Sampling, subsampling, and pipeting two-phase or three-phase samples may introduce
serious errors. Make and keep such samples homogeneous during transfer. Use special handling
to insure sample integrity when subsampling. Mix small samples with a magnetic stirrer. If
suspended solids are present, pipet with wide-bore pipets. If part of a sample adheres to the
sample container, consider this in evaluating and reporting results. Some samples dry with the
formation of a crust that prevents water evaporation; special handling is required to deal with
this. Avoid using a magnetic stirrer with samples containing magnetic particles.
The temperature at which the residue is dried has an important bearing on results, because
weight losses due to volatilization of organic matter, mechanically occluded water, water of
crystallization, and gases from heat-induced chemical decomposition, as well as weight gains
due to oxidation, depend on temperature and time of heating. Each sample requires close
attention to desiccation after drying. Minimize opening desiccator because moist air enters.
Some samples may be stronger desiccants than those used in the desiccator and may take on
water.
Sampling, subsampling, and pipeting two-phase or three-phase samples may introduce
serious errors. Make and keep such samples homogeneous during transfer. Use special handling
to insure sample integrity when subsampling. Mix small samples with a magnetic stirrer. If
suspended solids are present, pipet with wide-bore pipets. If part of a sample adheres to the
sample container, consider this in evaluating and reporting results. Some samples dry with the
formation of a crust that prevents water evaporation; special handling is required to deal with
this. Avoid using a magnetic stirrer with samples containing magnetic particles.
The temperature at which the residue is dried has an important bearing on results, because
weight losses due to volatilization of organic matter, mechanically occluded water, water of
crystallization, and gases from heat-induced chemical decomposition, as well as weight gains
due to oxidation, depend on temperature and time of heating. Each sample requires close
attention to desiccation after drying. Minimize opening desiccator because moist air enters.
Some samples may be stronger desiccants than those used in the desiccator and may take on
water.
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