Very High Standard Deviation in Excitation Emission Matrix Measurement

AI Thread Summary
High standard deviations (13-20%) in excitation-emission spectra for phenolic compounds in olive oil are reported, despite using a method that involves diluting 0.05g of olive oil in 25ml of cyclohexane. This approach aims to maintain linearity for absorbance measurements and correct for filter effects. Measurements were taken from five equivalent samples, each measured five times, using both a Shimadzu RF-6000 and an Aqualog spectrometer, with settings optimized for sensitivity and bandwidth. The high variability persists even after confirming the accuracy of the devices through various validity and calibration tests. Potential causes such as solvent issues, contamination, scattering, and photodecay have been ruled out. The discussion raises questions about the influence of Rayleigh scattering and the appropriateness of the current settings, while also noting the difficulty in obtaining viable spectra at low concentrations. Input from others in the field is sought, particularly regarding signal-to-noise ratio assessments and blank analysis.
JonasFnr
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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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