Assessing Background Contamination of Sample Tubes Used in Human Biomonitoring by Non-Targeted Liquid Chromatography–High Resolution Mass Spectrometry

Abstract

Controlling and minimising background contamination is crucial for maintaining a high quality of samples in human biomonitoring targeting organic chemicals. We assessed the contamination of three previous types and one newly introduced medical-grade type of sample tubes used for storing human body fluids at the German Environmental Specimen Bank. Aqueous extracts from these tubes were analysed by non-targeted liquid chromatography-high resolution mass spectrometry (LC-HRMS) before and after employing a dedicated cleaning procedure. After peak detection using MZmine, Bayesian hypothesis testing was used to group peaks into those originating from instrumental and laboratory background contamination, and true tube contaminants, categorized whether their peak height was reduced, increased or not affected by the cleaning procedure. For all four tube types 80-90% of the 2475 peaks (1549 in positive and 926 in negative mode) were assigned to laboratory/instrumental background, which we have to consider also as potential sample tube contaminants. Among the tube contaminants, results suggest a considerable difference in the contaminant peak inventory and the absolute level of contamination among the different sample tube types. The cleaning procedure did not affect the largest fraction of these peaks (50-70%). For the medical grade tubes, the removal of contaminants by the cleaning procedure was strongest as compared to the previous tubes, but in all cases a small fraction increased in intensity after cleaning, probably due to a release of oligomers or additives. Among the identified laboratory background contaminants were mainly semi-volatile polymer additives such as phthalates and phosphate esters. A few compounds could be assigned solely as tube-specific contaminants, such as N,N-dibutylformamide and several constituents of the oligomeric light stabilizer Tinuvin-622. Cleaning sample tubes before use is an effective way to standardize sample tubes used and to minimize background contamination, and hence to increase sample quality and therewith analytical results.

Keywords: Non-target-screening, Human Biomonitoring, Quality control, Background contamination, sample tubes