Absorption measurements were performed using a UVvisible spectrophotometer (Agilent Technologies Cary 60). Temperature was maintained at 20 °C with Peltier accessory. Quartz fluorescence cuvettes were used to collect absorbance spectra for solutions of 1mL sample volume. E-liquid samples and pure PG:VG continuing SCs were diluted in EtOH and were background subtracted. Absorbance recorded between 800-200nm with a scan rate of 600nm/min and 1nm intervals between datapoints.