Development of a hydrophilic interaction liquid chromatography-mass spectrometry method for detection and quantification of urea thermal decomposition by-products in emission from diesel engine employing selective catalytic reduction technology

Characteristics and source apportionment of water-soluble organic nitrogen (WSON) in PM2.5 in Hong Kong: With focus on amines, urea, and nitroaromatic compounds

Water-soluble organic nitrogen (WSON) is ubiquitous in fine particulate matter (PM2.5) and poses health and environmental risks. However, there is limited knowledge regarding its comprehensive speciation and source-specific contributions. Here, we conducted chemical characterization and source apportionment of WSON in 65 PM2.5 samples collected in Hong Kong during a 1-yr period. Using various mass-spectrometry-based techniques, we quantified 22 nitrogen-containing organic compounds (NOCs), including 17 nitroaromatics (NACs), four amines, and urea. The most abundant amine and NACs were dimethylamine and 4-nitrocatechol, respectively. Two secondary (i.e., secondary formation and secondary nitrate) and five primary sources (i.e., sea salt, fugitive dust, marine vessels, vehicle exhaust, and biomass burning) of WSON and these three categories of NOCs were identified. Throughout the year, secondary sources dominated WSON formation (69.0%), while primary emissions had significant contributions to NACs (77.1%), amines (75.9%), and urea (83.7%). Fugitive dust was the leading source of amines and urea, while biomass burning was the main source of NACs. Our multi-linear regression analysis revealed the significant role of sulfate, NO3, nitrate, liquid water content, and particle pH on WSON formation, highlighting the importance of nighttime NO3 processing and heterogeneous and aqueous-phase formation of NOCs in the Hong Kong atmosphere.

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

The application of urea-based selective catalytic reduction products (i.e., Urea-SCR) provides a reduction of NOx and, therefore, minimizes pollution emissions from vehicles fueled by diesel. Such products can be easily found in the market; however, they are often susceptible to adulteration, mainly in terms of the urea content and dilution with non-mineralized water. In this study, we propose a simple, low-cost, disposable, and straightforward paper-based microfluidic device for the quality-control of Urea-SCR products for the first time by quantifying urea and water hardness simultaneously via colorimetric reactions using a small volume of sample. 4-(dimethylamino)benzaldehyde and Eriochrome T were used as colorimetric indicators for urea and water hardness determination, respectively. Each reagent (1.5 µL) was combined with 6 µL of sample for analysis, contributing to an expressive reduction of waste generation. Digital images of the µPAD were obtained, and linear relations between color intensity and urea and Ca2+ and Mg2+ concentrations in the range of 0.2 to 1.0% and 0.1 to 3.5 mmol L−1 were obtained with a correlation coefficient higher than 0.99. Recovery experiments were employed to evaluate the accuracy of the methodology, revealing suitable values between 91.5 and 115%. Brazilian Urea-SCR samples were acquired from different distributors and submitted to the proposed procedure to evaluate its applicability. The application of microfluidic paper-based devices with colorimetric reactions enables the quality control of Urea-SCR products with high accuracy, portability, low consumption of reagents, and no generation of toxic residues; thereby contributing to the green analytical chemistry field.

Solar Urea: Towards a Sustainable Fertilizer Industry

Urea, an agricultural fertilizer, nourishes humanity. The century-old Bosch-Meiser process provides the world's urea. It is multi-step, consumes enormous amounts of non-renewable energy, and has a large CO₂ footprint. Thus, developing an eco-friendly synthesis for urea is a priority. Herein we report a single-step Pd/LTA-3A catalyzed synthesis of urea from CO₂ and NH₃ under ambient conditions powered solely by solar energy. Pd nanoparticles serve the dual function of catalyzing the dissociation of NH₃ and providing the photothermal driving force for urea formation, while the absorption capacity of LTA-3A removes by-product H₂ O to shift the equilibrium towards urea production. The solar urea conversion rate from NH₃ and CO₂ is 87 μmol g^-1  h^-1 . This advance represents a first step towards the use of solar energy in urea production. It provides insights into green fertilizer production, and inspires the vision of sustainable, modular plants for distributed production of urea on farms.

Hybrid synthetic receptor composed of molecularly imprinted polydopamine and aptamers for impedimetric biosensing of urea

An electrochemical aptamer-based method is described for highly specific sensing of urea. Urea-imprinted polydopamine was obtained by electropolymerization of dopamine (DA). The molecularly imprinted polymer (MIP) also contains DNA aptamers on gold nanoparticles decorated with a carbon nanotube network (AuNP/CNT). The material was placed on a glassy carbon electrode (GCE). After removal of urea from the MIP cavities, the GCE display double recognition capability which makes it superior to conventional MIP-only or aptamer-only based assays. On exposure of the modified electrode to urea, the interfacial charge transfer of the redox probe hexacyanoferrate is traced, typically measured at a peak voltage of 0.22 V vs. Ag/AgCl. The change in charge transfer resistance depends on the urea concentration. The assay has a 900 fM detection limit, and response is the linear up to 500 nM urea concentrations. Graphical abstract ᅟ.

Ambient Melamine Exposure and Urinary Biomarkers of Early Renal Injury

Information about environmental exposure to melamine and renal injury in adults is lacking. We investigated this relationship in 44 workers at two melamine tableware manufacturing factories in Taiwan (16 manufacturers, eight grinders, ten packers, and ten administrators) and 105 nonexposed workers (controls) at one shipbuilding company who were enrolled in August-December of 2012. For melamine workers, personal and area air samples were obtained at the worksite over 1 workweek (Monday-Friday). In the same week, pre- and post-shift one-spot urine samples were collected each workday and one first-spot urine sample was collected on each weekend morning and the following Monday morning. For each control, a one-spot urine sample was collected on Friday morning. A blood sample was also obtained from each participant at this time. Melamine levels were measured in air, urine, and serum, and early renal injury biomarkers were measured in urine. Urinary melamine concentrations in manufacturers increased sharply between pre- and post-shift measurements on Monday, remained significantly elevated throughout the workweek, and decreased over the weekend; changes in urinary melamine concentrations were substantially lower for other melamine workers. Manufacturers were exposed to the highest concentrations of ambient melamine and had significantly higher urinary and serum melamine concentrations than did the controls (P<0.001). Urinary melamine levels were positively associated with urinary N-acetyl β-d-glucosaminidase (NAG) levels but not microalbumin levels, and the detectable β2-microglobulin rate increased in the manufacturers group. In conclusion, ambient melamine exposure may increase the levels of urinary biomarkers of renal tubular injury in this occupational setting.

Retention prediction of highly polar ionizable solutes under gradient conditions on a mixed-mode reversed-phase and weak anion-exchange stationary phase

In the present work the retention of three highly polar and ionizable solutes - uric acid, nicotinic acid and ascorbic acid - was investigated on a mixed-mode reversed-phase and weak anion-exchange (RP/WAX) stationary phase in buffered aqueous acetonitrile (ACN) mobile phases. A U-shaped retention behavior was observed for all solutes with respect to the eluent organic modifier content studied in a range of 5-95% (v/v). This retention behavior clearly demonstrates the presence of a HILIC-type retention mechanism at ACN-rich hydro-organic eluents and an RP-like retention at aqueous-rich hydro-organic eluents. Hence, this column should be promising for application under both RP and HILIC gradient elution modes. For this reason, a series of programmed elution runs were carried out with increasing (RP) and decreasing (HILIC) organic solvent concentration in the mobile phase. This dual gradient process was successfully modeled by two retention models exhibiting a quadratic or a cubic dependence of the logarithm of the solute retention factor (lnk) upon the organic modifier volume fraction (φ). It was found that both models produced by gradient retention data allow the prediction of solute retention times for both types of programmed elution on the mixed-mode column. Four, in the case of the quadratic model, or five, in the case of the cubic model, initial HILIC- and RP-type gradient runs gave satisfactory retention predictions of any similar kind elution program, even with different flow rate, with an overall error of only 2.5 or 1.7%, respectively.

Measurements of gas phase acids in diesel exhaust: a relevant source of HNCO?

Gas-phase acids in light duty diesel (LDD) vehicle exhaust were measured using chemical ionization mass spectrometry (CIMS). Fuel based emission factors (EF) and NOx ratios for these species were determined under differing steady state engine operating conditions. The derived HONO and HNO3 EFs agree well with literature values, with HONO being the single most important acidic emission. Of particular importance is the quantification of the EF for the toxic species, isocyanic acid (HNCO). The emission factors for HNCO ranged from 0.69 to 3.96 mg kgfuel(-1), and were significantly higher than previous biomass burning emission estimates. Further ambient urban measurements of HNCO demonstrated a clear relationship with the known traffic markers of benzene and toluene, demonstrating for the first time that urban commuter traffic is a source of HNCO. Estimates based upon the HNCO-benzene relationship indicate that upward of 23 tonnes of HNCO are released annually from commuter traffic in the Greater Toronto Area, far exceeding the amount possible from LDD alone. Nationally, 250 to 770 tonnes of HNCO may be emitted annually from on-road vehicles, likely representing the dominant source of exposure in urban areas, and with emissions comparable to that of biomass burning.