Sampling methods pretreatments

ES-EPA (Expert System for Environmental Pollutant Analysis) is an expert system for producing laboratory test plans, including the appropriate sampling methods, pretreatments, test methods and their order. ES-EPA generates test plans in a stepwise manner from abstract plans called "templates" to detailed plans, using a hierarchical planning mechanism. The knowledge base contains information on analysis items, test methods, test equipment, pretreatments and other necessary information. The prototype system has been successfully tested for various cases in the domain. The development of a delivery version has been completed and it will soon be used in the field on a daily basis to further verify its feasibility. 

The Analysis Task KB contains all kinds of analysis plan elements from abstract task components to specific tasks. Abstract components have information for plan refinement in the form of templates. Specific tasks include sampling methods, pretreatments, equipment tests, analysis methods defined in the Japan Industrial Standards and others. A specific task has information on the conditions and constraints of the task application, instructions for the task execution and so on. 

The objective ia any analytical procedure is to determine the composition of the sample (speciation) and the amounts of different species present (quantification). Spectroscopic techniques can both identify and quantify ia a single measurement. A wide range of compounds can be detected with high specificity, even ia multicomponent mixtures. Many spectroscopic methods are noninvasive, involving no sample collection, pretreatment, or contamination (see Nondestructive evaluation). Because only optical access to the sample is needed, instmments can be remotely situated for environmental and process monitoring (see Analytical METHODS Process control). Spectroscopy provides rapid real-time results, and is easily adaptable to continuous long-term monitoring. Spectra also carry information on sample conditions such as temperature and pressure. 

The most common method for preparing samples for pretreatment and subsequent measurement of IR spectra is the self-supporting pellet technique. In this... 

In terms of applicability, the waste used in the two scales of tests must come from the same origin, must be sampled at the same date and must follow the same pretreatments and procedures. The sampling method used must ensure that a representative sample of the waste to be assessed will be obtained. 

Fig. 3. Densitometer scans showing electrophoretic separation of Chl-protein complexes in P. laminosum. Samples were pretreated with LDAO at a ratio LDAO Chl=3.5 l and treated with SDS at a ratio SDS Chl=20 l as described under Materials and Methods, (a) membrane fragments isolated according to Stewart and Bendall (1980), (b) PSI-enriched particles. The area of the peaks corresponding to the free pigment (FP) bands was similar in both cases.

Laboratory methods have been adapted for field-measurement, taking into account three main steps sampling, possible pretreatment and detection. 

The UV method has been described as a simple and reliable procedure for the determination of sulphide in wastewater. Compared with some reference methods, it is less sensitive but do not need any sample preparation (pretreatment, filtration, etc.) and is unaffected by interferences (salinity, suspended matter, organics compounds, etc.). 

Specific surface area was measured by the N2-BET (Brunner-Emmett-Teller) method on a Micromeritics ASAP2400 automatie adsorption meter. Samples were pretreated in a muffle furnace at 573 K for 1 h. The sample in system was outgassed at 523 K for 4 h, then, cooled down in liquid nitrogen. Nitrogen adsorption isotherms were recorded for BET calculation. 

Only a small amount of absorbed MBOCA is excreted in urine as MBOCA in animals, and probably in humans as well (see Section 2.3). The methods used to detect MBOCA in urine are somewhat limited since they commonly measure unmetabolized MBOCA-not its metabolic by-products. Some methods have been developed to directly measure major MBOCA metabolites in urine. Other analytical methods pretreat urine samples with acid, base and/or heat to release MBOCA from its various conjugates. Another approach is to analyze the longer-lived complexes, such as MBOCA-hemoglobin adducts. The specific methods used are noted in the following text and in Table 6-1. 

Sample pretreatment is dependent on the sampling method. VOCs collected on adsorbents are typically desorbed thermally directly into the GC. The filter and impactor samples typically require extraction into a suitable solvent, such as n-hexane or a mixture of n-hexane acetone, although thermal desorption can be utilised also for filter samples. 

To qualitatively test for Bronsted acidity using the colorimetric method, 50 mg of the zeolite sample was pretreated at 300°C under vacuum for approximately 12 hrs. 1 mL of a dilute solution of retinol (Aldrich) or retinyl acetate (Aldrich) in dry hexane was injected onto the activated zeolite (10,11). A color change to blue indicated the presence of Bremsted acid sites. 

A gravimetric method was used to deteimine the C02 adsorbing capacities of the prepared hydiotalcites. The amount of sample loaded into the TGA unit (C-1100, CAHN INSTRUMENTS. INC.) was 6S mg. The sample was pretreated in flowing Hie at 500 for 3 h. Afto- the temperature was lowered to 450 C, CO2 was introduced to the balance and the weight change was measured. The range of adsorption pressure was between 0 to 1000 mmHjg. 

Analyte Sample Method/derivatizatlon reaction Detection Typical working range Features/sample pretreatment... 

The detection limits for TXRF are significantly lower than for conventional XRF and comparable to most atomic spectrometric methods used for trace analysis or surface characterization. They range from several picograms to a few nanograms for the lighter elements in real samples and are somewhat lower for pure aqueous solutions. Improvement of detection limits is possible when the sample is pretreated and/ or the matrix removed. This is particularly important... 

Indeed AMS is a state-of-art ultrasensitive technique for trace analysis, but the success of AMS depends on many crucial steps before the actual measurement in the AMS system. In fact, sometimes expertise from several areas of science is required to make the AMS experiments reliable. Some of the crucial points are sample collection, pretreatment, sample preparation for ion source, development of separation methods for isobars, etc. Like all other analytical techniques, it is also necessary to measure standard, blank, and background, simultaneously with the sample. Below some of the crucial steps are described in nutshell. 

One of the most commonly used colorimetric methods is based on the adsorption of a dye by magnesium hydroxide to form a colored lake in alkali hydroxide solution. Titan yellow [methylbenzothiazole-(l, 3)-4,4 -diazominobenzene-(2,2 )-disulfonic acid] is the most widely used dye [97]. Typically, the sample is pretreated by incineration or acid extraction. Iron, aluminum, manganese, copper, zinc, nickel, and phosphorus must be removed from the sample due to interference of these elements with the color formation [97]. 

Graphite furnace atomic absorption spectrometry (GFAAS) is an excellent method to provide sub-ng/mL minimum detection limits [110]. Continuing advancements such as Zeeman correction, and stabilized temperature platform furnaces, have made GFAAS an effective analytical method for magnesium determination. Depending on the sample matrix, pretreatment can vary from direct analysis of fluids, to wet mineralization, dry ash, acid extraction, and by using PPRs (e.g., Triton X-100). 

Where possible, use a sampling method that does not involve any sample pretreatment or modification that is, analyze the sample as is. It is recognized that this is not always possible. For routine sampling, some of the newer diamond-based accessories allow many different sample types to be analyzed in an original, native form. However, it is recognized that not all laboratories have this facility, therefore, sample pretreatment may be the only answer. A few of the common sample pretreatments are noted in the following Sections. If any of these procedures are used, it is important to ensure that a comment is provided relative to the use of the method within the sample documentation. Failure to do this can lead to erroneous results or misleading answers. 

---