Elemental analysis of airborne dust samples with TXRF: Comparison of oxygen-plasma ashing on sapphire carriers and acid digestion for sample preparation

The concentrations of 13 elements (As, Ca, Co, Cd, Cr, Fe, Ga, Ni, Pb, Pt, Ti, V and Zn) were determined in air particulate matter using total reflection X-ray fluorescence spectrometry (TXRF). For silicon analysis synthetic sapphire was chosen as a new sample carrier material – it is silicon-free, resistant to oxygen-plasma, microwaves and concentrated acids. The dust samples were collected on cellulose acetate filters. The decomposition of the filters was carried out by oxidation in a microwave-generated low-pressure oxygen-plasma directly on the TXRF sample carriers. The recovery of the investigated elements was verified with the standard reference material SRM 1648 (urban particulate matter) and ranged from 90 to 97%. The oxygen-plasma method was compared with conventional sample preparation by acid digestion. Received: 9 April 1999 / Revised: 18 May 1999 / Accepted: 3 June 1999     

Trace Element Determination in Diesel Particulates by Total-Reflection X-Ray Fluorescence Analysis

 Particulate matter of Diesel emissions collected from diluted exhaust during standard test runs with two Diesel fuels of different sulfur content was analysed by total-reflection X-ray fluorescence (TXRF). The trace elements determined were S, Ca, Cr, Mn, Fe, Ni, Cu, Zn and Pb. Additionally, some filter materials were tested with respect to their applicability for sample collection. Quartz fibre filters were found to be most suitable, both from a technical and a chemical point of view. A clear reduction of total particulate emissions during the whole test was observed when the fuel with very low sulfur content was used. In addition, it was found that the wear metal content of particulate matter emitted by a cold engine was higher than that observed during normal engine working temperature. Received September 10, 1998. Revision March 2, 1999     

Sapphire sample carriers for silicon determination by total-reflection X-ray fluorescence analysis

Sapphire is presented as a new sample carrier material for total-reflection X-ray fluorescence spectrometry (TXRF). A comparison with conventional sample carrier materials such as quartz glass, Perspex®, glassy carbon and boron nitride demonstrates that sapphire has all the physical and chemical properties required for TXRF micro and trace analysis. Moreover, sapphire sample carriers allow the determination of silicon in many matrices in a comparatively simple way. Especially for airborne particulate matter, acid digestion can be avoided by cool-plasma ashing of suitable filter materials directly on the sample carrier. This technique has been successfully applied to environmental samples.     

Size-fractionated sampling and chemical analysis by total-reflection X-ray fluorescence spectrometry of PMx in ambient air and emissions

PM 10 and PM 2.5 (PMx) have been recently introduced as new air quality standards in the EU (Council Directive 1999/30/EC) for particulate matter. Different estimates and measurements showed that the limit values for PM 10 will be exceeded at different locations in Europe, and thus measures will have to be taken to reduce PMx mass concentrations. Source apportionment has to be carried out, demanding comparable methods for ambient air and emission sampling and chemical analysis. Therefore, a special ambient-air sampler and a specially designed emission sampler have been developed. Total-reflection X-ray fluorescence analysis (TXRF) was used for multi-element analyses as a fast method with low detection limits. For ambient air measurements, a sampling unit was built, impacting particle size classes 10–2.5 μm and 2.5–1.0 μm directly onto TXRF sample carriers. An electrostatic precipitator (ESP) was used as back-up filter to also collect particles <1 μm directly onto the TXRF sample carriers. Air quality is affected by natural and anthropogenic sources, and the emissions of particles <10 μm and <2.5 μm, respectively, have to be determined to quantify their contributions to the so-called coarse (10–2.5 μm) and fine (<2.5 μm) particle modes in ambient air. For this, an in-stack particle sampling system was developed, according to the new ambient air quality standards and in view of subsequent analysis by TXRF. These newly developed samplers, in combination with TXRF analyses, were employed in field campaigns to prove the feasibility and capabilities of the approach. Ambient air data show the quantification of a wide spectrum of elements. From those concentrations, PMx ratios were calculated as an indicator for different sources of elements. Results useful for source apportionment are also the elemental day/night ratios calculated to determine local contributions to PMx mass concentrations. With regard to the emission measurements, results of mass and elemental concentrations obtained in two different processes (steel industry) show that the new PM 10/PM 2.5 cascade impactor and measurements with TXRF give characteristic fingerprints for different sources. Size-fractionated ambient air and emission sampling, together with multi-element analysis, prove to be a useful approach to derive information for source–receptor modeling, a method necessary to set up effective abatement strategies to reduce PMx mass concentrations.     

Trace elements in PM2.5 in Gothenburg,Sweden

Ambient aerosol particles smaller than 2.5 µm (PM_2.5) are getting more and more attention worldwide. While legal focus is mainly on sample mass, the composition of the particles is an important research field gaining increased interest. The interest is not only connected to possible health effects of the elemental content of the particles, but the elemental determination can also add valuable information for source apportionment. Samples were collected during 20 days in November 2007 at the campus of the Chemistry Department, University of Gothenburg, Gothenburg, Sweden. The particles were collected using a cyclone that separates the PM_2.5 particles from the air stream and impacts them on polycarbonate filters. Filters were changed at early afternoon. The samples were analyzed for particulate mass, black carbon (BC) and the elements S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, As, Br, Cd and Pb. Several of the elements were above detection limit in only a few of the samples. Total reflection X-ray fluorescence (TXRF) spectrometer based on the Wobi TXRF module supplied by the International Atom Energy Agency (IAEA) has been used for the determination of most trace elements in the samples. A Graphite Furnace Atomic Absorption Spectrometer (GF-AAS) was used for complementary trace element analysis and a reflectometer was used to analyze black carbon. Before elemental analysis the filters were digested using a microwave digestion system with temperature and pressure control. The results showed a large variation in sample mass, BC and analyzed elemental concentrations. The variation of the different constituents did not show the same pattern. This added to the picture of different sources for different pollutants. The highest S concentration was noted on a day when the air masses were determined to come from the southeast, i.e. Poland and some other Eastern European countries. From the results it can be concluded that more work is needed on the TXRF spectrometer to optimize it for determination of the EU legally regulated elements As, Ni, Pb and Cd. Despite this the study shows that there is no problem in meeting the AAQS limits for Cd and Pb in Gothenburg.     

TXRF法测定松花粉中的9种生命元素

建立了微波消解前处理,全反射X射线荧光法(TXRF)同时测定松花粉中K、Ca、Ti、Mn、Fe、Ni、Cu、Zn和Rb9种生命元素含量的分析方法.松花粉原料经过微波消解前处理后,采用全反射X射线荧光光谱净计数、QXAS分析软件解谱和单一内标法进行定量分析.比较了干灰化法、湿消解法和微波消解法3种前处理方法的效果,并确立微波消解法作为样品前处理方法.用微波消解- TXRF法测定了花粉标准物质中的上述9种元素,并计算得到其仪器检出限(LLD)为0.002～0.054 mg/L,方法检出限(LDM)为0.004～0.122 mg/kg.TXRF法测定各元素的相对标准偏差(RSDs)为1.0％～5.5％.该方法操作简单、样品用量少、检出限低,对实际样品松花粉的测定结果与ICP - MS法无显著性差异.     

Atomic emission spectrometric analysis of airborne particulate matter by direct nebulization of suspensions into the inductively-coupled plasma

A method is described for the rapid, direct emission spectrometric determination of iron in airborne particulate matter collected on polystyrene fiber filters using a conventional high-volume sampler and a Japanese low-volume sampler. The suspension prepared by dissolving the filter material in xylene was directly nebulized into the inductivelycoupled plasma excitation source. An ultrasonic immersion device was used for stirring purposes. Particles within the size range 0.1–100 μm in diameter are collected on the high-volume filters, while the largest particles on low-volume filters do not exceed 10 μm in diameter. The difference in the particle size composition entailed the use of a separate set of standard suspensions for each sample type. Standard suspensions for calibration were prepared from NBS SRM-1648 (urban particulates) as originally received and from its ground powder for high-volume and low-volume samples, respectively. The relative standard deviation was usually below 5%, which is acceptable for large-scale air pollution survey work. The possibility of determining other major and minor elements in airborne particulate matter was also examined.     

Multi-element analysis of airborne particulate matter by various spectrometric methods after microwave digestion

A microwave digestion procedure in combination of the measurement of various spectrometric methods including atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry was developed for the multi-element analysis of airborne particulate matter collected on PTFE filters by a dichotomous sampler. In order to achieve more sensitive and rapid multi-element analyses, special PTFE-lined digestion vessels were used. It was found that complete digestion of airborne particulates with an acid mixture of HNO₃-HClO₄-HF (3:7:1, v/v) can be achieved in the microwave-irradiated closed vessel system and direct spectroscopic measurement of the digested sample after appropriate dilution. A recovery study was conducted using a multi-element standard and NIST Standard Reference Material 1648 Urban Particulate. Sixteen major, minor, and trace elements in airborne particulate matter were determined.     

Optimisation of total-reflection X-ray fluorescence for aerosol analysis

The capabilities of total-reflection X-ray fluorescence (TXRF) analysis were investigated to develop an efficient, simple, rapid and low cost analytical method for aerosols. The technique involves direct impaction of airborne particulate matter on the quartz sample-reflector discs for TXRF. Special attention was paid to bounce-off effects, and hence the aerosol size distributions for the impactor stages; influence of siliconizing the quartz discs on the adhesion of particles; choice of the internal standard; local distribution of the material deposited on the quartz disc; and alternative materials for aerosol collection. Moreover, the proposed method could be used in combination with a one-stage impactor for total aerosol mass collection and analysis.     

An investigation of calibration materials for the measurement of metals in ambient particulate matter on filters by LA-ICP-MS

Three different types of simple and low-cost calibration material for the measurement of the metals content of ambient particulate matter (PM) on filters using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) have been compared: cellulose ester filters spiked with multi-element calibration solutions, pellets of compressed ambient particulate matter certified reference material (CRM), and powdered ambient particulate matter CRM adhered to a surface. Elements determined were As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn, each at approximate levels of 1000?ng per filter. Blank filters spiked with multi-elemental standards were found to be significantly more reproducible and repeatable than materials based on powdered reference materials. However, a comparison of these spiked filters with real samples of ambient PM showed that the analytical sensitivities obtained per mass of analyte were significantly different. It is concluded that the spiked filters could act as very effective quality control standards correcting, to within 1%, drifts in LA-ICP-MS measurements of up to 10%, or as indirect calibration materials supported by additional measurements using traditional wet chemical techniques.     

Heavy metal determination in atmospheric particulate matter by Instrumental Neutron Activation Analysis

Instrumental Neutron Activation Analysis (INAA) is employed for its important analytical properties. Fundamentally, INAA is a multi-elemental technique allowing the determination of about 40 elements with a good Limit of Detection. In this paper we applied this nuclear technique to study the element composition in PM10 determining about 30 elements.25 filters were collected in downtown Rome from October 1999 to April 2000 and irradiated at the nuclear reactor Triga Mark II (ENEA-Casaccia Laboratories). The γ-ray measurements have allowed the quali- and quantitative analysis. The element levels in PM10 with the relative correlations have been determined: basically, the concentrations are very low.Furthermore, the enrichment factors of all elements will be reported in order to understand the natural or anthropogenic origins of the particulate matter: some elements may be attributed to long-range transport phenomena from other natural and/or anthropogenic sources.     

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.     

The use of a portable total reflection X-ray fluorescence spectrometer for field investigation

A newly developed, portable total reflection X-ray fluorescence (TXRF) spectrometer was tested during a field campaign on Chilean lakes and a German river in January 2002. The field measurements were compared with laboratory measurements carried out on a stationary instrument in the German laboratory. For method validation certified reference material (NIST SRM 1640 Trace elements in natural water) and water samples from different freshwater sources were analyzed with both techniques and evaluated statistically. Based on these preliminary results, it could be concluded that the portable TXRF is a useful technique for the quantitative elemental screening of freshwater samples during field campaigns. Future tests with biological samples (e.g. biofilms and zooplankton), and suspended matter will provide information about the suitability of the portable TXRF for these materials.     

Optimization of an urban particulate matter multi-element analysis method by inductively coupled plasma--atomic emission spectrometry (ICP-AES)

In the present work a method for simultaneous metals determination, in urban air particulate matter by ICP-AES has been set up. A large number of elements (18) has been analyzed, including major (Al, Fe, K, and Mg), minor (Na, Pb and Zn) and trace (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Sb, Sr and V) elements. The procedure consists of microwave sample acidic total digestion by HNO3/HF mixture and subsequent analysis by ICP-AES, using different assemblies depending on sample treatment procedure: a quartz Meinhard nebulizer/cyclonic chamber, if HF excess was eliminated, or a cross-flow nebulizer/plastic Scott chamber, suitable for application with HF. A cyclonic chamber for hydride generation was used for As, Sb and Hg determination. The procedure was tested with Standard Reference Materials 1648 NIST Urban Particulate Matter and Certified Reference Material No8 NIES "Vehicle Exhaust Particulates". Two sampling supports, quartz fibre and polycarbonate filters, have been examined in order to find the most suitable i.e. the one characterized by less interference. Some real samples of urban air particulate matter, TSP, PM10 and PM2.5 fractions, collected during an intercomparison campaign promoted by Regione Lombardia, have been analyzed with the procedure developed.     

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.     

Particle Size Determination of Trace Elements in Urban Air

Abstract

Airborne urban particulate matter was collected and fractionated according to size by cascade impactors. The elements zinc, cadmium, copper and lead on each size fraction were analyzed by anodic stripping voltammetry. The elements aluminum, iron, manganese, calcium and magnesium were analyzed by atomic absorption spectrophotometry. The data showed three different classes of particle size distribution for these nine elements. Lead and cadmium belonged to the first class with more than 70 % of the total collected element associated with particles having aerodynamic diameters below 0.5 micron. The calculated average mass median equivalent diameter (MMD) of cadmium and lead was approx. 0.1 micron. In the second class about 60% of the elements Zn, Cu, Mg and Fe was associated with particles smaller than 0.5 micron. The average MMD's for these elements were between 0.3 and 0.4 micron. For the elements Al, Ca and Mn about 50% of the metal was associated with particles smaller than 0.5 micron and the MMD's were between 0.5 and 0.6 micron. Examination of elemental ratios (using Al as a reference element) showed that Pb and Cd were about 1000 times more concentrated in atmospheric particulate matter than in average crustal material and that in general the Pb/Al and Cd/Al ratios are inversely proportional to particle size. The Zn/Al and Cu/Al ratios of atmospheric partides were age or less independent of particle size and approx. 20 times higher than these same ratios in average crustal material. The ratios Fe/Al, Mn/AI, Ca/M and Mg/AI in all sizes of particulate matter were essentially identical to the same ratios in average crustal material.     

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.     

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.     

INAA for the characterization of airborne particulate matter from the industrial area of Islamabad city

Air particulate matter (PM) was collected in two size fractions using stacked filter units (SFUs) provided by the International Atomic Energy Agency (IAEA) from the industrial area of Islamabad. Nucleopore polycarbonate filters were used for collecting from Oct 98 to Jun 99 the particulate matter in coarse and fine size fractions. The samples were characterized by the instrumental neutron activation analysis (INAA). About 33 elements were quantified using different irradiation and counting protocols.     

微波消解-电感耦合等离子体质谱测定大气颗粒物中痕量稀土元素

研究了电感耦合等离子体质谱（ICP-MS）测定大气颗粒物中痕量稀土元素（REEs）的分析方法。在微波条件下,采用HNO3 ＋ H2O2（3 ＋ 1）混合介质能快速而有效地分解颗粒物样品。详细讨论了测定稀土元素的质谱干扰。通过分析不同粒径颗粒物中稀土元素的含量,初步探讨了大气颗粒物中稀土元素的分布规律。结果表明：颗粒物试样的粒径越小,稀土元素的含量越高。分析方法的检出限为0．7～2．8pg／mL,用于大气颗粒物国际标样（SRM 1648）中稀土元素分析,结果与推荐值有良好的一致性。