How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, GC

raghu_1968

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#1
Hi!

Can any one help me on how to calculate and apply measurement uncertainty calculations in chemical analysis such as HPLC, GC analysis.

Regards / Raghu
 
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Coury Ferguson

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#2
Re: How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, G

Does anyone have suggestions?
 
Z

zamclachia

#3
Re: How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, G

The traditional method is long winded, time consuming etc etc.:confused:
Here is how we are doing it.
Run a reproducibility experiment over a minimum of 10 days. ( Same lab, same equipment, if possible different analysts, different reagents - Include as much variability as possible).
At the end of the experiment, determine the SD(Reproducibility). To get your measurement uncertainty @ 95% confidence, multiply the SD(R) by a coverage factor of 2. For 99% confidence, multiply by a coverage factor of 3.

Use this as your initial MU. Carry on with the Reproducibility experiment over time and review the MU periodically based on the information you get.

We use this approach for all our chemistry and micro analysis in the lab.

An alternative (to determine a starting point) is to use a certified reference material. Run a minimum of six replicates and follow the latest EURACHEM guide. (Drop me a mail if you want the calculations in EXCEL format)
 
D

DsqrdDGD909

#5
Re: How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, G

Hi!

Can any one help me on how to calculate and apply measurement uncertainty calculations in chemical analysis such as HPLC, GC analysis.

Regards / Raghu
I would look at two ways.
One - are the analyses a standard method?
Methods typically have some discussion of measurement uncertainty.

Two - instrumentation. Do the user manuals for these instruments have a discussion of MU?

Three - the old laborious way. Take a look at the method as a whole and estimate/calculate all of the sub-steps: weighing, pipetting, integration uncertainty...etc.
 
V

Voodoo Queen

#6
Re: How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, G

The traditional method is long winded, time consuming etc etc.:confused:
Here is how we are doing it.
Run a reproducibility experiment over a minimum of 10 days. ( Same lab, same equipment, if possible different analysts, different reagents - Include as much variability as possible).
At the end of the experiment, determine the SD(Reproducibility). To get your measurement uncertainty @ 95% confidence, multiply the SD(R) by a coverage factor of 2. For 99% confidence, multiply by a coverage factor of 3.

Use this as your initial MU. Carry on with the Reproducibility experiment over time and review the MU periodically based on the information you get.

We use this approach for all our chemistry and micro analysis in the lab.

An alternative (to determine a starting point) is to use a certified reference material. Run a minimum of six replicates and follow the latest EURACHEM guide. (Drop me a mail if you want the calculations in EXCEL format)
Use your method validation/verification data to start with and then continue on with QC data (if any). Calculate the MU and check if everything is still within your established limits - this should give you a good picture if your method is still operating correctly. This is what our auditor suggested to us, at least.
 

raghu_1968

Involved In Discussions
#7
Re: How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, G

Zamclachia,

Thanks.

It will be helpful if i get the excel sheet to get some idea on this.

Regards / Raghu





 
Z

zamclachia

#8
Re: How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, G

Here is the excel file. You are welcome to check the calculations, I am sure they are correct. If you need help, give a shout.

Hight of irony;

40 people die of swine flu and half the word wears a mask.

Million plus die of HIV - Very few want to wear a condom. :confused:
 

Attachments

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#9
Re: How to calculate and apply Measurement Uncertainty in Chemical Analysis - HPLC, G

You might also want to look at the Eurochem document on uncertainty analysis. A Google search should turn it up.
 
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