Function Of The Evaporation Trap; Description Of The 5 Ml Sample Cup - AND BM Series Instruction Manual

1-4 Function of the Evaporation Trap

In the pipette accuracy test using the gravimetric method, to obtain the mass of the test liquid, distilled
water is dispensed from the pipette into the sample cup installed on the balance. The obtained value,
however, is generally smaller due to evaporation loss of the test liquid. To prevent evaporation of the test
liquid, the evaporation trap is used. The ISO 8655 standard recommends that the humidity of the
measurement environment be greater than 50% RH.
Water is poured into the groove of the evaporation trap. This helps to maintain the humidity inside
the evaporation trap high and reduces evaporation. Using the evaporation trap reduces the
evaporation of the test liquid, compared with the value when the evaporation trap is not used. This
yields a measurement environment where there is no need to consider measurement errors due to
evaporation loss of the test liquid.
Another function of the evaporation trap is one as a breeze break, to prevent drafts in the
measurement environment from influencing the weighing operation and enable a stable weighing.
The evaporation trap is designed for an easy dispensing of the test liquid. The upper part has a
sloped surface so that the pipette can be inserted from obliquely above.

1-5 Description of the 5 mL Sample Cup

When dispensing a test liquid from the pipette, to perform an accuracy test of the volume of a pipette, a
possible cause of errors is water droplets remaining on the edge of the pipette tip. Using the
water-absorbent sheet in the sample cup prevents this and increases the accuracy of a test.
As shown in the illustration below, a water-absorbent sheet is rolled into a cylinder and is placed
along the inner wall of the sample cup.
By dispensing the test liquid with the edge of the pipette tip touching the sheet, the sheet will absorb
any droplet which may otherwise remain on the edge of the tip. Thus all the test liquid will be
dispensed into the sample cup.
The water-absorbent sheets are made of a RoHS-compliant material for safety.
The sheet, once used, can be cleaned and used repetitively.
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