Sample collection and

Several manual and continuous analytical techniques are used to measure SO2 in the atmosphere. The manual techniques involve two-stage sample collection and measurement. Samples are collected by bubbling a known volume of gas through a liquid collection medium. Collection efficiency is dependent on the gas-liquid contact time, bubble size, SO2 concentration, and SO2 solubility in the collection medium. The liquid medium contains chemicals which stabilize SO2 in solution by either complexation or oxidation to a more stable form. Field samples must be handled carefully to prevent losses from exposure to high temperatures. Samples are analyzed at a central laboratory by an appropriate method. 

The continuous methods combine sample collection and the measurement technique in one automated process. The measurement methods used for continuous analyzers include conductometric, colorimetric, coulometric, and amperometric techniques for the determination of SO2 collected in a liquid medium (7). Other continuous methods utilize physicochemical techniques for detection of SO2 in a gas stream. These include flame photometric detection (described earlier) and fluorescence spectroscopy (8). Instruments based on all of these principles are available which meet standard performance specifications. 

Sample collection and work-up artifacts (D) exist, as do impurities and problems with the workers (experience, motivation, turnover, deadlines, and suboptimal training), all of which impact the quality of the obtained results. 

Sample Collection and Enzyme Stability. Serum samples are collected with chemically clean, sterile glassware. Blood is allowed to clot at room temperature, the clot is gently separated from the test tube with an applicator stick, and the blood is centrifuged for 10 minutes at 1,000 g. If the red cells are known to contain the enzymes whose activity is being measured, as in the case of LD, even slightly hemolyzed serums must be discarded. When acid phosphatase is to be measured, the serum should be placed immediately in ice and processed as soon as possible, or it should be acidified by the addition of a small amount of sodium citrate. Anticoagulants such as EDTA, fluoride and oxalate inhibit some serum enzymes. However, heparin activates serum lipoprotein lipase. 

The sampling took place between August 16 and 24, 1983. Most of the 274 samples collected for shipment to contract laboratories were to be analyzed for the purpose of more fully delineating contamination boundaries. Other samples were collected for comparing sample collection and handling techniques. 

OPPTS 860.1500, p. 16, indicates that 3-5 sampling points should be included in the decline trials. For applications close to the normal harvest time, the RAC may be harvested at selected intervals between the time of final application and a normal harvest or slightly delayed harvest. If the application is made long before the normal harvest, then representative plant tissues (including immature RAC) may need to be harvested in order to stretch the harvest period. A single composite sample is all that is required from each selected time point, but two or more samples may be harvested to reduce uncertainty about the actual amount of residue present at each sample time interval. These decline samples should be collected and treated the same as normal RAC samples. The samples should be frozen as soon as possible after collection. The instructions for decline sample collection and handling described in the protocol should be followed closely. 

The design of the survey must address where samples should be collected. There are two parts to the where component of this point. The first where component addresses the geographic location for sample collection, and the second where addresses the type of retail outlet. In other words, products might be collected across the USA, or collection could be confined to one state or geographic region. Products might, for example, be collected from grocery stores, convenience stores, and superettes or only from supermarkets. 

The OPMBS was sponsored by a task force, consisting of major registrants of organophosphate pesticides, and utilized three contract organizations to carry out study management, design and conduct of sample collection, and quality assurance (QA). Four analytical laboratories performed the necessary residue analyses. 

To be successful, an LSMBS requires a clear definition of the responsibilities of each participating individual or group. Preparation of an organization chart may be appropriate, as would its inclusion in the study protocol. Key study participants could include Study Directors, Principal Investigators in the sample collection and analytical phases, sponsor representatives, technical consultants, residue analytical laboratories, and QA specialists. 

Adequate pre-shop provision, thorough training, and strict oversight of the shoppers, as described above, were critical to the successful execution of the sample collection phase of the OPMBS. Each shopper received a kit containing sample labels and containers to hold the sampled commodities, ice packs and packaging materials, labels and boxes for use in shipping the collected commodities, written instructions, and forms well before the scheduled date of collection. The sample coordinator monitored sample collection and advised shoppers of actions to take when problems inevitably arose. 

QA is an important aspect of any technical study. It is particularly crucial in an LSMBS, because several hundred participants, widely separated geographically, are involved. The analytical laboratories typically have standard provisions for QA inspections and reviews, and the field phase management organization is also likely to have standard provisions for QA inspection and review. Shoppers, however, are typically external to study management and analytical laboratories and, thus, are not directly covered by existing QA systems. The study design must include a means by which the field phase, i.e., sample collection and shipment by the shoppers, is made to comply with QA requirements. 

Label sample bottles prior to sample collection and always double check the label prior to collecting a sample. All sample labels should include the study number... 

The need for additional samples to compensate for soil heterogeneity must be reconciled with labor, storage, transportation, analytical, and other constraints that add significantly to study costs. Satisfactory results have been obtained from numerous field studies using three or four treated replications with 5-10 soil cores collected from each replication per sampling period. These replication/repetition numbers strike a reasonable balance between the need for samples sufficient in number to characterize agrochemical dissipation versus financial and logistical constraints associated with sample collection and analysis. 

Each of the five main steps in field conduct (site selection, test plot layout, test substance application, sample collection, and sample storage/handling) is addressed below. 

Proper sample collection and handling are the key to acceptable agrochemical recovery at zero time. The zero-time sample interval is defined as the first sample collected after application. Zero-time soil samples should be collected within 3h after application. Zero-time soil core concentrations, such as those given in Table 3,... 

The modem HPLC system is a very powerful analytical tool that can provide very accurate and precise analytical results. The sample injection volume tends to be a minor source of variation, although fixed-loop detectors must be flushed with many times their volume in sample to attain high precision. Assuming adequate peak resolution, fluorimetric, electrochemical, and UV detectors make it possible to detect impurities to parts per billion and to quantitate impurities to parts per thousand or, in favorable cases, to parts per million. The major sources of error in quantitation are sample collection and preparation. Detector response and details of the choice of chromatographic method may also be sources of error. 

Extrinsic wastes are more functional in nature and are not necessarily inherent to a specific process configuration. These may occur as a result of unit upsets, selection of auxiliary equipment, fugitive leaks, process shutdown, sample collection and handling, solvent selection, or waste handling practices. Extrinsic wastes can be, and often are, reduced readily through administrative controls, additional maintenance or improved maintenance procedures, simple recycling, minor... 

The industry task forces (ARTF, ORETF, and others) are generating model protocols, efficient and accurate methods of sample collection, and analytical methods of appropriate detectability for use in field-worker exposure studies. Subsequently, the task forces are conducting field studies that will generate data for inclusion in several generic databases. It is understood that the databases will be the property of the member companies who have financed the work of the task forces. It is hoped, however, that the task forces will see fit to publish their protocols, methods, study designs, and other useful information in a volume like this one so that other scientists working in this discipline may access the information. 

For analyses in the field, the ionization chamber will usually be connected to an automated module for sample collection and preparation. 

On-line techniques are easily automated, but are more expensive as they require additional valves with associated switching equipment. Off-line methods are rather easier to carry out, but, because of the sample collection and re-injection steps, they are slower and tend... 

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