An algorithm for data processing in neutron activation analysis

An algorithm for processing NAA data is described. Input data are the output data from a multichannel pulse-height analyzer with a microprocessor. This algorithm permits to calculate the concentrations of the analyzed elements (using a standard or a standard curve), the error of concentrations in the analysis of one or several parallel samples and the sensitivity of the analysis according to Currie's criteria in counts, g and g/g. Some other intermediate data (e.g. corrected net area of the peaks, parameters of the standard curve) may have individual importance in differenct cases.     

Image evaluation with chemometric strategies for quality control of paints

In this study a complementary analytical methodology for quality of paints evaluation was developed. Four different primers applied to steel substrates and submitted to accelerated laboratory and outdoor exposure tests were taken into account. After this, digitalized images were obtained from these samples using a conventional scanner. The images were converted in gray color scale histograms, the resulting data were organized into a matrix form and analyzed with the help of principal component analysis (PCA) and hierarchical cluster analysis (HCA). It was possible to identify the best primers performance avoiding subjective interpretation.     

Rapid quantitative and qualitative confirmatory method for the determination of monofluoroacetic acid in foods by liquid chromatography-mass spectrometry

Many environmental samples contain complex mixtures of organic compounds with different sources, polarities and reactivities. This study reports a method for the analysis of both polar/water-soluble and apolar organic compounds in several kinds of environmental samples. The analytical method consists of extraction with a mixture of dichloromethane:methanol (2:1, v/v), silylation using BSTFA (N,O-bis-(trimethylsilyl)trifluoroacetamide) and analysis by gas chromatography-mass spectrometry (GC-MS), a common device in chemical and environmental laboratories. Fifty individual sugar standards, including monosaccharides, sugar alcohols, anhydrosugars, disaccharides and trisaccharides, were analyzed for the determination of their fragmentation patterns and retention times. Recoveries (at three concentrations) and limits of detection (LOD) were determined for a standard mixture containing glucose (monosaccharide), sorbitol (sugar alcohol), levoglucosan (anhydrosugar) and sucrose (disaccharide), and they varied from 68 to 119% and 130 to 360 ng mL(-1), respectively. The method was used for the analysis of aerosol particle, soil and sediment samples, and demonstrated its feasibility in detecting not only several important environmental sugars (e.g., glucose, fructose, inositol, mannitol, sorbitol, levoglucosan, sucrose, mycose), but also a large range of organic compound classes from other polar components (e.g., dicarboxylic acids) to apolar compounds such as n-alkanes. Therefore, the analytical method presented here demonstrated its usefulness for a better understanding of sources and transport of various organic compounds in different environmental compartments.     

A TrAC journey into water-chemical metrology in the European Union

Measuring water quality for various purposes (e.g., drinking, environmental or wastewater) generally relies on analysis of a wide variety of physico-chemical parameters and chemical substances, including toxic and carcinogenic substances at various levels of concentrations, in a wide variety of (raw or filtered) matrices. Measurement strategies (covering sampling, sample pre-treatment, storage, and laboratory analyses) have evolved over the past 25 years with the development of new instruments and new techniques, as well as the harmonization of procedures throughout Europe, particularly through increasing awareness of quality assurance (QA) of environmental analysis. In this context, TrAC has played a significant role in disseminating information on trends, with a series of special issues on emerging trends in analytical developments and related features (e.g., QA, on-site methods, automated analytical instrumentation, and emerging pollutants, including endocrine disruptors). This article gives examples of analytical developments in the water sector as seen from TrAC perspectives.     

Preparation steps in environmental trace element analysis - facts and traps

The laboratory of CERVA is for several decades involved in the Belgian environmental research. The activity was associated to national monitoring programs dealing with trace metal pollution of all compartments of the environment (sea and river waters, sediments and organisms but also soils, plants, animal and food samples). Such a monitoring dealing with the total analyte contents in samples needed a comprehensive development of the whole methodology associated to the analyses using atomic absorption and emission spectroscopy techniques. This includes measurement but also preparation steps. The latter is the subject of this work. Long-term experience has shown that precisely sample preparation is the most critical part of the analysis because it is responsible for the largest and often hidden sources of errors. Errors due to contaminations may be usually overcome if necessary precautions are taken concerning reagents, tools and the manner of working. The problem is different for analyte losses: in this case, the responsible factor is an inappropriate methodology. This is particularly true for preparation of solid samples that have to be brought in a solution in order to satisfy needs of introduction systems of most spectroscopic techniques utilized in routine laboratories. For some types of samples (e.g. animal tissues), the dissolution is not a problem: it may be readily achieved by several procedures. This is not the case for samples that contain silicates in their matrix (e.g. soils, sediments, plants) because their complete dissolution cannot be ensured by a simple procedure. This review describes the present knowledge regarding possibilities and errors that concern preparation steps. In addition, possible effects of the preparation procedure on the quality of measurement are also systematically discussed.     

A clean laboratory for ultralow concentration heavy metal analysis

Summary Laboratory facilities and methods are described which have been developed in our laboratory in collaboration with C. Patterson's group at the California Institute of Technology for the reliable measurement of various heavy metals at extremely low concentration levels down to the sub pg/g level in Antarctic and Greenland snow and ice. All analytical work is performed inside a clean laboratory pressurized with air filtered through high efficiency particle air filters and equipped with all-plastic laminar flow clean benches. High-purity water is produced by ion-exchange resins, and high purity acids from the US National Institute of Science and Technology are used. The various containers which are in contact with the samples are made of conventional low density polyethylene and FEP teflon. These containers are cleaned by immersion during several weeks in a succession of heated acid baths of increasing purity. Extremely careful blank determinations are made in order to quantitatively determine how much of the investigated metals is added to the samples from each separate reagent, from the walls of the various containers and from the air of the clean laboratory.     

Optimizing separations in online comprehensive two‐dimensional liquid chromatography

Online comprehensive two‐dimensional liquid chromatography has become an attractive option for the analysis of complex nonvolatile samples found in various fields (e.g. environmental studies, food, life, and polymer sciences). Two‐dimensional liquid chromatography complements the highly popular hyphenated systems that combine liquid chromatography with mass spectrometry. Two‐dimensional liquid chromatography is also applied to the analysis of samples that are not compatible with mass spectrometry (e.g. high‐molecular‐weight polymers), providing important information on the distribution of the sample components along chemical dimensions (molecular weight, charge, lipophilicity, stereochemistry, etc.). Also, in comparison with conventional one‐dimensional liquid chromatography, two‐dimensional liquid chromatography provides a greater separation power (peak capacity). Because of the additional selectivity and higher peak capacity, the combination of two‐dimensional liquid chromatography with mass spectrometry allows for simpler mixtures of compounds to be introduced in the ion source at any given time, improving quantitative analysis by reducing matrix effects. In this review, we summarize the rationale and principles of two‐dimensional liquid chromatography experiments, describe advantages and disadvantages of combining different selectivities and discuss strategies to improve the quality of two‐dimensional liquid chromatography separations.     

Sampling of organic volatiles in the atmosphere at moderate and low pollution levels

Several techniques are available for measuring organic volatiles in the atmosphere. For measurements at low and moderate pollution levels (between several μg m^?3 and a fraction of a μg m^?3), the existing methods can be adopted to a broad range of different compounds. Whole-air sampling in stainless-steel containers with metal bellows valves combined with subsequent gas chromatographic separation after preconcentration in the laboratory is probably the best procedure for low and medium molecular weight trace gases of moderate or low polarity and reasonable chemical stability (e.g., hydrocarbons and halocarbons). For organic compounds of lower volatility, adsorptive sampling on non-polar porous organic polymers (e.g., Tenax) and thermal desorption combined with cryotrapping and gas chromatographic separation of the sampled compounds is widely used. However, there are often substantial problems due to artefact formation or loss reactions. Owing to the generally larger sample volumes, these problems are even more pronounced for sorptive sampling techniques combined with sample recovery by solvent extraction. Unfortunately, the general understanding of the various processes of sample degradation due to chemical reactions of reactive components of the atmosphere with each other or with the sorbent is not yet sufficient to allow reasonable estimates of the extent of such interferences without elaborate test procedures.     

Applicability of solid-phase microextraction followed by on-fiber silylation for the determination of estrogens in water samples by gas chromatography-tandem mass spectrometry

A solvent-free method for the determination of five estrogens in water samples at the low ng/l was optimized. Compounds were first concentrated on a polyacrylate (PA) solid-phase microextraction (SPME) fiber, directly exposed to the water sample, and then on-fiber silylated on the headspace of a vial containing 50 microl of N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA). Derivatized analytes were determined using GC with MS/MS detection. Influence of several factors on the efficiency of the microextraction step (e.g. time, sample volume, pH, ionic strength and fiber coating) is systematically described. Derivatization conditions were optimized in order to achieve the complete silylation of all hydroxyl groups contained in the structure of the compounds. Detection limits (from 0.2 to 3 ng/l) are compared with those obtained using the same detection technique and different sample preparation strategies, such as solid-phase extraction followed by silylation of the analytes in the organic extract and SPME without derivatization. The method was applied to the analysis of sewage water samples. Two of the investigated species were detected above the quantification limits of the procedure.     

Analysis,fate studies and monitoring of the antifungal agent clotrimazole in the aquatic environment

The analysis and presence of clotrimazole, an antifungal agent with logK _OW > 4, was thoroughly studied in the aquatic environment. For that reason analytical methods based on gas chromatography–mass spectrometry and liquid chromatography–tandem mass spectrometry were developed and validated to quantify clotrimazole with limits of quantification down to 5 and 1 ng/L, respectively. Both methods were compared in an intercalibration exercise. The complete mass-spectrometric fragmentation pattern could be elucidated with the aid of quadrupole time of flight mass spectrometry. Since clotrimazole tends to adsorb to laboratory glassware, studies on its adsorption behaviour were made to ensure the appropriate handling of water samples, e.g. pH, storage time, pretreatment of sampling vessels or material of the vials used for final extracts. The phenomena of adsorption to suspended matter were investigated while analysing different waste-water samples. Application of the methods in various investigated wastewater and surface water samples demonstrated that clotrimazole could only be detected in the low nanogram per litre range of anthropogenic influenced unfiltered water samples after acidification to pH 2.     

Determination of Pu,Am, U and Cs in large soil samples in the vicinity of the USDOE Waste Isolation Pilot Plant

The determination of actinides in environmental soil and sediment samples are very important for environmental monitoring. A rapid actinide separation method has been developed and implemented that allows measurement of U, Pu and Am isotopes in large soil samples (10–15 g) with high chemical yields and effective removal of matrix interferences. The radiochemical procedures involve the total dissolution of soil samples, separation on anion-exchange resin, and separation and purification by extraction chromatography, e.g., UTEVA, TEVA, and TRU with measurements of radionuclides by alpha-spectrometry. The validation of the method is performed through the analysis of reference materials or by participating in laboratory intercomparison programs.     

Determination and interpretation of environmental water samples contaminated by uranium mining activities

Interpretation of environmental behavior of uranium is based on several steps of data analysis and statistical inference. First step is sampling and analyzing of uranium in field samples by routine laboratory methods. Such methods have to fulfill multiple requirements like robustness, efficiency, low detection limit and precision. A comparison of different approaches in assigning uncertainty to experimentally obtained analytical data shows that classical error estimation is not significantly inferior to more sophisticated modern techniques like inverse regression or orthogonal regression. A second step is the correlation of analytical data with current state of insight into environmental behavior of uranium. Such a correlation furthers the choice of adequate geochemical models and quality of geochemical data base for subsequent detailed analysis, e.g. by geochemical modeling. An appraisal of the individual steps in this complex analysis is given on the basis of statistical procedures for calibration and an E_H-pH diagram of uranium for atmospheric conditions.     

Sampling and sampling strategies for environmental analysis

Sampling errors are generally believed to dominate the errors of analytical measurement during the entire environmental data acquisition process. Unfortunately, environmental sampling errors are hardly quantified and documented even though analytical errors are frequently yet improperly reported to the third decimal point in environmental analysis. There is a significant discrepancy in directly applying traditional sampling theories (such as those developed for the binary particle systems) to trace levels of contaminants in complex environmental matrices with various spatial and temporal heterogeneities. The purpose of this critical review is to address several key issues in the development of an optimal sampling strategy with a primary goal of sample representativeness while minimizing the total number of samples and sampling frequencies, hence the cost for sampling and analysis. Several biased and statistically based sampling approaches commonly employed in environmental sampling (e.g. judgmental sampling and haphazard sampling vs. statistically based approaches such as simple random, systematic random, and stratified random sampling) are examined with respect to their pros and cons for the acquisition of scientifically reliable and legally defensible data. The effects of sample size, sample frequency and the use of compositing are addressed to illustrate the strategies for a cost reduction as well as an improved representativeness of sampling from spatially and temporally varied environmental systems. The discussions are accompanied with some recent advances and examples in the formulation of sampling strategies for the chemical or biological analysis of air, surface water, drinking water, groundwater, soil, and hazardous waste sites.     

Performance and robustness of a multi-user, multi-spectrometer system for INAA

The laboratory for instrumental neutron activation analysis at the Reactor Institute Delft, Delft University of Technology uses a network of 3 gamma-ray spectrometers with well-type detectors and 2 gamma-ray spectrometers with coaxial detectors, all equipped with modern sample changers, as well as 2 spectrometers with coaxial detectors at the two fast rabbit systems. A wide variety of samples is processed through the system, all at specific optimized (and thus different) analytical protocols, and using different combination of the spectrometer systems. The gamma-ray spectra are analyzed by several qualified operators. The laboratory therefore needs to anticipate on the occurrence of random and systematic inconsistencies in the results (such as bias, non-linearity or wrong assignments due to spectral interferences) resulting from differences in operator performance, selection of analytical protocol and experimental conditions. This has been accomplished by taking advantage of the systematic processing of internal quality control samples such as certified reference materials and blanks in each test run. The data from these internal quality control analyses have been stored in a databank since 1991, and are now used to assess the various method performance indicators as indicators for the method’s robustness.     

Bio-analytical applications of mid-infrared spectroscopy using silver halide fiber-optic probes

Infrared-spectroscopy has proved to be a powerful method for the study of various biomedical samples, in particular for in-vitro analysis in the clinical laboratory and for non-invasive diagnostics. In general, the analysis of biofluids such as whole blood, urine, microdialysates and bioreactor broth media takes advantage of the fact that a multitude of analytes can be quantified simultaneously and rapidly without the need for reagents. Progress in the quality of infrared silver halide fibers enabled us to construct several flexible fiber-optic probes of different geometries, which are particularly suitable for the measurement of small biosamples. Recent trends show that dry film measurements by mid-infrared spectroscopy could revolutionize analytical tools in the clinical chemistry laboratory, and an example is given. Infrared diagnostic tools show a promising potential for patients, and minimal-invasive blood glucose assays or skin tissue pathology in particular cannot be left out using mid-infrared fiber-based probes. Other applications include the measurement of skin samples including penetration studies of vitamins and constituents of cosmetic cream formulations. A further field is the micro-domain analysis of biopsy samples from bog mummified corpses, and recent results on the chemistry of dermis and hair samples are reported. Another field of application, for which results are reported, is food analysis and bio-reactor monitoring.     

Interlaboratory comparison study for the determination of the Fusarium mycotoxins deoxynivalenol in wheat and zearalenone in maize using different methods

Seventeen laboratories from six different countries, using their usual in-house methods, participated in an interlaboratory comparison test for the determination of the Fusarium mycotoxins deoxynivalenol (DON) in wheat and zearalenone (ZON) in maize. The toxins generally were extracted from maize and wheat employing mixtures of water, acidified water with an organic solvent or even pure water (for DON). While participants who used enzyme linked immuno sorbent assays (ELISA) for the determination of DON did not perform any clean-up, various techniques were applied for the purification of raw extracts (e.g. liquid/liquid extraction, solid phase extraction (SPE), immuno affinity chromatography (IAC)). For the final separation/quantification step either high performance liquid chromatography (HPLC) (mostly for ZON), gas chromatography (GC) (for DON) or ELISA were employed by participants. The aim of this study was to obtain information about the state of the art of mycotoxin analysis in cereals and to support a knowledge and experience exchange between the participating laboratories in the field of mycotoxin analysis. For each mycotoxin 5 different sample types were distributed, standard solutions (10.10 μg/ml ZON in methanol, 10.09 μg/ml DON in ethyl acetate), blank materials, spiked samples (75.1 μg/kg and 378.3 μg/kg ZON in maize, 126.2 μg/kg and 2519 μg/kg DON in wheat) and naturally contaminated maize and wheat. Coefficients of variation (CV) between laboratory mean results (outliers excluded) ranged from 6.2 to 27.7% for ZON and from 18.9 to 30.0% for DON. Except for the maize samples spiked at 75.1 μg/kg ZON the overall means (outliers rejected) statistically could not be distinguished from the respective target values. Average recoveries of the reported results ranged from 87.7 to 96.2% for ZON and from 94.2 to 108.5% for DON.     

A Colorful Investigation of a Diprotic Acid: A General Chemistry Laboratory Exercise

A general chemistry laboratory experiment that can be completed in a single laboratory period is described that familiarizes students with the acid—base chemistry of a diprotic acid and with the use of visible spectroscopy to determine species concentrations. This experiment is a modified version of a previously described laboratory exercise developed for an upper-division quantitative analysis course. Students work in teams and as a class to generate different ionization states of various highly absorbing dyes. Both spectroscopic and potentiometric (pH) data is collected using LabWorks II stations, but other inexpensive pH meters and visible spectrometers (e.g., Spec 20s) are suitable. A spreadsheet template is used to determine the percent composition of various ionization states of a diprotic acid and to determine the pK_a values. Besides introducing students to fundamental tools and key chemical concepts, this laboratory is also inexpensive to operate and utilizes nontoxic, colorful solutions.     

X-ray crystallography at macromolecular resolution: A solution of the phase problem

The problem of crystal structure analysis at macromolecular resolution is tackled using notions borrowed from small-angle solution-scattering studies. The mathematical procedure - essentially a pattern recognition approach - consists of generating all the phase combinations compatible with the data and screening them: the critical steps are the choice of the “pattern” and of the criteria which preside the “recognition”. Two strategies are adopted. One is based upon use of the histogram of the electron density maps, a function more dependent on chemical composition than on physical structure: the histograms of samples of different structure and similar chemical composition are compared in search for similarity. The other strategy operates on the electron density maps and involves the principle of maximum smoothness. From the practical viewpoint, one single parameter, (Δp)⁴, is found to play an outstanding role in the two cases. Algorithms are worked out, implemented on the computer and tested using a variety of lipid-water phases. The comparison of samples of different structure and similar chemical composition is found to provide a powerful screening criterion. The principle of maximum smoothness is also of great help, at least to the extent that the electron density distribution is a fairly smooth function, devoid of sharp peaks (associated with heavy atoms). The practical aspects of the algorithms are discussed, as well as their possible application to crystallographic problems of more general interest.     

Capillary Electrophoresis as a Monitoring Tool for Flow Composition Determination

Flow analysis is the science of performing quantitative analytical chemistry in flowing streams. Because of its efficiency and speed of analysis, capillary electrophoresis (CE) is a prospective method for the monitoring of a flow composition withdrawn from various processes (e.g., occurring in bioreactors, fermentations, enzymatic assays, and microdialysis samples). However, interfacing CE to a various flow of interest requires further study. In this paper, several ingenious approaches on interfacing flow from various chemical or bioprocesses to a capillary electrophoresis instrument are reviewed. Most of these interfaces can be described as computer-controlled autosamplers. Even though most of the described interfaces waste too many samples, many interesting and important applications of the devices are reported. However, the lack of commercially available devices prevents the wide application of CE for flow analysis. On the contrary, this fact opens up a potential avenue for future research in the field of flow sampling by CE.     

Quantitative Determination of Copper: Combining Project-Based Laboratories with Single-Analyte Detection

A multiweek experiment is presented for use in undergraduate instrumental analysis courses. The experiment combines project-based laboratories and single-analyte detection to provide students with experience in method development and validation, and to give them a more realistic experience in the analytical laboratory. Working together as a team, students develop methods for the detection of an analyte (i.e., copper) in water samples using at least two spectroscopic instruments (e.g., ICP-AES, AA, UV-vis, fluorescence). Student teams are given only topical information about their projects, and must research and plan the analyses, learn the instrumental methods to be used, obtain figures of merit (e.g., detection limits) from Beers law plots, analyze commercial water samples, and produce a standard operating protocol for one of their methods, which will be validated by another team during a subsequent laboratory. Goals of this approach include promoting teamwork and building student confidence in approaching and operating unfamiliar instrumentation. Even more importantly, students are placed in the position of being scientists and having to make decisions and recommendations. Each step of the analytical process must be carefully considered, and its significance assessed as there are no recipes to follow as they develop their methods and make comparisons between different techniques for the determination of a single analyte.