MethodologyAn accurate laboratory scales is essential for weighing filter paper. These scales are electronic and very sensitive. The scales should be in good working condition and placed on a level surface in the laboratory.
In addition, for the measurement to have meaning, the scales must be set to zero before the first weighing, a procedure known as "tare." Most scientific scales have a "tare" button that will accomplish this. If a scales does not, you must manually set the scales to zero. If you need to weigh more than one piece of filter paper, then tare the scales between each piece to maintain accuracy.
Any identifying marking that needs to be made on the filter paper, such as writing "#1" or a student's name in pencil along the edge, should be done before weighing so that any graphite from the pencil will be included in the original measurement. At times, the procedure also calls for the filter paper to be dried in an oven before weighing.
Equally important is for the person measuring to record the original weight of each piece of filter paper before the filtering process.
After the filtering procedure, each piece of filter paper must be weighed again and the weight recorded. It is imperative to use the same scales as you did to weigh the filter paper before the procedure. Tare the scales before this measurement, as well as between this and any subsequent measurements.
Gravimetric TestingAs an example, consider a process known as gravimetric, or Millipore, testing. Internal machine parts that must be checked for cleanliness to adhere to industry standards are tested this way to assure an objective, scientific determination of presence or absence of contamination.
In this case, the machine is flushed with solvent and the solvent is then filtered through filter paper. The filter paper is weighed before and after the flushing. The difference in weight is the amount of contaminant found inside the machinery.
Gravimetric testing is relatively simple and highly accurate, given that the filter paper is measured properly. Scientists, science students and technical test personnel use filter paper as an important part of experiments involving such things as testing for the amount of solid contaminants in a liquid. Filter paper must be accurately weighed before and after the liquid passes through it. By subtracting the weight recorded before filtering from the weight recorded after filtering, the examiner can determine how much contaminant has been screened from the liquid by the filter paper.