Bivoltametric titrations using electrodes with innovative geometry

Electrodes with different surface areas were investigated for the determination of reversible, quasireversible, irreversible or electroinactive substrates. Two kinds of electrodes were constructed, a helical electrode with a given asymmetry and a platinum array electrode with a variable area. These electrodes were applied for the cerimetry of ammonium iron(II) sulfate and for the bromatometry of various organic substances. The theoretically derived effects on the shape of the voltametric titration curve are verified experimentally. It is possible to sharpen one side of the peak and to broaden the other side, depending on the system and the side of the peak one is interested in. It is possible to improve the bivoltametric determination of hydroquinone, benzocaine and sulfaguanidine by bromatometry by the directed employment of electrodes of different areas. For the bromatometric determination of electrochemically irreversible substrates the use of the electrode geometries proposed is a way to obtain a sharp bend and a steep decrease of titration curves with low values of the constant current which is a basic requirement for the accuracy.     

Bestimmung von Diphenhydramin, Dequaliniumchlorid und Dexamethason in einer Emulsionssalbe

Ohne Zusammenfassung

---

Determination of diphenhydramine, dequalinium chloride and dexamethasone in an ointment

     

Pyrolytic carbon film electrodes

Home-made pyrolytic carbon film electrodes (PCFE) were tested in voltammetric experiments. Different drugs were analyzed by differential pulse voltammetry. In many cases the reproducibility of the signals is as satisfactory as by using glassy carbon electrodes (GCE). The cleaning procedure is very easy to accomplish by wiping off the electrode surface with a paper tissue dipped into methanol. The peak- to residual current rate is much better at the PCFE than at the GCE. Therefore the detection limit is lowered at the former.     

Pre-column (hν-HPLC) photochemical reaction for the on-line characterization of photoproducts using p-aminobenzoic acid as a model substance

A special photochemical reactor on the basis of high-pressure resistant reaction coils has been constructed, which can be coupled to an HPLC-system before the separation column. By means of the so-called “on-line pre-column (hν-HPLC)”-method, the starting compounds can be irradiated on-line, the conversion products formed can be separated and detected subsequently. The efficiency of the proposed method was proved by using p-aminobenzoic acid (PABA) as a model substance.     

Anodic Stripping Voltammetry with Galinstan as Working Electrode

The liquid alloy galinstan is used to determine low concentrations in microgram per liter level of trace metals like copper, cadmium, lead, bismuth, antimony and thallium using anodic stripping voltammetry. Like the conventionally applied HMDE, the hanging galinstan drop electrode (HGDE) is able to accumulate the investigated metal ions at the electrode surface. Hence, simultaneous determination of Pb and Cd is possible. Both, DPASV and SWASV were used as measuring methods. The influence of different parameters like accumulation potential and time and the frequency in SWASV were studied. By the use of acetic buffer solutions, the potential window reaches from ?900 mV to 150 mV. The limit of detection (LOD) varies from 6 ppm (worst case, Sb³⁺) to 2 ppb (best case, Pb²⁺). Therefore, the use of galinstan in the form of the HGDE is possible as a “mercury‐free” and environmentally friendly electrode in stripping analysis.     

Phototoxicity testing by online irradiation and HPLC

A high-performance liquid chromatography (HPLC) system was developed for the determination of drug photostability and phototoxicity based on an automated column-switching system with aqueous online UV-A irradiation and hyphenated organic separation of the drug and its photoproducts. The photoreactor is built with an poly(ethylene-co-tetrafluoroethylene) (ETFE) reaction coil knitted around a UV-A light source. The chromatographic separation was performed with two special C₁₈ columns, which are also suitable for using with pure water as eluent. Degradation of chlorpromazine (CPZ) by ultraviolet light was investigated at pH 7 and pH 3. Furthermore chlorpromazine was irradiated in the presence of guanosine-5-monophosphate (GMP) in pH 7 buffered solution, leading to a new photoproduct. In the pH 3 irradiation studies of CPZ and GMP, no reaction was detected between the molecules.