Chlorines Are Not Evenly Substituted in Chlorinated Paraffins: A Predicted NMR Pattern Matching Framework for Isomeric Discrimination in Complex Contaminant Mixtures

Structure Characterization and Products Control of Technical Chlorinated Paraffins by Direct Injection Mass Spectrometry With Data Deconvolution and 1H NMR With Chemometrics Tools

The diverse industrial use of chlorinated paraffins (CPs) have led to their environmental dispersion, and special attention has been paid to their ecotoxicology. Among them, short-chain chlorinated paraffins (SCCPs) have been listed as potential persistent organic pollutants (POPs). However, currently, technical CPs produced by manufacturers are usually labeled by their chlorination degree, but such structural label is not enough to reflect CPs' environmental fate and toxicity. Ecotoxicology research suggested that the chain length, chlorination degree and the chlorine distribution pattern are all factors that can determine CPs' environmental fate and toxicity. Herein, we present a cost-effective method for the structure characterization of technical CPs. By using direct injection mass spectrometry with data deconvolution, chain length distribution and homologous distribution in technical CPs mixture can be delineated. By using 1H NMR with chemometrics tools, the chlorine distribution pattern can be elaborated. Combining the abovementioned two analytical strategies, structural information at different levels that related to CPs' environmental fate and toxicities were revealed. This method is expected to be easily applied in both industry and academia, aiming for quality control of technical CPs, by permitting only nontoxic or noncarcinogenic CPs into industrial use.

Cumulative exposure assessment to polychlorinated alkanes (C8-36) to indoor dust from Iranian kindergartens: Occurrence and health risk

The environmental and public health concerns associated with chlorinated paraffins (CPs) are significant, given their widespread use, long-lasting persistence, and potential adverse health effects. The objective of this study was to assess the contamination of polychlorinated alkanes (PCAs-C8-36), the major contaminants in the CP technical mixtures, in kindergartens in Tehran, Iran, and to evaluate the cumulative exposure risks through various routes, including ingestion, dermal contact, and inhalation of dust. The results revealed a pervasive contamination with PCAs. The sum of PCAs-C10-20 across all samples was found to be 1370 ng/g dw, with median values of 500 ng/g dw for ∑PCAs-C10-13, 620 ng/g dw for ∑PCAs-C14-17, and 280 ng/g dw for ∑PCAs-C18-20. These levels did not correlate with outdoor environmental factors or indoor characteristics. Dermal contact constituted 64-84 % of total exposure, with toddlers showing higher intake than caretakers. A cumulative exposure assessment was conducted to calculate the hazard quotient (HQ). The highest HQ value was observed for girls in the case of ∑PCAs-C10-13 (6.2 × 10-5), and the HQ for all groups remained well below the risk threshold. Despite the low level of immediate risks, chronic exposure in vulnerable population groups justifies proactive measures. Further investigation of exposure sources and implementation of interventions to reduce potential health risks are recommended, given the ubiquity of CPs in indoor environments. ENVIRONMENTAL IMPLICATIONS: This study highlights significant environmental implications of pervasive polychlorinated alkanes (PCAs-C8-36) contamination in Tehran's kindergartens, highlighting their persistence and potential long-term ecological impacts. Despite cumulative exposure risks (HQs <1) via dust ingestion, dermal contact, and inhalation, the ubiquity of PCAs (∑PCAs-C10-20: 1370 ng/g dw) raises concerns about chronic low-dose exposure in vulnerable toddlers. The lack of correlation between contamination levels and environmental/indoor factors suggests complex, unidentified emission sources. These findings emphasize the need for proactive regulatory measures to mitigate CP releases and prioritize indoor environmental quality, particularly in child-centric settings. Further research is critical to identify exposure pathways and inform policies safeguarding public health against persistent organic pollutants.

Polychlorinated alkanes in indoor environment: A review of levels, sources, exposure, and health implications for chlorinated paraffin mixtures

Polychlorinated n-alkanes (PCAs) are the main components of chlorinated paraffins (CPs) mixtures, that have been commonly grouped into short-chain (SCCPs, C10-13), medium-chain (MCCPs, C14-17), and long-chain (LCCPs, C18-30) CPs. PCAs pose a significant risk to human health as they are broadly present in indoor environments and are potentially persistent, bioaccumulative, and toxic. The lack of specific terminology and harmonization in analytical methodologies for PCA analysis complicates direct comparisons between studies. The present work summarizes the different methodologies applied for the analysis of PCAs in indoor dust, air, and organic films. The large variability between the reviewed studies points to the difficulties to assess PCA contamination in these matrices and to mitigate risks associated with indoor exposure. Based on our review of physicochemical properties of PCAs and previously reported sum of measurable S/M/LCCPs levels, the homologue groups PCAs-C10-13 are found to be mostly present in the gas phase, PCAs-C14-17 in particulate matter and organic films, and PCAs-C≥18 in settled dust. However, we emphasized that mapping PCA sources and distribution in the indoors is highly dependent on the individual homologues. To further comprehend indoor PCA distribution, we described the uses of PCA in building materials and household products to apportion important indoor sources of emissions and pathways for human exposure. The greatest risk for indoor PCAs were estimated to arise from dermal absorption and ingestion through contact with dust and CP containing products. In addition, there are several factors affecting indoor PCA levels and exposure in different regions, including legislation, presence of specific products, cleaning routines, and ventilation frequency. This review provides comprehensive analysis of available indoor PCA data, the physicochemical properties, applied analytical methods, possible interior sources, variables affecting the levels, human exposure to PCAs, as well as need for more information, thereby providing perspectives for future research studies.

A Quasi Real-Time Evaluation of High-Resolution Mass Spectra of Complex Chlorinated Paraffin Mixtures and Their Transformation Products

Chlorinated paraffins (CPs) are complex mixtures of polychlorinated n-alkanes with multiple carbon- (C-, nC = 9-30) and chlorine homologues (Cl-, nCl = 3-18). The mass spectrometric analysis of CPs is time-consuming and challenging, especially when interferences between CPs, their transformation products, or from the matrix are numerous. These analytical challenges and the lack of appropriate and accessible data evaluation tools are obstacles to their analysis. CP-Hunter is a web-based, open-access data processing platform for the automatic analysis of mass spectra of CPs and their transformation products. Extracts of two consumer plastic materials and sewage sludge were evaluated with CP-Hunter. C- and Cl-homologue distributions were obtained in quasi-real-time and the posterior calculated fingerprints were in agreement with the ones obtained by traditional methods. However, the data extraction and evaluation time were now reduced from several minutes to seconds. The implemented signal deconvolution method, i.e., to resolve mass spectrometric interferences, provides robust results, even when severe matrix effects are present. CP-Hunter facilitates the untargeted analysis of unknown products and the detection and elimination of false positive signals. Finally, data evaluation with CP-Hunter is performed locally without the transfer of data to external servers. The tool is safe, public, and accessible at https://cphunter.cheminfo.org/.

Are We Justified in Modeling Human Exposure to Chlorinated Paraffin Mixtures Using the Average Properties of Congeners and Homologues?

Concern over human exposure to chlorinated paraffin (CP) mixtures keeps increasing. The absence of a comprehensive understanding of how human exposure varies with the physicochemical properties of CP constituents has hindered the ability to determine at what level of aggregation exposure to CPs should be assessed. We answer this question by comparing exposure predicted with either a "complex" method that utilizes isomer-specific properties or "simplified" methods that rely on median properties of congener, homologue, or short-/medium-/long-chain CP groups. Our results demonstrate the wide range of physicochemical properties across CP mixtures and their dependence on molecular structures. Assuming unit emissions in the environment, these variances translate into an extensive disparity in whole-body concentrations predicted for different isomers, spanning ∼11 orders of magnitude. CPs with 13-19 carbons and 6-10 chlorines exhibit the highest human exposure potential, primarily owing to moderate to high hydrophobicity and slow environmental degradation and biotransformation. Far-field exposure is dominant for most CP constituents. Our study underscores that using average properties of congener, homologue, or S/M/LCCP groups yields results that are consistent with those derived from isomer-based modeling, thus offering an efficient and practical framework for future risk assessments and human exposure studies of CPs and other complex chemical mixtures.

Quantification of chlorinated paraffins by chromatography coupled to high-resolution mass spectrometry - Part A: Influence of gas chromatography and ionisation source parameters

The analysis of chlorinated paraffins (CPs) has become a major analytical challenge. GC-ECNI-HRMS coupling is often used to analyse and quantify them. However, the influence of certain GC and ECNI parameters on the responses of polychlorinated n-alkanes (PCAs), the dominant components of CPs, has hardly been studied. In this paper, we investigated not only the influence of GC column characteristics, but also oven, GC inlet and source temperatures for simultaneous analysis of PCAs with chain-length ranging from 10 up to 20 carbon atoms (PCAs-C10-20). Particular attention was paid to the absolute response and PCA homologue group pattern obtained for a CP technical mixture. The optimum conditions for a wide homologue group determination were GC inlet, final gradient and ion source temperatures set at 220-240 °C, 340 °C and 200 °C. At the same time, a higher response was obtained with the Optima 5HT column compared to Optima 1 column, and with a length and film thickness of 12.5 m and 0.25 μm, respectively. The homologue group pattern of the technical mixture studied was significantly modified as a function of the source and GC inlet temperatures, film thickness and composition of the stationary phase. Here we recommend conditions that will improve the overall PCA pattern, in order to better characterise their occurrence in future environmental monitoring and exposure assessment.

Quantification of chlorinated paraffins by chromatography coupled to high-resolution mass spectrometry - Part B: Influence of liquid chromatography separation

The analysis of chlorinated paraffins (CPs) is today an analytical challenge. Indeed, it is still impractical to describe their real composition in terms of polychlorinated alkanes (PCAs) homologue groups, which dominate technical mixtures. The co-elution of PCA congeners generates interferences due to the competition phenomena which occur during the ionisation process as well as to the dependence of the ionisation sources on the PCA chemistry. Therefore, the aim of this study was to investigate the influence of chromatographic separation, by LC-ESI-HRMS coupling, on the PCA homologue group pattern and, eventually, on their determination in food samples from interlaboratory studies. For this, three different mobile phases and six LC chromatographic columns were studied in order to optimise the analysis of CP mixtures. The first results showed that the use of a MeOH/H2O mobile phase reveals more appropriately the higher chlorinated PCAs. However, using ACN/H2O led to less ion species, with almost exclusively [M + Cl]- adducts, formed using post-column dichloromethane addition. Regarding the choice of the stationary phases, Hypercarb column provided a completely different homologue group pattern from the other chromatographic columns, in relation with the stronger retention of PCAs. Among the other columns, the C30 column better highlighted the short-chain PCAs compared to the C18 column conventionally used. Because the regulations now concern short-chain CPs, the quantification of food samples was then carried out on the C30 column. The optimised LC-ESI-HRMS conditions using C30 column and MeOH/H2O solvent mixture led to a quantification of PCAs in samples from interlaboratory studies with satisfactory accuracy (|Z-score| ≤ 2) and precision (<15%).

Calibration and Application of PUF Disk Passive Air Samplers To Assess Chlorinated Paraffins in Ambient Air in Australia, China, and Vietnam

Ambient air samples were collected in Brisbane (Australia), Dalian (China), and Hanoi (Vietnam) during Mar 2013-Feb 2018 using polyurethane foam based passive air samplers. A sampling rate calibration experiment was conducted for chlorinated paraffins (CPs, i.e., short-chain, medium-chain, and long-chain CPs), where the sampling rates were 4.5 ± 0.7, 4.8 ± 0.3, and 4.8 ± 2.1 m3 day-1 for SCCPs, MCCPs, and LCCPs, respectively. The atmospheric concentration of CPs was then calculated and the medians of ∑CPs were 0.079, 1.0, and 0.89 ng m-3 in Brisbane, Dalian, and Hanoi, respectively. The concentration of CPs in Brisbane's air remained at low levels, with no significant differences observed between the city background site and the city center site, indicating limited usage and production of CPs in this city. The highest concentration of MCCPs was detected in Dalian, while the highest concentration of SCCPs was detected in Hanoi. A decrease of SCCP concentration and an increase of MCCPs' were found in Brisbane's air from 2016 to 2018, while increasing trends for both SCCPs and MCCPs were observed in Dalian. These results indicated impacts from different sources of CPs in the investigated cities.

Biomonitoring, exposure routes and risk assessment of chlorinated paraffins in humans: a mini-review

Chlorinated paraffins (CPs), which were conventionally classified into short- (SCCPs), medium- (MCCPs) and long- (LCCPs) chain CPs, have received growing attention due to their wide usage and extensive detection in environmental samples and biota. The number of studies regarding the biomonitoring of CPs in human beings increased rapidly and their health risk gained great concern. This review summarized their occurrence and homologue patterns in human matrices including blood/serum, placenta, cord serum and breast milk. As the production and usage of SCCPs was progressively banned after being listed in Annex A of the Stockholm Convention, the production of MCCPs and LCCPs was stimulated. Accordingly, the ratio of MCCPs/SCCPs in human samples has increased rapidly in the last 5 years. The current understanding of exposure routes and risk assessments of CPs was also reviewed. Oral dietary intake is the most predominant source of daily CP intake, but dust ingestion, inhalation and dermal exposure is also nonnegligible, especially for MCCPs and LCCPs. Furthermore, the reported upper bound of the estimated daily intakes (EDIs) in various risk assessment studies was close to or exceeded the tolerable daily intakes (TDIs). Considering the bioaccumulation and long-lasting exposure of CPs, their health impacts on humans and the ecosystem required continuous monitoring and evaluation.

Assessment of silicone wristbands for monitoring personal exposure to chlorinated paraffins (C8-36): A pilot study

Chlorinated paraffins (CPs) are a major environmental concern due to their ubiquitous presence in the environment. Since human exposure to CPs can significantly differ among individuals, it is essential to have an effective tool for monitoring personal exposure to CPs. In this pilot study, silicone wristbands (SWBs) were employed as a personal passive sampler to measure time-weighted average exposure to CPs. Twelve participants were asked to wear a pre-cleaned wristband for a week during the summer of 2022, and three field samplers (FSs) in different micro-environments were also deployed. The samples were then analyzed for CP homologs by LC-Q-TOFMS. In worn SWBs, the median concentrations of quantifiable CP classes were 19 ng/g wb, 110 ng/g wb, and 13 ng/g wb for ∑SCCPs, ∑MCCPs, and ∑LCCPs (C_18-20), respectively. For the first time, lipid content is reported in worn SWBs, which could be a potential impact factor in the kinetics of the accumulation process for CPs. Results showed that micro-environments were key contributors to dermal exposure to CPs, while a few outliers suggested other sources of exposure. CP exposure via dermal contact showed an increased contribution and thus poses a nonnegligible potential risk to humans in daily life. Results presented here provide proof of concept of the use of SWBs as a cheap and non-invasive personal sampler in exposure studies.

Dietary Intake Contributed the Most to Chlorinated Paraffin Body Burden in a Norwegian Cohort

Determining the major human exposure pathways is a prerequisite for the development of effective management strategies for environmental pollutants such as chlorinated paraffins (CPs). As a first step, the internal and external exposure to CPs were quantified for a well-defined human cohort. CPs in participants' plasma and diet samples were analyzed in the present study, and previous results on paired air, dust, and hand wipe samples were used for the total exposure assessment. Both one compartment pharmacokinetic modeling and forensic fingerprinting indicate that dietary intake contributed the most to body burden of CPs in this cohort, contributing a median of 60-88% of the total daily intakes. The contribution from dust ingestion and dermal exposure was greater for the intake of long-chain CPs (LCCPs) than short-chain CPs (SCCPs), while the contribution from inhalation was greater for the intake of SCCPs than medium-chain CPs (MCCPs) and LCCPs. Significantly higher concentrations of SCCPs and MCCPs were observed in diets containing butter and eggs, respectively (p < 0.05). Additionally, other exposure sources were correlated to plasma levels of CPs, including residence construction parameters such as the construction year (p < 0.05). This human exposure to CPs is not a local case. From a global perspective, there are major knowledge gaps in biomonitoring and exposure data for CPs from regions other than China and European countries.

Nuclear magnetic resonance as a tool to determine chlorine percentage of chlorinated paraffin mixtures

A new simple method for chlorine percentage calculations (method C), from proton nuclear magnetic resonance (¹H NMR) spectroscopy, has been established and applied to an industrial chlorinated paraffin (CP) mixture and 13 single-chain CPs of known carbon chain lengths. Two modified methods (method A and B), originating from the work of Sprengel et al., have been utilized on the same single-chain mixtures. All samples were analysed by ¹H NMR and two-dimensional heteronuclear quantum coherence (HSQC) for this purpose. All three methods worked well for medium chlorinated (45-55% Cl) single-chain mixtures of known carbon chain lengths. Method A yielded the best result for mixtures of lower chlorine content (<45% Cl), method C gave better estimations for higher chlorine contents (>55% Cl). Compared to Mohr's titration, method A showed a deviation of 0.7-7.8% (3.6% average), method B 4.1-11.3% (7.0% average) and method C 0.6-11.6% (5.2% average), for all 13 single-chain mixtures. The new method C is the only method that could be applied for determining the chlorine percentage of industrial mixtures of multiple, unknown chain lengths.

The Next Frontier of Environmental Unknowns: Substances of Unknown or Variable Composition, Complex Reaction Products, or Biological Materials (UVCBs)

Substances of unknown or variable composition, complex reaction products, or biological materials (UVCBs) are over 70 000 "complex" chemical mixtures produced and used at significant levels worldwide. Due to their unknown or variable composition, applying chemical assessments originally developed for individual compounds to UVCBs is challenging, which impedes sound management of these substances. Across the analytical sciences, toxicology, cheminformatics, and regulatory practice, new approaches addressing specific aspects of UVCB assessment are being developed, albeit in a fragmented manner. This review attempts to convey the "big picture" of the state of the art in dealing with UVCBs by holistically examining UVCB characterization and chemical identity representation, as well as hazard, exposure, and risk assessment. Overall, information gaps on chemical identities underpin the fundamental challenges concerning UVCBs, and better reporting and substance characterization efforts are needed to support subsequent chemical assessments. To this end, an information level scheme for improved UVCB data collection and management within databases is proposed. The development of UVCB testing shows early progress, in line with three main methods: whole substance, known constituents, and fraction profiling. For toxicity assessment, one option is a whole-mixture testing approach. If the identities of (many) constituents are known, grouping, read across, and mixture toxicity modeling represent complementary approaches to overcome data gaps in toxicity assessment. This review highlights continued needs for concerted efforts from all stakeholders to ensure proper assessment and sound management of UVCBs.

Chlorinated paraffins - A historical consideration including remarks on their complexity

Chlorinated paraffins (CPs) are high production volume chemicals currently produced and used in higher quantities than any other medium-size polyhalogenated compound (class). In addition, the composition of industrial CP mixtures is highly complex and poorly understood. In this article, we searched in the literature for the beginning of the chlorination of alkanes and how this substance class developed from niche applications to unmatched quantities in various industrial applications. Also, an estimation was made on the theoretical variety of chloroparaffins and the possible complexity of industrial CP mixtures. These data may explain why little is known about CPs although the production volume throughout the industrial generation was virtually always higher than the one of PCBs and has continued to increase after the ban of the latter.

Determination of chlorinated paraffins (CPs): Analytical conundrums and the pressing need for reliable and relevant standards

The determination of chlorinated paraffins (CPs) has posed an intractable challenge in analytical chemistry for over three decades. The combination of an as yet unspecifiable number (tens - hundreds of thousands) of individual congeners in mass produced commercial CP mixtures and the steric interactions between them, contrive to defy efforts to characterise their residual occurrences in environmental compartments, food and human tissues. However, recent advances in instrumentation (mass spectrometric detectors and nuclear magnetic resonance), combined with interlaboratory studies, have allowed a better insight into the nature of the conundrums. These include the variability of results, even between experienced laboratories when there is insufficient matching between analytical standards and occurrence profiles, the poor (or no) response of some instrumentation to some CP congener configurations (multiple terminal chlorines or < four chlorines) and the occurrence of chlorinated olefins in commercial mixtures. The findings illustrate some limitations in the existing set of commercially available standards. These include cross-contamination of some standards (complex CP mixtures), an insufficient number of single chain standards (existing ones do not fully reflect food/biota occurrences), lack of homologue group standards and unsuitability of some configurationally defined CP congeners/labelled standards (poor instrument response and a smaller likelihood of occurrence in commercial mixtures). They also indicate an underestimation in reported occurrences arising from those CPs that are unresponsive during measurement. A more extensive set of standards is suggested and while this might not be a panacea for accurate CP determination, it would reduce the layers of complexity inherent in the analysis.

A new synthesis approach for the generation of single chain CP mixtures composed of a few major compounds

Chlorinated paraffins (CPs) are complex mixtures, which consist of thousands of individual compounds with no dominant representative. Consequently, knowledge on structure and environmental relevance of individual CP congeners is poor. Similarly to the synthesis of individual CPs, the generation of less complex CP mixtures that can be thoroughly analyzed may be used to overcome some drawbacks of the highly complex technical CP mixtures. Here, we present a new synthesis approach to generate such simple CP mixtures by decarboxylation of polyunsaturated fatty acids followed by saturation of the double bonds by chlorination. Specifically, α-linolenic acid (18:3Δ9,12,15) was decarboxylated to heptadecatriene. The resulting raw product was chlorinated with SO₂Cl₂. Purification by column chromatography led to a main fraction consisting of four major peaks originating from hexachloroheptadecane (C₁₇H₃₀Cl₆) isomers (∼80% of the total peak area) along with ∼20 low abundant by-products, according to gas chromatography with electron capture negative ion mass spectrometry. In the same way, decarboxylation and subsequent chlorination of other polyunsaturated fatty acids may lead to further simple CP mixtures with other chain lengths. Although these simple CP mixtures cannot fully reflect the various structural features present in technical mixtures they could be beneficial for transformation studies because changes in the CP pattern can easily be noted which is in contrast to technical CP mixtures. Such simple CP mixtures could also be used in toxicity tests which are difficult to perform with technical CP mixtures because of their high complexity.

Which of the (Mixed) Halogenated n-Alkanes Are Likely To Be Persistent Organic Pollutants?

Short-chain polychlorinated n-alkanes are ubiquitous industrial chemicals widely recognized as persistent organic pollutants. They represent only a small fraction of the 184,600 elemental compositions (C_10-25) and the myriad isomers of all possible (mixed) halogenated n-alkanes (PXAs). This study prioritizes the PXAs on the basis of their potential to persist, bioaccumulate, and undergo long-range transport guided by quantitative structure-property relationships (QSPRs), density functional theory (DFT), chemical fate models, and partitioning space. The QSPR results narrow the list to 966 elemental compositions, of which 352 (23 Br, 83 Cl/F, 119 Br/Cl, and 127 Br/F) are likely constituents of substances used as lubricants, plasticizers, and flame retardants. Complementary DFT calculations suggest that an additional 1367 elemental compositions characterized by a greater number of carbon and fluorine atoms but fewer chlorine and bromine atoms may also pose a risk. The results of this study underline the urgent need to identify and monitor these suspected pollutants, most appropriately using mass spectrometry. We estimate that the resolving power required to distinguish ∼74% of the prioritized elemental compositions from the most likely interferents, i.e., chlorinated alkanes, is approximately 60,000 (full width at half-maximum). This indicates that accurate identification of the PXAs is achievable using most high-resolution mass spectrometers.

Refinement and extension of COSMO-RS-trained fragment contribution models for predicting the partition properties of C10-20 chlorinated paraffin congeners

COSMO-RS-trained fragment contribution models (FCMs) to predict the partition properties of chlorinated paraffin (CP) congeners were refined and extended. The improvement includes (i) the use of an improved conformer generation method for COSMO-RS, (ii) extension of training and validation sets for FCMs up to C20 congeners covering short-chain (SCCPs), medium-chain (MCCPs) and long-chain CPs (LCCPs), and (iii) more realistic simulation of industrial CP mixture compositions by using a stochastic algorithm. Extension of the training set markedly improved the accuracy of model predictions for MCCPs and LCCPs, as compared to the previous study. The predicted values of the log octanol/water partition coefficients (Kow) for CP mixtures agreed well with experimentally determined values from the literature. Using the established FCMs, this study provided a set of quantum chemically based predictions for 193 congener groups (C10-20 and Cl0-21) regarding Kow, air/water (Kaw), and octanol/air (Koa) partition coefficients, subcooled liquid vapor pressure (VP) and aqueous solubility (Sw) in a temperature range of 5-45 °C as well as the respective enthalpy and internal energy changes.

Combining High-Resolution Gas Chromatographic Continuous Fraction Collection with Nuclear Magnetic Resonance Spectroscopy: Possibilities of Analyzing a Whole GC Chromatogram

This study presents, for the first time, the successful application of analyzing a whole gas chromatography (GC) chromatogram by nuclear magnetic resonance (NMR) spectroscopy using a continuous repeatable and stable (n = 280) high-resolution (HR) GC fractionation platform with a 96-well plate. Typically with GC– or liquid chromatography–mass spectrometry analysis, (isomer) standards and/or additional NMR analysis are needed to confirm the identification and/or structure of the analyte of interest. In the case of complex substances (e.g., UVCBs), isomer standards are often unavailable and NMR spectra too complex to achieve this. This proof of concept study shows that a HR GC fractionation collection platform was successfully applied to separate, purify, and enrich isomers in complex substances from a whole GC chromatogram, which would facilitate NMR analysis. As a model substance, a chlorinated paraffin (CP) mixture (>8,000 isomers) was chosen. NMR spectra were obtained from all 96 collected fractions, which provides important information for unravelling their full structure. As a proof of concept, a spectral interpretation of a few NMR spectra was made to assign sub-structures. More research is ongoing for the full characterization of CP isomers using multivariate statistical analysis. For the first time, up to only a few CP isomers per fraction were isolated from a highly complex mixture. These may be further purified and certified as standards, which are urgently needed, and can also be used for persistency, bioaccumulation, or toxicity studies.

Congener-specific partition properties of chlorinated paraffins evaluated with COSMOtherm and gas chromatographic retention indices

Chlorinated Paraffins (CPs) are high volume production chemicals and have been found in various organisms including humans and in environmental samples from remote regions. It is thus of great importance to understand the physical-chemical properties of CPs. In this study, gas chromatographic (GC) retention indexes (RIs) of 25 CP congeners were measured on various polar and nonpolar columns to investigate the relationships between the molecular structure and the partition properties. Retention measurements show that analytical standards of individual CPs often contain several stereoisomers. RI values show that chlorination pattern have a large influence on the polarity of CPs. Single Cl substitutions (-CHCl-, -CH₂Cl) generally increase polarity of CPs. However, many consecutive -CHCl- units (e.g., 1,2,3,4,5,6-C₁₁Cl₆) increase polarity less than expected from the total number of -CHCl- units. Polyparameter linear free energy relationship descriptors show that polarity difference between CP congeners can be explained by the H-bond donating properties of CPs. RI values of CP congeners were predicted using the quantum chemically based prediction tool COSMOthermX. Predicted RI values correlate well with the experimental data (R², 0.975-0.995), indicating that COSMOthermX can be used to accurately predict the retention of CP congeners on GC columns.

Predicting Partition Coefficients of Short-Chain Chlorinated Paraffin Congeners by COSMO-RS-Trained Fragment Contribution Models

Chlorinated paraffins (CPs) are highly complex mixtures of polychlorinated n-alkanes with differing chain lengths and chlorination patterns. Knowledge on physicochemical properties of individual congeners is limited but needed to understand their environmental fate and potential risks. This work used a sophisticated but time-demanding quantum chemically based method COSMO-RS and a fast-running fragment contribution approach to enable prediction of partition coefficients for a large number of short-chain chlorinated paraffin (SCCP) congeners. Fragment contribution models (FCMs) were developed using molecular fragments with a length of up to C₄ in CP molecules as explanatory variables and COSMO-RS-calculated partition coefficients as training data. The resulting FCMs could quickly provide COSMO-RS predictions for octanol-water (K_ow), air-water (K_aw), and octanol-air (K_oa) partition coefficients of SCCP congeners with an accuracy of 0.1-0.3 log units root-mean-squared errors. The FCM predictions for K_ow agreed with experimental values for individual constitutional isomers within 1 log unit. The distribution of partition coefficients for each SCCP congener group was computed, which successfully reproduced experimental log K_ow ranges of industrial CP mixtures. As an application of the developed FCMs, the predicted K_aw and K_oa were plotted to evaluate the bioaccumulation potential of each SCCP congener group.