Total Reflection X-ray Fluorescence

Total reflection X-ray fluorescence (TXRF) spectrometry is a non-destructive and surface sensitive multi-element analytical method based on energy dispersive X-ray fluorescence spectrometry with detection limits in the lower picogram range. It utilizes the total reflection of the primary X-ray beam at or below the critical angle of incidence. At this angle, the fluorescence intensity is substantially enhanced for samples present as small granular residue or as thin homogenous layer deposited at the surface of a thick substrate. Generally, two types of application exist: micro- and trace-analysis as well as surface and thin-layer analysis. For micro- and traceanalysis, a small amount of the solid or liquid sample is deposited on an optically flat substrate, typically quartz or polycarbonate. The dried residue is analyzed at a fixed angle setting slightly below the critical angle. Quantification is carried out by means of internal standardization. For surface and thin-layer analysis, the surface of an optically flat substrate is scanned. Variations of the incident angle of the primary X-ray beam provide information about the type and sometimes also the amount of material present at or slightly below the surface of the substrate. Major fields of application are environmental samples, biological tissues, objects of cultural heritage, semiconductors and thin-layered materials and films

Quantification of Surface Contamination on Genesis Solar Wind Samples

The Genesis mission was the only mission returning pristine solar material to Earth since the Apollo program up to date [1, 2]. Unfortunately, the return of the spacecraft on September 8, 2004 resulted in a crash landing shattering the solar wind collectors into small fragments and exposing them to desert soil and other debris at the landing site. To permit analysis of solar wind material embedded within a collector, surface cleaning is a necessity. Cleaning should remove surface contamination quantitatively, but leave the embedded solar wind intact. However, contamination varies from sample to sample and each fragment requires an individual cleaning approach. To ensure that cleaning is effective a sample has to be inspected carefully before and after cleaning was performed. This is done optically using a microscope and also spectroscopically by using total reflection X-ray fluorescence (TXRF) analysis. Total reflection X-ray fluorescence is a nondestructive surface sensitive multi element analysis method and has been applied to a number of Genesis solar wind samples before and after various cleaning methods. [3-5]. In case contaminants remain after cleaning, quantification of those is important to evaluate the effectiveness of the procedure itself and to provide information about a sample for other investigators. Quantification is typically done by addition of an internal standard for TXRF analysis, but this approach is not possible for Genesis samples as it would introduce additional contamination. In this study, external calibration curves were produced instead and the concentration of remaining elements determined for three flight samples after different cleaning procedures were applied

Multivariate Statistical Analyses of Air Pollutants and Meteorology in Chicago During Summers 2010–2012

Aerosol, trace gas, and meteorological data were collected in Chicago, Illinois during 2010–2012 summer air studies. Ozone, nitrogen oxides, acetate, formate, chloride, nitrate, sulfate, and oxalate concentrations as well as temperature, wind speed, wind direction, and humidity data were explored by both principal component analysis (PCA) and canonical correlation analysis (CCA). Multivariate statistical techniques were applied to uncover existing relationships between meteorology and air pollutant concentrations and also reduce data dimensions. In PCA, principal components (PC) revealed a relationship of ozone and nitrate concentrations with respect to temperature and humidity, coupled with transport of species from the south in relation to the sampling site (PC1). PC2 was a measure of secondary aerosols but also suggested acetate and formate presence was a result of primary emissions or transport. Both PC3 and PC4 contained residual information with the former representing days of lower pollution and the latter representing northerly wind transport of chloride, nitrate, and ozone to the sampling site. In CCA, three canonical functions were statistically significant. The first indicated high temperature and low wind speed had a strong linear relationship ozone, oxalate, and nitrogen oxides concentrations whereas the second function showed a strong influence of wind direction on acetate, formate, and chloride concentrations. Residuals of temperature, wind speed, trace gases, and oxalate also were in the second function. The only new information in the third function was humidity. Overall, PCA and CCA bring forth multi-variable relationships, not represented in descriptive statistics, useful in understanding pollution variability

Steps toward accurate large-area analyses of Genesis solar wind samples: evaluation of surface cleaning methods using total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence spectrometry (TXRF) was used to analyze residual surface contamination on Genesis solar wind samples and to evaluate different cleaning methods. To gauge the suitability of a cleaning method, two samples were analyzed following cleaning by lab-based TXRF. The analysis comprised an overview and a crude manual mapping of the samples by orienting them with respect to the incident X-ray beam in such a way that different regions were covered. The results show that cleaning with concentrated hydrochloric acid and a combination of hydrochloric acid and hydrofluoric acid decreased persistent inorganic contaminants substantially on one sample. The application of CO2 snow for surface cleaning tested on the other sample appears to be effective in removing one persistent Genesis contaminant, namely germanium. Unfortunately, the TXRF analysis results of the second sample were impacted by relatively high background contamination. This was mostly due to the relatively small sample size and that the solar wind collector was already mounted with silver glue for resonance ion mass spectrometry (RIMS) on an aluminium stub. Further studies are planned to eliminate this problem. In an effort to identify the location of very persistent contaminants, selected samples were also subjected to environmental scanning electron microscopy. The results showed excellent agreement with TXRF analysis

Heavy Metal Analysis in Lens and Aqueous Humor of Cataract Patients by Total Reflection X-Ray Fluorescence Spectrometry

The human eye is continuously exposed to the environment yet little is known about how much of toxins, specifically heavy metals are present in its different parts and how they influence vision and acuity. To shed light into this subject, aqueous humor and lens samples were collected from 14 cataract patients to study the presence and concentration of selected metals in the eye. Subjects undergoing routine cataract surgery were consecutively enrolled for study by simple random sampling. Prior to surgery, subject demographic were compiled. The surgical procedure involved small incision cataract removal using phacoemulsification. During the procedure, a small aliquot of aqueous humor was retained for analysis, whereas homogenized lens fragments were obtained during phacoemulsification. A balanced salt solution was used as control for each set of samples. Both ocular specimens were analyzed by total reflection X-ray fluorescence spectrometry after dilution and addition of an internal standard. The data obtained show substantial variations in elemental signature between the two media (aqueous humor and lens) and the patients themselves. Most commonly found heavy metals in both types of media were chromium and manganese. Barium was found in the lens, but not in aqueous tissue, whereas nickel was found only in the aqueous humor. Concentrations were generally higher in aqueous samples. Further study and increased sample size are required to more accurately elucidate the relationship between systemic and ocular metal accumulation and the impact of metal accumulation on measures of visual function and ocular disease

Statistical Analysis of Aerosol Species, Trace Gases, and Meteorology in Chicago

Both canonical correlation analysis (CCA) and principal component analysis (PCA) were applied to atmospheric aerosol & trace gas concentrations and meteorological data collected in Chicago during the summer months of 2002, 2003, and 2004. Concentrations of ammonium, calcium, nitrate, sulfate, and oxalate particulate matter, as well as, meteorological parameters temperature, wind speed, wind direction, and humidity were subjected to CCA & PCA. Ozone and nitrogen oxide mixing ratios were also included in the data set. The purpose of statistical analysis was to determine the extent of existing linear relationship(s), or lack thereof, between meteorological parameters and pollutant concentrations in addition to reducing dimensionality of the original data to determine sources of pollutants. In CCA, the first three canonical variate pairs derived were statistically significant at the 0.05 level. Canonical correlation between the first canonical variate pair was 0.821, while correlations of the second and third canonical variate pairs were 0.562 and 0.461, respectively. The first canonical variate pair indicated that increasing temperatures resulted in high ozone mixing ratios, while the second canonical variate pair showed wind speed and humidity’s influence on local ammonium concentrations. No new information was uncovered in the third variate pair. Canonical loadings were also interpreted for information regarding relationships between data sets. Four principal components (PCs), expressing 77.0% of original data variance, were derived in PCA. Interpretation of PCs suggested significant production and/or transport of secondary aerosols in the region (PC1). Furthermore, photochemical production of ozone & wind speed’s influence on pollutants were expressed (PC2) along with overall measure of local meteorology (PC3). In summary, CCA and PCA results combined were successful in uncovering linear relationships between meteorology and air pollutants in Chicago and aided in determining possible pollutant sources

Steps Toward Accurate Large Area Analyzes of Genesis Solar Wind Samples: Evaluation of Surface Cleaning Methods Using Total Reflection X-ray Fluorescence Spectrometry

Total reflection X-ray fluorescence spectrometry (TXRF) was used to analyze residual surface contamination on Genesis solar wind samples and to evaluate different cleaning methods. The Genesis mission collected solar wind during a period of 854 days by embedding the charged particles into collectors made of various ultra clean materials such as silicon, sapphire and silicon-on-sapphire. The sample return capsule unexpectedly crashed on return to Earth fracturing the collectors and exposing them to the desert soil of the landing side. The ubiquitous contaminants are separated from the atoms of solar wind by only 5-15 nm, presenting significant challenges for solar wind analysis as well as the development of cleaning techniques. Currently, an ultrapure water and ozone UV radiation treatment is routinely applied to the collectors by the curatorial team at NASA’s Johnson Space Center. Additional cleaning steps involving various forms of acid treatment and/or carbon dioxide snow treatment are being evaluated as well. To gauge the suitability of the cleaning method, two samples were analyzed following cleaning by lab-based TXRF. The analysis comprised of an overview and a crude manual mapping of the samples by orienting them with respect to the incident X-ray beam in such way that different regions were covered. The results showed that cleaning with concentrated hydrochloric acid and a combination of hydrochloric acid and hydrofluoric acid decreased persistent inorganic contaminants substantially on one sample. Application of carbon dioxide snow for surface cleaning tested on the other sample appears to be effective in removing one persistent Genesis contaminant, namely germanium. Unfortunately, the TXRF analysis results of the second sample were impacted by relatively high background contamination. This was mostly due to the relatively small sample size and that the solar wind collector was already mounted with silver glue for resonance ion mass spectrometry (RIMS) on an aluminum stub. Further studies are planned to eliminate this problem. In an effort to identify the location of very persistent contaminants, selected samples were also subjected to environmental scanning electron microscopy. The results showed excellent agreement with TXRF analysis

Investigation of Heavy Metals in Zebrafish Tissue by Total Reflection X-ray Fluorescence

Heavy metals are present in the environment, in many consumer products and can be found in food. Some heavy metals like zinc and copper are essential for enzymatic and metabolic function while others like lead and mercury are toxic and interfere with biological pathways. Zebrafish are a very popular model organism for monitoring toxicity of heavy metals and investigating vertebrate development. In this study we explore the possibility of using total reflection X-ray fluorescence spectrometry to analyze histological sections of zebrafish embryos after exposure to nickel and lead. A methacrylate resin embedding protocol and a paraffin embedding protocol were evaluated as possible options for sample preparation for TXRF analysis of zebrafish embryos. It was found that paraffin is the superior material after an alkaline phosphatase stain was introduced. The stain made the normally transparent fish embryo embedded in paraffin clearly visible on the sample reflector material thus allowing for easy positioning and identification of the area of interest

Differentiation of Surface Contaminants and Implanted Material on Genesis Solar Wind Samples Using Total Reflection X-Ray Fluorescence Spectometry and Grazing Incidence X-Ray Fluorescence

During the Genesis mission solar wind was implanted in collector materials for analysis by various instrumental methods. Unfortunately the space craft crash landed upon return to Earth shattering the collectors into small fragments and exposing them to desert soil and spacecraft debris. Thus only small fragments are available for analysis with each having different degrees of contamination present at and embedded within the surface. Cleaning procedures were developed and applied to remove the contamination. To aid in this process bench top total reflection X-ray fluorescence spectrometry (TXRF) was used to characterize a sample surface before and after various cleaning steps. In contrast to TXRF, synchrotron grazing incidence X-ray fluorescence spectrometry (GI-XRF) is capable of probing at the surface and below the surface thus providing information about surface deposits as well as implanted material. A number of samples were subjected to both, TXRF and GI-XRF analysis and it was observed that some elements detected by TXRF were present not on top of but below the surface of the collector fragment. This suggested the possibility of using laboratory TXRF to distinguish between surface deposits and ion-implanted subsurface material. The feasibility of this approach was tested with a surface deposited and an ion implanted control sample. In addition a careful TXRF angle scan was also executed with one Genesis flight sample and compared to GI-XRF measurements, confirming the ability of bench top TXRF to distinguish between surface and subsurface material