The sample should occupy approximately one-half to three-fourths of the container volume. A solution of 10-percent buffered formalin is added to bring the total volume to within 2 cm of the top of the jar. The jar is then capped and slowly inverted several times to mix the contents of the jar with the formalin solution and to remove any air trapped in the sample matrix. The jar is then opened and topped off with 10-percent buffered formalin. Air in the sample container should be minimized in order to prevent damage to specimens during shipment. As an additional safeguard against leakage, plastic electrical tape is tightly wrapped around the junction between the jar and lid. The outside of the sample container is cleaned and dried, and an appropriate external sample label, indicating the sample-identification code number, is affixed to the outside of the jar with a large piece of transparent packaging tape.
Alcohol- and formalin- resistant inks are specified because contract laboratories will transfer samples fixed in 10-percent buffered formalin to 70-percent ethanol upon receipt. Consequently, study units should ship samples to the contract laboratory as soon as possible. If samples are rich in organic matter and will be held for a week or more before shipping to the contract laboratory, the formalin in the sample needs to be changed to 70-percent ethanol. Waste formalin is regarded as hazardous material and should be disposed of properly (U.S. Environmental Protection Agency, 1981).
The sample-identification code used in the internal (fig. 10) and external (fig. 11) labels is a 16-character sequence that uniquely identifies each sample container. Characters 1-4 are the abbreviation of the study-unit name (table 2) and 5-8 are the collection date (month and year). Characters 9-11 describe the type of sample contained in the sample jar. An "I" indicates an ecological survey benthic invertebrate sample. Other possibilities include algal and fish community samples for ecological surveys ("A" and "F," respectively), bed sediment samples ("S"), and tissue samples ("T"). The subtype codes (characters 10 and 11) listed in figure 11 are specific for the ecological survey benthic invertebrate sample type ("I") and must be interpreted in conjunction with character 9 (that is, letter codes in position 10 and 11 may be repeated among sample types). Character 10 indicates whether the sample is an RTH, a DTH, or a QMH sample. Character 11 identifies the sample component (large-rare, main-body, split, or elutriate). The sample number is represented by characters 12-15 and character 16 represents the bottle sequence code ("A to Z").
The sample-identification code presented in figure 11 indicates the following information about the contents of the jar: they are