Tracking AdBlue properties during tests of selective catalytic reduction (SCR) systems ‐ the suitability of various analytical methods for urea content determination

Abstract

Summary Reliability tests of selective catalytic reduction (SCR) systems are performed extensively in industry. The aim of this work was to track the AdBlue properties when testing SCR systems under enhanced temperatures (around 80 °C). To extend and improve the current practice in the automotive industry, HPLC and titration were chosen to develop and optimize appropriate analytical methods for urea content determination in various AdBlue samples. We showed that the testing (temperature loading) of SCR systems is associated with changes of the properties of AdBlue such as conductivity, alkalinity, density, urea content and absorbance. Our results demonstrate the unsuitability of refractometry as a method for tracking urea concentration in AdBlue during tests of SCR systems. HPLC and titration proved to be accurate and precise methods to determine urea in untreated as well as in treated AdBlue samples. Both analytical methods are not affected by matrix effects – accuracy ranged from 96.6% to 100.0% and precision ranged from 0.18% to 3.24%. We showed that the process of testing SCR system is associated with changes of properties of AdBlue such as conductivity, alkalinity, density, urea content and absorbance. Our results provide compelling evidence of the necessity to extend the list of possible methods to determine the urea content in AdBlue given by ISO 22241‐2 for the automotive industry. HPLC and titration were proved as accurate and precise methods for urea concentration determination.

A Green Analytical Methodology for Detecting Adulteration in Automotive Urea-SCR Products Using Microfluidic-Paper Analytical Devices

“…Recovery results were between 91.5 and 115%, indicating that some matrix effect should be present; however, a variation of ± 20% is accepted for quantitative analyses. The obtained sensitivities were suitable for the concentration range found in such products and, when compared to other techniques, the sample treatment is similar or simpler, considering that for HPLC analysis, the sample must be diluted with a mixture of water and acetonitrile [5,9].…”

“…As demonstrated in Sections 3.3 and 3.4, the analytical parameters obtained from the validation of the proposed methodology indicate that the quantification of urea and water hardness in Arla 32 samples can be performed with analytical reliability. Repeatability of both tests using standard solutions with RSD lower than 2% indicates that the method is precise and can be compared to instrumental techniques such as spectrometry or HPLC [5]. Recovery results were between 91.5 and 115%, indicating that some matrix effect should be present; however, a variation of ± 20% is accepted for quantitative analyses.…”

“…The second determination is performed by the refractive index method, which demands special attention to biuret interference and the sample thermal equilibrium at 20 ± 0.02 • C needed to take the measurements (ISO). Some alternative analytical methods have been reported for the determination of urea in AUS32 and other matrices [5]; however, they are based on traditional analytical techniques, such as electrochemical sensors [6], spectrophotometry UV-Vis [7], infrared spectroscopy (FTIR) [8,9], high-performance liquid chromatography (HPLC) [10], gas chromatography (GC) [11], and refractive index [12]. All mentioned methods provide suitable sensibility and selectivity; however, they are usually bulky, expensive, consume a high quantity of organic solvents, time-consuming, with high levels of waste generation-therefore not considered as green analytical methods-and not indicated for on-site determination.…”

Label- and Reagent-Free Optical Sensor for Absorption-Based Detection of Urea Concentration in Water Solutions

“…However, it is well known that RI measurements are "non-specific", meaning that alterations in DEF with substances that do not affect the refractive index or that are added to compensate for the reduction in index due to dilutions would not be identified. For this reason, measurements of urea content in DEF with commercial refractometers requires subtraction of the RI contribution due to the biuret, which can represent an issue in correct urea determination in heat-treated (i.e., exhaust) AdBlue™ [4]. Moreover, commercial refractometers need to spill out the liquid to perform the measurement and they are not suitable for in-line continuous measurements.…”