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The choice of materials used shall be considered with respect to the parameter being sampled. <br /> The factors to be considered are: <br /> • Negative Contamination — The potential for the measured analyte concentration to be <br /> artificially low because of losses that are due to precipitation, volatilization, or absorption. <br /> • Positive Contamination — The potential for the measured analyte to be artificially high <br /> because of leaching or introduction of foreign matter into the sample by particle fallout or <br /> gaseous air contaminants. <br /> • Cross-contamination —The introduction of part of one sample into a second sample. <br /> B.6.5. Equipment Selection Considerations <br /> Because each sampling situation is unique, the sampling technician may have to modify <br /> equipment and applications to ensure that a representative sample is collected and to maintain <br /> the sample's physical and chemical integrity. No one particular device will fit every situation. <br /> The sampling technician shall understand the various sampling devices and their advantages <br /> and disadvantages to effectively use them to collect samples. The following items shall be <br /> considered when selecting a sampling device: <br /> • Potential impact of the device on sample integrity <br /> • Method of sample delivery <br /> • Flow controllability <br /> • Depth of sampling interval <br /> • Ease of operation, cleaning, and maintenance <br /> • Reliability and durability <br /> • Portability of the device <br /> • Initial cost and operational cost <br /> There are four basic types of sampling devices: <br /> • Grab mechanisms <br /> • Suction-lift mechanisms (not currently used by NS) <br /> • Positive-displacement mechanisms <br /> • Submersible pumps <br /> A discussion of the uses, advantages, and disadvantages of these devices follows. <br /> B.6.6. Grab Mechanisms <br /> Grab mechanisms consist of bailers and dip-type samplers. These devices are the oldest and <br /> simplest for collection of liquid samples. They can be made of various materials and can be <br /> used to collect liquid samples from almost any source. Table 5 presents the advantages and <br /> disadvantages of a grab-type mechanism. <br /> Daub &Associates, Inc. Page B-14 Natural Soda LLC 2022 SAP <br />