Preliminary comparison of microplastic determination in drinking water by micro-Raman spectroscopy and micro-infrared spectroscopy

Objective To compare the applicable range of micro-Raman spectroscopy and micro-infrared spectroscopy for the determination of microplastics in drinking water.

Methods The simulated samples containing microplastics standards with particle sizes of 10-50 μm were prepared, and were determined after pretreatment by micro-Raman spectroscopy and micro-infrared spectroscopy, respectively. The recovery rate was used to evaluate the accuracy of the test method and investigate the applicable range of both methods.

Results The test result for microplastics with particle sizes of 10-50 μm varied with sampling method (three-point sampling method or quarter sampling method) determined by micro-Raman spectroscopy, and the average recoveries of the three-point sampling method and the quarter sampling method were 71.61%-106.2% and 41.92%-81.06%, respectively. Meanwhile, the recovery rate increased with the increasing particle size determined by micro-infrared spectroscopy, and microplastics with particle sizes of >40 μm had an average recovery rate of 91.38%.

Conclusion Considering the detection time and detection efficiency comprehensively, when the target particle size ranged largely, micro-Raman spectroscopy with the three-point sampling method can be used to detect microplastics sized less than 40 μm, and micro-infrared spectroscopy can be used to detect microplastics sized more than 40 μm.