Sample screening methods

Screening of incoming environmental samples is performed to obtain information that will guide the further detailed analysis and to assist in the shipment of samples to the NWAL. Samples that are known to be radioactive for the pmposes of shipment from the field to the IAEA are delivered directly to the nuclear laboratory of SAL for screening and archival storage because the CL is not licensed to handle such materials. All samples known to be below the limits for radioactive shipment purposes are delivered to the CL where they are screened. 

Member laboratories of the IAEA NWAL for environmental sample analyses. Techniques in use by the NWAL include FT-TIMS = fission-track thermal ionization mass spectrometry, AMS = accelerator mass spectrometry, SIMS = secondary ion mass spectrometry, HRGS = high-resolution gamma spectrometry, TIMS = thermal ionization mass spectrometry, ICP-MS = inductively coupled plasma mass spectrometry, SEM = scanning electron microscopy 

Australian Nuclear Science and Technology Organization, Lucas Heights, Australia AMS 

Air Force Technical Applications Center - Patrick Air Force Base, Florida, U.S.A FT-TIMS  

Department of Energy - Oak Ridge National Laboratory, Los Alamos National Laboratory, Pacific Northwest National Laboratory, Lawrence Livermore National Laboratory HRGS, TIMS and ICP-MS 

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Leblanc, C.J., W.M. Stallard, P.G. Green, and E.D. Schroeder. 2003. Passive sampling screening method using thin-layer chromatography plates. Environ. Sci. Technol. 37 3966-3971. 

The aim of most screening methods is to produce a yes/no decision, concerning whether the concentration of a certain substance in a sample exceeds a given limiting concentration or not. For instance, if the concentration of a substance lies below a permitted maximum concentration then there is probably no need to analyse the sample. However, if the content is in the region of or above the permitted limit, then the result must be confirmed by means of an exact quantitative determination. 

Such yes/no decisions are of great importance in foodstuffs control and environmental analysis. They also play an important role in pharmacy in the form of content uniformity tests. Without suitable screening methods for rapid detection of positive samples it would scarcely be possible to carry out economic doping controls and toxicological investigations or to recognize medicament abuse. 

The combined use of a continuous flow system and a spectrophotometer for sample screening to discriminate between synthetic and natural colorants is also available. With a very simple flow system on a column packed with natural materials, one can discriminate natural and synthetic colorants. The natural (not retained) ones can be determined in the first step and the synthetic (retained) ones in the second step after their elution. For yellow, red, green, blue, and brown, natural or synthetic colorants were chosen as models. The specific maximum wavelength for each color (400,530, and 610 mn, respectively) was selected by a diode array system. A complete discrimination of natural and synthetic colorants was obtained for concentrations of natural colorants (in the absence of synthetic ones) up to 2000 (yellow), 2000 (red), and 10,000 (brown) times that of the detection limits (DLs) of synthetic additives. This method was applied to screen fruit drinks and candies. ... 

In summary, the CSL guidelines can be simply applied in each laboratory and contain very clear instructions. The validated procedures do not focus on the central analytical part only. Important secondary aspects of the whole procedure (sample processing, analyte stability, extraction efficiency) are also considered. For each parameter which is determined, different criteria for the evaluation of quantitative, semi-quantitative and screening methods are given. Here, it should be noted that compared with other guidelines the requirement for the precision of quantitative methods is very stringent (RSD < 10%). 

A multi-residue method for 25 selected pesticides including propanil using an SPE disk has also been developed as a rapid screening method for organic contaminants in river, lake and seawater samples. Cig SPE disks are conditioned with 10 mL of acetone for 3 h. Water samples (1L) are allowed to percolate through the disks in order to trap the residues at a fiow rate of 50 mL min under vacuum. Residues trapped in the disks are extracted twice by eluting with 5 mL of dichloromethane-ethyl acetate (1 1, v/v). The more hydrophobic compounds (log/fow>3) seem to show no... 

Ishihama et al. [147] have describe a rapid screening method for determining pK values of pharmaceutical samples by pressure-assisted CE, coupled with a photodiode array detector. Each CE run was completed in less than 1 min, so a 96-well microtiter plate could be measured in one day. Determinations of the pKa values of 82 drugs illustrated this interesting new method. 

The amount of total lead in the blood can be measured to determine if exposure to lead has occurred. This test can tell if you have been recently exposed to lead. Lead can be measured lead in teeth or bones by X-ray techniques, but these methods are not widely available. These tests tell about long-term exposures to lead. Exposure to lead can be evaluated by measuring erythrocyte protoporphyrin (EP) in blood samples. EP is a part of red blood cells known to increase when the amount of lead in the blood is high. However, the EP level is not sensitive enough to identify children with elevated blood lead levels below about 25 micrograms per deciliter ( ig/dL). For this reason, the primary screening method is measurement of blood lead. For more information on tests to measure lead in the body, see Chapters 2 and 6. 

The application of screening methods requires that proper reference samples are available. These must contain the analyte exactly at or close to the specification level. Such reference samples have to be verified by quantitative analysis using reference methods. 

For 218Po sampled from a radon chamber free of particles (CN < 70 cm-3) and with no introduced SO2 concentration, our two multiple-screen methods yield a unimodal spectrum of diffusion coefficients, with the mode at. 08 . 01 cm /sec. 

Figure 16.1. Screening method for fentanyl analogs in blood using LC-MS/APCI. Monitored ions [M + H]+ were chosen from full scan spectra. The blood sample was spiked with fentanyl, its three analogs and internal standard to the concentration of 5 ng/mL [6].

Order Material Group of Compound Screening Method Sample Preparation Method... 

Local sensitivity analysis is of limited value when the chemical system is non-linear. In this case global methods, which vary the parameters over the range of their possible values, are preferable. Two global uncertainty methods have been used in this work, a screening method, the so-called Morris One-At-A-Time (MOAT) analysis and a Monte Carlo analysis with Latin Hypercube Sampling (Saltelli et al., 2000 Zador et al., submitted, 20041). The analyses were performed by varying rate parameters, branching ratios and constrained concentrations within their uncertainty interval,... 

Based on the quantitative determination of pentadecane it was calculated that—with a sample load of about 200pg—alkanes are detected by this screening method if their concentration is 5ppm or more. It is obvious that highly volatile compounds when present as such (e.g. dioxane) cannot be measured quantitatively because considerable losses of such components occur during the evaporation of the suspension liquid from the pyrolysis wire when it is prepared. Quantities measured for such compounds must therefore be considered as minimum values. 

TLC is a screening method a small percentage (5 to 10%) of the samples should be confirmed by a more sophisticated analytical method such as gas chromatography or high performance liquid chromatography... 

The FIA-MS screening approach using soft ionisation interfaces prior to any CID procedure provides an overview of the MS separation procedure, which is based on the different m/z ratios of the molecular or cluster ions generated. With the help of this very fast screening method—positive or negative FIA-MS by-passing the analytical column—the surfactant chemist is able to characterise complex blends and formulations without difficulty (Fig. 2.5.1) while the experienced analyst is able to make initial statements about the presence of frequently used and therefore most important surfactants in environmental samples (Fig. 2.5.2) despite the presence of complex matrices. The information provided by ESI or APCI—FIA—MS overview spectra for a first characterisation [8,17-19], which were also available with non-API soft ionising interfaces such as FAB [20] or TSI [9] in industrial blends as well as environmental samples, were obtained from ... 

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