Infrared (IR) spectroscopy has been used for measuring the amount of oil in water for many years. Recent advances in Fourier transform infrared (FTIR) spectrometers allow them to be both sensitive and portable, making onsite analysis of oil in water possible. These new capabilities are ideal for use at oil depots, refi neries, offshore rigs, and environmental remediation sites.
The method detailed in this application note is based on the ASTM D7678-11. This method uses cyclohexane as the solvent, replacing halogenated solvents such as Freon and fluorinated trimer (S-316), which are used in ASTM D3921 and ASTM D7066-04 respectively.
The onsite or routine process optimization oil in water procedure described here is fast, simple, and requires the minimal sample preparation necessary to achieve accurate oil in water results.
The simple five step process summary is:
1. Add 20 mL of cyclohexane to 900 mL of process water and vigorously shake for 2 minutes.
2. Allow layers to separate, add pure water until the top layer (cyclohexane) is near the top of the bottle. Pipette off the top layer into a clean 20 mL vial.
3. Add 2 g sodium sulfate (Na2SO4, drying agent) and 2 g Florisil to the cyclohexane extract and shake vigorously for 2 minutes. Allow the sample to settle for 2 minutes.
4. Filter the ‘cleaned’ cyclohexane with a 0.45 micron nylon syringe fi lter, 17 mm diameter.
5. Add the cleaned and filtered extraction cyclohexane to the DialPath or TumblIR cell (0.25 mL) and initiate the FTIR scanning. The result will be displayed after 30 seconds of scanning.
Measurement with Agilent MicroLab FTIR software
A method is available for the Agilent MicroLab FTIR software, which has the calibration files pre-installed.
This is suitable for use with the Agilent 4500 and 5500 FTIR, each using the DialPath or TumblIR sampling interface with a pathlength of 1000 microns. Like all component methods in the MicroLab FTIR software, this method is designed to walk the user through the complete measurement, presenting the quantitative result at the end. This makes the entire system easy to use for almost any skill level user. After following the sample preparation steps in ASTM D7678, the cyclohexane top layer is removed and analyzed on the unique DialPath or TumblIR liquid cell. The DialPath and TumblIR produce the accuracy of sealed cells in an easy-to-use and easy-to-clean design.