Low level detection of biodiesel in diesel fuel using the Agilent 5500t FTIR spectrometer

The Agilent 5500t FTIR spectrometer provides an easy to use means of measuring biodiesel in diesel. The EN 14078 method comes pre-programmed on the 5500t FTIR spectrometer; this method can determine the amount of biodiesel in the range between 1 % and 10 %. The design is easy to use and provides nearly instant answers.

In some cases, however, even lower levels of detection are required. To meet these needs, Agilent Technologies has modified the EN 14078 method to provide detection down to 0.025 % biodiesel in diesel. The Low Level Biodiesel in Diesel method can quantitatively determine the amount of biodiesel in the range from 0.025 % to 5 % with the same easy to use system.

Experiment

Six standards of biodiesel in diesel were made by successive dilution in the range from 0.0 to 1.5 %. Each concentration was measure using an Agilent 5500t FTIR spectrometer with a 100 µm path length TumblIR transmission cell; 32 scans were collected at 4 cm-1 resolution yielding a 15 second sample measurement time. Measurements were made in triplicate on two separate instruments.

A calibration curve was made using the 1745 cm-1 carbonyl band specified in the EN 14078 method. The EN method specifies peak height but to achieve lower limits of detection the peak area was used in this method.

Results

This figure shows the carbonyl region of the spectrum of the 6 samples tested plus a blank. The lowest concentration of 0.025 % is clearly visible with an absorbance which can be discerned over the blank. The absorbance increases linearly all the way to the highest concentration at 1.5 % biodiesel.

An example of the MicroLab software results screen is shown in this figure

Excerpt from Agilent Technologies Application Note 5990-7803EN