Direct and rapid screening of four organic compound metabolites in urine by paper spray mass spectrometry

Background Currently, incidents of organic solvent poisoning are occurring frequently. Rapidly and accurately qualitative and quantitative analysis of toxic substances is crucial for the treatment of affected individuals. In recent years, many biomarker assays with good specificity and high sensitivity have been developed for the detection of exposure to organic solvents, but they cannot meet the demand for real-time and fast detection.

Objective To establish a paper spray mass spectrometry method for direct and rapid detection of four organic compound metabolites (toluene diamine, 2,5-hexanedione, hippuric acid, and methylhippuric acid) in the urine of occupational populations.

Methods Toluene diamine and 2,5-hexanedione were analyzed using positive ion mode, while hippuric acid and methylhippuric acid were analyzed using negative ion mode. The ion transfer tube temperature was 275 °C. The ion transfer tube voltage was 35 V. For positive ion mode, the scan range was 50-150 m/z. For negative ion mode, the scan range was 150-250 m/z. The distance from the paper substrate tip to the mass spectrometry inlet was 8 mm. The applied voltage was 3.5 kV. The spray solvent was methanol/water (90:10). The spray solvent volume was 15 μL. Under the optimized experimental conditions, both external standard and internal standard methods were used for quantitative analysis. Limit of detection, limit of quantification, accuracy, and precision of the proposed method were determined by spiking blank urine samples. To evaluate the feasibility of the method, the established approach was compared with current national standard detection methods or methods described in the literature. All methods were used to analyze 40 urine samples collected from occupationally exposed individuals (20 exposed to n-hexane and 20 exposed to toluene and xylene).

Results The four biomarkers showed good linearity within their respective measurement ranges and the correlation coefficients were higher than 0.9990. The limits of detection of the method were in the range of 0.00027 to 0.020 μg·mL⁻¹, and the limits of quantification were in the range of 0.0009 to 0.067 μg·mL⁻¹. The spiked recoveries at low, medium, and high concentrations ranged from 96.5% to 106.9%, with relative standard deviations (RSDs) between 5.6% and 9.7%. When applying the method to 40 urine samples from occupationally exposed individuals, the detection rates for toluene diamine, 2,5-hexanedione, hippuric acid, and methylhippuric acid were 0%, 45%, 20%, and 37.5%, respectively. For biomarkers detected by both this method and the reference methods, the detection values were generally consistent. The analysis time per sample was approximately 1-2 min using paper spray mass spectrometry, compared to 1-2 h for reference methods.

Conclusion The paper spray mass spectrometry method established in this study for detecting four organic compound metabolites in urine is characterized by its simplicity, rapidity, efficiency, and high accuracy. It can obtain results within 1-2 min, which significantly improves the timeliness of detection. It is suitable for direct and rapid screening of four organic compound metabolites in urine, and can provide technical support for the diagnosis and treatment of organic solution poisoning.