Very High Standard Deviation in Excitation Emission Matrix Measurement

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Discussion Overview

The discussion revolves around the high standard deviations observed in Excitation-Emission Spectra measurements of phenolic compounds in olive oil, specifically within the emission range of 290-350nm. Participants explore potential causes for the variability in measurements and seek insights into the measurement methodology and settings.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant describes their method of preparing samples and measuring, noting high standard deviations (13-20%) despite validity and calibration tests indicating accurate device performance.
  • Another participant inquires about the signal-to-noise (S/N) ratio, suggesting it may be relevant to the discussion.
  • A subsequent reply states that the S/N ratio is normal according to the device manufacturer, referencing the water Raman peak as a benchmark.
  • Another participant asks if a blank has been analyzed, implying that this could be a factor in understanding the high variability.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the cause of the high standard deviations, and multiple viewpoints regarding potential contributing factors remain. The discussion includes inquiries and suggestions, but no definitive solutions have been established.

Contextual Notes

Limitations include the lack of exploration into the effects of blank analysis and the potential influence of measurement settings on the results. The discussion does not resolve whether the observed variability is due to the measurement technique or other factors.

Who May Find This Useful

Researchers and practitioners involved in spectroscopy, particularly those working with phenolic compounds or similar measurement challenges in analytical chemistry.

JonasFnr
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TL;DR
I get very high standard deviations for phenolic compounds in EEM measurements of olive oil. Any thoughts/input highly appreciated.
Hi,

I obtain really high standard deviations in Excitation-Emission Spectra mainly for the phenolic compounds in olive oil (Em: 290-350nm).

Method:
I weigh 0.05g of olive oil and dilute it up to 25ml with cyclohexane to remain in the range of linearity for absorbance measurements to correct for filter effects.
To estimate the standard deviation of measurements, I made five equivalent samples and measured each five times.

Both within and between the samples the s.d. is very high in this area (13-20%).
All validity and calibration tests I have tried thus far seem to indicate that the device is working accurately.

I get those results both with a Shimadzu RF-6000 and an Aqualog (which already corrects for filter effects) from 200-800nm.

Settings for the Shimadzu: Datainterval: 2nm each, Scanspeed 6000nm/min, Ex. Bandwith 5nm, Em. Bandwith 3nm, Sensitivity: High.

I don't think the solvent, contamination, scattering, runtime-dependent spectrometer performance or photodecay of the phenols could explain this.
Is the proximity to the rayleigh scattering or are the settings an issue here?
I couldn't obtain a viable spectrum with any other settings for such low concentrations though, which I need to correct for filter effects.

I couldn't find anything on this in the literature, so any thoughts or input would be HIGHLY appreciated.

Thank you and kind regards.
 
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What do you estimate for S/N?
 
S/N ratio is in the normal range according to the device manufacturer (water raman peak).
 
Have you analyzed a blank?
 

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