Timing of samples

Interpreta.tlon, Whereas statistical tests estabhsh whether results are or are not different from (over) an exposure criteria, the generaUty of this outcome must be judged. What did the samples represent May the outcome, which is inferred to cover both sampled and unsampled periods, be legitimately extrapolated into the future In other words, is the usual assumption of a stationary mean vaUd AH of these questions are answered by judgment and experience appHed to the observations made at the time of sampling, and the answers are used to interpret the quantitative results. 

When sampling sludges and deposits (waterside and fireside), the precise location, quantity estimate, and any deposit accumulation pattern should be noted and, where possible, compared with previous inspections. The color should also be identified at the time of sampling (deposits commonly are white, yellow, gray, blue-green, brown, or black). 

Air samples collected in the Sacramento Valley area of California near sites where methyl parathion was heavily used on rice were analyzed by Seiber et al. (1989). Methyl parathion concentrations ranged from 0.2 (minimum detectable level) to 25.67 ng/m depending on the location and time of sampling. Methyl paraoxon, the oxygen analog of methyl parathion, was also detected at a maximum of 3.07 ng/m. The highest concentrations of both compounds were found at sites near locations of heaviest use. 

Figure 1. HPLC analysis of product progression during hydrolysis of 0.25 % polygalacturonate by PGII. Aliquots were withdrawn from the reaction mixture at timed intervals and reactions were stopped by raising the pH of the sample to pH 8.0 by mixing with 1 volume 25 mM Na-phosphate pH 9.5. Gl to G5 indicate the oligogalacturonates with corresponding degree of polymerization. The vertical axis shows the responce of the pulsed amperometric detector and the horizontal axis the elution time. Times of sampling are indicated above the trace.

For a set of 10 samples, the analytical method can be completed within 16 laboratory hours from the time of sample weighing to GC injection. 

When the well depth or diameter is unknown or a water-level measurement is not possible, purging should be carried out by pumping the well for a pre-determined period of time (e.g., at least 30min). Measurement of groundwater parameters should be monitored at intervals during the purging process and at the time of sample collection (Figure 3). 

The goal of a groundwater monitoring plan for pesticides is to produce water samples that are representative of the aquifer under study at the time of sample collection. Materials and methods must be established prior to implementing a monitoring program... 

The times of sample collection for a single paddy survey are set with respect to the application time, such as just before an application, immediately after, and 1, 3, and 7 days post-application, and at longer intervals as appropriate. For an area survey of water and waterway sediments, samples are usually collected periodically over a cultivation season focusing on the application time. 

The 0.05 M K2S04 - tractable (soluble) organic C content of the seven land uses referred to in Sect. 3 is shown in Fig. 1. It is evident that annually-tilled ryegrass and maize and sugarcane have the lowest values suggesting they had the lowest concentrations of soluble substrate C for microbial growth and activity at the time of sampling. 

Area (time of sampling) Depth n Average VOC concentrations (hg C/l) Range (ggC/1) Average Range VOGTOC < (%) ratio (%) ... 

Figure 1 Schematic diagram of a typical FIA peak. S, time of sample introduction T, residence time H, peak height A, area under peak Wb peak width at fixed height fw, wash time.

The time elapsed since separation from the atmosphere is calculated from the ratio of the activity at the time of sampling to the estimated activity in the atmosphere at the time of separation. 

Wells are purged until stable readings are obtained for field chemical parameters including pH, temperature, dissolved oxygen, redox and electrical conductivity. Samples are then collected for a wide variety of chemical parameters. Time sensitive parameters are analyzed within specific holding times. For example, alkalinity and hydrogen sulphide are measured at the time of sampling, iodide... 

On-the-go measurements are accomplished as the equipment moves across the field. GPS location and the duration of time of sampling, measuring, and recording must be accurate to make sure that the data refer to the place where... 

Samples gathered and solutions prepared by laboratory personnel must be properly labeled at the time of sampling or preparation. In addition, a complete record of the sampling or preparation should be maintained. Sound quality assurance practices include a notebook record where one can find the source and concentration of the material used, the identity and concentration of the standard being prepared, the name of the analyst who prepared it, the specific procedure used, the date it was sampled or prepared, and the expiration date for any stored solutions. The reagent label should have a clear connection to the notebook record. A good label includes an ID number that matches the notebook record, the name of the material and its concentration, the date, the name of the analyst, and the expiration date. See Workplace Scene 2.5. 

Measurable levels of endrin have not been found in adipose tissue of the general population (Stanley 1986 Williams et al. 1984). Measurable tissue concentrations of endrin have been observed in cases of acute poisoning. The time of sample collection is critical as endrin residues in tissues decline rapidly after exposure has ceased. 

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