Stability of materials

As accredited pt provider iis has investigated and evaluated the stability of the packed materials that are used in the proficiency tests. This has been done in 3-4 months during investigations at slightly elevated temperatures (30 degrees Celsius) to simulate worth case transport conditions. All materials did proof to be stable enough for this period and thus no significant changes are expected during the one month period of a regular proficiency test.

In april 2006 there has been extended proof of the stability of the packed materials. Since 1996 iis did produce several reference materials. These reference materials were given a shelf life of only a limited period of one year as long term stability was unknown. In order to keep the stock available for sale, a limited number of critical and sensitive parameters were tested on the materials on regular intervals. First each six months, then each 12 months and later each 24 months. Now, after nine years, all reference materials produced appear to be stable as expected, except the MTBE reference material. After investigation it appeared that tis latter material contained dissolved gasses that evaporated very slowly through the plastic cap of the bottles and thus the density of the MTBE slowly increased. An example of part of such a stability evaluation is shown in below graph of the testing of the density and the distillation parameters of Jet Fuel A1 reference material RM_JF011097.