[FrancisZ]

Does atmospheric moisture affect the weight of borosilicate glassware?
Any references or advice would be much appreciated. Many thanks in advance from a humble biologist!

Background: I am collecting wood extracts (0.0050g to 0.4000g) in borosilicate glass Petri dishes.

The method that I have requires that empty Petri dishes be oven dried at 103degC for 2 hours with lids off. Lids are placed on before dishes are removed from oven. Petri dishes with lids on are then transferred to a desiccator containing silica and phosphorous pentoxide for 1.5 hours before weighing.

[1] Would humidity fluctuations (eg at different times of the year; dry or rainy) affect the weights if they were measured in room conditions?
Dishes containing extracts need to be oven dried as some of the components of the extracts are hygroscopic. Presumably they would be protected by the lid, so the main concern would be how much atmospheric moisture would ‘stick’ to the glass?

[1a] Do empty Petri dishes really need to go into the desiccator, or can they cool at room conditions?

[2] Would precision be better if weights (0.0050g to 0.4000g) were measured in a controlled environment room?

[Stepan]

In my work I see 1-3mg weight change between oven-dry and ambient-dry glassware.