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, Philippines, 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 ion-selective 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.

Determination of platinum metals and gold by optical emission spectrometry with a radiofrequency inductively-coupled argon plasma source.

Optimum operating conditions in a 2-kW inductively-coupled argon plasma source for the detection of the elements platinum, palladium, rhodium, ruthenium, iridium, osmium and gold have been established. Detection limits obtained for aqueous solutions introduced into the plasma by pneumatic nebulization range from 1.5 ppb (Rh) to 34 ppb (Ir). No interelement effects caused by chemical interference have been observed between the elements investigated or from a number of base metals; several spectral interferences were observed with the spectrometer employed. The effect of the presence of mineral acids on the nebulization of sample solutions is reported.

Application of a simple photoionization detector for non-dispersive atomic spectrometry in the vacuum ultraviolet region.

The construction and operation of a simple, solar-blind photoionization detector which responds to incident radiation between 125 and 140 nm is described. The detector, the response characteristics of which are controlled by the ionization potential of the ethylamine filler gas and the calcium fluoride window employed, is shown to provide for efficient detection of atomic line emission from carbon, oxygen and chlorine in this wavelength region. The spectral sources employed for non-dispersive work with this detector are a microwave-excited argon plasma and a demountable hollow-cathode lamp.

Direct determination of nanogram amounts of iodine by atomic-absorption spectroscopy using a graphite-tube atomizer.

The direct determination of iodine by AAS at its 183.0 and 178.2 nm resonance lines by using a small graphite-tube atomizer, electrodeless discharge-lamp source and vacuum monochromator is described. Optimum conditions for the determination of iodine have been established; similar sensitivity is obtained when iodide or iodate samples are examined. With 10 mul aqueous samples sensitivities (for 1% absorption) of 4 x 10(-10) g and 2 x 10(-10) g of I were obtained at 183.0 and 178.2 nm respectively; a detection limit of 2 x 10(-10) g was observed at both lines. Non-specific molecular absorption from common inorganic salts causes interference with the determination; the iodine non-resonance line at 184.4 nm may be employed to correct for this interference when moderate amounts of common salts are present.

Application of indirect methods in analysis by atomic-absorption spectrometry.

The use of indirect methods for the determination by atomic-absorption spectrometry of those elements not normally amenable to sensitive determination by this technique is reviewed. The available indirect methods are classified into five general types of procedure; specific reported procedures for the determination of metals, non-metals and some compounds are discussed.

Determination of manganese by atomicpluorescence spectroscopy using a carbon-filament atom-reservoir.

The atomic-fluorescence characteristics of manganese heated on a carbon-filament atom-reservoir (CFAR) are described and compared with (a) the atomic-absorption behaviour of the element on the same filament apparatus, and (b) its fluorescence behaviour in a separated air-acetylene flame. By fluorescence at 279.5 nm, using 1-mul samples, manganese may be determined down to 0.6 pg (6 x 10(-4) ppm) by use of an electrodeless discharge lamp source (3 pg or 3 x 10(-3) ppm by absorption, and 20 ng or 1 x 10(-2) ppm by flame emission at 403 nm). The effects of fourteen representative cations and anions examined showed no interference at 10-fold and 100-fold levels and serious interference only from magnesium at the 1000-fold level, with ca. 10% suppression from Cr, V, Na and K. No fluorescence signals were observed at any wavelength other than 279.5 nm when the CFAR device was used.

Spectroscopy in separated flames--VII: Determination of bismuth by atomic-fluorescence spectroscopy in a separated air-acetylene flame with electronically modulated electrodeless discharge tube sources.

The application of electronically modulated and unmodulated bismuth and iodine electrodeless discharge lamps as sources for the excitation of bismuth atomic fluorescence in conventional and nitrogen-separated air-acetylene flames has been investigated. Separation of the flame results in improved detection limits for bismuth even when a modulated source is employed. The effect of 500-fold weight excesses of foreign ions on the determination of bismuth at 302.46 nm with a modulated iodine source and separated flame has been studied; only calcium and zirconium are found to cause significant interference. The determination of bismuth in aluminium alloy samples is reported.

Atomic-fluorescence characteristics and analytical determination of manganese in an air-acetylene flame.

The atomic-fluorescence characteristics of manganese atoms in a premixed nitrogen-shielded air-acetylene flame are described. Excitation is obtained at 280 nm from a microwave-excited electrodeless discharge tube. A detection limit of 0-001 ppm for the determination of manganese by atomic-fluorescence spectroscopy is obtained by measurement of the resonance fluorescence observed at this wavelength. In addition to several other weaker atomic-fluorescence signals observed from manganese atoms in the flame, weak resonance fluorescence at 258 and 260 nm from manganese ions stimulated by ion line-emission from the source has been recorded. Linear calibration graphs for atomic-fluorescence measurement at 280 nm are obtained over the range 0.0025-10 ppm of manganese in aqueous solution. Of 26 foreign anions and cations examined for interference at the 1000-fold weight excess level only four produced interference. Large amounts of Si, Th and V interfere by scattering of the incident radiation, while Mg causes depression of the atomic fluorescence by a chemical effect.

spectroscopy in separated flames-VI The argon or nitrogen-sheathed nitrous oxide-acetylene flame in atomic-absorption spectroscopy.

The separation of the premixed nitrous oxide-acetylene flame at a 50-mm slot burner by sheathing with argon or nitrogen is described. In comparison with the conventional flame, the interconal zone of the hot, slightly fuel-rich separated flames provides better conditions for the maintenance of free atoms of elements which form refractory oxides. Optimum conditions for the determination by atomic-absorption spectroscopy of the elements Al, Be, Ge, Mo, Si, Ti, V and Zr in both separated and conventional flames at the same burner have been established. Significant improvement in detection limits and sensitivities is obtained in the separated flames.

A simple low-power reduced-pressure microwave plasma source for emission spectroscopy.

The construction of a simple low-power microwave plasma source for emission spectroscopy is described.

Kinetochromic spectrophotometry-II Determination of sulphate by catalysis of the zirconium-methylthymol blue reaction.

A direct spectrophotometric method is proposed for the determination of sulphate, based on its ability to catalyse the slow reaction between Methylthymol Blue and zirconium in slightly aged solution. The procedure is operated in the same way as a normal spectrophotometric method but with stricter control of timing. The interference of 100-fold excesses of 40 other ions was studied. Of these, Ce(III), Sr, Fe(III), Th, Sn(II), U(V), Mn(II), Sb(III), Se(IV), Bi(III), Te(IV), SO(3)(2-), F(-), PO(4)(3-), AsO(4)(3-), S(2-), tartrate, oxalate and citrate interfered. Cationic interferences may be removed by cation-exchange. The interference of equimolar ratios of arsenate, fluoride and phosphate may be removed by preliminary treatment with magnesium oxide. Sulphate may be determined in the range 0.1-2.4 ppm by the recommended procedure with a net molar absorptivity of 2.0 x 10(4) at 586 nm. The colour development time is 60 min.

Determination of trace amounts of antimony by spectrofluorimetry in hydrobromic acid medium at liquid nitrogen temperature.

Trace amounts of antimony(III) may be determined in 6M hydrobromic acid by measurement of the red fluorescence of its bromide complex at -196 degrees , the optimum wavelengths of excitation and emission (360 and 586 nm respectively) being used. Calibration graphs are linear between 0.01 and 0.25 ppm. The effect of the presence of 50-fold molar amounts of 55 foreign ions has been studied. Of the ions studied, only iron(III) and tellurium(IV) interfere, and these may be tolerated at the 50- and 20-fold levels respectively. A 1000-fold molar amount of arsenic(III) causes no interference.

Spectroscopy in separated flames-V The argon- or nitrogen-sheathed nitrous oxide-acetylene flame in flame emission spectroscopy.

The separation of the premixed nitrous oxide-acetylene flame by sheathing with argon or nitrogen is described. The interconal zone of the hot, slightly fuel-rich flame exhibits low background and noise levels and an extended reducing atmosphere, providing better conditions for the excitation of atoms of elements which form refractory oxides. The limits of detection found for nine such elements are greatly superior to those obtainable in the conventional unsheathed flame under similar conditions.

Fluorescence characteristics of inorganic complexes in hydrochloric acid medium at liquid-nitrogen temperature.

A study of the low-temperature fluorescence characteristics of the ions of 55 elements in concentrated hydrochloric acid is reported. The spectral characteristics, effects of hydrochloric acid concentration and time, calibration linearity and sensitivity for Sb(III), Bi, Ce(III), Pb, Te(IV), Tl(I) and Sn(IV) have been investigated. Uranium(VI), copper(I) and antimony(V) also exhibit fluorescence under these conditions. The detection limits using a commercial spectrofluorimeter with modified sample cells are Sb(III), 10(-6)M; Bi(III), 10(-8)M; Ce(III), 10(-7)M; Pb, 10(-8)M; Te(IV), 10(-7)M; Tl(I), 10(-6)M; Sn(IV), 10(-4)M. The suitability of some inorganic acid solvents for clear glass formation at -196 degrees is also investigated.

Spectroscopy in separated flames-IV: application of the nitrogen-separated air-acetylene flame in flame-emission and atomic-fluorescence spectroscopy.

The primary and secondary combination zones of an air-acetylene flame have been separated by a stream of nitrogen flowing parallel to the flame to prevent access of atmospheric oxygen to its base. The flame is very stable over a wide range of fuel-air mixture strengths, and organic solvents may be aspirated without difficulty. The low flame background enables thermal-emission and atomic-fluorescence measurements to be made with high sensitivity. Bismuth, for example, has been determined in the range 5-200 ppm by its thermal emission at 306.8 nm, with a detection limit of 2 ppm in aqueous solution, and in the range 1-10 ppm with a detection limit of 0.3 ppm in 50% ethanolic solution. Zinc and cadmium have been determined at 213.9 nm and 228.8 nm by atomic-fluorescence spectroscopy in this flame with detection limits of 2 x 10(-4) ppm and 5 x 10(-4) ppm respectively, vapour-discharge lamps being used as sources of excitation. The results obtained represent a considerable improvement over those available by the same methods in a conventional air-acetylene flame.