Preparation and characterization of a set of IAEA reference air filters for quality control in air-pollution studies

Several sets of reference air filters were prepared as part of an IAEA evaluation of the performance of laboratories involved in air-pollution studies. Each set comprised three polycarbonate membrane filters, two of which were loaded with urban air particulate matter (APM) obtained in Vienna or Prague, and one unloaded filter. The filters were loaded by filtration of a suspension of the APM materials in water. The homogeneity both of bulk APM materials and of the loaded filters was evaluated and found suitable by determining several elements by instrumental neutron-activation analysis (INAA), proton-induced X-ray emission (PIXE), and micro-X-ray energy-dispersive fluorescence analysis (micro-EDXRF). After evaluation of the homogeneity, INAA, PIXE, EDXRF, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), and ICP mass spectrometry (ICP-MS) were used to characterize the filter materials and establish "target values" and their associated standard deviations for 15 elements. Problems encountered during the preparation of these unique, simulated air filters and the criteria for setting both the target values and standard deviations are presented.     

Preparation and characterization of a new set of IAEA reference air filters using instrumental neutron activation analysis, proton-induced X-ray emission and Rutherford backscattering

A new set of reference air filters was prepared for proficiency testing of laboratories involved in air pollution studies organized by the International Atomic Energy Agency (IAEA). The set consists of one filter loaded with airborne particulate matter (APM) and one blank filter. Target values and their standard deviations were established using instrumental neutron activation analysis (INAA) and proton induced X-ray emission (PIXE) with proven accuracy. Rutherford backscattering (RBS) was used to help in deriving the necessary corrections in PIXE. Losses of individual elements from APM due to the wet deposition procedure were evaluated.     

Use of INAA, PIXE and XRF in Homogeneity Testing of New IAEA Reference Air Filters

About 250 sets of polycarbonate (Nuclepore, Costar) membrane filters loaded with two urban air particulate matter (APM) obtained in Vienna and Prague were prepared by filtration of a watter suspension of the above APM materials. The homogeneity of both bulk APM materials and the loaded filters was tested by determining a number of elements by instrumental neutron activation analysis (INAA), proton induced X-ray emission (PIXE) and micro-X-ray fluorescence (-XRF). Relative standard deviations due to inhomogeneity (s _inh ) were below 3% for many elements in the bulk APM materials. In the loaded filters, the s _inh values increased significantly. Nevertheless, for up to 20 elements important in air pollution studies the s _inh values were below 15%, allowing target values with a reasonably low uncertainties (up to 20%) to be derived for the future use of the filters in proficiency testing of laboratories involved in air pollution monitoring.     

Examination of a procedure for the production of a simulated filter-based air particulate matter reference material

An approach for producing simulated air particulate matter (APM) deposited on filters has been developed and investigated as to its usefulness for yielding large batches of filters as a future reference material. The APM deposited on the filters was a material collected from an urban industrial area, and had been milled to approximate a material of PM-2.5 particle size distribution. The milled APM material was loaded onto filter substrates (Nuclepore) through the deposition of aliquots from a liquid suspension via vacuum filtration. It should be noted that these filters do not represent a typical PM-2.5 elemental composition, since the milling increased the proportion of crustal materials and the suspension in liquid decreased the sulfate content. Homogeneity between filters was tested using INAA (whole filter analysis) and ED-XRF and PIXE and was estimated to be in the 5% range (relative standard deviation). Homogeneity within the filters and among the filters was also tested using micro-XRF and found to be acceptable for the elements tested. The results of the tests carried out on the filters indicate that this approach is appropriate for large-scale production of similar filters for distribution as reference materials.     

Neutron activation analysis: Still a reference method for air particulate matter measurements

At ITN, PM10 and PM2.5 aerosols were collected on Nuclepore^® polycarbonate filters of 47 mm diameter, using Gent samplers at 15–17 l/min air flux. Filters were analyzed by INAA and PIXE. The availability of certified filters was very scarce, viz.: (1) fly ash embedded in a methyl cellulose 47 mm foil 10 µm thick, BCR CRM128, (2) particle-size reduced air particulate matter (APM) to simulate PM2.5 aerosol matter deposited on a 47 mm polycarbonate filter membrane, NIST SRM 2783. The high price and scarcity of APM standards did not permit their frequent use for analytical quality control. At ITN, to control the filter results' accuracy, the chemical elements potassium, iron and zinc, determined by both techniques, were systematically compared. After a few improvements introduced in INAA, this technique was now considered at ITN as the reference technique in air particulate measurements. Comparison of INAA to PIXE was discussed. Compared to previously reported situation it was concluded that the results were in better agreement for iron and zinc, and potassium values were still biased to the same extent as before.     

Quality control materials for the determination of trace elements in airborne particulate matter

The development of quality control materials for the determination of selected trace elements in air pollution studies is described. Three types of test samples were prepared for proficiency testing: (1) filters loaded with PM10 fraction of urban air particulate matter (APM) using high-volume air samplers, which were subsequently divided into smaller sections, (2) a bulk sample of APM collected in an automobile tunnel in Prague, and (3) simulated air filters loaded with APM using a wet deposition process. Homogeneity of the test samples was studied using instrumental neutron activation analysis, proton induced X-ray emission and atomic absorption spectrometry, and inductively coupled plasma optical emission spectrometry and mass spectrometry. Sufficiently homogeneous samples were prepared by all three procedures. The simulated air filters appeared to be the most suitable test samples for proficiency testing.     

Study on the retention of uranyl ions on modified clays with titanium oxide

Four analytical techniques—instrumental neutron activation analysis (INAA), inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscope energy dispersive X-ray fluorescence (SEM-EDXRF), and proton induced X-ray emission (PIXE)—were evaluated in the context of air pollution biomonitoring studies. Three combinations INAA/ICP-MS, ICP-MS/PIXE and ICP-MS/SEM-EDXRF are illustrated by experimental results.     

Comparison of inductively coupled plasma–atomic emission spectrometry, anodic stripping voltammetry and instrumental neutron-activation analysis for the determination of heavy metals in airborne particulate matter

The capability of three analytical techniques, inductively coupled plasma–atomic emission spectrometry (ICP–AES), anodic stripping voltammetry (ASV), and instrumental neutron-activation analysis (INAA) have been compared for the determination of Cd, Fe, Pb, and Zn in airborne particulate matter, collected on cellulose filters, from the atmosphere of the large area of Thessaloniki, Greece. Two procedures were tested for quantitative leaching of these elements from the filters before ICP–AES and ASV, digestion with aqua regia in a Teflon autoclave, after dissolution of the organic matter with HClO₄ under ambient conditions, and ultrasonic extraction with a mixture of HNO₃ and HCl. Validation of the leaching and digestion procedures revealed that digestion in the autoclave is more effective, especially for Fe. The concentrations of these elements over a decade in both industrial and urban areas of the investigated region are compared.     

Nuclear techniques applied to air particulate matter studies

The most important fraction of aerosols with respect to human health is the respirable fraction, which has particles less than 10 m in equivalent aerodynamic diameter (EAD), the so called PM 10 fraction. The collection of these respirable particles and the determination of their trace element composition is the focus of an IAEA Co-ordinated Research Programme (CRP). The IAEA Laboratory participated in this Programme and established collection sites for the air particulate samples on the grounds of the Atominstitute of the Austrian Universities in Vienna and the IAEA Laboratories, Seibersdorf, representing an urban residential site and a rural site. The collected samples as well as samples of simulated air filters (used also for blind controls) and control materials were analyzed sequentially and/or in sections by X-ray fluorescence (XRF), proton induced X-ray emission (PIXE), instrumental neutron activation analysis (INAA), and atomic absorption spectrometry (AAS). Results demonstrate the applicability of the PM-10 sampling approach, provided PIXE and/or INAA are used in the determinations. Reliable results can be obtained that will lead in comparable air pollution data for many regions in the world through CRP.     

A study of uniformity of elements deposition on glass fiber filters after collection of airborne particulate matter (PM-10), using a high-volume sampler

A study was conducted to evaluate the homogeneity of the distribution of metals and metalloids deposited on glass fiber filters collected using a high-volume sampler equipped with a PM-10 sampling head. The airborne particulate matter (APM)-loaded glass fiber filters (with an active surface of about 500 cm²) were weighed and then each filter was cut in five small discs of 6.5 cm of diameter. Each disk was mineralized by acid-assisted microwave (MW) digestion using a mixture of nitric, perchloric and hydrofluoric acids. Analysis was performed by axial view inductively coupled plasma optical emission spectrometry (ICP OES) and the elements considered were: Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Ti and V. The validation of the procedure was performed by the analysis of the standard reference material NIST 1648, urban particulate matter. As a way of comparing the possible variability in trace elements distribution in a particular filter, the mean concentration for each element over the five positions (discs) was calculated and each element concentration was normalized to this mean value. Scatter plots of the normalized concentrations were examined for all elements and all sub-samples. We considered that an element was homogeneously distributed if its normalized concentrations in the 45 sub-samples were within ±15% of the mean value ranging between 0.85 and 1.15. The study demonstrated that the 12 elements tested showed different distribution pattern. Aluminium, Cu and V showed the most homogeneous pattern while Cd and Ni exhibited the largest departures from the mean value in 13 out of the 45 discs analyzed. No preferential deposition was noticed in any sub-sample.     

Variability of total and mobile element contents in ash derived from biomass combustion

Seven samples of the ash derived from biomass, representing both fly and bottom ash, were analysed for a wide spectrum of total and mobile contents of nutrient and potentially risk elements. Several techniques, X-ray fluorescence (XRF) spectrometry, instrumental neutron activation analysis (INAA), proton-induced gamma-ray emission (PIGE) and proton induced X-ray emission (PIXE), inductively coupled plasma-atomic emission spectrometry (ICP-OES), and flame atomic absorption spectrometry (F-AAS) were compared. The results showed fairly good agreement between the XRF and INAA results, where the correlation coefficients (r) varied between 0.96 and 0.98. Lower contents documenting insufficient dissolution of the ash samples in the applied acid mixture were observed for both ICP-OES and AAS. In this case, weaker correlation with the INAA results not exceeding r = 0.7 were obtained. Therefore, the sample decomposition step is a bottleneck of the accurate analysis of this type of materials. For the assessment of plant-available portions of the elements in the ash samples, the Mehlich III extraction procedure and the extraction with a 0.11 mol L^?1 solution of CH₃COOH were applied. The results showed relatively low mobility of the elements (especially micronutrients) in the ash samples regardless of their source and composition, suggesting limited immediate effect of direct ash application as a fertilizer.     

Determination of Ca, P, Sr and Mg in the synthetic biomaterial aragonite by NAA

Implanted ⁷⁴Ge and ¹²⁰Sn concentrations in silicon (Si) layers were investigated by particle induced X-ray emission (PIXE), instrumental neutron activation analysis (INAA), Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS). Slight differences were observed in the results obtained. It was shown that PIXE and INAA are as powerful as the traditional RBS and SIMS spectroscopy for the investigation of thin layered Si.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis of no-carrier-added 6-[11C]methyl-l-DOPA

Taking advantages of nuclear analytical techniques (NATs) with non-destruction, multielement capability, small and estimable uncertainties over a wide range of sample sizes, the sampling behavior of multielements for a home-made natural matrix material was studied with sample sizes ranging from several hundred mg down to tenths ng, namely nine orders of magnitude, by a combination of three NATs, neutron activation analysis (NAA), proton induced X-ray emission (PIXE) and synchrotron radiation X-ray flurescence (SR-XRF), in an effort to explore a procedure for the development of certified reference materials (CRMs) suitable for quality control of microanalysis. For accurately weighable sample sizes (>1?mg), sampling uncertainties for 13 elements were found to be less than 1% by INAA. For sample sizes unable to be accurately weighed (<1?mg), PIXE and SR-XRF were used, respectively. Sampling uncertainties were found to be less than 1% at sample sizes of tenth mg level for seven elements, and less than 10% on ng levels for three elements. Considering these three elements have satisfied homogeneity (sampling uncertainty less than 10%) at ng sample size level, any one of them can be served as a ??relative balance?? in sampling behavior characterization of multielements on sample size levels larger than ng (e.g., ??g level). On this basis, sampling uncertainties for nine elements were found to be less than 10% on ??g sample size level by INAA. The results indicate that the matrix is eligible as a candidate of CRMs suitable for quality control of solid sampling microanalysis.     

Neutron activation analysis for identification of African mineral dust transport

A Gent stacked filter unit sampler was used to collect air particulate matter (APM) in separate coarse (PM_2.5–10) and fine (PM_2.5) size fractions, at a sub-urban site in Lisbon, Portugal. The sampling was done during the year 2001 and two daily samples were taken per week. The filters were analyzed for particulate mass by instrumental neutron activation analysis (INAA). The chemical analysis of APM levels and the study of the atmospheric dynamics by back-trajectories showed that most of the PM_2.5 and PM_2.5–10 peaks events were associated with air masses transport from the Saharan desert. High mineral load in ambient particulate matter levels were registered during the Saharan dust outbreaks. The accuracy of INAA to measure Fe, Sc and Sm was evaluated by NIST filter standards, revealing results with an agreement of ± 10%. This method constituted an important tool to identify these events.     

Sequential multielement analysis of a single aerosol filter by different instrumental and wet-chemical methods

Summary The direct instrumental methods X-ray fluorescence spectrometry (XRFS) and instrumental neutron activation analysis (INAA), and, after digestion of the sample, inductively coupled plasma mass spectrometry (ICP-MS) were applied in sequence to analyse small single aerosol filters. XRFS detected up to 19, INAA up to 22, and ICP-MS up to 33 elements. In total, up to 45 elements were determined, and, for a number of additional elements limits of detection could be given. For many elements, the data quality could be checked by cross-comparison of the results of two or all three methods. These methods very meaningfully complement each other and, in the manner used, allow the determination of all elements of interest in a small aerosol filter sample.     

Comparison of different types of filters for atmospheric trace element analysis by three analytical methods

Different atmospheric aerosol samples were collected on three types of filters. From both of the loaded and clean areas of each kind of filter, different disks were cut and investigated by XRF, PIXE and scanning electron microscopy (SEM). The blank concentration values of the elements Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br and Pb in the three types of filter are discussed. It is found that for trace elemental analysis, the Nuclepore membrane filters are the most suitable for sampling. These filters have much lower blank element concentrations than the glass fiber and ash free filters. It was found also that PIXE is a more reliable analytical technique for atmospheric aerosol particles than the other methods used.     

ICP–AES法测定铬镍不锈钢中锰、铬、镍、硅、磷、铜、钼的含量

建立电感耦合等离子体原子发射光谱(ICP–AES)法测定铬镍不锈钢中锰、铬、镍、硅、磷、铜、钼7种元素含量的方法。试样用盐酸与硝酸混合酸溶液溶解,采用溶解国家标准样品的方法制备校准曲线溶液,确定了元素最佳分析谱线。各元素的含量在其测试范围内与原子发射强度呈良好的线性关系,线性相关系数不小于0.999,7种元素的检出限在0.000 3%~0.003 0%之间。该方法应用于铬镍不锈钢标准样品的测定,测定值与认定值相符,测定值的相对标准偏差在0.12%~1.15%之间(n=8)。应用于铬镍不锈钢样品测定时,加标回收率在90%~110%之间。该方法操作简便、迅速,可满足日常铬镍不锈钢中多元素含量的检测需要。     

Iron, manganese, copper and titanium in welding fume dust on filters for internal and external quality assurance

Summary Filters charged with welding fume dust were developed and produced for internal and external quality assurance to evaluate and improve the performance of analytical methods used for monitoring iron, manganese, copper and titanium in the working environment. The filters were simultaneously loaded, using a Sputnic air sampling unit containing 100 cellulose nitrate filters. The welding fume dust was collected in industrial working conditions where Metal Inert Gas welding in construction steel was being carried out. The metal concentrations on the filters were close to the metal concentrations from environmental and industrial exposure. The homogeneity of the filter materials was evaluated to document the suitability of the air sampler in producing quality control materials. The filters were homogeneous within 5.0–12.7% according to amount of metal. The welding fume dust loaded on the filters was (0.2021±0.0093 mg/filter) and the amounts of metals loaded on the filters were (34.6±6.4 g/filter, 16.0±0.8 g/filter, 2.4±0.1 g/filter) for iron, manganese and titanium, respectively. Normalizing the amount of metal according to the welding fume dust improved the homogeneity. The most satisfactory results were obtained for manganese and titanium, for which within batch variation was below 6.3%. The Sputnic air sampler was shown to be suitable in preparing quality control materials, although a few improvements are needed for future experiments, such as the method of charging the dust and rules for outlier exclusion.     

Combined application of INAA and PIXE for studying the regional aerosol composition in Southern Africa

As part of the SAFARI-92 biomass buming experiment, aerosol collections were carried out with several size-fractionating sampling devices at a number of sites in Southern Africa. One of the samplers used at all ground-based sites was a stacked filter unit (SFU). The SFU samples were analyzed by both INAA and PIXE analysis. The present paper gives an intercomparison of the analytical results obtained in order to assess the accuracy and to check the quality assurance of the analytical procedures. Twenty-one common elements were determined by both INAA and PIXE. Concentrations of 13 elements (i.e., Na, Mg, Al, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Zn and Br) were generally measured with sufficient precision in both techniques for performing the intercomparison. The INAA and PIXE data were compared in terms of PIXE/INAA concentration ratios on a sample by sample basis for the coarse and fine size fraction separately. the atmospheric concentrations for K, Mn and Fe agreed within 5–10%, the agreement between the data for the other common elements was typically better than 15%. Possible explanations for lower than 1.0 ratios for Cl, Br and Na are presented. The common elements were classified into groups according to their detectability and sensitivity in each technique.     

Characterization of dust material emitted during harbour activities by k<Subscript>0</Subscript>-INAA and PIXE

The growing concern about air quality in harbours is a result of the high impact of the operations on human health and environment. Harbour activities such loading, unloading and transport of dusty materials are important emission sources of Atmospheric particulate matter (APM). The assessment of these fugitive emissions is a difficult task because they depend on the materials, the type of operation and the meteorological scenarios. The main objectives of this work were (1) to evaluate if the techniques k₀-based Instrumental neutron activation analysis (k₀-INAA) and Particle induced X-ray emission (PIXE) are suitable techniques to assess fugitive emissions in harbours and (2) to estimate the impact of harbour activities on APM levels and composition. Several experimental campaigns were carried out in a Portuguese harbour, during unloading operations of fertilizer and phosphorite provided from Syria and Morocco. PM_2.5 and PM_2.5–10 were collected, in polycarbonate filters, by Gent samplers. The techniques k₀-INAA and PIXE were applied as sensitive analytical tools to perform a complete chemical characterization of the collected samples. Results showed that manipulation of these materials during harbour operations resulted in high emissions of particles, principally from the coarse fraction. These emissions were very affected by the granulometry and nature of the handled materials. Fertilizer emissions were characterized by high concentration of Ca, P, K, Cr, Br and Zn, whereas phosphorite handling contributed principally for the increase of Ca, P and Cr levels.