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several different sized metal sieves, cups to hold the samples.
CAUTION: All test equipment must be kept clean to prevent
contamination of samples.
5.2 Cleaning Your Equipment
5.2.1 Sample Preparation
Prior to analysis, the material should be dry and well homogenized. Ideally, the
entire sample should be dried to constant weight, sifted to remove gravel and debris,
and ground or milled to a fine powder.
Dry the sample if it is moist and cohesive. The sample can be dried in any of
several ways. Choose one of the following:
« Oven dry the sample for approximately 2 hours at 150° C, until the sample
reaches a constant weight. Note: Oven drying is inappropriate when volatile
compounds may be present in the sample. For example, lead present as
tetraethyl lead would be driven off by the heat of drying. Some forms of
mercury and arsenic are volatile. Air drying will preserve more of these
volatile substances.
« Air dry the sample overnight at room temperature in a shallow pan.
« Stir gently and warm the sample in a pan over a hot plate or burner.
5.2.2 Coning and Quartering
You may need to divide your sample at various times during preparation. Coning
and quartering is a method for dividing the sample into homogenous quarters.
« Pour the dry material slowly and carefully onto a flat sheet or pan, forming a
symmetrical cone. Divide the cone into equal piles using a flat thin-bladed
tool, such as a knife or ruler. Divide these in half again.
« Now you have four samples, each one-quarter the size of the original and
each more homogenous than the original.
« Grind the sample to break up dirt clods and/or paint chips.
WARNING! Grinding and sifting dried samples produces dust. Even
clean soil contains silica, which may be hazardous
when airborne. Prepare all samples in a ventilated area;
wear a mask, gloves, and an apron; and spread a drop
cloth.
Sift using the #10 (2mm) mesh and separate out the larger pieces (stones, organic
matter, metallic objects, etc. Examine the larger particles by eye but do not include in
the sample. Grind the sample again so its particles will be finer and more homogenous.
Use mortar and pestle, or an electrically powered grinding mill. Sift at least 10 grams
