电脑技术英语作文

A packed-column supercritical fluid chromatography-atmospheric pressure ch emical ionization mass spectrometry

method was studied for the determination of artemisinin from Artemisia annua L. extracts. The technique does not

require any kind of derivatisation prior to the analysis. All samples were simply dissolved in methanol and

injected into the mobile phase. Detection was achieved by using mass spectro metry with atmospheric pressure

chemical ionisation. The ionisation technique is relatively soft and provides pr otonated molecular ion and

informative structural fragmentation for the compound. Benzophenone was us ed as a chromatographic standard for

the determination of the analytical reproducibility. The supercritical carbon dio xide mobile phase used in the

system was modified by 10% methanol. The average absolute retention time was 3.54 min with a standard

deviation of 0.017 min and a relative standard deviation of 0.4% with respect t o benzophenone for the procedure.

The correlation coefficient was 0.998 and detection limit 370 pg on column.

Introduction

Artemisinin (qinghaosu) is a sesquiterpene lactone with an endoperoxide oxy gen bridge across the seven member rings, Fig. 1. It is the clinically active a ntimalarial constituent isolated from the traditional Chinese herb Artemisia an nuaL. Several thousand cases of malaria in China have been successfully tr eated with artemisinin. Total chemical synthesis of artemisi-nin is complex (in cluding 11 steps) and gives a low yield(~30%). Therefore, the main source fo r artemisinin in pharmaceutical science is from plant extraction. The plant, Art emisia annua L., contains most of the artemisinin (89% of the total artemisini n) in the leaves at an average concentration less than 0.1% calculated by dr y weight. Elsewhere an average artemisinin content of 0.4% was also report ed. The content of artemisinin varies according to its origin and growing con ditions, such as temperature, humidity, light and nutrition. Interest in the antim alarial potential of artemisinin as well as its derivatives is currently the subjec t of numerous investiga-tions.

Several analytical techniques have been reported for the

qualitative and quantitative determination of artemisinin in

biological and crude plant extracts. Methods such as thin layer chromatography (TLC), HPLC with electrochemical detec-tion,

ultraviolet detection, polarographic detec-tion, thermospray and electrospray mass spectrometric

detection, evaporative light scattering detection (ELSD), chemiluminescent d etection (CL), and gas chromatography

with mass spectrometric detection, enzyme-linked im-munosorbant assay (EL ISA), and electrophoresis with UVdetection are the most commonly used tech