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T Dülffer

Publications and source records attributed to T Dülffer.

5 recordsLinked to original sources
PubMed1997

Candidate reference methods for hemoglobin A1c based on peptide mapping.

A reference method that specifically measures hemoglobin (Hb) A1c is an essential part of the reference system for the international standardization of Hb A1c/glycohemoglobin. We have developed a new method for quantification, based on the specific N-terminal residue of the hemoglobin beta-chains. Enzymatic cleavage of the intact hemoglobin molecule with endoproteinase Glu-C has been optimized to obtain the beta-N-terminal hexapeptides of Hb A1c and Hb A0. These peptides have been separated by reversed-phase HPLC and quantitated by electrospray ionization-mass spectrometry (method A) or by capillary electrophoresis (method B). With these peptides and hyphenated separation techniques, it has been possible to overcome the insufficient resolution of currently used protein separation systems for Hb A1c.

Chromatography, High Pressure Liquid↗
PubMed1992

Multidimensional high-performance liquid chromatography on Pinkerton ISRP and RP18 columns: direct serum injection to quantify creatinine.

A two-dimensional high-performance liquid chromatographic method for the determination of creatinine with direct serum injection without sample pretreatment has been developed. The column-switching technique allowed a switch from columns packed with internal surface reversed-phase (ISRP) material to columns of almost any other material, even if the eluents necessary in a particular case do not appear to be directly compatible. A Pinkerton ISRP column, which stands out because of its very good stability when loaded with undiluted serum samples, was used as precolumn. The creatinine-containing fraction was switched to a reversed-phase Shandon RP18 column and was focused there by alteration of the eluent from pH 6.5 to phosphoric acid-ion-pair reagent. The separation occurs via a pH gradient, with ultraviolet detection at 234 nm. This method stands out particularly for its good long-term stability, simple sample handling without pretreatment, high selectivity, a broad linearity (0.3-30 mg/dl creatinine), good reproducibility (inter-assay coefficient of variation less than 3%) and high recovery (97-100%) relative to values obtained with gas chromatography-mass spectrometry.

Chromatography, High Pressure Liquid↗
PubMed1977

Synthesis and application of cleavable and hydrophilic crosslinking reagents.

Bifunctional imidoesters are due to their mild reaction especially suitable for the crosslinking of proteins. Most often used are diimidates with a medium span (4 or 6 CH2-groups). Reagents with a wider span might be of interest. In such a case, however, the bridge should be more hydrophilic. Bifunctional imidoesters have, therefore, been prepared from dinitriles NC-(CH2)2-X-(CH2)2-CN; X being -O-, -O-(CH2)n-O- or -O-(CH2)m-O-(CH2)n-O-. The bridge of diimidoesters can also be labelled by coloured or fluorescent groups. Diimidoesters containing -S-S-bonds in the bridge can be cleaved more easily after their reaction with proteins. Dimethyl-3.3' -(8- delta -dithiahexamethylenedioxy)-dipropionimidate, a "long", cleavable and more hydrophilic diimidate, is a promising new reagent. In cases, where HS-(CH2)3-C(=NH)-OCH3- HC1 is is used for crosslinking of proteins, this reagent can possibly be replaced by 2-iminothiolane hydrochloride, a cyclic thioimidate, which is easier to prepare and to handle.

Chemical Phenomena↗