Determination of the Yields of meso-Tetraphenylporphyrins by Densitometry

JPC – Journal of Planar Chromatography – Modern TLC - Thin-layer chromatography with densitometric detection has been used to monitor different compounds produced by condensation of...     

Solid‐State NMR Spectroscopy to Probe Photoactivation in Canonical Phytochromes

The photoreceptor phytochrome switches photochromically between two thermally stable states called Pr and Pfr. Here, we summarize recent solid‐state magic‐angle spinning (MAS) NMR work on this conversion process and interpret the functional mechanism in terms of a nano‐machine. The process is initiated by a double‐bond photoisomerization of the open‐chain tetrapyrrole chromophore at the methine bridge connecting pyrrole rings C and D. The Pr‐state chromophore and its surrounding pocket in canonical cyanobacterial and plant phytochromes has significantly less order, tends to form isoforms and is soft. Conversely, Pfr shows significantly harder chromophore–protein interactions, a well‐defined protonic and charge distribution with a clear classical counterion for the positively charged tetrapyrrole system. The soft‐to‐hard/disorder‐to‐order transition involves the chromophore and its protein surroundings within a sphere of at least 5.5 Å. The relevance of this collective event for signaling is discussed. Measurement of the intermediates during the Pfr → Pr back‐reaction provides insight into the well‐adjusted mechanics of a two‐step transformation. As both Pr → Pfr and Pfr → Pr reaction pathways are different in ground and excited states, a photochemically controlled hyper‐landscape is proposed allowing for ratchet‐type reaction dynamics regulating signaling activity.     

Optimization of electrochemical hydride generation in a miniaturized electrolytic flow cell coupled to microwave-induced plasma atomic emission spectrometry for the determination of selenium

The optimization of a continuous flow system for electrochemical hydride generation coupled to microwave-induced plasma atomic emission spectrometry (MIP-AES) for the determination of Se is presented. A small electrolytic cell with a porous glassy carbon working electrode was used for hydride generation. When using an Ar MIP operated in a TE101 cavity a detection limit of 0.6 ng mL(-1) (3sigma) could be achieved. The calibration curve was linear up to 1 microgram mL(-1). A standard deviation of less than 2% (10 replicate analyses) could be achieved. It was shown that interferences of transition metals are of the same order of magnitude as with a larger electrolysis cell described earlier, and light elements hardly caused any signal depression as tested. It was possible to distinguish between Se(IV) and Se(VI) species and seleno-DL-methionine, because under optimized conditions of an electrolysis current of 10 mA, a microwave power of 210 W, an Ar flow rate of 15 L h(-1) and a sample flow rate of 2.5 mL min(-1) only Se(IV) was transformed to H2Se and transferred into the plasma. Finally, the possibility of an electrochemical pre-enrichment was shown to enable it to further decrease the detection limit.     

Densitometric Determination of Kinetics of Hydrolysis of Flavonoid Glycosides

JPC – Journal of Planar Chromatography – Modern TLC - In this paper we report the possibilities and advantages of HPTLC for investigation of the acid hydrolysis of six flavonoid...     

Modified programmed multiple gradient development (MGD) in the analysis of complex plant extracts

Summary Two extracts from medicinal plants have been analysed by thin-layer chromatography using a modification of programmed stepwise multiple development. The plant extracts were developed with solvents of increasing solvent strength over decreasing distances that were chosen to maintain the separation of the leading peaks obtained in previous steps. Improvement of separation (number and shape of peaks) was observed.     

Isocratic Liquid Chromatography with Segmented Columns and Simultaneous UV and Dual Electrochemical Detection: Application to the Selectivity Enhancement for the Determination of Explosives

The concept of stationary‐phase optimized liquid chromatography (POPLC) was studied in the context of separation and detection aspects for the determination of explosives. A tailor‐made segmented column assembly with three complementary reverse‐phase materials enabled the separation of 14 priority target nitroaromatic explosives. This experimental approach resulted in excellent selectivity without using gradient‐elution protocols which can considerably deteriorate the performance of electrochemical detection. Consequently, the POPLC separations could be operated under isocratic conditions which were very important for the reliable use of electrochemical detection. Simultaneous UV and dual electrochemical detection resulting in three detection traces was exploited as an additional means for the further enhancement of selectivity in more complex samples.     

Die polarographische reduktion von NO3− in gegenwart von CrO42−

It has been observed, that on the d.c. polarograms of nitrate, even at the very small concentration of CrO₄^2? (of the order 10^?7 mol dm^?3) a maximum appears at the potential ?1.7 V. The maximum is of catalytic nature and may be used for analytical purposes.     

Advances in fast electrophoretic separations based on short capillaries

Capillary electrophoretic separations performed in short capillaries under high field strengths have recently emerged as a promising alternative to chip-based separations. However, the injection and detection approaches have to be adapted appropriately to enable high-throughput determinations. This paper addresses current challenges and trends in this field of research.