 mmole), cesium carbonate (360 mg, 0.950 mmole), piperazine (215 mg, 2.5 mmole), Pd2(dba)3 (10 mg, 0.010 mmole), and 1.5 mL of DMF. The reaction vessel was purged with nitrogen and heated to reflux. After three hours, the reaction mixture was cooled to room temperature, and the solvent was removed under reduced pressure. The residue was purified by thin-layer chromatography on a 500 micron silica gel preparative plate with an elution mixture of chloroform methanol water ammonia (80 20 2 0.2) to give 101 mg of 15a as an off-white solid in 58% yield and, separately, 29 mg of 17 as a light brown solid in 22% yield. Using this procedure, the yield of 15a... 

Quantitative recoveries of endogenously labeled bile acids in homogenized human feces can be obtained by continuous extraction for 48 hr with hot chloroform-methanol, 1 1 (18). After saponification, acidification, and continuous diethyl ether extraction, the bile acids are purified on silicic acid (Section IIIB 4 and Ref. 18) to give one mono- and disubstituted, and one trisubstituted bile acid fraction. For identification purposes further subfractionation can be made [see Table V (69, 77, 126, 127)]. The subfrac-ticns are subsequently subjected to small-scale preparative thin-layer chromatography of methylated bile acids. The fractions eluted from the thin-layer plates are next subjected to peak-shift analyses followed by final identification by gas chromatography-mass spectrometry. When the fecal bile acid composition has been elucidated in this way the mono-, di- and trisubstituted bile acids from the first silicic acid column may be quantitated after methyla-tion and by analysis on QF-1. These results are then compared with those obtained after trifluoroacetylation of the bile acid methyl esters. (18). 

The formulation of any biosynthetic pathway depends on the isolation or at least on the detection of all the presumed intermediates. Polyacetylenic compounds are often unstable molecules whose successful isolation depends on the techniques used in handling both the plants and their extracts. The possible influence of work-up procedures on the yields of isolated components has been recently investigated with thin-layer chromatography over silica gel, a standard analytical and preparative procedure in natural products analysis. The recovery of 1 and a-terthienyl (Tl) placed on silica gel plates ranged between 77% and 97%... 

Grebian et al.49) apply biological material directly (urine) or after adding methanol and centrifuging (plasma, faecal samples) on thin-layer plates. After the chromatography the pteridines triamterene, hydroxytriamterene and its sulphate ester are measured. The average variation coefficient with 20 ng/spot from urine is 2.9%, with smaller concentrations it is higher with plasma it is indicated as 6%, with faecal samples it has not been noted. The recovery from urine and plasma is 100%, from faecal samples 95 %. 

In the older literature, PAH are first isolated as a compound class by column chromatography on alumina and subsequently separated by thin layer or paper chromatography ISawicki et al. (15)). Acetylated cellulose has been recommended as an excellent adsorbent for the reversed phase separation of PAH (Pierce and Katz (16)). Identification and quantitation will usually require the recovery of the individuals spots in order to measure them by spectrofluori-metry. Two kinds of problems may arise low or irreproducible recovery from the plates and possible photochemically induced oxidation of compounds. 

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