NASGLP soil sample, <63 µm size fraction
Samples were removed from pails and left to air dry in the Kraft paper bags used for field collection in a warm, dry and uncontaminated storage area. The drying process took from several weeks to several months depending on the type of sample. Sample bag numbers were compared with manifest lists and field data submitted by the sampling crew. Errors or omissions were resolved through discussions with the field crew and project leader.
When dry the samples were moved to the sample preparation laboratory. There were generally two Kraft bags of material from each of the soil horizons or depth intervals sampled at each field site. Soil materials from one type of sample (e.g., A-horizon) were processed together.
The slab-cake method was used for sub sampling. All material for a given sample was poured into a pile on a large clean sheet of Kraft paper. A large spatula and/or rubber mallet was used to break down aggregated materials until there were no pieces larger than 5 mm. The material was then shaped into a uniform elongated pile across the Kraft paper. For the archived sub-sample, stored in plastic containers, two flatbottomed plastic scoops were used to scoop 5 diagonal bands across the elongated pile. This procedure was repeated to obtain the various splits. The radiometric split for laboratory gamma ray spectrometry analysis (LGRS) was wrapped in plastic wrap before being placed in an 8 oz shallow seamless tin to avoid possible trace metal contamination so that the sample could be used for chemical analysis if required. Any excess material from each step was placed in a labelled Ziploc bag and archived.
Two size fractions, a <2 mm and <0.063 mm, were prepared. Before sieving large pebbles were removed and clumps of dried sample were gently disaggregated using a porcelain pestle. The collected sieved material was transferred to a spinning riffler equipped with a 16 tube carousel from which splits of proper size/weight were created. With the 0.063 mm sieve, a coarse sieve (2.0 mm) was used to protect the fine mesh from damage. Between each sample the sieves were wiped down with Kim wipes that had been dampened with distilled water. Also as required, the sieves were cleaned by placing them into an ultrasound bath for 5 minutes, rinsing them with distilled water and drying them in a 105°C oven for 10 to 15 minutes.
Portions of various splits of the <2 mm fraction were ball milled prior to the 4 acid digestion. This was done at a commercial lab using a ceramic mill. Samples were ground until the final grain size was <0.063 mm.
Category: Sample preparation procedures
Keywords corresponding to sample preparation procedures. Taken from the “Sample_Preparation_Methodss_SHARED” database table.
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