Elemental analysis by high‐energy electron excitation

The possibility of using high‐energy β‐particles (10²–10³ keV) to induce the emission of characteristic x‐rays from pure chemical elements, with important improvements with respect to conventional excitation methods, has been recently reviewed. An excitation procedure named BIXE (β‐induced x‐ray emission) is used for implementing a spectrometric technique along the lines developed for EPMA (electron probe microanalysis). We have found that by using BIXE it is possible to determine binary sample compositions of elements present at concentrations higher than 1%, by comparisons with reference samples to obtain calibration curves. Experience with EPMA shows that when ternary and higher order samples are analyzed, the use of reference samples is not enough and it is necessary to perform theoretical corrections to the relationship between the line intensity and the corresponding concentrations, as a suitable complement to the analytical procedure. Semi‐quantitative results are thus obtained with corrections applied through the ZAF method usually used in EPMA. In this work we concentrated in finding whether calibration curves as used in EPMA (where the electron beam is monochromatic) can be used in BIXE, where the electron beam is polychromatic (the β spectrum). We expect that BIXE can be developed as a spectrometric technique whose main advantages are that it is a low‐cost technique suitable for in situ studies and that the experimental arrangement and data acquisition and its evaluation are comparatively simple. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparison of the quantitative results corrected by fundamental parameter method and difference calibration specimens in X-ray fluorescence spectrometry

Three kinds of standard specimens, including low-alloy steels (Japanese iron and steel CRM), glass from NIST and Chinese geological reference materials were analyzed by wavelength dispersive X-ray fluorescence spectrometry as unknown samples. The fundamental parameter method was used to correct the matrix effect and different specimens including pure element specimens and type specimens were employed as calibration samples. The quantitative results were compared in order to study the influence of calibration samples on the accuracy of quantitative results. The study showed that the fundamental parameter method could correct the matrix effects very well and relatively accurate quantitative results could be obtained, corrected by simple specimens, in case of type calibration specimens’ absence.     

油页岩热解过程中的光谱学研究

光谱学分析方法对分析物质结构及组成具有独特的优势。为了分析和认识油页岩及其干酪根的矿物结构特点,以及在不同热解温度下油页岩热解过程中矿物结构变化,分别采用偏光显微镜(POM)、傅里叶变换红外光谱(FTIR)、X射线衍射光谱(XRD)和扫描电镜(SEM)等光学和光谱学手段,研究了甘肃窑街油页岩和酸洗脱灰干酪根的矿物形态结构和组成以及在不同热解温度下(温度300～1 000 ℃,升温速率10 ℃·min-1)矿物质和干酪根的形态结构演化特性及其机理。结果表明,甘肃窑街油页岩富含石英、粘土矿和黄铁矿等无机矿物,干酪根呈条块状不规则地镶嵌于无机矿物中;干酪根的变质程度高,富含芳香族和脂肪族结构;在实验温度范围内,随热解温度的升高,油页岩中矿物质开始分解,300 ℃时高岭石因脱水转变成偏高岭石,在650 ℃时高岭石、蒙脱石等完全分解生成偏高岭石,当温度升高至1 000 ℃时偏高岭石分解生成Si—Al尖晶石和无定型SiO₂,SiO₂与含铁矿物在半焦表面析出了(FeO—Al₂O₃—SiO₂)低熔点共融物;干酪根随温度升高分解,半焦的芳香族和脂肪族C—H基团的强度降低,芳香碳的强度升高,分解后在半焦中形成“沟壑”状残炭印记。研究结果对油页岩热解过程矿物结构演化研究和油页岩矿物的资源综合利用具有重要的现实意义。     

基于LIBS技术的钢铁合金中Cr和Ni元素SVM定量分析方法研究

针对钢铁合金样品中存在基体效应复杂的问题,通过优化支持向量机模型的输入特征,建立多元素变量的定量分析模型,预测钢铁合金样品中Cr和Ni元素的含量。研究结果表明,分别以特征谱线的峰值强度和积分强度作为支持向量机模型的输入时,积分强度因为包含了谱线的谱宽和形状信息,模型训练效果较好;相比于单一元素谱线的特征信息,采用多元素的多条谱线信息输入支持向量机模型时,模型训练效果较好,这是由于多种谱线信息的输入可以有效校正基体效应的影响。在此基础上,通过归一化变量将内标法与多变量定标方法有效结合,不仅可以减小实验测量误差还能有效校正基体效应的影响,而且有效提高了模型的重复率和准确率。归一化变量作为支持向量机模型的输入变量,对待测样品S₁和S₂中Cr元素含量预测的相对误差为6.58%和1.12%,对Ni元素浓度预测的相对误差为13.4%和4.71%。通过归一化变量将内标法与多变量定标方法有效结合,可以充分发挥SVM算法的非线性学习优势,为LIBS技术应用于复杂样品定量定标分析提供理论基础。     

钢铁中钒、钛元素的激光诱导击穿光谱定量检测

采用激光诱导击穿光谱(LIBS)技术测量钢铁中钒、钛元素的含量。选取V Ⅰ 440.85 nm和Ti Ⅰ 334.19 nm作为定量分析谱线、基体元素谱线Fe Ⅰ 438.35 nm作为内标谱线,分别建立了基本定标法和内定标法的钢铁样品中V和Ti含量的光谱分析定标曲线,并将它们用于检验样品的定量分析。研究表明,V和Ti基本定标曲线的拟合相关系数R2分别为0.987 5和0.990 9,对检验样品中V和Ti元素的测定相对误差最大分别为11.1%和4.0%;而采用内定标法时,V和Ti的拟合相关系数R2分别达到0.995 2和0.992 1,对检测样品中V和Ti元素的测定相对误差均可降低到4.0%以下。结果证明,采用内定标的激光诱导击穿光谱分析方法更适于钢铁样品中钒、钛含量的测定。     

Multivariate calibrations for the SR‐TXRF determination of trace concentrations of lead and arsenic in the presence of bromine

A synchrotron radiation source and total reflection x‐ray fluorescence (SR‐TXRF) spectrometry were used for the determination of lead and arsenic in aqueous samples. To overcome the serious spectral interference between the two species and the overlap of another interfering element (bromine), a partial least‐squares regression (PLSR) method was used. The calibration models PLSR2 and PLSR1 were based on the x‐ray fluorescence emission signals (9.550–13.663 keV) for a set of 26 different mixtures containing the elements of interest, lead and arsenic, as well as bromine. The results obtained by PLSR1 and PLSR2 were compared with those obtained by the conventional univariate methodology. In the latter case, the areas of the secondary emission lines (Lβ for lead and Kβ for arsenic) were used to elaborate the analytical curves. The capacity of all optimized models was verified using five synthetic samples (external validation). Subsequently the best model was used to determine lead and arsenic recovery capacities when these metals are retained on two ion‐exchange resins (Dowex 50‐X8 and Dowex 1‐X8). The best multivariate model (PLSR1) allowed the determination of lead and arsenic with root mean square errors of prediction (RMSEPs) of 0.03 and 0.24 mg l^?1, respectively. The reduction of this parameter, with respect to the values obtained by conventional univariate methodology (0.26–0.03 mg l^?1 for lead and 0.30–0.24 mg l^?1 for arsenic), indicates that the proposed multivariate methodology really overcomes the problems associated with spectral interferences and minimizes the influence of an interfering agent (bromine). Copyright © 2005 John Wiley & Sons, Ltd.     

Quantitative analysis of chromite ores using glass discs in moderate dilutions of lithium tetraborate by x‐ray fluorescence spectrometry

A method for the quantitative analysis of chromite ores by x‐ray fluorescence spectrometry using beads is proposed. The work concerned the serious problems caused by the refractory nature of these materials which prevents the use of glass discs in x‐ray fluorescence. An in‐depth study was done to optimise the variables which influence the glass disc formation process. Sufficiently homogeneous glass discs were obtained under the following experimental conditions: lithium tetraborate as flux with moderate sample dilution (1:40), with the addition of one or two drops of LiBr solution(250 g l^?1), at a temperature of 1200 °C for 30 min. The qualitative and semiquantitative results for the chromite ores provided synthetic standards based on combinations of similar reference materials and different pure ignited oxides. These standards were used to obtain the calibration curves for Cr, Si, Al, Fe, Ti, Ca, Mn, Mg, Na and K oxides, with root mean square error always below 0.357. The calibration curves were used in the quantitative analysis of chromite ores with satisfactory accuracy, justifying compensation of the interelemental effects. The suggested method is an efficient solution to the problems with the quantitative analysis of this type of material by XRF. Copyright © 2006 John Wiley & Sons, Ltd.     

Multivariate calibration in TXRF analysis of water

The aim of this paper is the application of multivariate linear calibration for quantitative determination of elements (K, Cd, Co, Hg, As, Pb, Ni, and Al) in water by using Total Reflection X‐ray Fluorescence Analysis with partial least squares (PLS) as a regression method to improve a result of common univariate method. In purpose of elimination of matrix effects in X‐ray fluorescence analysis, experimental design was applied. As a set of standard samples for multivariate calibration, a five‐level eight‐factor calibration design of 25 samples was chosen, ensuring mutual orthogonality of factors. For model's validation, the independent test set of 15 samples was examined. The collection of spectra and quantitative measurements was carried out on S2 PICOFOX. The PLS regression was performed by using software package STATISTICA. Quality indicators of multivariate calibration as slope (b) and intercept (a) of calibration, correlation coefficient (r), determination coefficient (R²), root mean square errors of calibration and of prediction, standard errors of calibration and of prediction, biases of calibration, and biases of prediction were calculated. These results were compared with the univariate model, and as a result, the multivariate calibration method exceeds the univariate one. The obtained results could be applied in a laboratory for an analysis of water solutions in the concentration range 0.05–2.00 mg/L. In many real situations, when analytical chemist deals with multi‐element mixtures, multivariate calibration approach combined with orthogonal design for multivariate calibration set could be successfully used to improve a conventional univariate calibration.     

Application of PIXE for the determination of transition elements in the grouping study of archaeological clay potteries

Trace element concentrations play an important role in grouping and provenance studies of archaeological artifacts. Particle‐inducedX‐ray emission (PIXE) using low energy proton beams (1.5 and 3 MeV) from a tandem particle accelerator was used to analyze the ancient clay potteries collected from an ancient Buddhist site in India. Concentrations of 13 elements, including eight transition elements, were determined. The concentrations of transition elements were used for the grouping study by statistical cluster analysis according to the similar and dissimilar elemental distribution within the samples. Two International Atomic Energy Agency Reference Materials (RMs) were analyzed to validate the PIXE method. Two samples were analyzed by both PIXE and instrumental neutron activation analysis (INAA) as a part of quality assurance. Grouping results were used for preliminary provenance study. Copyright © 2017 John Wiley & Sons, Ltd.     

利用LIBS技术实现钢液中多元素含量检测

在钢铁冶炼中,成分含量检测是保证冶炼质量的关键之一,激光诱导击穿光谱技术(LIBS)具有遥测的特点,非常适合于炉内钢水成分的检测。实验室搭建了一熔融合金LIBS检测实验系统,该系统由 Nd:YAG调Q激光器(重复频率10 Hz,波长1 064 nm,脉冲宽度10 ns,单脉冲能量约240 mJ),高频感应电炉(温度1 600 ℃),光谱仪(波长范围186～310 nm,光谱分辨率0.1 nm),激光聚焦和信号光收集系统组成。实现了对钢液中多元素的LIBS光谱检测,通过内标法建立了相应元素的定标曲线,并给出了系统的检测限。采用深紫外镀膜探测器的光谱仪和抗紫外曝光处理的光纤,在大气环境下得到的C,S,Mn和Cr元素定标曲线的线性相关系数优于0.96,检测限分别达到169,15,58.9和210 μg·g-1。对比发现,不同元素得到最佳定标曲线所需延时条件不同。     

基于激光诱导击穿光谱技术检测分析原铝中硅、铁元素含量

利用自行搭建的LIBS装置对原铝中硅铁含量进行了分析测试，测试前对原铝试样进行了微观形貌分析，研究发现原铝中硅元素除有个别区域聚团现象外，其分布相对较为均匀；铁元素多以团状汇聚形态出现，且无明显的分布规律。实验分别考察了激光脉冲能量对激光诱导原铝等离子体光谱的影响，发现随着激光脉冲能量的增大，硅、铁元素信噪比先增加后减小，硅、铁谱线信噪比最大值均出现在160 mJ处，实验选取的激光脉冲能量为160 mJ。在上述较为合理的实验条件下，以内标法为基础，分别采用两种标样（纯铝标样与自选标样）建立了定标模型；结果表明：相比于纯铝标准试样，采用自选试样建立的定标模型不够理想，且数据的离散程度较大，铁元素直线拟合优度仅为0.921 3，相对标准偏差也较大。采用纯铝标样时，在试样不旋转的情况下，硅、铁元素定标曲线拟合优度分别为0.961 1与0.974 1，相对标准偏差分别为8.85%与9.43%，且误差棒显示误差随定标试样的硅、铁含量升高而增大。当试样台保持转速50 r·min-1条件下进行实验，发现硅、铁元素定标曲线的拟合优度分别为0.978 5与0.988，相对标准偏差分别为3.78%与3.4%，相比于试样平台固定情况下的定标结果，拟合优度明显改善，相对标准偏差也有所降低，定标模型明显优于自选试样建立的模型。使用两种定标模型对25个测试样进行了分析测试，比较了两种测试结果的相对误差，纯铝定标试样由于含量梯度较大，跨度较宽，采用该标样建立的定标模型对低铁原铝试样测试适应性相对较差，而自选试样建立的定标模型虽然不够理想，但针对低铁原铝试样的测试适应性相对较好。对激光诱导原铝产生的等离子体进行了诊断，通过镁元素几条离子谱线的玻耳兹曼图，计算出了等离子体温度约为9 163.63 K，利用镁元素一条谱线的Stark展宽估算出等离子体电子密度为1.69×1017 cm-3，验证了激光诱导原铝等离子体处于局部热力学平衡状态的假设是成立的。     

Synchrotron‐induced EDXRF determination of uranium and thorium in mixed uranium–thorium oxide pellets

Uranium and thorium in their mixed oxides were determined by synchrotron‐induced energy dispersive X‐ray fluorescence (EDXRF) spectrometry. Mixed oxide calibration mixtures containing uranium and thorium in different relative amounts and approximately fixed amount of yttrium were prepared in the form of pellets. The EDXRF spectra of the pellets were measured at the microfocus XRF (BL‐16) beam line of Indus‐2 synchrotron radiation facility (Raja Ramanna Centre of Advanced Technology, Indore, India). Characteristic X‐ray lines U Lα, Th Lα, and Y Kα were used as analyte lines. Calibration plot for the determination of uranium was prepared by plotting amount ratios of U and Y against the intensity ratios of U Lα and Y Kα. Similarly, a calibration plot for thorium analysis was also made. The amounts of uranium and thorium in the sample mixtures prepared in similar way as the calibration mixtures were determined using the aforementioned calibration plots. The precision values obtained for uranium and thorium determinations were found to be 0.3 and 0.2% (relative standard deviation, 1σ), respectively. The EDXRF results deviated from the expected values by 1% for uranium and 0.9% for thorium determinations. These analytical features are much superior compared with laboratory‐based analysis results. Copyright © 2012 John Wiley & Sons, Ltd.     

Using chemometric methods for overlap correction of sodium–zinc spectral lines generated by wavelength dispersive X‐ray fluorescence in mineral samples

Partial least squares, principal component regression and support vector machine multivariate methods were used for overlap correction of sodium–zinc (Na(Kα)–Zn(Lα)) spectral lines generated by means of wavelength dispersion X‐ray fluorescence (WDXRF) combined with standard‐less software (IQ+) technique for the analyses of mineral samples. This methodology uses one scan channel using PX1 analyzer crystal, 550‐µm collimator, flow detector (Ar + CH₄), and rhodium (Rh) tube for determination of Na and Zn in mineral compositions in minimum time. The calibration matrix was made up of 35 samples containing different amounts of Na₂O and ZnO. The considered concentration ranges were 0–5% for both Na₂O and ZnO. The values for 2θ angle were recorded between 25° and 29.9° at every 0.1°. Variable tube powers (kV ? mA) were used to investigate the effect of tube power on the analyses of elements. The validation of the multivariate methods was realized by analyzing soil samples. Atomic absorption and flame photometry methods were used as reference methods for analyzing Zn and Na in the soil samples, respectively. The results of using chemometric methods, WDXRF (standard‐less software) and reference method determined partial least squares and support vector machine models obtained more acceptable results for Na₂O in presence of ZnO than those of WDXRF (standard‐less software). Copyright © 2013 John Wiley & Sons, Ltd.     

Partial Least Squares Processing of Near‐Infrared Spectra for Discrimination and Quantification of Adulterated Olive Oils

Abstract

A new processing based on partial least squares (PLS) algorithm for the discrimination and determination of adulterants in pure olive oil using near‐infrared (NIR) spectroscopy has been introduced. The 280 adulterations of olive oil with corn oil (n=70), hazelnut oil (n=70), soya oil (n=70), and sunflower oil (n=70) were prepared, and their NIR spectra in the region 12,000–4550 cm^?1 were collected. The 70 spectra of each adulteration of olive oil were divided into two sets, 50 spectra for a calibration set and 20 spectra for a prediction set. The spectra of a total calibration set (n=200) were separated into individual adulterant calibration sets (n_i=50, i=corn, hazelnut, soya, sunflower) by using discriminant PLS (DPLS) analysis, and PLS calibration models for the quantification of adulterants with corn oil, hazelnut oil, soya oil, or sunflower oil were developed separately. A variety of wavelength ranges and data pretreatments were examined for obtaining optimal results for the discrimination and quantification objects. Four PLS models for differentiating the adulterant types were evaluated by classifying the NIR spectra of a total prediction set (n=80) into known adulterant types. Then, these known adulterant spectra were analyzed by the PLS calibration models developed for each type to determine the content of an adulterant in pure olive oil. The results of evaluation revealed that the processing reported in this article works excellently for the discrimination and quantification of the adulterations of olive oil.     

激光诱导击穿光谱定量分析玉石中的Mg,Fe和Ca

基于对样品进行的激光诱导击穿光谱和X射线荧光光谱分析测试建立了天然玉石中主要元素Mg,Ca和微量元素Fe的定标曲线。实验采用纳秒级的Nd∶YAG激光器(波长:1 064nm)为光源,在延迟时间为3μs,激光脉冲累积数量为110,单个脉冲能量为100mJ,脉冲重复频率为10Hz的实验条件下,采用激光诱导击穿光谱技术装置对天然南阳独山玉石样品中的元素进行等离子体激发测试,得到波长在300~1 000nm的等离子光谱图。通过将得到的光谱图中特征峰与美国国家标准与技术研究院数据库进行对比,发现测试样品中含有Mg,Fe和Ca等元素,以X射线荧光光谱分析技术对四种南阳独山玉标准样品中测量出的Mg,Fe和Ca元素氧化物含量作为标准数据,选取含量比较高的Al元素作为内标元素,采用内标法对玉石光谱图中Mg,Fe和Ca元素特征峰值进行线性拟合,从而得出Mg,Fe和Ca三种元素的定标曲线,求出待测样品中这3种元素氧化物的含量,结果表明这三种元素氧化物的含量与中国珠宝宝石收藏鉴赏全集资料中所给出的元素氧化物含量的百分比范围MgO(0.28%~1.73%),Fe2O3(0~0.8%),CaO(18%~20%)相符合,相比于常用的方法,激光诱导击穿光谱技术可以快速地对待测样品进行检测,样品预处理简单且对样品损害较小。进一步验证了激光诱导击穿光谱技术对于玉石应用的可行性。     

Monochromator Wavelength Calibration Standards Extending into the Near-Infrared Using Second- and Third-Order Emission Lines from Mercury Vapor Lamps

The emission spectra of four mercury vapor lamps are used to obtain wavelength calibration curves for the double-grating emission monochromator of a spectrofluorimeter. The use of second- and third-order diffraction lines and emission lines from the argon carrier gas provides a rich spectrum, which extends well into the near-infrared spectral region and produces an improved calibration curve. More than 60 emission lines are listed between 250 and 900 nm, which is sufficient to produce an extremely accurate monochromator calibration. Additional second- and third-order lines can be used to even longer wavelengths (>1200 nm). The effectiveness of three scattering surfaces is compared.     

Application of the background standard method for the determination of Rb,Sr, Y,Zr, and Nb contents in phosphorites by x‐ray fluorescence

The aim of the present work is to demonstrate the application of the x‐ray fluorescence (XRF) technique to the determination of Rb, Sr, Y, Zr, and Nb contents in phosphorites. The effect of a chemical sample composition on fluorescence intensities of analytical lines has been taken into account using the background standard method. A novelty of the work is the detailed study of a background to choose the background position, free from the spectral line overlaps of the elements presented in the sample. The most suitable background position is the position at the angle 2θ = 29° when using the analyzing crystal LiF(200). During our investigation we faced a problem of choice of Certified Reference Materials (CRMs) for the calibration of the phosphorites. To estimate interelement effects and to choose CRMs for the calibration the intensities were theoretically calculated. The statistical processing of analytical results of the technique is carried out. This technique may be applied to the determination of Rb, Sr, Y, Zr, and Nb contents in the phosphorites. Also, the possibility has been demonstrated to use the XRF technique for geochemical investigations of rocks. Phosphorites of Bokson‐Khubsugul Basin were selected as an example. As a result of the investigation the genetic type of phosphorites was established, which corresponded to the present geodynamical depositional environment. The character of the distribution of Rb, Sr, Y, Zr, and Nb contents in the phosphorites was also studied. Copyright © 2008 John Wiley & Sons, Ltd.     

Combining CdTe and Si detectors for Energy‐Dispersive X‐Ray Fluorescence

Most energy‐dispersive X‐ray fluorescence (EDXRF) instruments use Si diodes as X‐ray detectors. These provide very high energy resolution, but their sensitivity falls off at energies of 10–20 keV. They are well suited for measuring the K lines of elements with Z < 40, but for heavier elements, one must use K lines at low efficiency or use L or M lines that often overlap other lines. Either is a challenge for accurate quantitative analysis. CdTe detectors offer much higher efficiency at high energy but poorer energy resolution compared with Si diodes. In many important EDXRF measurements, both high and low Z elements are present. In this paper, we will compare the precision and accuracy of systems using the following: (1) a high resolution Si detector, (2) a high efficiency CdTe detector, and (3) a composite system using both detectors. We will show that CdTe detectors generally offer better analytical results than even a high resolution silicon drift detectors for K lines greater than 20 or 25 keV, whereas the high resolution Si detectors are much better at lower energies. We will also show the advantages of a combined system, using both detectors. Although a combined system would be more expensive, the increased accuracy, precision, and throughput will often outweigh the small increase in cost and complexity. The systems will be compared for representative applications that include both high and low Z elements. Copyright © 2012 John Wiley & Sons, Ltd.     

ICP-MS测定淀粉铝含量的不确定度评定及改进方法

测量不确定度,表征合理地赋予被测量之值的分散性。应用ISO/IEC Guide 98: 1993 Guide to the expression of uncertainty in measurement(简称GUM方法)的自下而上的策略进行测量不确定度的评定,剖析完整的分析测量过程,可以找出影响测量结果准确性的主要因素;采取针对性的措施,设法消除或降低这些因素的影响,可以改进测量方法。以电感耦合等离子体质谱法测定淀粉和面包糠中铝含量为例,其不确定度来源于测量重复性、最小二乘法拟合工作曲线的过程、标准储备液及其分取稀释过程的不确定度、溶液体积及样品称量过程的不确定度。经过各不确定度分量的评定,得知主要分量是由最小二乘法拟合工作曲线引入的相对标准不确定度u_rel(c_Al)₁,其次是由配制标准溶液系列的稀释过程引入的相对标准不确定度u_rel(c_Al)₃、由测量结果的重复性引入的相对标准不确定度u_rel(rep)。因此,采取较高灵敏度的质谱工作模式、增加测定次数、合理选取校准曲线的系列浓度点数值、选用相对误差较小的量器等措施进行方法改进。改进之后,三个主要分量u_rel(c_Al)₁,u_rel(c_Al)₃,u_rel(rep)分别从(0.035 8,0.013 2,0.008 5)降为(0.006 0,0.010 5和0.003 3),铝量的合成相对标准不确定度从0.039降为0.013,扩展不确定度从1.8 mg·kg-1降为0.4 mg·kg-1(k=2),效果显著。     

Quantitative major and trace elemental mapping by PIXE of concretionary pyrite from the Witwatersrand Basin,South Africa

Several concretionary pyrite grains displaying multiple, massive sulphide or silicate inclusion‐rich, annuli from two gold‐bearing reef horizons (Ventersdorp Contact Reef, Kimberley Reefs) in different parts of the Witwatersrand Basin were analysed by particle‐induced X‐ray emission (PIXE) and electron microprobe analysis (EMPA) for their major and trace element compositions. Both PIXE spot analysis and mapping of the distributions of major and trace elements were carried out, and EMPA was employed to obtain major element abundances for matrix corrections of PIXE analysis. Spatial analysis by PIXE is excellent in comparison with EMPA, as PIXE detection limits are lower by 1–2 orders of magnitude at comparable, short‐duration counting times (12 h for 4096 pixel analyses by PIXE). EMPA was successful in the identification of individual zones, for example on the basis of locally enriched minor elements Ni or As. This technique also provided essential standard‐based control on major element abundances for the standardless PIXE dynamic analysis. The compositional results obtained on concretionary pyrite grains by PIXE are distinctly different for each analysed grain, in terms of relative enrichment of certain minor and trace elements in specific zones. Gold was detected locally in the interiors of grains and/or along grain margins. The different results are discussed with regard to their possible meaning related to the origin of gold mineralization in the Witwatersrand ore deposit. Copyright © 2004 John Wiley & Sons, Ltd.