Peak Height Sensitivity Research Articles

Study of the possible benefits of flow injection sample introduction for flame atomic absorption spectrometry

Flow injection techniques for use with atomic spectrometry are briefly reviewed, from which it is apparent that there has been a considerable increase in interest recently in on-line pre-concentration and matrix isolation methods. In addition to the use of immobilised reagents and solvent extraction, methods based on precipitation and collection of the precipitate in the manifold have been reported. The possible benefits of running the nebuliser under starvation conditions both with and without air compensation are examined, together with the benefits of peak-area as opposed to peak-height measurements, claimed in some previous studies to lead to improved detection limits. It is shown that, with a Baird Atomic A3400 nebuliser, the depressive effect of phosphate on calcium may be removed at low flow-rates and that with a Philips SP9 nebuliser the best detection limits are obtained when strategies for maximising the peak height are adopted. Preliminary results for the generation of a volatile metal chelate (copper trifluoroacetylacetonate) as the basis for matrix isolation show a considerable improvement in peak-area sensitivity over conventional nebulisation, although the peak-height sensitivity is similar.

Transient atomisation by cathodic sputtering in a glow discharge for atomic absorption spectrometry

Analytical applications of cathodic sputtering in a glow discharge have almost wholly involved producing a steady-state atomic vapour, which suffers from relatively poor sensitivity and limit of detection common to the steady-state mode of atomisation. The formation of atoms in and loss of atoms from an analysis volume (defined by the geometry of the incident radiation from the hollow-cathode lamp) can be described by consecutive, first-order reactions, [graphic omitted], where D is the pre-atomisation species, B is the analyte atom that absorbs, C is the analyte atom that is lost and k1 and k2 are first-order rate constants. For k2≫k1, d[B]/dt= 0 (t is time in seconds) and the system is said to have reached a steady state. At the steady state, [B]=[D]0k1/k2, which makes [B] much less than [D]0, the initial concentration of the analyte atoms. Hence, the steady-state mode of atomisation gives low sensitivity.The objective of transient atomisation is to maximise [B] by making k1≫k2. For k1≫k2, [B]≈[D]0, and [B] then reaches its maximum possible value, giving the maximum absorbance. This paper presents the results of a preliminary study on transient atomisation with an Atomsource, used in conjunction with a Perkin-Elmer Model 5000 atomic absorption spectrometer and a Perkin-Elmer Model 7500 professional computer. Aqueous solutions of salts of Al, Cd, Co, Cu, Fe, Mn, Mo, Ni and V, one element in one solution, were used. The rate constants, k1 and k2, were evaluated from kinetic profiles and yielded k1/k2≫ 1, which satisfied the condition required for making [B]≈[D]0, yielding high peak-height sensitivity and an excellent detection limit for the above elements. Kinetic analysis revealed that the rate constant for atom formation in the early stages of the reaction (after a transition period), attained a much larger value (to be called k3) at later times. This rate constant for atom formation, k3, obtained from later times of atomisation, rather than k1 obtained from earlier times of atomisation, was used (i.e., k3≫k2) as the criterion for the peak-height sensitivity.

Fast, microbore, and fast microbore high-performance liquid chromatography of nucleic acid constituents

Fast high-performance liquid chromatography (HPLC) (5–10 cm × 4.6 mm I.D. columns), microbore HPLC (25 cm × 2.1 mm and 1 mm I.D. columns), and fast microbore HPLC (5–10 cm × 2.1 mm and 1 mm I.D. columns) were successfully applied to the separation of nucleic acid constituents in standard mixtures and physiological fluids. Separations were obtained in isocratic and gradient elution modes. The separations obtained were compared with those achieved on a conventional 25 cm × 4.6 mm I.D. column. Factors evaluated included separation time, retention time reproducibility, peak height reproducibility, resolution, efficiency, sensitivity and linear response range. Practical factors, such as the amount of sample required and cost per analysis, were also examined.

Glassy carbon tubes for electrothermal atomic absorption spectrometry

The use of glassy carbon as a tube material in electrothermal atomic absorption spectrometry requires modifications to the power supply if temperatures and heating rates comparable to those for graphite tubes are to be obtained. Glassy carbon tubes frequently have a longer lifetime than pyrolytic graphite coated tubes made of polycrystalline electrographite. Peak height sensitivity for glassy carbon is better by a factor of two for some volatile elements, but up to a factor of five inferior for less volatile elements than that for pyrolytic graphite coated tubes. Peak area sensitivity is generally inferior by about a factor of two. Sample volume is limited to 5–10 μl because of the smooth surface.

Study of r.f. magnetron-sputtered MoSe2 films by electron spectroscopy for chemical analysis

Abstract Thin MoSe2 films were prepared by r.f. planar magnetron sputtering and studied by photoelectron spectroscopy. The chemical state of the surface species was identified by the location and separation of the 3d lines of molybdenum and selenium. The chemical shifts of these lines for the thin films were found to be in good agreement with those of a stoichiometric single-crystal reference. Quantitative analysis was conducted by determination of peak area and peak height sensitivity factors. The results show the influence of the sputter deposition parameters on the surface chemical composition of the films.

Simultaneous multi-element analysis by continuum source atomic-absorption spectrometry with graphite probe electrothermal atomisation

An automatic graphite probe atomiser has been used in conjunction with a continuum source atomic-absorption spectrometer system (SIMAAC) for the simultaneous determination of up to 15 elements. The influence of the atomisation stage temperature on the magnitude and precision of peak-height and peak-area signals has been investigated for a range of elements. A compromise atomisation temperature of 2700 °C was found to give efficient atomisation and good peak-height sensitivity for all the elements studied. In comparison with tube-wall and platform atomisation, probe-SIMAAC detection limits (0.01–7.0 µg l–1) are equivalent or superior, except for the less volatile elements (e.g., V, Mo). Analysis of NBS Standard Reference Materials (bovine liver, rice flour and wheat flour) indicated that the probe procedure was more accurate than tube-wall atomisation methods, but less precise than platform atomisation methods.

Sensitivity enhancement of beryllium determination in graphite furnace-atomic absorption spectrometry by use of atomization under pressure

Using pressurized atomization both peak height and area sensitivity of beryllium is considerably improved. The enhancement may probably be explained by the fact that the Lorentz broadening and shift is more than compensated for by the lower diffusion rate of atoms with increasing pressures. The alteration of peak shapes and parameters should result in a diminishment of vapor phase interferences with increasing pressure. The relative time resolution of the detection system also improves with increasing pressures, with a consequent improvement of precision and accuracy. In the absorbance domain calibration curves are more linear with pressurized atomization than at atmospheric pressure.

Determination of silver by graphite furnace?atomic absorption spectrometry with atomization under pressure

When determined with pressurized atomization silver shows a lower peak height sensitivity than under normal conditions. Peak area is less influenced by pressure. The peak parameters are somewhat changed as compared to normal atomization. Notable is the prolongation of the mean residence time and peak time. Interferences are reduced with atomization under pressure. The linearity of the calibration curves is extended with atomization under pressure.

Isothermal atomization from a platform in graphite furnace atomic absorption spectrometry

Studies of absorption pulses of Pb and Cd from the wall and the platform atomization have revealed the importance of isothermal atomization in reducing or eliminating matrix interferences. The measured platform temperature and the effect of the wall temperature on the degree of the isothermal atomization are presented and discussed. A low charring temperature, a fast (wall) heating rate, and a low (wall) atomization temperature, all tend to shift the analyte absorption pulse towards the isothermal region of the wall temperature curve, thereby resulting in higher peak-height sensitivity and greater freedom from matrix interferences. Matrix interferences with Pb and Cd by the chloride matrix are greatly reduced by the platform technique. An explanation for reduction or elimination of the chloride matrix interference based on isothermal atomization from the platform is presented.

Graphite Furnace Modification for Second Surface Atomization

Preliminary results from a simple furnace modification are presented. A graphite condensation site has been located inside a commercial graphite furnace atomizer. Solution samples are deposited on the furnace wall and the analyte and other condensible species “distilled” to this site during a high temperature ash. During the atomization cycle, the analyte is revaporized from the “plug” into the higher temperature furnace environment. The plug is radiatively heated and can lag behind the wall temperature by more than 1000 K, thus providing atomization into a higher temperature environment which is more nearly isothermal. The heating program with analyte transfer permits extremely high ash temperatures to be used and offers the possibility of separating the analyte from gaseous, thermal decomposition products from the matrix. Additionally, distortions of the analytical absorbance signal caused by degradation in the pyrolytic surface of the furnace are minimized when atomization from the secondary surface is employed. Limits of detection for Ag, Cr, Cu, Fe, Pb, Sn, and Zn are within a factor of 2 of values determined using wall atomization. Studies are presented on the interference of sulfate on Sn analysis. Improved peak height sensitivity and a decreased dependency on sulfate concentrations have been observed.

A microanalytical method for the analysis of gold in biological media by flameless atomic absorption spectroscopy.

A simple and sensitive method is presented for the determination of gold in various biological matrices by flameless atomic absorption spectrometry (FAAS). The effects of the biological media on the atomic absorption of gold and the application of some of the important fundamental principles in relation to the measurement of the analyte are also discussed. The results demonstrate that, in FAAS analysis, to obtain maximum peak height sensitivity the samples must be confined to the centre of the graphite atomiser, and for accurate background correction the light paths of the analyte and the continuum lamps through the atomised sample must be synchronised. for measurement of gold in the presence of sodium chloride, the concentration of the salt in the gold standards and the samples must be matched to neutralise the severe depression of the gold signal by sodium.

Determination of Palladium by Graphite Furnace-Atomic Absorption Spectrometry with Vaprization from a Platform

Abstract Vaporizing palladium from a graphite platform increases peak area and in some cases peak height sensitivity. The absorption pulse is considerably delayed so that vaporization takes place under isothermal conditions. Many vapor phase interferences are thus overcome. The relative sensitivity of the 340.5 nm non-resonance line exceeds that of the 276.3 nm resonance line. The mass of the platform as well as its contact surface with the graphite tube was found to exhibit a marked influence on peak height sensitivity. Calibration curves are more linear than with vaporization from the wall.

Determination of Thallium by Graphite Furnace- Atomic Absorption Spectrometry with Atomization Under Pressure

Abstract Atomization under pressure worsens peak height sensitivity of both the 276.79 and the 377.57 nm resonance lines. Peak area is also worsened as atomization pressure increases, though much less than peak height. Atomization under pressure alters peak times. Most notable is the prolongation of mean residence time and delay of peak time. As a consequence of this vapor phase interferences are reduced. Linearity of calibration curves is improved by pressure.

Some aspects of electrothermal atomization of elements from large amounts of involatile matrices

Non-volatile matrices which cannot diffuse into the graphite walls of an electro-thermal atomizer (as obtained by direct sampling of solids, injection of solutions into tubes with pyrolytic coatings or with a hydrophobic film) make a “miniplatform” in the centre of the atomizing tube. A delay in the temperature increase of this platform at the beginning of the atomization step compared to that of the atomizer walls causes enhancement of the peak height sensitivity. This was proven by atomization of nanogram quantities of copper and iron from solutions of aluminium salts.