Matrix effects demystified: Strategies for resolving challenges in analytical separations of complex samples.

Matrix effects can significantly impede the accuracy, sensitivity, and reliability of separation techniques presenting a formidable challenge to the analytical process. It is crucial to address matrix effects to achieve accurate and precise measurements in complex matrices. The multifaceted nature of matrix effects which can be influenced by factors such as target analyte, sample preparation protocol, composition, and choice of instrument necessitates a pragmatic approach when analyzing complex matrices. This review aims to highlight common challenges associated with matrix effects throughout the entire analytical process with emphasis on gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, and sample preparation techniques. These techniques are susceptible to matrix effects that could lead to ion suppression/enhancement or impact the analyte signal at various stages of the analytical workflow. The assessment, quantification, and mitigation of matrix effects are necessary in developing any analytical method. Strategies can be implemented to reduce or eliminate the matrix effect by changing the type of ionization, improving extraction and clean-up methods, optimization of chromatography conditions, and corrective calibration methods. While development of an effective strategy to completely mitigate matrix effects remains elusive, an integrated approach that combines sample preparation, analytical extraction, and effective instrumental analysis remains the most promising avenue for identifying and resolving matrix effects.

Rapid Screening and Quantification of PFAS Enabled by SPME-DART-MS.

Per- and polyfluoroalkyl substances (PFAS), an emerging class of toxic anthropogenic chemicals persistent in the environment, are currently regulated at the low part-per-trillion level worldwide in drinking water. Quantification and screening of these compounds currently rely primarily on liquid chromatography hyphenated to mass spectrometry (LC-MS). The growing need for quicker and more robust analysis in routine monitoring has been, in many ways, spearheaded by the advent of direct ambient mass spectrometry (AMS) technologies. Direct analysis in real time (DART), a plasma-based ambient ionization technique that permits rapid automated analysis, effectively ionizes a broad range of compounds, including PFAS. This work evaluates the performance of DART-MS for the screening and quantification of PFAS of different chemical classes, employing a central composite design (CCD) to better understand the interactions of DART parameters on their ionization. Furthermore, in-source fragmentation of the model PFAS was investigated based on the DART parameters evaluated. Preconcentration of PFAS from water samples was achieved by solid phase microextraction (SPME), and extracts were analyzed using the optimized DART-MS conditions, which allowed obtaining linear dynamic ranges (LDRs) within 10 and 5000 ng/L and LOQs of 10, 25, and 50 ng/L for all analytes. Instrumental analysis was achieved in less than 20 s per sample.

Leveraging multi-mode microextraction and liquid chromatography stationary phases for quantitative analysis of neurotoxin ß-N-methylamino-L-alanine and other non-proteinogenic amino acids.

Effective quantitative analysis of BMAA (ß-N-methylamino-L-alanine) and its isomers without the need for derivatization has always been an analytical challenge due to their poor retention and separation on various liquid chromatography stationary phases. Previous studies that utilized conventional hydrophilic interaction chromatography (HILIC) demonstrate false negatives compared to reverse-phase workflows with derivatization. This work evaluates the chromatographic behavior of BMAA and its isomers, in their underivatized forms, on selected stationary phases, in particular fluorophenyl-based columns, to attain effective retention and separation. Detection and quantification were achieved with an ion-trap mass spectrometer. Extraction and preconcentration were achieved via solid phase microextraction (SPME) by assessing the effectiveness of multiple extraction phases, including hydrophilic-lipophilic balanced (HLB) and mixed-mode (MM). A MM extraction phase consisting of C8 and benzene sulfonic acid moieties provided ideal extraction performance for BMAA and its isomers (2,4-diaminobutyric acid, DABA; N-(2-aminoethyl) glycine, AEG). Chromatographic separation was achieved within 8 min on a fluorophenyl stationary phase, ensuring high throughput without derivatization, and showing exceptional improvement from conventional HILIC methods. Limits of quantification in water for BMAA and AEG were 2.5 µg L-1 and DABA was 5 µg L-1, with linear dynamic ranges from 2.5 µg L-1 - 200 µg L-1 for BMAA and AEG and 5 µg L-1 - 200 µg L-1 for DABA.

Unraveling the Complex Composition of Produced Water by Specialized Extraction Methodologies.

Produced water (PW), a waste byproduct of oil and gas extraction, is a complex mixture containing numerous organic solubles and elemental species; these constituents range from polycyclic aromatic hydrocarbons to naturally occurring radioactive materials. Identification of these compounds is critical in developing reuse and disposal protocols to minimize environmental contamination and health risks. In this study, versatile extraction methodologies were investigated for the untargeted analysis of PW. Thin-film solid-phase microextraction with hydrophilic-lipophilic balance particles was utilized for the extraction of organic solubles from eight PW samples from the Permian Basin and Eagle Ford formation in Texas. Gas chromatography-mass spectrometry analysis found a total of 266 different organic constituents including 1,4-dioxane, atrazine, pyridine, and PAHs. The elemental composition of PW was evaluated using dispersive solid-phase extraction followed by inductively coupled plasma-mass spectrometry, utilizing a new coordinating sorbent, poly(pyrrole-1-carboxylic acid). This confirmed the presence of 29 elements including rare earth elements, as well as hazardous metals such as Cr, Cd, Pb, and U. Utilizing chemometric analysis, both approaches facilitated the discrimination of each PW sample based on their geochemical origin with a prediction accuracy above 90% using partial least-squares-discriminant analysis, paving the way for PW origin tracing in the environment.

Ion exchange solid phase microextraction coupled to liquid chromatography/laminar flow tandem mass spectrometry for the determination of perfluoroalkyl substances in water samples.

Per- and polyfluoroalkyl substances (PFAS) are toxic and bioaccumulative compounds that are persistent in the environment due to their water and heat resistant properties. These compounds have been demonstrated to be ubiquitous in the environment, being found in water, soil, air and various biological matrices. The determination of PFAS at ultra-trace levels is thus critical to assess the extent of contamination in a particular matrix. In this work, solid phase microextraction (SPME) was evaluated as a pre-concentration technique to aid the quantitation of this class of pollutants below the EPA established advisory limits in drinking water at parts-per-trillion levels. Four model PFAS with varying physicochemical properties, namely hexafluoropropylene oxide dimer acid (GenX), perfluoro-1- butanesulfonate (PFBS), perfluoro-n-octanoic acid (PFOA) and perfluoro-1-octanesulfonate (PFOS) were studied as a proof of concept. Analysis was performed with the use of ultra-high pressure liquid chromatography-laminar flow tandem mass spectrometry (UHPLC-MS/MS). This study proposes the use of hydrophilic-lipophilic balance-weak anion-exchange/polyacrylonitrile (HLB-WAX/PAN) as a SPME coating, ideal for all model analytes. A sample volume of 1.5 mL was used for analysis, the optimized protocol including 20 min extraction, 20 min desorption and 6 min LC/MS analysis. This method achieved LOQs of 2.5 ng L- 1 (PFOS) and 1 ng L - 1 (GenX, PFBS and PFOA) with satisfactory precision and accuracy values evaluated over a period of 5 days.

Minimizing transient microenvironment-associated variability for analysis of environmental anthropogenic contaminants via ambient ionization.

The rapid and quantitative analysis of anthropogenic contaminants in environmental matrices is crucial for regulatory testing and to elucidate the environmental fate of these pollutants. Direct ambient mass spectrometry (AMS) methodologies greatly increase sample throughput, can be adapted for onsite analysis and are often regarded as semi-quantitative by most developed protocols. One of the limitations of AMS, especially for on site analysis applications, is the irreproducibility of the measurements related to the occurrence of transient microenvironments (TME) and variable background interferences. In this work we report an effective strategy to minimize these effects by hyphenating, for the first time, solid phase microextraction (SPME) arrow to mass spectrometry via a thermal desorption unit (TDU) and direct analysis in real time (DART) source. The developed method was optimized for the extraction and analysis of pesticides and pharmaceuticals from surface water. It was demonstrated that the hyphenation of the SPME and TDU-DART resulted in reduced background contamination, indicating the suitability of the method for onsite analysis even in variable and non-ideal environments. Model analytes were quantitated in the low µg/L range with a total analysis time of less than 5 min, linear dynamic ranges (LDR) and interday reproducibility for most compounds being 2.5-500 µg/L and lower than 10%, respectively. The developed approach provides an excellent analytical tool that can be applied for the onsite high-throughput analysis of water samples as well as air and aereosols. Considering the tunability of our extraction process, time-resolved environmental monitoring can be achieved onsite within minutes.

Optimization of thin film solid phase microextraction and data deconvolution methods for accurate characterization of organic compounds in produced water.

The continued rise in the extraction of unconventional oil and gas across the globe poses many questions about how to manage these relatively new waste-streams. Produced water, the primary waste by-product, contains a diverse number of anthropogenic additives together with the numerous hydrocarbons extracted from the well. Due to potential environmental hazards, it is critical to characterize the chemical composition of this type of waste before proper disposal or remediation/reuse. In this work, a thin film solid phase microextraction approach was developed and optimized to characterize produced water. The thin film device consisted of hydrophilic-lipophilic balance particles embedded in polydimethylsiloxane and immobilized on a carbon mesh surface. These devices were chosen to provide broad extraction coverage and high reusability. Various parameters were evaluated to ensure reproducible results while minimizing analyte loss. This optimized protocol, consisting of a 15 min extraction followed by a short (3 s) rinsing step, enabled the reproducible analysis of produced water without any sample pretreatment. Extraction efficiency was suitable for both produced water additives and hydrocarbons. The developed approach was able to tentatively identify a total of 201 compounds from produced water samples, by using one-dimensional gas chromatography hyphenated to mass spectrometry and data deconvolution.