System stability and signal enhancement with analyte protectants: Gas chromatography analysis of oxygenated-polycyclic aromatic hydrocarbons.

Matrix effects can affect detection limits, precision, and accuracy and lead to signal enhancement or suppression effects in gas chromatography analysis. Analyte protectants, such as shikimic acid and gluconolactone, can imitate the effect of matrix components and reduce the differences in matrix effect between samples. This study aimed to investigate the ability of analyte protectants to enhance gas chromatography detector signals of different oxygenated-polycyclic aromatic hydrocarbons. Addition of 100 µg L-1 shikimic acid and 200 µg L-1 gluconolactone effectively enhanced detector response of the investigated target compounds. Addition of a higher content of analyte protectants did not result in any further enhancement. It was found that between four and eleven consecutive injections of a standard solution with analyte protectants were required to obtain a stable compound response. The long-term signal stability was then maintained with subsequent injections, though an overall negative drift of the system was observed over the sequence of 200 investigated injections. Analysis of the actual sample matrix instead of standards in pure solvent, as presented in this study, could also be a way to minimize the required number of injections. Shikimic acid and gluconolactone were first and foremost able to enhance signals of oxygenated-polycyclic aromatic hydrocarbons with similar functional groups (hydroxyl) in their molecular structure. It can be relevant to consider alternative analyte protectants with different functional groups according to the type of target compounds investigated.

Catchment area, fate, and environmental risks investigation of micropollutants in Danish wastewater.

This study aimed to investigate the spatial distribution of micropollutants in wastewater related to catchment area, and their environmental risks and fate. About 24-h flow proportional effluent (n = 26) wastewater samples were collected from eight WWTPs across Denmark. From five of these WWTPs corresponding influent samples (n = 20) were collected. Samples were enriched by multi-layer solid phase and analysed by liquid chromatography-high-resolution mass spectrometry and comprehensive two-dimensional gas chromatography with high-resolution mass spectrometry detection. We detected and quantified 79 micropollutants from a list of 291 micropollutants in at least one influent or effluent wastewater sample. From this we found that 54 micropollutants decreased in concentrations during wastewater treatment, while O-desmethylvenlafaxine, carbamazepine, amitriptyline, benzothiazole, terbutryn, and citalopram increased in concentrations through the WWTP.The toxicity of effluent wastewater samples was assessed by EC50 using Raphidocelis subcapitata (R. subcapitata) and LC50 using the crustacean Daphnia magna (D. Magna), for which six micropollutants were detected above the predicted no-effect concentration. Our study demonstrates that catchment area influences the micropollutant composition of wastewater. Out of 19 pharmaceuticals, the measured concentration in influent wastewater was predicted within a factor of 10 from sale numbers and human excretion, which demonstrates the strong influence of catchment area on micropollutant composition.

Supercritical Fluid Chromatography Coupled to High-Resolution Mass Spectrometry Reveals Persistent Mobile Organic Compounds with Unknown Toxicity in Wastewater Effluents.

Broad screening approaches for monitoring wastewater are normally based on reversed-phase liquid chromatography (LC) coupled to high-resolution mass spectrometry (HRMS). This method is not sufficient for the very polar micropollutants, neglected in the past due to a lack of suitable analytical methods. In this study, we used supercritical fluid chromatography (SFC) to detect very polar and yet-undetected micropollutants in wastewater effluents. We tentatively identified 85 compounds, whereas 18 have only rarely been detected and 11 have not previously been detected in wastewater effluents such as 17α-hydroxypregnenolone, a likely transformation product (TP) of steroids, and 1H-indole-3-carboxamide, a likely TP from new synthetic cannabinoids. Suspect screening of 25 effluent wastewater samples from 8 wastewater treatment plants revealed several distinct potential pollution sources such as a pharmaceutical company and a golf court. The analysis of the same samples with LC-HRMS showed clearly how SFC increases the ionization efficiency for low-molecular-weight micropollutants (m/z < 300 Da) by a factor 2 to 87 times, which significantly improved the mass spectra for identifying very polar compounds. In order to assess which micropollutants might be of environmental concern, literature and toxicological databases were screened. There was a lack of available hazard and bio-activity data for regulatory-relevant in vitro and in vivo assays for >50% of the micropollutants. Especially, 70% of the data were lacking for the whole organism (in vivo) tests.

Can analyte protectants compensate wastewater matrix induced enhancement effects in gas chromatography - mass spectrometry analysis?

This study aimed to investigate the ability of analyte protectants to enhance GC-MS signals and compensate matrix effects for a range of micropollutants in pure standard, effluent, and influent wastewater samples during analysis and detection. Wastewater samples were prepared for analysis using multilayer solid phase extraction for the purpose of extracting sample components with a broad range of physical-chemical properties. The sample extracts were either spiked or not spiked with target compounds and four analyte protectants: 3-ethoxy-1,2-propanediol, D-sorbitol, gluconolactone, and shikimic acid. In this way, it was possible to evaluate the matrix effects of wastewater samples and compare the use of analyte protectants with the conventional correction method of allocating a best matching internal standard to each target compound. A relation was observed between level of wastewater treatment and matrix effects, with the largest effects observed for influent samples and the smallest effects for effluent samples. Compensation of matrix effects with analyte protectants gave comparable results with the conventional correction method of allocating a best matching internal standard to each of the 13 investigated micropollutants. The best overall compensation was observed using analyte protectants and the internal standard correction method in combination.

From data to reliable conclusions: Identification and comparison of persistent micropollutants and transformation products in 37 wastewater samples by non-target screening prioritization.

In this study, micropollutants in wastewater effluents were prioritized by monitoring the composition of influent and effluent wastewater by liquid chromatography - high-resolution mass spectrometry (LCHRMS) non-target screening (NTS) analysis. The study shows how important data pre-processing and filtering of raw data is to produce reliable NTS data for comparison of compounds between many samples (37 wastewater samples) analyzed at different times. Triplicate injections were critical for reducing the number of false-positive detections. Intensity drift corrections within and between batches analyzed months apart made peak intensities comparable across samples. Adjustment of the feature detection threshold was shown to be important, due to large intensity variations for low abundance compounds across batches. When the threshold correction cut-offs, or the filtering of relevant compounds by the occurrence frequency, were too stringent, a high number of false positive transformation products (TPs) were reported. We also showed that matrix effect correction by internal standards can over- or under-correct the intensity for unknown compounds, thus the TIC matrix effect correction was shown as an additional tool for a retention time dependent matrix effect correction. After these preprocessing and filtering steps, we identified 78 prioritized compounds, of which 36 were persistent compounds, defined as compounds with a reduction in peak intensity between influent and effluent wastewater <50%, and 13 compounds were defined as TPs because they occurred solely in the effluent samples. Some examples of persistent compounds are 1,3-diphenylguanidine, amisulpride and the human metabolites from losartan, verapamil and methadone. To our knowledge, nine of the identified TPs have not been previously described in effluent wastewater. The TPs were derived from metoprolol, fexofenadine, DEET and losartan. The screening of all identified compounds in effluent samples from eight wastewater treatment plants (WWTPs) showed that potential drugs of abuse, anti-psychotic and anti-depressant drugs were predominant in the capital city region, whereas the anti-epileptic agents and agricultural pesticides were dominant in more rural areas.