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Lock-In Amplifier + VODS Sample Results

Riboflavin Fluorescence

Riboflavin is one of a number of B group vitamins. The compound strongly absorbs blue light and fluoresces in the yellow-green part of the spectrum.

Riboflavin (Vitamin B2) for this experiment was obtained by dissolving a multi-vitamin tablet in a small quantity of water and decanting the solution, then diluting to obtain the desired concentration (based on the stated mass of riboflavin in the tablet).

At left is the calibration curve obtained using the LIA-ODS system at a fixed gain of 40 and with a VODS having a blue source LED and a 900 TSL257 detector. A blue cut-off filter was placed in front of the detector for these measurements.

Although multi-vitamin tablets usually contain several B group vitamins one can reasonably assume that the response seen here is primarily from the B2 molecule. The results demonstrate that the instrument can easily detect a few tens of ppb of riboflavin.

Riboflavin Fluorescence @ 100 ppb

This is the same experiment as the one above, but now at fixed riboflavin concentration and testing the on-board gain control.

A slight bend-over in the output response is evident at the highest gain settings.

Quinine Fluorescence

Quinine has a demonstrated anti-malarial action and the compound is present in tonic water at about 70 parts-per-million.

A 100-fold dilution of a tonic water sample would therefore result in a quinine concentration of ~ 700 ppb.

The calibration curve recorded opposite was measured using a VODS fitted with a 370 nm LED and a TSL257 light-to-voltage converter for the detector. The voltage gain was set to 200x for these measurements.

In these results the signal rides on a pedestal due to the significant background fluorescence from the plastic cuvette used in the experiment.

Quinine Fluorescence

The data here shows the fluorescence signal for the 1ppm quinine sample as a function of the voltage gain setting - again some curvature is observed.