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A high-throughput, automated technique for microplastics detection, quantification, and characterization in surface waters using laser direct infrared spectroscopy
Citation:
Whiting, Quinn T., K. O'Connor, Phillip M. Potter, AND Souhail R. Al-Abed. A high-throughput, automated technique for microplastics detection, quantification, and characterization in surface waters using laser direct infrared spectroscopy. Analytical and Bioanalytical Chemistry. Springer, New York, NY, 414:8353-8364, (2022). https://doi.org/10.1007/s00216-022-04371-2
Impact/Purpose:
Microplastic pollution is a relatively new type of pollution in freshwater systems. It is important to study and monitor the concentrations of microplastics in the environment, for this a simple and efficient analysis method must be used. Currently, there is no standard method for microplastic analysis, including sampling, sample preparation, and instrumental analysis. Due to the lack of standardization, comparison of microplastic research between laboratories is difficult. Current instrumental methods such as FTIR and Raman Spectroscopy are time consuming. The LDIR is implemented here for quick and accurate analysis of microplastics in surface waters such that it can be a standard method for analysis among researchers. We followed a standard ASTM method for microplastic sampling in aquatic environments and implemented a common oxidation reaction (i.e., Fenton reaction) followed by filtration onto an IR reflective gold-coated membrane. This sample preparation method was simple and quick, allowing for other researchers to use the same method for large sampling events that produce numerous samples. Analysis of the gold-coated filter containing the particles was conducted on the LDIR. Shape parameters, size, and polymer identification were found for each particle on the filter. This method allows for relatively quick quantification and characterization of microplastics and was performed such that other researchers with LDIR instrumentation can easily replicate the analysis method.
Description:
A high-throughput approach to detecting, quantifying, and characterizing microplastics (MPs) by shape, size, and polymer type using laser direct infrared (LDIR) spectroscopy in surface water samples is demonstrated. Three urban creeks were sampled for their MP content near Cincinnati, OH. A simple Fenton reaction was used to oxidize the surface water samples, and the water samples were fltered onto a gold-coated polyester membrane. Infrared (IR) analysis for polymer identifcation was conducted, with recoveries of 88.3%±1.2%. This method was able to quantify MPs down to a diameter of 20 µm, a size comparable to that of MPs quantifed by other techniques such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. A shape-classifying algorithm was designed using the aspect ratio values of particles to categorize MPs as fbers, fbrous fragments, fragments, spherical fragments, or spheres. Cut-of values were identifed from measurements of known sphere, fragment, and fbrous particles. About half of all environmental samples were classifed as fragments while the other shapes accounted for the other half. A cut-of hit quality index (HQI) value of 0.7 was used to classify known and unidentifed particles based on spectral matches to a reference library. Center for Marine Debris Research Polymer Kit 1.0 standards were analyzed by LDIR and compared to the given FTIR spectra by HQI, showing that LDIR obtains similar identifcations as FTIR analysis. The simplicity and automation of the LDIR allows for quick, reproducible particle analysis, making LDIR attractive for high-throughput analysis of MPs.
URLs/Downloads:
DOI: A high-throughput, automated technique for microplastics detection, quantification, and characterization in surface waters using laser direct infrared spectroscopy
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