Very High Standard Deviation in Excitation Emission Matrix Measurement

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SUMMARY

The discussion centers on the high standard deviations observed in Excitation-Emission Spectra measurements of phenolic compounds in olive oil, specifically within the emission range of 290-350nm. The method employed involves diluting 0.05g of olive oil in 25ml of cyclohexane, with measurements taken using both a Shimadzu RF-6000 and an Aqualog spectrometer. Despite rigorous calibration and validity tests indicating accurate device performance, standard deviations of 13-20% persist, raising concerns about potential issues related to Rayleigh scattering or measurement settings.

PREREQUISITES
  • Understanding of Excitation-Emission Spectroscopy
  • Familiarity with Shimadzu RF-6000 and Aqualog spectrometers
  • Knowledge of standard deviation calculations in analytical chemistry
  • Basic principles of solvent effects in spectroscopic measurements
NEXT STEPS
  • Investigate the impact of Rayleigh scattering on spectroscopic measurements
  • Learn about optimizing settings for Shimadzu RF-6000 for low concentration samples
  • Research methods for reducing standard deviation in spectroscopic analysis
  • Explore literature on phenolic compound measurement techniques in olive oil
USEFUL FOR

This discussion is beneficial for analytical chemists, food scientists, and researchers focused on spectroscopic analysis of phenolic compounds in food products, particularly those working with olive oil and related matrices.

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.
 
Last edited:
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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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