Photochemical reaction detection in HPLC

The versatility of post-column reaction detection in chromatography is greatly enhanced by exploiting the principles of organic photochemistry. Improvements in photochemical reactor design will result in further advantages.     

Combined ultraviolet-fluorescence detection in high-pressure liquid chromatography of pharmaceuticals.

The use of combined UV-fluorescence detection for the evaluation of incompletely resolved compounds and trace components in the presence of large quantities of major components is described, analysis for thioridazine and some of its oxidation products by high-pressure liquid chromatography being chosen as a practical example. Mesoridazine and the ring oxide of thioridazine have been determined quantitatively with relative standard deviations (n = 6) of 2.0 and 3.6%, respectively, at concentrations below 0.1 mug per injection. Resolution of the two components is difficult and, in this instance, unnecessary. By a similar approach, it was possible to determine the highly fluoresecent sulforidazine at a concentration of 0.4% of the thioridazine with 6.2 mug of thioridazine injected. A relative standard deviation of 5% was attainable at this concentration. Fluorescence detection limits for mesoridazine and sulforidazine at a signal-to-noise ratio of 4:1 are between 5 and 10 ng per injection; this corresponds to about 0.1% of the active substance for the above example.     

Fluorescence derivatization for trace determination of some alkaloids and adrenaline.

Derivatization with dans-Cl was studied for adrenaline, cephaeline, codeine, emetine, ephedrine and morphine. Titrimetry was used to study the derivatization step and to determine the ratios of reagent to reactant. Only codeine did not react. The other five compounds formed single derivatives with emission maximum wavelengths between 490 and 515 nm. Reactions were quantitative after 20 min at 45°C with a 6–7-fold excess of reagent. Fluorescence was measured after extraction into benzene. Detection limits between 0.12 and 0.44 $\text{nmole}\text{5 ml}$ were observed. The relative standard deviation at 2 $\text{nmole}\text{5 ml}$ was ±2%. Derivatives could be separated by t.l.c. to eliminate fluorescence or quenching interferences; fluorescence was then measured after elution of the spots. About a 7-fold lowering of the detection limit was achieved.     

Die Konstitution des Pachyrrhizins

Ohne ZusammenfassungMit 6 AbbildungenHerrn Prof. Dr.F. Wessely zum 60. Geburtstag gewidmet.     

An HPLC fluorescence detection system for amines

A detection system is described which is based on fluorescent ion-pair formation between tertiary amine drugs and dimethoxyanthracene sulphonate. A dynamic micro-extraction principle is then used to isolate the ion-pairs from the excess reagent. The band broadening of this extraction detector was kept below 20% using standard auto-analyser equipment. With the enhanced selectivity and sensitivity of this approach it was possible to analyse chloropheniramine in urine at ppb concentrations using a pre-column clean-up trace enrichment step.     

Dynamics of CO in mesoporous silica monitored by time-resolved step-scan and rapid-scan FT-IR spectroscopy

Carbon monoxide molecules generated in the channels of mesoporous MCM-41 silica sieve from a precursor (diphenyl cyclopropenone) by photodissociation with a nanosecond laser pulse were monitored by time-resolved Fourier transform infrared (FTIR) spectroscopy using the step-scan and rapid-scan methods. A very broad absorption of CO is observed in the region 2200-2080 cm(-1) at room temperature that decays in a biphasic mode. Two-thirds of the band intensity decays on the hundreds of microsecond scale (lifetime 344 +/- 70 micros). The process represents the escape of the molecules through the mesopores into the surrounding gas phase, and a diffusion constant of 1.5 x 10(-9) m(2)/s is derived (assuming control by intra-MCM-41 particle diffusion). The broad profile of the absorption is attributed to contact of the random hopping CO with siloxane and silanol groups of the pore surface. Measurements using MCM-41 with the silanols partially capped by trimethyl silyl groups gave further insight into the nature of the IR band profile. These are the first observations on the diffusion behavior of carbon monoxide in a mesoporous material at room temperature. The residual carbon monoxide remains much longer in the pores and features distinct peaks at 2167 and 2105 cm(-1) characteristic for CO adsorbed on SiOH groups C end on and O end on, respectively. The bands decrease with time constants of 113 +/- 3 ms (2167 cm(-1)) and 155 +/- 15 ms (2105 cm(-1)) suggesting that CO in these sites is additionally trapped by surrounding diphenyl acetylene coproduct and/or precursor molecules.