Detection Limits Of Trace Elements Research Articles

Statistical characterization of PIXL trace element detection limits

Trace element detection and mapping are key capabilities of the Planetary Instrument for X-ray Lithochemistry (PIXL) on board the Mars 2020 rover Perseverance. However, poor signal-to-noise ratios due to the short integration times required to make high-spatial-resolution map scans operationally feasible raise the possibility of misidentifying statistical noise as a signal from a trace element, which can cause many false detections of a trace element among the hundreds to thousands of data points in each PIXL scan. Here, we apply a statistical technique to quantify the likelihood of such misidentifications and determine what concentration of a trace element must be present to reach statistical confidence in a detection. This approach is anticipated to be applicable both when analyzing existing PIXL data to ensure that noise is not misinterpreted as signals from trace elements and operationally to inform scan parameters when trace elements of interest are anticipated to be present.

Rapid quantitative analysis of trace elements in plutonium alloys using a handheld laser-induced breakdown spectroscopy (LIBS) device coupled with chemometrics and machine learning.

We present the first reported quantification of trace elements in plutonium via a portable laser-induced breakdown spectroscopy (LIBS) device and demonstrate the use of chemometric analysis to enhance the handheld device's sensitivity and precision. Quantification of trace elements such as iron and nickel in plutonium metal via LIBS is a challenging problem due to the complex nature of the plutonium optical emission spectra. While rapid analysis of plutonium alloys has been demonstrated using portable LIBS devices, such as the SciAps Z300, their detection limits for trace elements are severely constrained by their achievable pulse power and length, light collection optics, and detectors. In this paper, analytical methods are evaluated as a means to circumvent the detection constraints. Three chemometric methods often used in analytical spectroscopy are evaluated; principal component regression, partial least-squares regression, and artificial neural networks. These models are evaluated based on goodness-of-fit metrics, root mean-squared error, and their achievable limits of detection (LoDs). Partial least squares proved superior for determining content of iron and nickel in plutonium metal, yielding LoDs of 15 and 20 ppm, respectively. These results of identifying the undesirable trace elements in plutonium components are critical for applications such as fabricating radioisotope thermoelectric generators or nuclear fuel.

Stationary model of laser-induced plasma: Critical evaluation and applications

We present an algorithm for both laser-induced plasma emission spectra simulation and rapid peak-identification suitable for selection of analytical lines (free of spectral interferences, minimally self-absorbed, most intense lines). Calculations of plasma composition and radiation transport are based on the model of a uniform plasma under local thermodynamic equilibrium (LTE) requiring 3 + (K − 1) parameters – temperature T, electron density ne, plasma mass m and array of K mass fractions of chemical elements {c}. A simple cost function based on Pearson's r with a sole maximum in T–ne space is proposed to achieve the best convergence between the experimental and model spectra. We have found the best fitted T, ne, m for spatially integrated experimental spectra of standard samples of high- and low-alloy steels at delays of 1–10 μs (gate 0.4 μs) after a laser pulse within three spectral ranges (255.1–276.4, 392.6–412.2, 529.3–547.0 nm) by a brute force technique. The instrumental function of the Czerny–Turner spectrometer equipped with an intensified charge coupled device (ICCD) detector has been accurately accounted for which has been notably improved the model and experimental spectra similarity. Several optimizations including a fast Fourier transform (FFT) convolution and a polynomial approximation of Voigt profile allowed acceleration of computing to several milliseconds per spectrum.We observed a discrepancy between the best-fitted values of T obtained in the ultraviolet (UV) and visible ranges, while the ne values were close to each other in these ranges. The UV range is dominated by the ionic Fe II lines but most of the lines in the visible range are atomic Fe I lines. Thus, a possible explanation of the T difference is an inhomogeneity of the plasma (different temperatures for the “hot” plasma core and the “cold” periphery). As a spectacular example for line identification, we demonstrate that 275 emission lines are ascribed to 106 peaks within the UV range out of a total of ~12,000 lines found in spectral databases. Selection of analytical lines to determine chromium in cast iron and carbon in steels is discussed. Applicability of the algorithm to reveal analytical lines for silver, lanthanum and yttrium determination in soils and ores is mentioned. The developed algorithms are useful for choice of the best analytical line under certain plasma and spectrometer parameters in terms of: (i) spectral interferences, (ii) transmittance and (iii) intensity, for estimation of detection limits of trace elements in a known sample matrix, for detection of erroneous entries in databases, including transition probabilities and Stark parameters.

Standard Reference Line Combined with One-Point Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) to Quantitatively Analyze Stainless and Heat Resistant Steel.

Due to the influence of self-absorption of major elements, scarce observable spectral lines of trace elements, and relative efficiency correction of experimental system, accurate quantitative analysis with calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is in fact not easy. In order to overcome these difficulties, standard reference line (SRL) combined with one-point calibration (OPC) is used to analyze six elements in three stainless-steel and five heat-resistant steel samples. The Stark broadening and Saha-Boltzmann plot of Fe are used to calculate the electron density and the plasma temperature, respectively. In the present work, we tested the original SRL method, the SRL with the OPC method, and intercept with the OPC method. The final calculation results show that the latter two methods can effectively improve the overall accuracy of quantitative analysis and the detection limits of trace elements.

Laser-induced breakdown spectroscopy: technique, new features, and detection limits of trace elements in Al base alloy

Laser-induced breakdown spectroscopy (LIBS) has proven to be extremely versatile, providing multielement analysis in real time without sample preparation. The principle is based on the ablation of a small amount of target material by interaction of a strong laser beam with a solid target. The laser must have sufficient energy to excite atoms and to ionize them to produce plasma. We aimed to improve the LIBS limit of detection (LOD) and the precision of spectral lines emitted from the produced plasma by optimizing the parameters affecting the LIBS technique. LIBS LOD is affected by many experimental parameters such as interferences, self-absorption, spectral overlap, signal-to-noise ratio, and matrix effects. The plasma in the present study is generated by focusing a 6-ns pulsed Nd–YAG laser at the fundamental wavelength of 1,064 nm onto the Al target in air at atmospheric pressure. The emission spectra are recorded using an SE 200 Echelle spectrometer manufactured by the Catalina Corporation; it is equipped with an ICCD camera type Andor model iStar DH734-18. This spectrometer allows time-resolved spectral acquisition over the whole UV-NIR (200–1,000 nm) spectral range. Calibration curves for Cu, Mg, Mn, Si, Cr, and Fe were obtained with linear regression coefficients around 99 % on the average in aluminum standard alloy samples. The determined LOD has very useful improvements for Cu I at 521.85 nm, Si I at 288.15 nm, Mn I at 482.34 nm, and Cr I at 520.84 nm spectral lines. LOD is improved by 83.8 % for Cu, 49 % for Si, 84.3 % for Mn, and 45 % for Cr lower with respect to the previous works.

THE APPLICATION OF TIME‐OF‐FLIGHT SECONDARY ION MASS SPECTROMETRY (ToF‐SIMS) TO THE CHARACTERIZATION OF OPAQUE ANCIENT GLASSES*

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used, for the first time, for the characterization of opaque ancient glasses. Isotope‐specific chemical imaging with sub‐micron resolution enabled the separate analysis of opacifiying inclusions and the surrounding glass matrix. Phase identification has been demonstrated and quantification of the matrix composition has been investigated by use of Corning Glass Standard B as a model. Trace element detection limits are typically in the range 0.5–5.0 ppm atomic—in favourable cases down to 0.01 ppm. For the analysis of inclusions in particular, this has the potential to provide new information of use in establishing provenance and trade routes by ‘fingerprinting’ as well as the investigation of manufacturing techniques, as demonstrated by comparisons between glasses and with EDX data from the same samples.

Analytical procedures for improved trace element detection limits in polar ice from Arctic Canada using ICP-SMS

Analytical procedures have been developed for the reliable determination of 19 trace elements (Ag, Al, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Pb, Rb, Sb, Sc, Sr, Tl, U, V, Zn) in ice samples at pg g −1 and fg g −1 concentrations using ICP-sector field mass spectrometry (ICP-SMS). Concentrations of most elements in the high purity water and doubly distilled HNO 3 employed were distinctly lower than previously reported values. The accuracy of the results was carefully evaluated using the certified water reference material SLRS-4. Contributions of unwanted trace elements due to acidification of the ice samples (0.5% HNO 3) to the total element budget amounted to only 0.001 pg g −1 for Bi, 0.34 pg g −1 for Cr, 0.2 pg g −1 for Fe, 0.004 pg g −1 for Pb, 0.00015 pg g −1 for U and 0.0025 pg g −1 for V: compared to the concentrations of the metals in ice these are negligible. The use of a detergent (0.05%) in the rinsing solution (0.5% HNO 3), helped to reduce memory effects by 59–98%, depending on the element considered; this resulted in shorter washing times between samples (i.e. 1 min) and improved analysis time. Adopting strict clean room procedures, the detection limit for Pb (0.06 pg g −1) is a factor of ten lower than the current state-of-the-art. Compared to previous studies, the improved LODs obtained here for other trace elements amount to 2× (Ag), 4× (Sb), 5× (Ba), 6× (Cu, Mn, U), 9× (Bi), 13× (Cd), 18× (Fe) and 21× (V). The developed analytical protocols were successfully applied to the determination of selected trace elements in age-dated ice samples from the Canadian High Arctic. The toxic trace element Tl (median: 0.16 pg g −1; range: 0.03–1.32 pg g −1) and the lithogenic reference element Sc (0.53 pg g −1; 0.06–2.9 pg g −1) have been determined in a polar ice core for the first time.

Multi-element analysis of soils and sediments by wavelength-dispersive X-ray fluorescence spectrometry

Soil and sediment reference materials were used to calibrate and evaluate an analytical method for the determination of major (Si, Al, Fe, Mg, Ca, Na, K, Mn, P, Ti) and trace elements (As, Ba, Cd, Co, Cr, Cu, Ga, Mo, Mb, Ni, Pb, Rb, S, Sb, Sn, Sr, Th, U, V, Y, Zn, Zr) by sequential wavelength X-ray fluorescence spectrometry. Samples were prepared as pressed pellets and analysis was done with a total measuring time of thirty minutes per sample. Special attention was given to the selection of the thirty reference materials used for calibration of the spectrometer. Another set of eleven RM (reference materials) was analyzed for the evaluation of accuracy. Detection limits for trace elements (1-2 mg kg-1) are adequate both for geochemical and environmental purposes, except for Cd and Sb. Accuracy for trace elements falls within the expected interval of certified or recommended values in most cases, but for some major elements, like SiO2, some results showed discrepancies, evidencing difficulties associated with the determination of light elements in complex matrices. But when quality criteria proposed by mapping programs are applied to the results, their requirements are fulfilled. Both instrumental precision, obtained by twelve sample replicate analyses, and analytical precision, considering also sub-sampling and pellet preparation, lie between the limits of the Horwitz expression, except at concentrations close to the detection limits.

Measurement of individual particle atomic composition by aerosol mass spectrometry.

Advances in instrumentation used for particle compositional analysis have enabled real-time identification and classification of individual particles. However, precise quantitation of individual particle compositions has been elusive. Here, we demonstrate that real-time quantitative single-particle compositional analysis is possible. This is illustrated for individual particles of sodium chloride (70 nm), ammonium sulfate (70 nm), and silica (40-2000 nm) using a real-time aerosol mass spectrometer. Atomic fractions for major components (> 1% concentration) of individual multicomponent particles have been measured within +/-20% accuracy. Trace element detection limits of 20 ppm are also demonstrated when individual particle compositions are ensemble averaged.

Component selection for a compact micro‐XRF spectrometer

AbstractThe performances of a number of commercially available components which together can be employed to assemble a compact micro‐XRF spectrometer were compared. The purpose of such a spectrometer is to permit local, non‐destructive analysis of various materials; its compact nature will allow it to be used on‐site, i.e. at the location where the investigated objects/materials are present rather than in a laboratory. The performances of two polycapillary lenses (of different manufacture) and one monocapillary tube were compared in combination with a mini‐focus x‐ray tube with Mo anode. The use of an Si‐drift chamber and an Si PIN‐diode detector was investigated and the achievable minimum detection limits for trace elements in glass and silver matrices were determined. Finally, the effect of using mini‐focus tubes (with 250 µm focus) as opposed to the use of a more conventional x‐ray source (1 mm focus) on the obtained beam size was investigated. Copyright © 2001 John Wiley & Sons, Ltd.

Determination of trace elements in pharmaceutical substances by graphite furnace atomic absorption spectrometry and total reflection X-ray fluorescence after flow injection ion-exchange preconcentration

Flow injection iminodiacetic acid ethyl cellulose (IDAEC) microcolumn preconcentration and graphite furnace atomic absorption spectrometry determination of trace metals (Cd, Co, Ni, Pb) were carried out without decomposition of the drug matrix. The two forms of chromium Cr(III) and Cr(VI) were separated using IDAEC and anion exchanger diethylaminoethyl (DE)-cellulose, respectively. The detection limits of trace elements in pharmaceutical substances (sugars, sorbitol, mannitol, paracetamol, amidopyrine, chloral hydrate) after a 10-fold preconcentration in 1–5% m/v solution of pharmaceuticals were in the 0.3–29 ng g −1 range. The measured concentration of trace elements in substances investigated was below 100 ng g −1. The spike recovery was close to 100%. The capability of total reflection X-ray fluorescence technique for the determination of trace elements in pharmaceuticals with and without preconcentation was explored.

Improved detection limits for trace elements on aerosol filters using Compton suppression counting and epithermal irradiation techniques

Aerosol samples were collected on Whatman 41 filters at two sites near Lake Huron and one site near Lake Ontario. These samples were then analyzed by instrumental neutron activation analysis (NAA) at the University of Illinois. The detection limits for certain trace elements were enhanced by irradiation with both thermal and epithermal neutrons and also by counting with Compton suppression techniques. The sample was divided in half to allow for four irradiations. Short-lived thermal NAA resulted in the determination of Al, Br, Ca, Cl, Cu, K, Mn, Na, Ti, and V. A short epithermal irradiation was used to determine Cu, I, In, Si, Sn and U. A one and one-half hour epithermal irradiation was utilized for the determination of As, Au, Br, Sm, Sb, and W. The elements Cr, Cs, Fe, Hf, Ni, Sc, Se, Th. Zn, and several rare earths were determined with a long thermal irradiation. Utilizing a Compton suppression gamma-ray counting system reduced the background and enhanced the detection of several isotopes which primarily emit only a single gamma-ray upon decay. Counting was simultaneously performed with a normal counting mode so that the detection of isotopes with multiple decay gamma-rays was not impaired.

Strategies of multielement calibration for maximising the accuracy of geochemical analysis by inductively coupled plasma-atomic emission spectrometry

The design of multielement calibration schemes for ICP-AES has a critical effect upon the the accuracy of analyte determinations. Matrix effects within multielement calibration solutions are unavoidable, and produce changes in sensitivity and calibration curvature that are not necessarily equal to those in the sample solutions. Differential matrix effects that occur between calibration solutions and samples lead to analytical bias. The problem is most severe where samples are analysed at high concentration factors to maximize trace-element detection (typical > 10 g1 −1). The bias affects both major and trace elements. Various calibration strategies are considered in this paper for their ability to reduce differential matrix effects between calibration solutions and samples. The internal standard method is considered the most appropriate, but it is limited by its inability to allow for the variations in bias for different analytes in the same matrix. A general solution to the problem is proposed that applies the parameter-related internal standard method (PRISM) to the intensity measurements of the calibration solutions. This reduces the bias due to the matrix effects which concomitant analytes produce. The sensitivity of each analyte is returned to that which would have been measured if the analyte were present in a single-element solution, with no matrix effects. At the same time PRISM also reduces the self-matrix effect that can contribute to the curvature of an analyte calibration. The linear range of Ca II 317.93 nm, for example, can be extended by an order of magnitude using this method. The strategy enables a multielement calibration to be designed for minimum detection limits of trace elements in a wide range of sample compositions, and obviates the need for matrix matching.

Mass spectrometry with an inductively coupled plasma as an ion source: the influence on ultratrace analysis of background and matrix response

An outline is provided of the mode of operation of the atmospheric pressure inductively coupled plasma (ICP) when used as a mass spectrometer ion source. The generation of doubly charged ions and molecular peaks is discussed for the author's system in relation to the limitations they impose on trace element detection limits and on the analysis of samples with high matrix concentrations. Detection limits obtained under compromise operating conditions are shown for a range of elements in both single ion and multielement detection modes.

Determination of trace element detection limits in air and oxygen inductively coupled plasmas

Detection limits for 19 elements with emission line excitation potentials from 1.6 to 16 eV have been measured in air and oxygen inductively coupled plasmas (ICP). Spectral scans of air and oxygen ICPs were recorded at positions in and above the induction coil. Spatial dependence of elemental emission in air and oxygen ICPs is also discussed.

Optimization of PIXE sensitivity for biomedical applications

A technical discussion of beam handling for PIXE in vacuo is presented, directed towards achievement of low detection limits for trace elements in biomedical specimens. A quantitative comparison is given of elemental backgrounds from commonly used specimen backings, e.g. Kapton, Mylar, Kimfol and very thin polystyrene films. The new problems presented by operation in a helium atmosphere are reviewed, with emphasis on gamma ray background arising from nuclear reactions in the proton exit window. Backgrounds and detection limits are discussed for analysis of biomedical specimens both in vacuo and in helium. A brief review is given of some current applications of PIXE in the medical area.

Detection limits in epithermal neutron activation analysis of geological material

The improvement of detection limits for trace elements in geological samples by epithermal neutron activation analysis is examined. The relative merits of cadmium, boron and composite cadmium+boron filters are compared for trace elements Ni, As, Pd, Cd, Sb, W, Ir, Pt and Au, and interfering elements Na, K, Sc, Cr, Fe, Co and Cu. A boron filter gives optimum sensitivity for the trace elements based on interference from46Sc, but the detection limits are only improved 2–5 times. Ma imum possible improvement, which is shown by Ni, gives sensitivities 5 times better under cadmium and 15 times under boron.

Results on a UHV–Ion Microprobe for Surface and Trace Analysis

A microfocus SIMS with following specifications has been designed and built: primary beam Ar+≤30 keV, focused on a spot 1 µ-2 mm, current density 10-9–100 mA/cm2. Secondary analyser system: tandem 4-sector double focusing, 20 cm magnet, ion acceleration ≤10 keV. The complete system is bakeable, background pressure in the target chamber <10-9 Torr, <10-8 Torr with primary gun operating. Detection limits for trace elements are in the ppbrange, the instrument is also capable of doing static SIMS with fractional monolayer sensitivity. Examples of applications in surface corrosion work and trace analysis are given. Quantitative interpretation of SIMS. Spectra on the basis of a LTE-plasma theory is attempted.