PEFTEC 2019 - Abstract

Abstract Title: CFC-free oil and grease measurement of aqueous samples using IR spectroscopy
Abstract Type: Oral
Session Choice: Environmental Monitoring of Water
Presenter Name: Dr Christoph Wagner
Company/Organisation: eralytics GmbH
Country: Austria

Abstract Information :

Measuring oil-in-water can be achieved by various methods ranging from gravimetry to infrared based techniques to gas chromatography. The preferred infrared technique from the past using an FTIR spectrometer measuring the CH stretching vibrations is nowadays withdrawn around the world. This is due to the fact that it needed CFC solvents for the extraction procedure which harm the ozone layer. There are two possible ways to circumvent the CFC solvent and still being able to run an IR measurement. First of all the solvent can be evaporated and the dried extract is then measured. This technique, however, loses all light ends that evaporate together with the solvent. The second approach uses a cyclic alkane - typically cyclohexane - for the extraction process. The measurement itself is then performed in the spectral region were only the CH3 deformation vibration causes a signal in the spectrum. Cyclohexane contains only CH2 groups and is therefore transparent in that spectral region. The advantage here is that no time consuming evaporation process is needed and no light ends are lost.

In this paper we present data from water samples spiked with different API gravity crude oils. The samples were extracted using cyclohexane. The measurement of the extracts was then done using a newly developed measurement setup based on an optical filter in the mid-IR spectral region. Data for total oil and grease (TOG) and total petroleum hydrocarbon (TPH) values were recorded. TOG denominates everything that was extracted by cyclohexane whereas TPH values lack polar substances as they are removed by a filtration step using Florisil™ prior to the measurement.

We present sample extraction efficiencies, sample recoveries, method detection limits for TOG and TPH. Repeated measurements at every concentration step were performed to evaluate the instruments repeatability for TOG and TPH as well. We also compare the results of this optical filter based measurement technique to results obtain according to ASTM D7678.