Steve J. Hill

The classification of tea according to region of origin using pattern recognition techniques and trace metal data

Trace metals in tea originating from various Asian and African countries were determined by using inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry. Pattern recognition techniques were then used to classify the tea according to its geographical origin. Principal component analysis (PCA) and cluster analysis (CA), as exploratory techniques, and linear discriminant analysis (LDA) and soft independent modelling of class analogy (SIMCA), were used as classification procedures. In total, 17 elements (Al, Ba, Ca, Cd, Co, Cr, Cu, Cs, Mg, Mn, Ni, Pb, Rb, Sr, Ti, V, Zn) were determined in a range of 85 tea samples (36 samples from Asian countries, 18 samples from African countries, 24 commercial blends and seven samples of unknown origin). Natural groupings of the samples (Asian and African teas) were observed using PCA and CA (squared Euclidean distance between objects and Wards method as clustering procedure). The application of LDA gave correct assignation percentages of 100.0% and 94.4% for the African and Asian teas, respectively, at a significance level of 5%. SIMCA offered percentages of 100.0% and 91.7% for African and Asian groups, respectively, at the same significance level. LDA, also at a significance level of 5%, allowed a 100% of correct case identification for the three classes China, India and Sri Lanka. However, a satisfactory classification using SIMCA was only obtained for the Chinese teas (100% of cases correctly classified), while teas from India and Sri Lanka appear to form the same class.

Inductively coupled plasma spectrometry and its applications

1. Introduction - a forward looking perspective. 2. Fundamental principles of inductively coupled plasmas. 3. Basic concepts and Instrumentation for Plasma Spectrometry. 4. Aerosol generation and sample transport. 5. Fundamental aspects of ICP-MS. 6. Use of ICP-MS for isotope ratio measurements. 7. Alternative and Mixed Gas Plasmas. 8. Electrospray ionisation mass spectrometry: A complementary source for trace element speciation analysis. 9. Geological applications of plasma spectrometry. 10. Environmental and clinical applications of inductively coupled plasma spectrometry. 11. Applications of plasma spectrometry in food science

Preliminary study using trace element concentrations and a chemometrics approach to determine the geographical origin of tea

A preliminary study to classify tea by geographical origin using trace metal concentrations was made. Fifteen types of tea from ten different countries were digested using nitric acid. The digests were then analysed for their trace metal contents using either inductively coupled plasma-atomic emission spectrometry for the more concentrated analytes (Al, Ba, Ca, Cu, Fe, La, Mg, Mn, Sr, Ti and Zn) or inductively coupled plasma mass spectrometry for the less concentrated analytes (Cd, Co, Cr, Cs, Hg, La, Li, Nd, Ni, Pb, Pr, Rb, Se, Sn, Ti, V and Zr). The data obtained from these results were then analysed using UNSCRAMBLE, a chemometrics package that incorporates principal component analysis, and by using Matlab 4.2cl High Performance Numeric Computation and Visualisation software. The results of the chemometrics analysis indicated that a distinction between African and Asian and between Chinese and other Asian teas could be made.

Arsenic speciation in biological samples by on-line high performance liquid chromatography-microwave digestionhydride generation-atomic absorption spectrometry

Abstract A system capable of the separation of arsenic species by on-line high performance liquid chromatography prior to their online decomposition by microwave digestion, pre-reduction with l -cysteine and analysis by hydride generation-atomic absorption spectrometry has been developed. This approach enables the full speciation of arsenobetaine, monomethylarsonic acid, dimethylarsinic acid and total inorganic arsenic (arsenite + arsenate) in biological samples. Simple modification of the system allows for the determination of the total arsenic content of the sample. In addition quantification of the total reducible arsenic species (arsenite, arsenate, monomethylarsonic acid and dimethylarsinic acid) can be achieved by on-line prereduction-hydride generation-atomic absorption spectrometry. Procedures were validated by analysis of the certified reference materials NRCC DORM-1 and TORT-1 and gave results in good agreement with the certified values.

Methodologies for determination of antimony in terrestrial environmental samples.

Methodologies for the environmental analysis of total antimony and aqueous chemical speciation are critically reviewed, including preparation techniques for aqueous and solid matrices and the determination of solid state partitioning and recommendations are given for future research directions. Concentrations of total antimony commonly present in aqueous and solid environmental samples are readily determined using present day analytical techniques. This has resulted primarily from technological advances in microwave digestion for solid matrices and the development of plasma based analyte detection systems. ICP-AES and ICP-MS techniques are both utilised for the environmental analysis of total antimony concentrations. However, ICP-MS is increasingly favoured as a result of reduced spectral interferences and the potential for analyte detection in the pg mL(-1) range. Determination of aqueous antimony speciation presents a number of complex analytical challenges and highly selective separation and identification techniques are required prior to detection. The majority of published techniques including common applications of hydride generation are insufficiently selective for the determination of intrinsic chemical speciation and often only oxidation state data are obtained. The recent in-line applications of HPLC-ICP-MS offer the potential for highly selective separations of aqueous antimony species and determination of detailed chemical speciation data. However, considerable development work is required to optimise chromatographic separations and identify uncharacterised species resident in environmental systems. Analytical techniques to aid the determination of antimonys associations with solid environmental matrices include the application of chemical extraction procedures and leaching experiments. To date, this area of analytical research has received little attention and further studies are required to elucidate this aspect of antimonys environmental chemistry.

Coupled chromatography-atomic spectrometry for arsenic speciation—a comparative study

Several methods for the quantitative determination of different forms of arsenic (AsIII, AsV, monomethyl and dimethyl) in a variety of samples are described and compared. In each instance separation is achieved by chromatographic means, using either gas (GC) or high-performance liquid chromatography (HPLC), with detection by atomic spectrometry, namely flame atomic absorption spectrometry (FAAS), flame atomic fluorescence spectrometry (FAFS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). For the GC separation it is necessary to derivatise the As compounds either as the hydrides or as the methylthioglycolates. As the arsenic hydrides can be pre-concentrated using cryogenic trapping, this yields the lowest detection limits. The As species studied can be separated without derivatisation by HPLC but after HPLC separation hydride generation can be used to increase the sensitivity for FAAS, FAFS and ICP-AES. While each technique is best suited to certain applications, the hydride generation-cryogenic trapping-GC-FAAS system is capable of detection at the sub-p.p.b. level (0.22–0.55 ng absolute for different species) and is preferred for low-level As samples. When levels permit, HPLC-hydride generation-FAAS is probably the simplest routine method and HPLC-hydride generation-ICP-AES will probably be preferred for multi-element analysis.

Speciation of tin in natural waters using coupled high-performance liquid chromatography-flame atomic-absorption spectrometry

A simple yet effective high-performance liquid chromatography-flame atomic-absorption spectrometry coupling utilising pulse nebulisation and a slotted tube atom trap is described for the speciation of tin in natural waters. The effects of the various parameters on analytical performance are discussed. A detection limit of 200 ng for tin was obtained and the separation of Sn(II), Sn(IV) and tributyltin was possible within 8 min. Tributyltin compounds have been quantified in local harbour waters, and in one harbour situation were observed at levels up to 0.47 µg l–1.

THE RELEASE OF COPPER-COMPLEXING LIGANDS BY THE BROWN ALGA FUCUS VESICULOSUS (PHAEOPHYCEAE) IN RESPONSE TO INCREASING TOTAL COPPER LEVELS

The growth of Fucus vesiculosus L. germlings in chemically defined culture media containing a range of Cu concentrations (20–1000 nM) was monitored simultaneously with measurement of the Cu speciation in the media by competitive equilibrium‐adsorptive cathodic stripping voltammetry. Fucus vesiculosus germlings were found to exude Cu‐complexing ligands with conditional stability constants of the order of 1.6 × 1011. Ligand concentrations increased with increasing total dissolved Cu concentrations (CuT) until a concentration of 500–800 neq Cu·L−1 was reached. Concentrations of the ligand exceeded CuT in treatments containing 20 and 100 nM Cu, were similar to CuT in the 500‐nM Cu treatment, but were less than CuT in the 1000‐nM treatment. Therefore, [Cu2+] were calculated to be at concentrations of 10−11− 10−10 M in the 20‐ and 100‐nM treatments, 10−9 M in the 500‐nM treatment, and 10−7 M in the 1000‐nM treatment. Growth rates were lowest at Cu2+ concentration > 10−9. These results are discussed within the context of the potential roles for exuded copper‐complexing ligands.

Selenium speciation using high-performance liquid chromatography-hydride generation atomic fluorescence with on-line microwave reduction

This paper describes an on-line method for the determination of inorganic selenium species in aqueous samples. Separation of the species is achieved using high-performance liquid chromatography, after which the analyte is acidified before flowing through an on-line microwave system. This latter stage leaves the selenium (iv) unaltered, but transforms selenium(vi) to selenium (iv) and thus converts it into a suitable oxidation state to undergo hydride generation. The selenium hydride is then determined using an atomic fluorescence detector. The method was validated by the analysis of a standard reference material (NIST SRM 1643c Trace Elements in H2O).

Development of a coupled liquid chromatography-isotope dilution inductively coupled plasma mass spectrometry method for lead speciation

A method has been developed for lead speciation using liquid chromatography with isotope dilution inductively coupled plasma mass spectrometry (LC-ID-ICP-MS). Inorganic lead (Pb2+), trimethyllead (Me3Pb+) and triethyllead (Et3Pb+) were separated on a 5-μm Hypersil ODS column using a programmed gradient of 10:90 to 30:70 methanol-buffer eluent. The buffer was prepared by mixing equal amounts of 0.1 mol l−1 sodium acetate and acetic acid each containing 4 mmol l−1 sodium pentanesulfonic acid. To minimise the dead volume of the interface a single pass 40 ml volume spray chamber with a concentric glass nebuliser was used to coupled the LC and ICP-MS. Best precision isotope ratio measurements were obtained with peak jumping and short dwell times (80 μs). The overall detection limit (3σ) for trimethyllead ions was 0.48 ng g−1 as lead.