Simultaneous determination of ascorbic acid and dehydroascorbic acid by HPLC with postcolumn derivatisation and fluorometric detection

Summary A reproducible method is described for the separation and simultaneous and specific quantitation of ascorbic acid and dehydroascorbic acid by ion-pairing reversed-phase HPLC with fluorometric detection. Copper sulphate and copper acetate were compared as oxidizing reagents for ascorbic acid and 1,2-diaminobenzene dihydrochloride and 1,2-diamino-3,4-dimethylbenzene dihydrochloride as derivatising reagents. The HPLC-method was applied to human plasma. The detection limit reaches 16 ng for ascorbic acid and 3 ng for dehydroascorbic acid. Sample preparation is carried out by solid phase extraction with a recovery of 98%; it is compared with conventional precipitation of plasma proteins by metaphosphoric acid.     

New disc-shaped mesogens based on pentakis(phenylethynyl)benzene derivatives

First examples of amphiphilic alkyl pentakis(phenylethynyl)benzene ethers containing functional groups at the terminal position of their alkoxy chains were synthesized by etherification of pentabromophenol with 11-bromoundecan-1-ol and 11-bromoundecanoic acid ethyl ester, respectively, and subsequent palladium catalyzed, fivefold coupling reactions with the substituted phenylacetylene. Two undecanoic acid derivatives with different pentakis(phenylethynyl)phenoxy substituents in the ω-position were prepared by ester cleavage from the corresponding ethyl esters. The thermal behaviours of five penta-alkynes in their pure states, as well as of their charge transfer complexes formed from mixtures with 2,4,7-tri-nitrofluorenone, were examined.     

Doppler-free two-photon absorption spectroscopy ofn 2 P J -levels (n=7, 8, 9) in203,205Tl

The hyperfine splittings and isotope shifts of n²P_J-levels in^203,205Tl have been measured by high resolution two-photon spectroscopy with a cw dye-laser and an actively stabilized marker cavity for laser frequency scancalibration.     

Chelation of carbocations by polyethers and polyamines

Chelates formed by carbocations and cyclic polyethers and polyamines are studied with semiempirical and ab initio MO methods.     

Kinetik und Mechanismus der Diazotierung, 18. Mitt.: Kinetik und Mechanismus der Diazotierung des Anilins in chlorwasserstoffsaurem Methanol

Ohne ZusammenfassungI.H. Schmid undG. Muhr, Ber. dtsch. chem. Ges.70, 421 (1937); II.H. Schmid, Z. Elektrochem.43, 626 (1937); III.H. Schmid, Atti X. Congr. internat. Chim. Roma2, 484 (1938); IV.H. Schmid undA. Woppmann, Mh. Chem.83, 346 (1952); V. und VI.H. Schmid undR. Pfeifer, Mh. Chem.84, 829, 842 (1953); VII.H. Schmid, Mh. Chem.85, 424 (1954); zusammenfassender Ber.:H. Schmid, Chemiker-Ztg.78, 565, 683 (1954); VIII.H. Schmid, Mh. Chem.86, 668 (1955); IX.H. Schmid undA. F. Sami, Mh. Chem.86, 904 (1955); X.H. Schmid undE. Hallaba, Mh. Chem.87, 560 (1956); XI.H. Schmid undA. Woppmann, Mh. Chem.88, 411 (1957);H. Schmid, Mh. Chem.88, 161, 344 (1957); XII.H. Schmid undM. G. Fouad, Mh. Chem.88, 631 (1957);H. Schmid, Österr. Pat. 191 399, Kl. 12e₂ (Juni 1957);H. Schmid, Chemiker-Ztg.81, 603 (1957); XIII. und XIV.H. Schmid undCh. Essler, Mh. Chem.88, 1110 (1957);90, 222 (1959); XV.H. Schmid undA. Woppmann, Mh. Chem.90, 903 (1959); XVI.H. Schmid undCh. Essler, Mh. Chem.91, 484 (1960); XVII.H. Schmid undG. Muhr, Mh. Chem.91, 1198 (1960);H. Schmid, Mh. Chem.92, 174 (1961).