John P. G. Wilkins

A polyphenolic pigment from black tea

A yellow polyphenolic compound has been isolated from black tea (fermented leaves of Camellia sinensis) and its structure characterized using a number of spectroscopic techniques. This compound, theacitrin A, represents a new class of polyphenolic pigments in black tea.

A New Type of Tea Pigment—From the Chemical Oxidation of Epicatechin Gallate and Isolated from Tea

( - )-Epicatechin-3-O-gallate (ECG), one of the major green tea poly-phenols, was oxidised chemically using potassium ferricyanide. The major oxidation product, termed theaflavate A, which gave a sharp peak on HPLC analysis, was separated and purified by a combination of chromatography on Sephadex LH-20 and a semi-preparative HPLC method. This compound was characterised by NMR spectroscopy (1H, 13C, HMQC, HMBC and ROESY) and mass spectrometry (Electrospray method) and was found to have a novel benzotropolone skeleton formed between the B-ring of one ECG molecule and the galloyl ester group of another. Compounds containing this type of benzotropolone link were also found to be present in black tea. This benzotropolone link is of great interest, since it shows that the galloyl ester groups of flavan-3-ols participate in oxidative condensation reactions. This illustrates the complexity of theaflavin-type compounds in black tea and provides an additional reaction pathway for the formation of thearubigins which has not been previously considered.

Organophosphorus sulphides, sulphoxides and sulphones. Part 2. Characterisation by gas chromatography-mass spectrometry

The gas-chromatographic behaviour and electron-impact mass spectrometric characteristics are reported for nearly 90 organophosphorus sulphides, sulphoxides and sulphones, used as or derived from pesticides.

Black Tea Dimeric and Oligomeric Pigments—Structures and Formation

Many of us consume tea daily, but it is surprizing how few know where it comes from or how it is made. Tea comes from the tea plant the botanical name for which is Camellia sinensis (L.) O. Kuntze.1 This is a white-flowered evergreen indigenous to the rainforests of Assam, Northwest Burma and South West China, but now cultivated in over 30 countries around the world in places as far apart as Argentina, China, Papua New Guinea, and Turkey. However, since most tea leaves are plucked by hand, the largest plantations are most often found in countries with low manual labor costs. Two main varieties of tea are cultivated; Camellia sinensis var sinensis and C. sinensis var assamica. There is some controversy as to whether these are varieties or two distinct species.1 C. sinensis var. sinensis L, is grown mainly in China and Japan; it is a slow-growing bush, has small narrow leaves and is used for green tea manufacture. The second variety Camellia sinensis var. assamica is grown primarily in India and Africa, is fast growing, has a treelike habit, large broad leaves, and is the source material for black tea. In its cultivated state, it is pruned to approximately 3 feet for ease of harvesting the young shoots (flush), from which the tea is manufactured. This process (plucking) is carried out every 7–14 days during the growing season.

Novel gas-phase ion–molecule aromatic nucleophilic substitution in β-carbolines

We report a novel gas-phase ion–molecule aromatic-nucleophilic substitution reaction between β-carbolines and water vapour, that accounts for the observation of ions with higher masses than the precursor ion in the MS/MS spectra.

Investigations by HPLC-electrospray mass spectrometry and NMR spectroscopy into the isomerisation of salinomycin

HPLC-MS studies have indicated that certain polyether ionophore veterinary drugs are prone to degradation when stored as water-methanol solutions at ambient temperature. Salinomycin and narasin were particularly susceptible, disappearing completely within weeks to produce more polar species, which were identified as isomers of the original compounds. Lasalocid appeared to be stable under such conditions. Structural elucidation of the principal ultimate salinomycin isomerisation product was achieved by 2D NMR spectroscopy. This indicated that the isomerisation process consists of the opening of the spiro rings in the salinomycin structure with the concomitant formation of a furan moiety. The MS data indicated that the isomers retain the ability to complex alkali metal ions and may therefore retain their pharmacological activity. These discoveries may have implications both for the development of legislation covering acceptable levels of polyether ionophore residues in foodstuffs and also for analytical protocols designed to detect them.

Organophosphorus sulphides, sulphoxides and sulphones. Part I. Determination of residues in fruit and vegetables by gas-liquid chromatography

Conditions have been established for the routine quantitative determination of residues of demephion, demeton-S-methyl, disulfoton, fenamiphos, fensulfothion, fenthion, phorate, terbufos, thiometon and their toxic metabolites following conversion into the sulphones. Packed column gas chromatography-mass spectrometry demonstrated that most of the sulphoxides tended to decompose under the conditions required for gas chromatography, whereas most of the sulphides and sulphones were unaffected by such conditions. Temephos and its metabolites and the metabolites of vamidothion decomposed completely during gas chromatography. Some suggestions are given for assessing and avoiding the column priming and enhancement problems often observed in the gas chromatography of these and other polar organophosphorus pesticides.

Determination of benzene in aqueous samples by membrane inlet, solid phase microextraction and purge and trap extraction with isotope dilution gas chromatography-mass spectrometry

The determination of benzene in aqueous samples is reported using membrane inlet, solid phase microextraction and purge and trap extraction techniques combined with gas chromatography-mass spectrometry. The membrane inlet and solid phase microextraction techniques have been applied to the analysis of soft drink samples and the performance characteristics of these methods compared to the established purge and trap method. Isotope dilution quantitative procedures with hexadeuterobenzene as internal standard were used in combination with all three sampling inlets. Detection limits were at, or below the parts per billion (µg l–1) level with analytical precision (%RSD) in the range 3–8%.

Investigation by gas chromatography-mass spectrometry of potential contamination incurred by the use of crimp-cap vial closures

Nine types of crimp-cap vial closures were examined to determine the propensity of their septa to discharge contaminants into sample vials under a range of conditions designed to simulate those that could occur in use. Gas chromatography-mass spectrometry was used to identify the solvent-extractable components. The presence of an unpierced polytetrafluoroethylene facing reduced the degree and rate of sample contamination. Sixty components identified at significant concentrations in the solvent extracts of the vial closures were characterised. Gas chromatographic retention times, quantitative and mass spectral data are presented. Of potential importance in the field of pesticide residue analysis was the identification of ethylenethiourea and diphenylamine as possible contaminants associated with certain vial closures.

Modified gas-liquid chromatographic method for determining bromide/total bromine in foodstuffs and soils

The widespread use of methyl bromide as a soil fumigant has necessitated the development of convenient and specific analytical methods for determining bromide/total bromine in foodstuffs and soils subsequent to fumigation. The gas-chromatographic method described by Heuser and Scudamore was initially adopted by this laboratory. However, for the substrates under investigation, i.e., salad crops and soils, we found that the method lacked resolution and reproducibility and was hindered by tailing and long retention-time peaks. The method proved suitable as a basis for development. The modified method, for dried ground substrates, is described. Mass spectrometry was used on a non-routine basis to identify the chromatogram peaks. The mean recovery for dried vegetable substrates is 97% for a wide range of bromide levels, equivalent to approximately 20–1000 mg kg–1 on a fresh mass basis. The method can be used to determine bromide down to 0.1 mg kg–1 of substrate fresh mass.