TY  - UNPB
A1  - Chandrasekera, Dhammitha Himali
M1  - Doctoral
PB  - University College London
UR  - https://discovery.ucl.ac.uk/id/eprint/10122282/
N2  - Products containing St. John's wort (Hypericum perforatum L.) have gained popularity as antidepressants. In the UK, they are available as unlicensed medicines and supplements, obtained in a variety of ways from different geographical sources. Some contain dried plant material, whereas others contain standardised extracts, usually to the hypericin and hyperforin content. This thesis describes the application of high performance liquid chromatography-mass spectrometry, to the problem of evaluating the phyto-pharmaceutical quality of St. John's wort preparations available in the UK. Products were compared using fingerprint chromatography and quantitative analysis. A method was established for profiling the major constituents, which were, hyperforin, hypericin, pseudohypericin, rutin, hyperoside, isoquercitrin, quercitrin and chlorogenic acid. Eleven products were analysed and most contained the major constituents. Variation occurred between products standardised to the same hypericin content, although those from established manufacturers were interchangeable. Products from established manufacturers had the highest levels of hyperforin. The cheaper products were not generally of poor quality but less likely to guarantee high levels of the active constituents. The herb was steamed and analysed to investigate the effects on the constituent profile. There was an increase in the level of some flavonoids, chlorogenic acid and hypericin and no change in the hyperforin content. The pseudohypericin content decreased. The degradation of hyperforin and hypericins in the product and extract was evaluated in a three month study. The results showed a low hyperforin and hypericin t90 in both. Hyperforin was more stable in the extract than in pure form. Tandem mass spectrometric investigations showed that hyperforin in extracts and products degraded to give a mixture of oxidation and other breakdovm products, whereas pure hyperforin degraded mainly to its oxidation products. St. John's wort is known to accumulate cadmium. To broaden the criteria for assessing quality, the cadmium content of the products was measured. The amounts of lead, copper, zinc, iron, sodium and potassium were also measured. Cadmium was detected in five, cheaper products, although the amounts found were not considered toxic.
ID  - discovery10122282
N1  - Thesis Digitised by Proquest.
Y1  - 2004///
AV  - public
EP  - 210
TI  - Analytical investigations of St. John's wort herbal preparations.
ER  -