Field screening

Environmental Applications Although ion-selective electrodes find use in environmental analysis, their application is not as widespread as in clinical analysis. Standard methods have been developed for the analysis of CN , F , NH3, and in water and wastewater. Except for F , however, other analytical methods are considered superior. By incorporating the ion-selective electrode into a flow cell, the continuous monitoring of wastewater streams and other flow systems is possible. Such applications are limited, however, by the electrode s response to the analyte s activity, rather than its concentration. Considerable interest has been shown in the development of biosensors for the field screening and monitoring of environmental samples for a number of priority pollutants. 

Motwani JN, Popp SA, Johnson GM, et al. 1986. Field screening techniques developed under the superfund program. The 7 national conference on management of uncontrolled hazardous waste sites. December 1-3, 1986, Washington, DC, 105-109. 

Applications Coupling of solid-phase micro-extraction and a micro-GC (separation times of 15 sec) is suitable for rapid field screening and potentially useful for process analysis. Odours at ppt level can be analysed by... 

In polar semiconductors, carrier-mediated generation occurs in the form of transient depletion field screening (TDFS) depicted in Fig. 2.5 [30]. The driving force in (2.1) can be expressed by the sum of the Raman term and the nonlinear longitudinal polarization [10] ... 

Teramobile, 112 Thomson scattering, 168, 179 Three-level system, 11 Three-step model, 65 Time-resolved second harmonic generation, 29 TOF spectroscopy, 5 Transient depletion field screening (TDFS), 28... 

A sensitive ELISA procedure was developed for the determination of TNT (221) and other nitroaromatic compounds. TNT can be detected within the range of 0.02-20 ng/L in water samples462. A simplified immunofiltration prepacked portable device for field screening tests of TNT in water and soil was also developed. A quantitative color response to concentrations of TNT in the range 1-30 ng/L in water and 50-1000 pg/g in soil was demonstrated463. 

Fig. 13.3 Equipotentials around various arrays of carbon nanotubes (a) Field enhancement at an array of widely spaced nanotube emitters, (b) closely spaced emitters, showing the field screening, (c) field screening at a randomly oriented nanotube forest.

IR-based TPH methods Laboratory and field screening—most appropriate for water and soil Primarily diesel and fnel oils Most hydrocarbons, with exception of volatile and very high hydrocarbons EPA Method 418.1... 

Immunoassay Field screening—most Varions products (but yields only Aromatic hydrocarbons EPA Method 4030... 

A number of procedures, based on microanalysis of samples for known physical properties (Chapter 8, 9, and 10), have also been employed. Eor example, field screening, which uses infrared spectroscopy, employing a portable version of the laboratory procedure has been used (Kasper et al., 1991). Eield turbido-metric methods favor the determination of high-boiling hydrocarbons and are... 

A portable and automated field screening, for assessing contamination by TNT in military sites, was reported by Pamula in 2004. Microfiter droplets of TNT in dimethylsulfoxide and KOH in water are reacted on a chip in a programmed way, to form the typical color. The reported detection of TNT is linear in the range of 12.5-50 Ig/ml [101]. 

Due to the tendency of hydrocarbons in the soil to undergo subsurface oxidation, measuring COj levels in the soil gas could be used as a cost-effective field screening tool. In one soil-gas survey, COj levels in soil gas correlated well with petroleum hydrocarbons in the soil (Diem et al. 1988). 

A Desk Reference Guide (EPA/R-93/003b), Vol. 1 Solids and Ground Water Vol. 2 The Vadose Zone, Field Screening and Analytical Methods... 

Lopez-Avila et al. [107] showed that microwave-assisted extraction of pesticides and polycyclic aromatic hydrocarbons from soil is a viable alternative to Soxhlet extraction and needs a smaller sample volume and extraction time [108,109]. These techniques have also been compared in the case of chlorophenols. Lopez-Avila et al. compared microwave-assisted extraction with electron capture gas chromatography to ELISA for the determination of polychlorinated biphenyls in soils. Both techniques are applicable to field screening and monitoring applications. Microwave-assisted extraction [111, 112] and solid-phase microextraction [113] have been applied to the extraction of pesticides from soil. It was observed by these and other workers [114] that the selectivity of microwave-assisted extraction is highly dependent on the soil composition. 

Easterling et al. [161] has reported a rapid field screening method for the determination of elemental mercury in soil. This method involves thermal desorption of the mercury onto gold, followed by thermal desorption from the gold film mercury analyser. 

Other techniques that have been used to determine polycyclic aromatic hydrocarbons in soil extracts include ELISA field screening [86], micellar elec-tr okinetic capillary chromatography [ 87], supersonic jet laser-induced fluorescence [88,89], fluorescence quenching [90], thermal desorption gas chromatography-mass spectrometry [81,90,100], microwave-assisted extraction [91], thermal desorption [92], immunochemical methods [93,94], electrophoresis [96], thin layer chromatography [95], and pyrolysis gas chromatography [35]. 

G-30026, norazine Norazine reached the level of field screening together with G-30027, atrazine. It showed a typical triazine activity pattern, without distinct advantages over simazine, atrazine, or propazine. In addition, its... 

The use of screening data enables project teams to estimate an environmental condition in a rapid manner and to facilitate real-time decision-making in the field. Screening results usually determine future action at the project site, and that is why screening data, imprecise as they may be, must reliably reflect the true site conditions. Screening data may help formulate important decisions for many types of environmental projects, such as the following ... 

Obtain the data on the rate of false positive and false negative results for field screening kits from the manufacture or from individuals who had used them. 

Before selecting a certain field screening kit, test it on the project matrix and compare results to laboratory data for the same samples. 

As a field screening option, consider a mobile laboratory with laboratory-grade instruments and standard analytical methods with relaxed QC requirements. 

Field screening techniques may be more expensive than laboratory analysis, considering the cost of screening kits, field portable instruments, supplies, and technician s time. 

Only properly trained personnel should conduct field screening. 

QA splits are particularly valuable for field screening with definitive analysis confirmation and for the verification of field laboratory analysis. The frequency of the QA sample collection is best determined based on the project duration and the total numbers of samples to be collected. Typically, they are collected at a 10 percent frequency (one QA sample for every 10 field samples). It is beneficial to establish data comparability in the early phase of field implementation. If data are comparable, the frequency of QA sampling may be reduced as the confidence in field screening or field laboratory results has been established. But if the data are not comparable, the project team needs to identify the cause of the differences and resolve them as soon as possible in order to avoid making decisions on inaccurate or unrepresentative data. 

Obtain field screening kits and all necessary supplies and verify that the quantity of supplies is sufficient for the project task. 

Always obtain spare field screening kits for backup in case more samples are collected than planned. 

After the planning phase of the data collection process has been completed and the foundation of the data collection pyramid has been built, the project moves into its second phase, implementation. The implementation phase takes place in the field and at the laboratory. This chapter addresses the tasks of field implementation, such as Task 3—Sampling and Field Data Collection and Task 5—Field QA/QC, shown within the data collection pyramid in Figure 3.1. The main features of these field tasks are sampling procedures sample custody and tracking preservation techniques equipment decontamination field screening and record keeping. 

The measurements of water quality parameters (oxidation-reduction potential, pH, temperature, conductivity, dissolved oxygen, and turbidity) and the collection of field screening data with field portable instruments and test kits constitute a substantial portion of field work. Field measurements, such as pH, stand on their own as definitive data used for the calculations of solubility of chemical species and chemical equilibrium in water, whereas others serve as indicators of well stabilization or guide our decision-making in the field. Table 3.8 shows the diversity of field measurement... 

Semiquantitative field screening for organic vapor in soil headspace, at wellheads, at sampling... 

There is no uniform operating procedure for field meters, field portable detectors, and field screening kits because different manufacturers make them in different formats. To use them correctly, we must strictly follow the manufacturer s instructions. When selecting a particular model, we need to evaluate its ruggedness, portability, selectivity, sensitivity, and reliability. To produce usable data, we must have a good understanding of the measurement mechanism, its applicability and limitations, and be concerned with the issues of field instrument calibration and maintenance. In this chapter, we will review some basic general chemistry definitions applicable to field measurements and focus on the common types of field analysis. 

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