How Long Can a UOA Sample Sit On the Shelf ...

[AEHaas]

How long can a used oil analysis sample sit on the shelf before you have to send it in for an analysis? How will shelf life effect the results?

I obtained an engine oil sample, divided it into two samples of equal size. I put them in identical lab supplied containers (plastic bottles). I sent one in immediately after the sampling and put the other on the shelf inside the air conditioned house. I then sent in the second sample for analysis, TWO years later. Here is the result:

Iron __________38_______41
Chromium _____1_______ Nickel _________ Aluminum ______9 ______9
lead __________ 1________1
Copper ________8_______8
Tin ____________5_______4
Silver ________ Titanium ______ Silicon ________ 6_______7
Boron ________ 9_______10
Sodium _______ 9_______10
Potassium _____ Molybdenum ____99______106
Phosphorus ____838_____923
Zinc _________ 963_____1035
Calcium ______2271_____2434
Barium _______ Magnesium ____17_______24
Antimony _____189______198
Vanadium _____ Fuel %Vol _____8.0______3.0
Vis CS 100C __ 8.3______ 8.9
SAE Grade ____20________20
Gly test ______Neg_______Neg
Abs Oxid______93_______100
Abs Nitr_______14________15


Test lab was: youroil.net

aehaas

 

[Quattro Pete]

So, what happened to the fuel in the second sample? It evaporated over time?

 

[hate2work]

Which set of numbers is the two year old sample? I would guess the second set, but before we talk about this, that needs to be clarified.

 

[AEHaas]

Originally Posted By: hate2work

Which set of numbers is the two year old sample? I would guess the second set, but I don't want to assume anything.


The right column is the two year one, sorry.

 

[mongo161]

How did the Boron, Moly, Phosphorus, Zinc and Calcium all increase in strength from sitting on a shelf for 2 years?

WAG....Wild A** Guess would be the equipment or chemists have improved at the lab for oil analysis?

Strange.......

 

[BobFout]

8% fuel

.... 3% fuel...

this come from a lawnmower?

 

[walk23]

not exact but the numbers are similar. Another tech or instrument.

 

[AEHaas]

My thought is that the fuel either evaporated out the top of the jar seal very slowly or even through the plastic itself. Maybe the plastic absorbed the fuel a little. Then the sample volume went down a small amount. Overall the values are around the same or showing a little bit of concentration due to a lower sample volume over time?

In any event, I think it is safe to assume that a sample can probably sit on the shelf safely for a few months at least, without significant changes.

aehaas

 

[Quattro Pete]

Originally Posted By: AEHaas
My thought is that the fuel either evaporated out the top of the jar seal very slowly or even through the plastic itself.

Yup. I've been storing some kerosene in a closed clear plastic container for the past half a year or so... seems like there is significantly less of it in there now, so it must be permeating and evaporating.

 

[JOD]

Originally Posted By: AEHaas
My thought is that the fuel either evaporated out the top of the jar seal very slowly or even through the plastic itself. Maybe the plastic absorbed the fuel a little. Then the sample volume went down a small amount. Overall the values are around the same or showing a little bit of concentration due to a lower sample volume over time?


That would be my guess as well; and when you take that into account, the lab has showed pretty amazing repeatability.

Originally Posted By: AEHaas
In any event, I think it is safe to assume that a sample can probably sit on the shelf safely for a few months at least, without significant changes.

aehaas


Agreed. I can't see any reason this wouldn't be the case, but it's still good to know that reality meets theory. This is also good to know since I have a bunch of old samples I'm getting ready to bulk-mail to have tested! Thanks for doing this and posting your results.

 

[daves87rs]

Originally Posted By: AEHaas
My thought is that the fuel either evaporated out the top of the jar seal very slowly or even through the plastic itself. Maybe the plastic absorbed the fuel a little. Then the sample volume went down a small amount. Overall the values are around the same or showing a little bit of concentration due to a lower sample volume over time?

In any event, I think it is safe to assume that a sample can probably sit on the shelf safely for a few months at least, without significant changes.

aehaas



I'd agree with that...

 

[Patman]

Great information to know! Thanks for doing this!

 

[JHZR2]

Analytical equipment is doing well if it can routinely provide better than 6% RSD. New calibration, new photomultiplier or other conversion device, etc. All can give differences.

For $10 analytical work, those results are the same. If you did some rough math on the concentration change, plus some rsd variability, the numbers will come out.

 

[BigTallV]

Thanks to the OP for doing this, great information to know.

I have also shelved a sample for a few weeks and was wondering if the results would be skewed as a result of significant delay between sampling and analysis.