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.     

Sampling strategies exploiting multi-pumping flow systems

In this work new strategies were exploited to implement multi-pumping flow systems relying on the utilisation of multiple devices that act simultaneously as sample-insertion, reagent-introduction, and solution-propelling units. The solenoid micro-pumps that were initially used as the only active elements of multi-pumping systems, and which were able to produce pulses of 3 to 25 microL, were replaced by syringe pumps with the aim of producing pulses between 1 and 4 microL. The performance of the developed flow system was assessed by using distinct sample-insertion strategies like single sample volume, merging zones, and binary sampling in the spectrophotometric determination of isoniazid in pharmaceutical formulations upon reaction with 1,2-naphthoquinone-4-sulfonate, in alkaline medium. The results obtained showed that enhanced sample/reagent mixing could be obtained with binary sampling and by using a 1 microL per step pump, even in limited dispersion conditions. Moreover, syringe pumps produce very reproducible flowing streams and are easily manipulated and controlled by a computer program, which is greatly simplified since they are the only active manifold component. Linear calibration plots up to 18.0 microg mL(-1), with a relative standard deviation of less than 1.48% (n=10) and a throughput of about 20 samples per hour, were obtained.     

Sampling and sample-preparation strategies based on solid-phase microextraction for analysis of indoor air

Applications of solid-phase microextraction (SPME) to the sampling and analysis of volatile organic compounds in indoor air are reviewed, including a summary of quantification methods, coatings, compounds, concentrations, sampling locations and times, and detection limits. Strategies for on-site and off-site sampling and analysis, advantages and challenges associated with SPME for air sampling are discussed.     

A water purification system for microanalysis

A water purification system producing conductivity water is described. It involves first distillation, second distallation from acidified potassium permanganate, and deionation by separate bed strong cation and anion-exchange resins. The purified water proved the validity for microanalysis by conductivity and spectrophotometry. The apparatus can be assembled easily in a laboratory from all Pyrex glass Quickfit units with some glass elaboration.     

Advances in CE-mediated microanalysis: an update

This review, as a continuation of two earlier reports, gives an overview of the recent developments, over the period from 2005 until now, in the use of electrophoretically mediated microanalysis (EMMA) methodology for the on-line study of enzymatic reaction and derivatization. The article is divided into two parts: (i) on-line enzymatic reaction by EMMA and (ii) on-line derivatization by EMMA. Following a brief introduction, a literature overview on enzymatic reaction is provided. The second part starts with an introduction of the purpose of derivatization and the nomenclature used in the area of in-capillary derivatization based on EMMA. The development of more integrated analytical platform that combines in-capillary derivatization and sample preconcentration is discussed. Reported derivatization procedures are summarized.     

Use of precision colorimetry for elemental microanalysis

Spectrophotometric techniques are useful for microdeterminations of many elements in organic compounds and some inorganic compounds. It is possible to determine most metals and some non-metals (Al, Co, F, Fe, Mo, P, Pd, Pt, Si, Sn, Ti...) by applying spectrophotometric techniques described in the literature (most often for trace analysis) and using commercial reagents.     

Sampling strategies for capillary isoelectric focusing with electroosmotic zone mobilization assessed by high-resolution dynamic computer simulation

The impact of initial sample distribution on separation and focusing of analytes in a pH 3–11 gradient formed by 101 biprotic carrier ampholytes under concomitant electroosmotic displacement was studied by dynamic high-resolution computer simulation. Data obtained with application of the analytes mixed with the carrier ampholytes (as is customarily done), as a short zone within the initial carrier ampholyte zone, sandwiched between zones of carrier ampholytes, or introduced before or after the initial carrier ampholyte zone were compared. With sampling as a short zone within or adjacent to the carrier ampholytes, separation and focusing of analytes is shown to proceed as a cationic, anionic, or mixed process and separation of the analytes is predicted to be much faster than the separation of the carrier components. Thus, after the initial separation, analytes continue to separate and eventually reach their focusing locations. This is different to the double-peak approach to equilibrium that takes place when analytes and carrier ampholytes are applied as a homogenous mixture. Simulation data reveal that sample application between two zones of carrier ampholytes results in the formation of a pH gradient disturbance as the concentration of the carrier ampholytes within the fluid element initially occupied by the sample will be lower compared to the other parts of the gradient. As a consequence thereof, the properties of this region are sample matrix dependent, the pH gradient is flatter, and the region is likely to represent a conductance gap (hot spot). Simulation data suggest that sample placed at the anodic side or at the anodic end of the initial carrier ampholyte zone are the favorable configurations for capillary isoelectric focusing with electroosmotic zone mobilization.     

Electrophoretically mediated microanalysis assay for sirtuin enzymes

An electrophoretically mediated microanalysis (EMMA) assay for the human sirtuin SIRT1 has been developed using 9-fluorenylmethoxycarbonyl (Fmoc)-labeled peptides, i.e. Fmoc-KK(Ac)-NH(2), Fmoc-KK(Ac)L-NH(2) and Fmoc-RHKK(Ac)-NH(2), as substrates. The partial filling mode was applied due to the incompatibility between the incubation buffer, pH 8.0, and the BGE that had a pH of 2.7 or 2.3 depending on the analytes. Incubation and subsequent analyte separation were carried out in a 37/30 cm, 50 μm id fused-silica capillary at 37°C. An injection sequence of incubation buffer, enzyme, substrate, enzyme and incubation buffer was selected because the electrophoretic mobility of SIRT1 was not known. The assay was optimized with regard to the length of the injected plugs, the mixing voltage and mixing time as well as the activity (concentration) of SIRT1. The EMMA assay was subsequently applied to the determination of the Michaelis-Menten constants, K(m), and the maximum velocity, V(max), as well as the determination of the inhibitory constants, IC(50), of inhibitors. Data obtained with the in-capillary assay were in accordance with the literature data or an offline SIRT1 assay.     

Molecular calculations for microanalysis on a programmable calculator : Microlab calculator programming

For the microanalytical staff that serves a strongly research-oriented laboratory, calculations are continuously being made which are to an extent repetitious in nature. The calculator has not always been superseded by the computer for this work. On the other hand, the card-programmable calculator offers convenience in accessibility and relief from tedious repetitive key-stroking. Two programs, ready for use in the Hewlett-Packard HP-65 calculator, are presented and discussed. These particular programs were chosen for their differences in operation, for their complementary format, and for their utility in microanalytical determinations. In a word, they were chosen to show the broad attack on microanalytical calculations offered by the card-programmable calculators with limited memory.     

Low energy ion implantation in polybithiophene: microstructuring and microanalysis

Low energy ion implantation in polybithiophene (thickness 200 nm) forms a 20 nm thin modified surface layer. Combining surface analysis and electrochemical methods a non destructive depth resolved investigation of the properties of the implanted layer was performed. The composition of the modified layer is dependent on the implanted species: N causes doping, O has a sputtering effect. The modified layer acts as an electronic and ionic barrier as shown by cyclic voltammetry and electron transfer reactions. The effectivity of barrier formation is dependent on the sample pretreatment and the redox state. For reduced samples the redox charge increases for repeated voltammograms (regeneration effect). The according dose dependent band scheme shows an increasing surface resistivity for low doses. At high doses the surface resistivity decreases again due to graphitization. By application of a microstructured mask the polybithiophene was structured within a m range. Laterally high resolving methods revealed sharp interfaces between implanted and pristine surface ranges. The doping pattern and the electronic properties are localized and do not alter even in an electrolyte. So conducting polymers can be microstructured to give stable structures with changed composition and modified electronic and ionic properties as required for microtechnological applications.     

Low energy ion implantation in polybithiophene: microstructuring and microanalysis

Low energy ion implantation in polybithiophene (thickness 200 nm) forms a 20 nm thin modified surface layer. Combining surface analysis and electrochemical methods a non destructive depth resolved investigation of the properties of the implanted layer was performed. The composition of the modified layer is dependent on the implanted species: N causes doping, O has a sputtering effect. The modified layer acts as an electronic and ionic barrier as shown by cyclic voltammetry and electron transfer reactions. The effectivity of barrier formation is dependent on the sample pretreatment and the redox state. For reduced samples the redox charge increases for repeated voltammograms (regeneration effect). The according dose dependent band scheme shows an increasing surface resistivity for low doses. At high doses the surface resistivity decreases again due to graphitization. By application of a microstructured mask the polybithiophene was structured within a microm range. Laterally high resolving methods revealed sharp interfaces between implanted and pristine surface ranges. The doping pattern and the electronic properties are localized and do not alter even in an electrolyte. So conducting polymers can be microstructured to give stable structures with changed composition and modified electronic and ionic properties as required for microtechnological applications.     

Comparison of Electrolytic Conductivity Theories: Performance of Classical and New Theories

Conductivity equations, based on the mean spherical approximation (MSA), haverecently been derived. We compare their performance with that of classicalequations at the level of experimental uncertainty using conductivity data forsome typical electrolyte solutions. For symmetrical electrolytes, the pictureisconsistent showing a better performance for the classical equations. The Leeand Wheaton equation also shows advantages at moderate concentrations. Forunsymmetrical electrolytes, the differences between MSA and classical equationsis larger. There is, however, an inherent inconsistency with the equilibriuminformation, which cannot be resolved at present.     

Quantitative electron probe microanalysis: Fluorescence correction uncertainty

Summary In order to evaluate the fluorescence correction uncertainty in electron probe microanalysis, effects of two general types were investigated. The effects of uncertainty in 1. microprobe operational variables, including X-ray emergence angle and operating voltage, and 2. errors in model input parameters, such as fluorescence yield factors and mass attenuation coefficients, were evaluated. The major conclusion of this study is, that even in cases requiring large fluorescence corrections, microprobe operation at high (30°) X-ray emergences angles, and at the lowest voltage compatible with a reasonable X-ray output is entirely satisfactory. This conclusion is reached by substituting into existing fluorescence correction models reasonable input parameter errors, X-ray emergence angles, and operating voltages. Results show that absolute compositional errors vary quite slowly with X-ray emergence angle and operating voltage. The chief source of error among input parameters is the fluorescence yield factor. The role of model selection as a source of potential error is also discussed.

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Zusammenfassung Für die Ermittlung der Unsicherheit der Fluoreszenzkorrektur bei der Elektronenstrahl-Mikroanalyse sind zwei prinzipielle Effekte zu berücksichtigen: 1. Unsicherheiten, bedingt durch den Austrittswinkel der Röntgenstrahlung und die Beschleunigungsspannung und 2. fehlerhafte Parameter, wie Fluoreszenzausbeute und Massenschwächungskoeffizienten. Das wichtigste Ergebnis der vorliegenden Arbeit ist, daß die Mikrosondenanalyse sogar in Fällen, die eine große Fluoreszenzkorrektur erwarten lassen, und selbst bei großem Austrittswinkel (30°) und bei niedrigster Spannung mit einer erträglichen Impulsausbeute völlig zufriedenstellend ist. Dieses Ergebnis wurde erhalten, nachdem annehmbare Parameter für Abnahmewinkel und Beschleunigungsspannung in bekannte Fluoreszenzkorrektur-Modelle eingesetzt worden waren. Die Resultate zeigen, daß der absolute Fehler für die Zusammensetzung nur wenig mit dem Abnahmewinkel variiert. Der Faktor für die Fluoreszenzausbeute ist die hauptsächliche Fehlerquelle. Die Auswahl der Korrekturverfahren als eine Quelle für einen möglichen Fehler wird ebenfalls diskutiert.