5 Jun 2017

Using FTIR spectroscopy to measure hydrocarbon pollution in water

According to the World Health Organization (WHO) and UNICEF’s 2015 Progress on Sanitation and Drinking Water report almost 700 million people around the world don’t have access to clean drinking water [1].

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Poor water quality is beginning to return to the developed world too. The strain of population growth, intensified agricultural practices and continued industrial expansion have are all contributing to rising contamination levels in water supplies. The Pearl liquid FTIR spectroscopy spectrometer transmission accessory is ideal for such liquid measurement.

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Chlorinated Aromatic Hydrocarbons (CHCs) Pollute Water Supplies

Much of this contamination comes from chlorinated aliphatic hydrocarbons and chlorinated aromatic hydrocarbons (CHCs). These contaminants are toxic and carcinogenic, and are usually found in environmental water samples.

CHCs are used extensively in a wide range of industrial processes, as chemical extractants, paint strippers and in the manufacturing of adhesives, oils, solvents lubricants and more. Despite growing opposition to the use of CHCs and the development of viable, eco-friendly alternatives CHC use remains widespread.

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They pose a serious threat to the ecosystem and to human health. Long chain CHCs are particularly harmful, due to their persistence in water, and their tendency to form films on the water’s surface. These films can prevent oxygen from entering the water, resulting in the suffocation of aquatic life.

Measuring the pollution levels in water, as a means of controlling CHC levels, is critical to protecting human and environmental health.  Governments around the world are looking for quick, reliable, and affordable methods to measure water pollution levels.

Developing A Method to Analyze Hydrocarbons in Water

When analyzing CHC levels in water, the challenge is to use a suitable liquid-liquid extraction method, to remove the water itself which would interfere with the measurement, with an environmentally friendly solvent. This makes it possible to quantitate hydrocarbons rapidly and safely.

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Fourier Transform Infrared Spectroscopy (FTIR) is an established technique for hydrocarbon ID and quantification. Each different CHC has its own infrared fingerprint which can be identified using infrared spectroscopy, once identified the amount of infrared absorption can be used to determine the concentration of each CHC in a sample.

FTIR spectroscopy was historically used to measure the oil and grease leached into water during offshore oil operations. However, the halogenated solvents that the FTIR method used were sources of ozone-depleting chemicals, and so they were considered hazardous. This led to a temporary decrease in the use of FTIR in environmental water analysis for hydrocarbons.

However, the benefits of FTIR based methods such as its sensitivity, simplicity and non-destructive nature led researchers to develop new, environmentally friendly FTIR based methods of CHC measurement which use non-halogenated solvents.  

Choosing the correct FTIR model for hydrocarbon analysis remains to be challenging. The ideal system should have a small footprint, so it’s not restricted to work in research labs. It should offer fast measurements, as well as a high accuracy and repeatability. The model should be easy to use and offer several pathlengths for added versatility.

Case Study: using Infrared Spectroscopy to Measure Hydrocarbon Levels

Attenuated total reflectance (ATR) FTIR has been used to study CHCs in water [2]. A variety of CHCs were discriminated against and detected, including monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, trichloroethylene, perchloroethylene, and chloroform. The authors conclude that ATR-FTIR has significant potential as a future method of measuring CHC levels in contaminated water.

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This research demonstrated that FTIR is capable of detecting CHCs in concentrations as low as parts-per-billion (ppb) and that all the CHCs present can be measured in one single step.

Infrared Accessories for Effortless Liquid Analysis

The Pearl™ liquid FTIR transmission spectrometer accessory from Specac is a high specification liquid transmission accessory, ideal for measuring hydrocarbon pollutants in water. It uses transmission, not ATR, which is mentioned above. Transmission offers a higher spectral resolution than ATR.

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It’s a great choice for any application that requires liquid analysis as it offers a faster, more accurate and more repeatable analysis than traditional liquid cells, and it is also extremely easy to use. The Pearl™ liquid analyser can be fitted with ZnSe or CaF2 windows, which can be interchanged in seconds.

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The Pearl’s liquid transmission Oyster™ cells are available in five pathlengths; 50μm, 100μm, 200μm, 500μm and 1,000μm, which allows for the simple calculation of sample concentrations without the need for dilutions or a calibration curve.

If you want more information on using the Pearl liquid FTIR transmission cell for water/oil analysis, or any other application, get in touch for a price and demonstration.

References

[1] W. H. Organization Unicef et al., “Progress on Sanitation and Drinking Water: 2015 Update”, World Health Organization, 2015

[2] R. Lu, B. Mizaikoff, W-W Li, C. Qian, A. Katzir, Y. Raichlin, G-P Sheng and H-Q Yu, “Determination of Chlorinated Hydrocarbons in Water Using Highly Sensitive Mid-Infrared Sensor Technology”, Scientific Reports 2013, 3, 2525 DOI: 10.1038/srep02525

[3] J. Mabin, E. Alghamdi, C. Hodges, S. J. Freakley and S. A. Lynch, "Monitoring the Photocatalytic Oxidation of Water-Based Organic Pollutants by FT-IR Spectroscopy in Real-Time," 2016 41st International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), Copenhagen, 2016, pp. 1-2 DOI: 10.1109/IRMMW-THz.2016.7758467

[4] B. E. Obinaju and F. L. Martin, “ATR-FTIR Spectroscopy Reveals Polycyclic Aromatic Hydrocarbon Contamination Despite Relatively Pristine Site Characteristics: Results of a Field Study in the Niger Delta”, Environment International, 89-90, 93-101 http://dx.doi.org/10.1016/j.envint.2016.01.012

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