Field sample conditions

Field Measurement Conditions Those gathering samples must be aware of the temperature, pressure, flamm ihty, and toxic characteristics of the samples for which they will be responsible. This is particularly important when samples are taken from unfamihar locations. Sample ports will have to be blown down to obtain representative samples. Liquid samples will have to be vented. Temperatures above... 

Approximate allowable bearing pressures on sedimentary rock and soils may be taken from Table 2-31 [1 and 37]. Where questionable surface and subsurface soil conditions exist allowable bearing pressures can be determined with the aid of field sampling, field tests (both surface and subsurface through borings), and laboratory tests. 

However, some of the conditions in the alpha ion source do differ significantly from those in conventional ion-molecule sources. The most important difference is caused by the absence of an electric field and the mode of sampling. Positive and negative particles are carried out by mass flow. Therefore it is necessary to understand the reaction and sampling conditions at least qualitatively. For this reason we are devoting this section to a description of the conditions and a discussion of some experiments which were done specifically to obtain a better understanding of the sample prehistory. 

Repeatability is defined as precision under conditions where independent test results are obtained with the same method on identical test material in the same laboratory by the same operator using the same equipment within short intervals of time. The replicate analytical portion for testing can be prepared from a common field sample containing incurred residues. This approach is used extremely rarely. Normally, repeatability is estimated by the relative standard deviation ofrecoveries, which should be lower than 20% per commodity and fortification levels according to SANCO/825/00. In justified cases, higher variability can be accepted. 

A system of record keeping must be used which eliminates any risk of confusing the samples. As a rule, samples should be recorded immediately after their arrival and, especially in the case of nonfrozen field samples, prior to preparation for analysis. A record should also be kept of the condition of the samples upon arrival at the receiving laboratory and of any packaging or labeling defects. 

Field fortification samples may be shipped with field samples but not with controls. Controls should be kept separate from treated samples and may be placed in a separate container within the container used to ship the treated samples. Samples shipped overnight should be shipped in coolers with sufficient dry-ice to maintain the samples in a frozen state for at least 48 h in case a delay in shipment of the samples occurs. Samples should not all be shipped together in one shipment but should be split to ensure that all the samples would not be lost at the same time. A chain of custody form should accompany each separate cooler or shipping box and should list each sample that is in each box. The receiver of the shipment should fill out the chain of custody form and record the conditions of the samples upon arrival at the analytical laboratory indicating whether or not the samples were frozen, ambient, or otherwise upon arrival and if the sample integrity had been compromised during shipping. 

Field forms may be used to document the movement of the field samples from the field to the analytical laboratory. Chain of custody forms may document the sample number, when it was sampled, when it was shipped, where it was being shipped from, and where it was going. The chain of custody form may also contain information on when the sample was received, by whom it was received, and the condition of the samples upon arrival at the laboratory. The chain of custody form also documents that the sample itself was taken. 

Under field exposure conditions, it is recommended to measure PA herbicides in 24-hr urine samples collected starting at the end of the work-shift. Spot samples collected at the end of exposure or the following morning can be used when a 24-hr urine collection is impractical. In this case, the concentration of the compounds should be normalized to creatinine concentration or adjusted for specific gravity. 

The most widely accepted method of evaluating the accuracy and precision of an analytical procedure is to sample known concentrations of contaminants in the atmosphere. Thus an important aspect of analytical method development is the generation of test atmospheres that simulate the conditions (i.e., concentration range, humidity, temperature and interferences) found during the field sampling. 

The many worst-case assumptions built into cancer risk assessments are there because of policy decisions, not because of scientific ones, and they confuse attempts to allocate money effectively for public health. For example, EPA estimates of synthetic pesticide residues in the diet have used the theoretical maximum human residue that is anticipated under the most severe field application conditions, which is often a large overestimate compared to the measured residues in food. Despite the EPA s estimated high risks from exposures to several pesticides, the U.S. Food and Drug Administration detected no residues of those pesticides in the food samples in its Total Diet Study.59... 

Field Samples. Each field sample is packed in an appropriate container and labeled. In addition to the harvest information listed above, information on the history of the sample (storage conditions and intervals) near the field location and on shipment to the laboratory is generated. 

If a temperature blank is not enclosed in the cooler with samples, the laboratory personnel will randomly measure the temperature in any part of the cooler, and this temperature may or may not accurately represent the true condition. Temperature blanks, being simulated samples, provide an accurate measurement of field sample temperature upon arrival to the laboratory. 

Preparation and analytical batches must be clearly identified with a unique number in laboratory bench sheets, notebooks, and computer systems. The same applies to QC check samples associated with each batch. During data quality assessment, the data user will determine the quality of the field sample data based in the results of the batch QC check samples that are part of the preparation and analytical batches. The data user will examine batch QC check samples first and, if they are acceptable, will proceed to individual sample QC checks. A complete examination of these QC checks will enable the data user to evaluate the quantitative DQIs (accuracy and precision). A combination of acceptable batch QC checks and individual QC checks makes the data valid on condition that the qualitative DQIs (representativeness and comparability) are also acceptable. 

Gently rinsed roots. For another set of 12 root samples, following incubation at field moist conditions, the roots were kept in the incubation jars and the gas was displaced by 3 changes of water in immediate succession. This was done to determine if wetting alone or both wetting and squeezing were required to stimulate sulfur gas emissions. 

Quantitative analysis of field samples must, of course, be performed under identical conditions to those used in analyzing the standards Prior to the actual analysis, a powder pattern of a bulk sample such as rafter dust, an area sample, or a heavily loaded filter is obtained to determine information about the matrix. This information may necessitate some modification to the analytical method, such as... 

---