Direct Analysis Of Solid Samples Research Articles

Determination of tellurium and antimony in nickel alloys by laser excited atomic fluorescence spectrometry in a graphite furnace

Analytical laser excited atomic fluorescence of the metalloids tellurium and antimony in an electrothermal atomizer was studied. The detection limits were 20 fg and 10 fg for tellurium and antimony respectively, equivalent to about 0.01 ng g −1 in nickel based alloys by direct solid sample analysis, for a 1 mg solid sample, or 1 ng g −1 by the dissolution method, for a 100 mg solid sample in 100 ml solution. The detection limits were three orders of magnitude better than those obtained by graphite furnace atomic absorption spectrometry. They were also comparable to, or better than, those by inductively coupled plasma mass spectrometry. The linear dynamic ranges of the calibration curves were found to be six and seven orders of magnitude for antimony and tellurium respectively. By use of aqueous calibration, tellurium was accurately determined in NIST nickel alloy Standard Reference Materials by both a solid sample method, with a relative standard deviation (RSD) of about 13%, and a dissolution method with an RSD of about 9%. Antimony in Pratt and Whitney “A” series nickel alloy standards was successfully determined by the dissolution method, with an RSD of about 7%, but by solid sampling the antimony method gave incomplete recovery. Molecular fluorescence backgrounds from nitric oxide and silicon monoxide were observed and discussed.

Evaluation of a modified electrothermal vaporization sample introduction system for the analysis of liquids by inductively coupled plasma atomic emission spectrometry

A Perkin-Elmer electrothermal vaporization (ETV) furnace was modified for use as a sample introduction device for inductively coupled plasma atomic emission spectrometry (ICP-AES). The major modification made is the addition of sheath and cooling gas flows. The sheath gas provides a thin sheath layer between the analyte vapour and the wall of the transport tube to prevent vapour condensation, and the cooling gas cools the analyte vapour to promote aggregate formation. Experiments with liquid samples showed that the addition of these gas flows increases the analyte transport efficiency and reduces matrix effects on the transport efficiency. The results also suggest that the carrier gas flow rate affects the peak shape and peak intensity of the copper signal, probably by changing the vaporization rate. With 10 µl sample solution loadings, the detection limits range from 1 to 6 ppb for Cd, Pb, Zn, Mn and Cu, and the precision (relative standard deviation) varies from 3 to 6%. The system is flexible and holds promises for direct solid sample analysis.

Methods of calibration in the direct analysis of solid samples by electrothermal atomic absorption spectrometry

One of the major problems involved in the direct analysis of solid samples by electrothermal atomic absorption spectrometry (ETAAS) lies in the calibration step because non-spectral interference effects are often pronounced. Three standardization techniques have been described and used in solid sampling-ETAAS: (i) standard additions method; (ii) calibration relative to a certified reference material; and (iii) calibration curve technique. However, an adequate statistical evaluation of the uncertainty in the analyte concentration in the solid sample is most frequently neglected, and reported errors may be seriously underestimated. This can be attributed directly to the complexity of the statistical expressions required to accurately account for errors in each of the calibration techniques mentioned above, and the general lack of relevant reference literature. The object of this work has been to develop a computer package which will perform the necessary statistical analyses of solid sampling-ETAAS data; the result is the program “SOLIDS” described here in the form of an electronic publication in Spectrochimica Acta Electronica, the electronic section of Spectrochimica Acta Part B. The program could also be useful in other analytical fields where similar calibration methods are used. The hard copy text, outlining the calibration models and their associated errors, is accompanied by a diskette containing the program, some data files, and a manual. Use of the program is exemplified in the text, with some of the data files discussed included on the diskette which, together with the manual, should enable the reader to become familiarized with the operation of the program, and the results generated.

Spark Ablation of Solid Samples for Analysis by Inductively Coupled Plasma-Mass Spectrometry

High-voltage spark ablation is used for the direct analysis of solid samples using ICP-MS detection. Separation of sample vaporization, excitation, and detection phenomena allows each event to be optimized independently, thereby facilitating (among other things) enhanced sampling efficiency. Qualitative evaluation of elemental constituents is demonstrated. A direct linear relationship between electron multiplier counts and concentration was observed for trace elements (ranging from 0.75 to 125 ppm) in a series of “pure” copper standards. It is significant that neither concentration normalization nor internal standardization procedures were required. Sample uptake and clean-out times are minimal. This technique can be applied for the direct determination of conductive samples (or materials that can be converted into conductive form) with little or no sample preparation. For such samples, spark ablation could serve as an alternative to laser sampling in cases where larger sampling sites (∼1–2 mm) can be tolerated. In contrast, this technique uses inexpensive instrumentation, is simple to operate, and shows good accuracy and precision, even in prototype form.

Direct analysis of liquid and solid samples without sample preparation using laser-enhanced ionization

Laser-enhanced ionization combined with rod–flame and graphite furnace atomizers–ionizers was used for direct analyses of high-purity orthophosphoric acid, germanium, CdHgTe alloy and silver nitrate. In standard aqueous solutions both systems give detection limits for elements down to the 1 × 10–15 g level. The examples of CdHgTe alloys and germanium show that the transition from the analysis of solutions to the direct analysis of solid samples in a rod–flame system leads to a decrease in the matrix background signal of over two orders of magnitude. This allows for the detection of elements in solid samples without sample preparation, with detection limits down to 1 × 10–6 ppm, which is 100 times better than for solutions. The problems with and prospects for the proposed approach are discussed.

On-line electrolytic dissolution of alloys and multi-element determination by inductively coupled plasma atomic emission spectrometry

A method for the direct simultaneous multi-element analysis of solid metal samples by flow-injection on-line electrolytic dissolution and inductively coupled plasma atomic emission spectrometry was developed and applied to the determination of Zn, Si, Fe, Mn, Cr, Mg and Cu in aluminium alloys. The suitable range for the determination was 10 μg g −1–100 mg g −1. The precision of the entire analysis, including electrolysis and determination, was in the range 1–6%, depending on the element and its concentration in the alloys and on the current density applied in electrolysis. The analysis of a sample can be accomplished in a few minutes.

Direct analysis of solid powder biological samples using a magnetron rotating direct-current arc plasma and graphite furnace sample introduction

Direct analysis of solid powder biological samples using a magnetron rotating direct-current arc plasma and graphite furnace sample introduction

Direct determination of cadmium and lead in geological and plant materials by electrothermal atomic absorption spectrometry

A laboratory-assembled atomic absorption spectrometer and graphite cup atomizer were evaluated for direct analysis of solid samples. A number of geological (soil and sediment) and botanical reference materials were analysed for lead and cadmium either by direct introduction (0.02–5 mg) or by a slurry technique (5–200 mg). Integrated absorbance was measured, and aqueous standards were used for calibration. An (NH4)2HPO4 chemical modifier was necessary in the analysis of botanical samples. The effect of particle size on the accuracy and precision of analytical results was studied. Atomization of small sample aliquots (20–500 µg) by direct ‘weighing in’ sample introduction technique requires fine grinding (1 µm) whereas slurry sample introduction is more tolerant to particle size effects.

Atomic mass spectrometry of solid samples using laser ablation-ion trap mass spectrometry (LAITMS)

Laser ablation sampling inside the cavity of an ion trap was used to provide direct atomic mass spectrometric analysis of solid metal samples. An ion trap was designed such that a pulsed Nd:YAG laser beam was used to ablate sample pins inserted radially through the ring electrode. To demonstrate the potential of this method, atomic mass spectra were obtained for metal alloy samples.

Direct Analysis of Solid Powder Samples with Electrically Vaporized Thin-Film Sampling and ICP Detection

Solid powder samples deposited on Ag thin films are electrically vaporized by capacitive discharge. The aerosol produced by this method is introduced into the ICP. A low-volume vaporization chamber has been designed for these experiments. A magnetic field of a few kG normal to the electric field in the thin-film plasma is used to improve the plasma/sample interaction. A continuous flow of Ar or 60%/40% Ar/O2 through the chamber carries the aerosol from the capacitive discharge plasma into the ICP. Analytical data will be presented for a number of NIST reference materials emphasizing the determination of Mn, V, and Ni in biological and refractory inorganic matrices.

On the direct analysis of solid samples by graphite furnace atomic absorption spectrometry

We have studied some limitations of the solid sampling, cup-in-tube technique by comparison with a constant temperature two-step atomiser and found consistently lower vapour-phase temperatures and greater interferences in the former. With the former, higher vapour-phase temperatures and improved analytical results for lead and cadmium were found using Pd(NO3)2+Mg(NO3)2 instead of NH4H2PO4+Mg(NO3)2 as modifier. Investigations of methods to extend the useful calibration range revealed reduced vapour-phase temperatures in the presence of a convective gas flow during atomisation, and a greater potential for errors using non-resonance lines. With respect to the latter, the absorbance signal is much more sensitive to matrix induced changes in the temperature interval in which atoms are formed compared to resonance lines. Furthermore, at the lead 261.4 nm non-resonance line we observed overcompensation errors caused by cobalt when using a Zeeman-effect system, and undercorrection due to the AlCl(g) molecule with a continuum source background corrector.

Synthetic reference material for direct analysis of solid biological samples by electrothermal atomic absorption spectrometry

A reference material for the direct analysis of solid samples by electrothermal atomic absorption spectrometry (EAAS) was prepared by coprecipitation of eight metal ions with magnesium(II) 8-quinolinate. The metal ions were quantitatively recovered and the distribution of the metal ions in the reference material was confirmed to be homogeneous. The reference material was more than adequate for multielemental analysis of biological samples by EAAS. For the analysis, an inner miniature cup, which was placed into a cupper-type graphite furnace, was also used. Analyses were conducted without any pretreatment of samples. The accuracy, precision, and limits of detection of the method are described. The accuracies of solid samples on a routine basis. The limits of detection for Al, Cd, Co, Cu, Mn, Ni, Pb, and Zn in solids are 0.087, 0.008, 0.012, 0.05, 0.003, 0.043, 0.14, and 0.013 ..mu..g/g, respectively.

Evaluation of the simplified generalised standard additions method for calibration in the direct analysis of solid samples by graphite furnace atomic spectrometric techniques

In combining the principles of experimental design and the simplified approach to the generalised standard additions method, a useful calibration strategy is obtained for the single-component analysis of solid samples. By varying both the solid sample mass and the amount of analyte added, the observed response is defined by these two variables and may be geometrically described as a surface in three-dimensional space. The use of multiple regression techniques then allows the analyte concentration in the solid to be computed from the response plane. Simultaneous blank correction and quantification is also performed. The importance of a well designed experimental lay-out and the effects of random errors or noise on the accuracy of the procedure are investigated, and some analytical results are given. It is shown that the approximation of the analyte concentration obtained is fairly insensitive to curvature in the calibration function, but tends to be biased high in the presence of intense noise. This latter effect is a major limitation given the inhomogeneity of most solid samples which leads to irreproducible or “noisy” results.

Laser Ablation for Direct Elemental Analysis of Solid Samples by Inductively Coupled Plasma Mass Spectrometry

The results of a preliminary study on direct analysis of solid metals and nonconductive samples by inductively coupled plasma mass spectrometry (ICP-MS) are described. The aerosols ablated from solid samples by a ruby laser are introduced into an inductively coupled plasma, with detection of the resulting ions by a mass spectrometer. With conventional solution introduction, polyatomic species from mineral acids and solvents prevent the accurate determination of some trace analytes. However, using laser ablation, these background peaks are greatly reduced. The relative sensitivity factors for the laser ablation method are seen to vary from unity, with volatile elements such as Pb and Bi being more sensitive. Detection limits of rare-earth elements, Th and U in silicate rocks are excellent (0.02-0.9ppm at the effective integrating time of 1.4s), being better than those of the examined elements in steel (1.7-29ppm at the effective integrating time of 0.6s).

Spatially and temporally constant-temperature graphite furnace for atomic absorption/emission spectrometry

The performance of a furnace providing spatial as well as temporal isothermality (two-step atomizer) is characterized and compared with an integrated contact cuvette (ICC, spatially isothermal) and a conventional Massmann-type furnace. It is concluded that the two-step atomizer offers some special features, such as superior performance for emission measurements, suitable conditions for fundamental studies, the direct analysis of solid samples and multi-element determinations. However, from both experimental and theoretical points of view, the two-step atomizer cannot always eliminate interference effects, and in many applications the advantages, relative to the ICC, are small. The provision of spatial isothermality is found to confer the greatest benefits on furnace performance e.g. by reducing interferences, signal tailing and memory effects, as compared to a Massmann-type furnace. Since such conditions are available using the ICC, graphite furnace design can be readily improved without adding to system complexity. Thus, although the two-step atomizer offers some advantages, the inherent losses in simplicity may not justify routine applications of this system.

Direct coupling of capillary supercritical fluid chromatography to high resolution mass spectrometry with minimum modification

The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a trit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO2 as the charge exchange medium were obtained.

Direct Analysis of Solid Sample with Ultrafine Particle Generation/Inductively Coupled Plasma Emission Spectroscopy

An ultrafine particle generation (UFP) system has been developed for the direct analysis of solid metal samples by inductively coupled plasma (ICP) emission spectrometry. In this system fine particles are generated from solid samples with the use of a spark discharge and then swept into the ICP. The spark discharge conditions involving the electrode gap and the analytical performance of the ICP system are investigated. Analytical calibration curves are presented for steel samples. The NBS standard reference materials are analyzed by the proposed system.

Direct determination of metals associated with airborne particulates using a graphite probe collection technique and graphite probe atomic absorption spectrometric analysis

A new analytical method has been developed for direct analysis of solid samples of airborne particulate matter by a graphite probe collection technique coupled with graphite furnace atomic absorption spectrometry. A porous graphite probe is used as a filter for air particles. The probe is then subjected to atomization by being inserted into a graphite furnace which has been pre-heated to a constant atomization temperature. Some aspects of the method have been tested by recovery studies using NBS Urban Particulate Matter, SR M No. 1648, and found to give recoveries of 91–107% for Pb, Cd, Ni, Cu and Mn. By combining a highly efficient filtering medium with the extremely high relative sensitivity of solid sampling, this method has the potential of monitoring sources of air particulate emission with sufficient temporal and spatial resolution for unequivocal identification of the pollution source (at least on a local scale).

Direct analysis of solid samples by atomic absorption spectrometry, following preconcentration of trace elements from seawater with 8-hydroxyquinoline

8-Hydroxyquinoline (8-HOQ) was used for the preconcentration of Cd, Cu, Mn, Pb and Zn from seawater prior to their determination by graphite furnace atomic absorption spectrometry using an inner miniature cup for solid sampling technique. The metal ions in seawater were precipitated quantitatively in the pH range 7–8.5 with 8-HOQ alone. The precipitate thus formed was directly analysed by an atomic absorption spectrometer equipped with a specially deviced graphite furnace and miniature cup. The present method was confirmed to be highly reliable for analysis of seawater. Detection limits (3δb) for Cd(II), Cu(II), Mn(II), Pb(II) and Zn(II) are 1.4, 10, 5, 10, and 6 ng l−1, respectively, for the analysis of a 400-ml portion of seawater samples. Corresponding precision of 6–14% is typical for determination 5-fold above the detection limits.

Determination of cadmium, copper, manganese and rubidium in plastic materials by graphite furnace atomic absorption spectrometry using solid sampling

The direct analysis of solid samples using (GFAAS) graphite furnace atomic absorption spectrometry (GFAAS) has considerable potential as a method for the determination of trace metals when only small amounts of sample are available, when the highest accurracy is not necessarily required, or when sample dissolution would be difficult and/or time consuming. Whereas the complete dissolution of many plastics is very difficult and often time consuming, the analysis by solid sampling offers the potential for avoiding sample dissolution. Using the cup-in-tube technique, Cd, Cu, Mn and Rb have been determined in solid plastic samples using Zeeman-effect GFAAS. The analytical conditions used permitted the determinations to be performed using aqueous reference solutions. Acceptable agreement of the results with reference values was achieved.