Gordon F. Kirkbright

Minor and Trace Elements in Human Milk from Guatemala, Hungary, Nigeria, Philippines, Sweden, and Zaire Results from a WHO/IAEA Joint Project

Concentrations of As, Ca, Cd, Cl, Co, Cr, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Se, Sn, V, and Zn were determined in human whole milk samples from Guatemala, Hungary, Nigeria, Phillippines, Sweden, and Zaire; in most of these countries, three groups of subjects representing different socioeconomic conditions were studied. Analytical quality control was a primary consideration throughout. The analytical techniques used were atomic absorption spectrophotometry, atomic emission spectrometry with an inductively coupled plasma, colorimetry, electrochemistry, using an ionselective electrode and neutron activation analysis.The differences between median concentrations of Ca, Cl, Mg, K, Na, and P (minor elements) were lower than 20% among the six countries. Among trace elements, concentrations observed in Filipino milk for As, Cd, Co, Cr, Cu, F, Fe, Mn, Mo, Ni, Pb, Sb, Se, and V were higher than for milk samples from other countries. The remaining five countries showed a mixed picture of high and low values. In the case of at least some elements, such as, F, I, Hg, Mn, Pb, and Se, the environment appears to play a major role in determining their concentrations in human milk. The nutritional status of the mother, as reflected by her socioeconomic status, does not appear to influence significantly the breast milk concentrations of minor and trace elements.Significant differences exist between the actual daily intakes observed in this study and current dietary recommendations made by, for example, WHO and the US National Academy of Sciences. These differences are particularly large (an order of magnitude or more!) for Cr, F, Fe, Mn, and Mo; for other elements, such as, Ca, Cu, Mg, P, and Zn, they amount to at least a factor 2. In the opinion of the present authors, these findings point to the need for a possible reassessment of the dietary requirements of young infants, with respect to minor and trace elements, particularly for the elements Ca, Cr, Cu, F, Fe, Mg, Mn, Mo, P, and Zn.

Fibre-optic pH probe based on the use of an immobilised colorimetric indicator

The construction of a pH sensor, having the configuration of a probe, is described. The probe utilises a plastic-fibre bundle at the end of which is fabricated a sensitive tip consisting of a styrene-divinylbenzene copolymer supporting an adsorbed colorimetric pH indicator, which is retained in position by a membrane of polytetrafluoroethylene (PTFE). Changes in pH in the vicinity of the sensitive tip cause a variation in the attenuation of specific reflected visible radiation bands. Initial results and performance specifications using bromothymol blue as the colorimetric indicator are presented.

Design consideration and temperature determination of an automated graphite furnace cup system used for direct sample introduction for ICP optical emission spectrometry

Abstract Four graphite cup furnace designs for use with an automated direct sample introduction device for ICP-OES are described. The heating rate and terminal temperature of each cup in the plasma is determined by means of a radiation thermometer operating in the range 0.7–1.0 μm and some correlation between heating rate and peak height for the four elements used in the study (nickel, chromium, manganese and lead) is observed. The use of a glassy carbon support improves sensitivity for nickel and a reduction in graphite rod diameter improves this significantly further. Detection limits and relative standard deviations using the four furnance designs are also discussed.

The rapid determination of arsenic by optical emission spectroscopy using a microwave induced plasma source and a miniature hydride generation device

Abstract A simple technique for the determination of trace concentrations of arsenic is described; a miniature hydride generation device is employed for sample introduction of the gaseous hydride directly to a microwave induced helium plasma operating at atmospheric pressure and detection is effected by optical emission spectroscopy. A rapid, inexpensive and precise analytical method has been developed for the determination of arsenic.

Determination of sodium N-methyldithiocarbamate (metham sodium) and methyl isothiocyanate in aqueous samples by high-performance liquid chromatography using a micellar mobile phase

A high-performance liquid chromatographic procedure was developed for the simultaneous determination of the fungicides sodium N-methyldithiocarbamate and methyl isothiocyanate. These fungicides were separated on a reversed-phase octadecyl bonded column with micellar hexadecyltrimethylammonium bromide in an eluent of methanol-water (50 + 50 V/V) buffered to pH 6.8 (10 mM phosphate). Detection was carried out at 247 nm with a UV detector. Recoveries of standards added to pond water and untreated sewage were >92% and >88%, respectively, for both fungicides. The detection limits for sodium N-methyldithiocarbamate and methyl isothiocyanate are 70 µg dm–3(p.p.b.) and 1 µg dm–3(p.p.b.), respectively.

Selectivity and efficiency measurements in high-performance liquid chromatography using micellar hexadecyltrimethylammonium bromide in the mobile phase

Good chromatographic efficiency in high-performance liquid chromatography (HPLC) was obtained using micellar hexadecyltrimethylammonium bromide (CTAB) in the mobile phase. Dithiocarbamate salts of varying hydrophobicity were used as test solutes. The efficiency measurements obtained for the hydrophobic solutes (phenol and benzene) were compared with those obtained for the ionic dithiocarbamate salts. The influence of CTAB concentration above the critical micellar concentration on retention, efficiency and selectivity and the effects of varying the concentration of organic modifier on the efficiency and retention with a micellar CTAB mobile phase were investigated.The chromatographic efficiency remained high when methanol was used as the mobile phase modifier. When acetonitrile was used as the modifier, the efficiency obtained was poor. Conductance measurements present a possible explanation for the difference in efficiencies obtained for these widely used mobile phase modifiers. The measurements obtained with a micellar mobile phase were compared with those obtained with a non-micelle forming quaternary ammonium salt, tetrabutylammonium bromide.

Impulse response photoacoustic spectroscopy of biological samples

The use of a pseudo-randomly modulated optical beam and a cross-correlation signal recovery technique to obtain impulse response photoacoustic signals is demonstrated. The application of this technique to provide depth-related physical and chemical information from plant tissues is described.

Thermal wave imaging of metallic coatings

Abstract Thermal wave imaging is a non-destructive testing technique which uses optically induced transient heat fluxes to probe the optical and physical properties of solid samples. This paper describes the application of the technique to the characterisation of thin opaque metal coatings on metal substrates. The capability of studying variations of coating thickness, the integrity of the coating-substrate interface and inclusions in the coating is demonstrated.

Thermal wave imaging of multi-layered films

Monitoring of the physical structure of a multi-layered composite film presents difficult analytical problems. Thermal wave imaging is used to distinguish between different layers of a photographic film and to provide information on the internal three-dimensional distribution of chromophores.