How to Handle Hygroscopic Reference Standards?

[syx]

Dear all,
As usual, we always divide raw material (standardized to primary reference standard) to vials in small amount for working standards. The problem is occured when we applied this procedure to hygroscopic material. There will be a bias due to moist absorption during the container opened.
What should we do to prevent this moist absorption?
Thanks in advances.

Regards,
Siswanto

[krickos]

Hi

Those can be tricky

Well we typically use a case by case approach and how hygroscopic the substance is. So if the reference is used purely for system tests like resolution we might settle for storing it in an exicator with a drying agent and recheck water content/assay etc depending on stability data once per year.

Ideally your lab floor is temp and moist controlled in reality one is glad if you have a room or two that are, that could be used for preparations and storage of hygroscopic materials. Still very hygroscopic substance will attract moist as you wont have a "zero moist" envoirement.

So I think you might need to do some investigation/stability tests unless you have such data from another department in your company or the supplier of the reference material.
But in most cases at my work we usually manage with working swiftly and storing hygroscopic references an exicator with an appropiate drying agent and recheck water content/assay etc depending on stability data once per year.

Again, I suggest a case by case approach depending on actual use of reference, how hydroscopic the substance really is and potential stability issues.

[syx]

it is very difficult... the area which have the facility with low humidity is in our production site. indonesia has very high humidity, especially in rainy season like this time. the humidity could reach >80%.
we always store the reference standards and raw materials in desiccator when mentioned in the document or monographs.

[krickos]

Hi

Yes obviously it is a problem, even though we do not have the same consistanly high humidity around my parts, summer rains can cause humidity spikes that in worst case interuptions in KF titrations in facilities with less controled air.
And our production units has been struggling a bit with a new API that R&D initiatly wanted to be kept below 30% RH.

Well the original suggestion stands I suppose, store and transport the reference in desiccator with suiteble drying agent and just keep it out during weighing. In addition you can consider drawing vaccum in the dessicator after opening or flush it with an inert dry gas (Helium/nitrogen) when closing desiccator.

[syx]

thanks, krickos.
is there an equipment like LAF with dry air blower suitable for this purpose in laboratory?

[krickos]

Hi again

Yes I am sure there is but sadly have no link etc to a supplier.

If your company has a microbiology department talk to them, they should know a few things about those as they normally have similar units with sterile/dry air flows for certain applications/work stations.

However that would only be needed if the simpler suggestions does not work.

[syx]

could we save the working standard as solution?

[krickos]

Hi

yes you can save the solution, but you have to back up the shelflife of the solution with stability data, especially if your in the pharma buissness, see robustness ICH Q2 R1.

So esseintially start saving a solution and regulary inject it and perform a trend analysis and document it.

You also need to set the storage condition, usually a refrigerator at 4-8°C will do as long it is controlled regulary.

[Peter Apps]

If you have some money to spend on solving this problem you could look at a glove box or glove bag - Sigma have some in the their catalogue, other suppliers probably have them as well.

Peter

[syx]

hi peter, thanks for the information. I will search the controlled humidity glove box.
alternatively, could we use moist-saturated substance? in this state the substance will reach the equilibrium and the weight tends to be stable. before we prepare the standard solution we need to determine its water content.

[Peter Apps]

Hi Syx

The problem with letting the substance equilibriate with the air is that the water content will fluctuate as the humidity changes, and so you have to do a moisture determination every time you weigh.

Peter

[krickos]

Hi Syx

The problem with letting the substance equilibriate with the air is that the water content will fluctuate as the humidity changes, and so you have to do a moisture determination every time you weigh.

Peter

Additionally the water content will likely not be homogenic, typically it will be higher in the upper layer, in worst case the upper layer will shift in physical property too and form like a "cake" layer. Some hygrscopic substances actually melt when too moist (like 4methylmorpholine-4-oxide).
Personnaly I would avoid going that way unless you have good data and procedures (water determination, homogenisation etc) in place.

[syx]

so far, the humidity controlled glove box is the best option... however, I found it has high price.

[Peter Apps]

Hi Syx

According to my copy of the Sigma catalogue the glove bags are a lot cheaper than the boxes.

Peter

[syx]

glove bags are cheaper, but I am not sure they could control the humidity as low as we need. I see plas-labs glove box that has this function in cole-palmer catalogue.