Spectroscopy Reporting Limit Validation

Discussions about GC and other "gas phase" separation techniques.

4 posts Page 1 of 1
Hello,

Hoping to find someone with extensive experience in FTIR method development to give me an expert opinion on this question:

Can you verify a quantitation limit in FTIR analysis without specifically having a standard at that reporting limit? Or would you only accept a quantitation limit (or reporting limit) if you had specifically analyzed a standard at that concentration?

I don’t want to get too far into it, but I used two methods from ISO 12828-1 “Validation Method for Fire Gas Analysis”. Main method 1 – Determination of LoD and LoQ from matrix data from blank samples, and Main method 2 – Determination of LoD and LoQ from the linearity of calibration data.

There is also a main method 3 – checking a given or prescribed quantification limit, but it is difficult to obtain gas standards at the concentrations that I calculated from main method 1 and 2.

My understanding was that since FTIR measures the entire spectral range during each scan, even “blank” analysis would yield a signal and therefore having a standard specifically at the desired reporting limit was not strictly necessary, or is this incorrect? Would you approve a method where the reporting limit was calculated using the main methods 1 and 2 above, but the limits had not been explicitly tested with a standard at that concentration, or would you not use a method without having tested a reporting limit specifically? Note the reporting limit is well below the specification limits for my desired commodity specifications. Those limits have been verified with a standard at those limits.
No, you should be using a 'pure' standard. In my case it was PDMS (Polydimethyl Siloxine) and I was developing a cleaning validation analytical method for 'siloxane' groups at 1260 cm-1. It had a 'discrete' wavelength and no interferences.

But there are compounds like diatomic molecules that have no or little IR spectra (Oxygen or Nitrogen).

Remember, weak radiation therefore you get a weak response. So weak in fact my LOQ was 25 ppm!

You should look around for a suitable standard or something chemically similar.
HPLC chemist wrote:
No, you should be using a 'pure' standard. In my case it was PDMS (Polydimethyl Siloxine) and I was developing a cleaning validation analytical method for 'siloxane' groups at 1260 cm-1. It had a 'discrete' wavelength and no interferences.

But there are compounds like diatomic molecules that have no or little IR spectra (Oxygen or Nitrogen).

Remember, weak radiation therefore you get a weak response. So weak in fact my LOQ was 25 ppm!

You should look around for a suitable standard or something chemically similar.


Thank you for the response.

Just for clarification; lets use take carbon monoxide, which has a straight forward IR spec and few interferences in my sample matrix. My specification limit to consider a sample as "passing" is <5 ppm. So I have a calibration curve developed using standards of 1, 3, 5, 7, and 10 ppm as well as blank scans such that my calibrated range is "0" to 10 ppm. I also have a large data set of "blank" results. My arbitrarily calculated LoQ using the main method 2 (my calibration curve data) is say 0.1 ppm, and my arbitrarily calculated LoQ using my blank determination data (main method 2) is 0.2 ppm. This 0.2 ppm represents my blank scan average + 10 times my standard deviation of the blank scan data. You would not accept this 0.2 ppm LoQ as valid until a validation study was run using a standard at 0.2 ppm?
You have already performed a validation study using a 0.2 ppm study. It is not a validation study until the protocol is signed so you may have to repeat it. Therefore, I consider it a pre-validation study. You know this method will work!

But if nobody else tells you, 'Good Job'.
4 posts Page 1 of 1

Who is online

In total there are 12 users online :: 0 registered, 0 hidden and 12 guests (based on users active over the past 5 minutes)
Most users ever online was 599 on Tue Sep 18, 2018 9:27 am

Users browsing this forum: No registered users and 12 guests

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry