Small-Footprint, Field-Deployable LC/MS System for On-Site Analysis of Per- and Polyfluoroalkyl Substances in Soil

Miniaturized liquid chromatography in environmental analysis. A review

The greater and more widespread use of chemicals, either from industry or daily use, is leading to an increase in the discharge of these substances into the environment. Some of these are known to be hazardous to humans and the environment and are regulated, but there is a large and increasing number of substances which pose a potential risk even at low concentration and are not controlled. In this context, new techniques and methodologies are being developed to deal with this concern. Miniaturized liquid chromatography (LC) emerges as a greener and more sensitive alternative to conventional LC. Furthermore, advances in instrument miniaturization have made possible the development of portable LC instrumentation which may become a promising tool for in-situ monitoring. This work reviews the environmental applications of miniaturized LC over the last 15 years and discusses the different instrumentation, including off- and on-line pretreatment techniques, chromatographic conditions, and contributions to the environmental knowledge.

Application of a portable ion chromatograph for real-time field analysis of nitrite and nitrate in soils and soil pore waters

Real-time monitoring of nitrite and nitrate is crucial for maintaining soil health and promoting plant growth. In this study, a portable ion-chromatograph (IC, Aquamonitrix) analyser, coupled with a field-applicable ultrasonic-assisted extraction method, was utilised for in-field determination of nitrate and nitrite in soils. This is the first application of this type of analyser to soil nutrients. On-site analysis of soil from a local sports field showed 94.8 ± 4.3 μg g-1 nitrate, with LODs of 32.0 μg g-1 for nitrate and 5.4 μg g-1 for nitrite. The results were in close agreement with those obtained using a conventional lab-based IC. Relative standard deviations (%RSDs) for soil analysis using Aquamonitrix were consistently below 10%. The obtained average recoveries of samples spiked with nitrite were 100% and 104% for the portable IC and conventional IC, respectively. Furthermore, to assess the suitability of portable IC for samples with high organic matter content, various natural organic fertilisers were extracted and analysed. The results showed 16.2 ± 0.7 μg g-1 nitrite and 28.5 ± 5.6 μg g-1 nitrate in sheep manure samples with LODs of 2.0 μg g-1 for nitrite and 12.0 μg g-1 for nitrate. The portable IC system was further demonstrated via real-time on-site analysis of soil pore-water acquired using a portable battery-based ceramic pore-water sampler. A continuous increase in nitrate concentration over time was observed (from 80 to 148 μg mL-1) in the soil pore-water in a vegetable garden four days after heavy rain. Unlike conventionally sampled natural waters, 7-day storage of the studied pore water samples revealed no changes in nitrate concentrations. An average of 558 ± 51 μg mL-1 nitrate was detected in the soil pore-water samples analysed on a spinach farm, immediately after irrigation.

Seamless integration of Internet of Things, miniaturization, and environmental chemical surveillance

IoT is a game-changer across all fields, including chemistry. Embracing sustainable practices and green chemistry, the miniaturization and automation of systems, and their integration into IoT is key to achieving these principles, as a rising trend with momentum. Particularly, IoT and analytical chemistry are linked in the rapid exchange of analytical data for environmental, industrial, healthcare, and educational applications. Meanwhile, cooperation with other fields of science is evident, and there is a prompt and subjective analysis of information related to analytical systems and methodologies. This paper will review the concepts, requirements, and architecture of IoT and its role in the miniaturization and automation of analytical tools using electronic modules and sensors. The aim is to explore the standards and perspectives of IoT and its interaction with different aspects of analytical chemistry. Additionally, it aimed to explain the basics and applications of IoT for chemists, and its relevance to different subfields of analytical chemistry, particularly in the field of environmental chemical surveillance. The article also covers updating IoT devices and creating DIY-based degradation devices to enhance the educational aspect of chemistry and reduce barriers to lab facilities and equipment. Lastly, it will explore how IoT is really important and how it's going to significantly impact analytical chemistry.

Computer-assisted multifactorial method development for the streamlined separation and analysis of multicomponent mixtures in (Bio)pharmaceutical settings

The (bio)pharmaceutical industry is rapidly moving towards complex drug modalities that require a commensurate level of analytical enabling technologies that can be deployed at a fast pace. Unsystematic method development and unnecessary manual intervention remain a major barrier towards a more efficient deployment of meaningful analytical assay across emerging modalities. Digitalization and automation are key to streamline method development and enable rapid assay deployment. This review discusses the use of computer-assisted multifactorial chromatographic method development strategies for fast-paced downstream characterization and purification of biopharmaceuticals. Various chromatographic techniques such as reversed-phase liquid chromatography (RPLC), hydrophilic interaction liquid chromatography (HILIC), ion exchange chromatography (IEX), hydrophobic interaction chromatography (HIC), and supercritical fluid chromatography (SFC) are addressed and critically reviewed. The most significant parameters for retention mechanism modelling, as well as mapping the separation landscape for optimal chromatographic selectivity and resolution are also discussed. Furthermore, several computer-assisted approaches for optimization and development of chromatographic methods of therapeutics, including linear, nonlinear, and multifactorial modelling are outlined. Finally, the potential of the chromatographic modelling and computer-assisted optimization strategies are also illustrated, highlighting substantial productivity improvements, and cost savings while accelerating method development, deployment and transfer processes for therapeutic analysis in industrial settings.

Multi-wavelength deep-ultraviolet absorbance detector based upon program-controlled pulsing light-emitting diodes

A novel approach for multi-wavelength ultraviolet (UV) absorbance detection has been introduced employing a single board computer (SBC) with a field programmable gate array (FPGA), Red Pitaya SBC, to generate separated micro pulses for three deep-ultraviolet light-emitting diodes (DUV-LEDs), λmax = 235, 250, and 280 nm, along with data acquisition and processing via a custom-made program. The pulse set generation and data acquisition were synchronized using the SBC. The outputs of the three pulsing DUV-LEDs were combined and transmitted to the flow cell via a solarisation resistant trifurcated optical fiber (OF). An ultra-fast responding photodiode was connected to the optical-fiber-compatible flow cell to record the intensity of the DUV pulses. Upper limit of detector linearity (A95 %) was found to be 1917 mAU, 2189 mAU, and 1768 mAU at 235 nm, 250 nm, and 280 nm, respectively, with stray light ≤0.9 %. In addition, the effective path length (Leff) was estimated to be ≥98.0 % of the length of the used flow cell (50 mm). The new pulsed multi-LEDs absorbance detector (PMLAD) has been successfully coupled with a standard liquid chromatograph and utilized for the analysis of pharmaceuticals. Paracetamol, caffeine, and aspirin were simultaneously determined at 250, 280, and 235 nm, respectively, using the PMLAD. The absorbance ratios between the different wavelengths were applied to further confirm the identity of the studied compounds. Excellent linearity was achieved over a range of 0.1-3.2 µg/mL for paracetamol, 0.4-6.4 µg/mL for caffeine, and 0.8-12.8 µg/mL for aspirin with a regression correlation coefficient (r2) ≥ 0.99996. The quantitation limits (LOQs) were 0.10 µg/mL, 0.38 µg/mL, and 0.66 µg/mL for paracetamol, caffeine, and aspirin, respectively.

Column selection considerations in compact capillary liquid chromatography

Recent years have seen significant advances in compact, portable capillary LC instrumentation. This study explores the performances of several commercially available columns within the pressure and flow limits of both the columns and one of these compact LC instruments. The commercially available compact capillary LC system with UV-absorbance detector used in this study is typically operated using columns in the 0.15-0.3 mm internal diameter (i.d.) range. Efficiency measurements (i.e., theoretical plates, N) for six columns with i.d.s in this range and of varying lengths and pressure limits, packed with stationary phases of different particle diameters and morphologies, were made using a mixture of standard alkylphenones. Kinetic plot comparisons between columns that vary by one (or more) of these parameters are described, along with calculated kinetic performance and Knox-Saleem limits. These theoretical performance descriptions provide insight into optimal operating conditions when using capillary LC systems. Based on kinetic plot evaluation of available capillary columns in the 0.2-0.3 mm i.d. range with a conservative upper pressure limit of 330 bar packed with superficially porous particles, a 25 cm column could generate ∼47,000 plates in 7.85 min when operated at 2.4 µL/min. For comparison, more robust 0.3 mm i.d. columns (packed with fully porous particles) that can be operated at higher pressures than can be provided by the pumping system (conservative pump upper pressure limit of 570 bar), a ∼20 cm column could generate nearly 40,000 plates in 5.9 min if operated at 6 µL/min. Across all capillary LC columns measured, higher pressure limits and shorter columns can provide the best throughput when considering both speed and efficiency.

Compact capillary high performance liquid chromatography system for pharmaceutical on-line reaction monitoring

Due to their size, conventional high performance liquid chromatographs (HPLCs) are difficult to place close to a reaction vessel within a pharmaceutical manufacturing or development site. Typically, long transfer lines are required to move sample from the reactor to the HPLC for analysis and high solvent usage is required. However, herein a compact and modular separation system has been developed to enable co-location of an HPLC with a small-scale reactor for reaction monitoring in the synthesis of active pharmaceutical ingredients. Using a framework based on capillary HPLC, a compact gradient separation system with a fully modular architecture is described. A custom miniature diode-array detector with a linear dynamic range (up to 1500 mAU at 210 nm) was integrated and evaluated for on-line reaction monitoring. In evaluating system suitability, average peak area %RSD of <3%, and an average retention time %RSD of <0.7%, were achieved. To demonstrate practical utility, the compact system was coupled directly to an on-line lab-scale flow through reactor for continuous reaction monitoring in the laboratory fume hood, where a study of the 3rd Bourne reaction was used to compare the performance of the compact system with a commercially available process HPLC instrument (Waters PATROL UPLC). Further, 33 off-line samples from a continuous crystallization reactor were analysed and it was found that the developed compact HPLC system showed equivalent quantitative performance to an Agilent 1290 Infinity II HPLC system.

Advances in rapid detection of SARS-CoV-2 by mass spectrometry

COVID-19 has already been lasting for more than two years and it has been severely affecting the whole world. Still, detection of SARS-CoV-2 remains the frontline approach to combat the pandemic, and the reverse transcription polymerase chain reaction (RT-PCR)-based method is the well recognized detection method for the enormous analytical demands. However, the RT-PCR method typically takes a relatively long time, and can produce false positive and false negative results. Mass spectrometry (MS) is a very commonly used technique with extraordinary sensitivity, specificity and speed, and can produce qualitative and quantitative information of various analytes, which cannot be achieved by RT-PCR. Since the pandemic outbreak, various mass spectrometric approaches have been developed for rapid detection of SARS-CoV-2, including the LC-MS/MS approaches that could allow analysis of several hundred clinical samples per day with one MS system, MALDI-MS approaches that could directly analyze clinical samples for the detection, and efforts for the on-site detection with portable devices. In this review, these mass spectrometric approaches were summarized, and their pros and cons as well as further development were also discussed.

Voltammetric Selectivity in Detection of Ionized Perfluoroalkyl Substances at Micro-Interfaces between Immiscible Electrolyte Solutions

Widespread contamination by per- and polyfluoroalkyl substances (PFAS) and concern about their health impacts require the availability of rapid sensing approaches. In this research, four PFAS, perfluorooctanoic acid (PFOA), perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonic acid (PFOS), were studied at micropipette-based interfaces between two immiscible electrolyte solutions (μITIES) to assess the potentiality for their detection by ion transfer voltammetry. All four PFAS substances were detected by ion transfer voltammetry at the μITIES, with half-wave transfer potentials (E_1/2 vs Ag/AgCl) for PFOS, PFHxS, PFBS, and PFOA of 0.34, 0.32, 0.25, and 0.23 V, respectively. The selectivity of the μITIES for detection of PFAS mixtures was investigated. Among the six combinations of the four compounds, most combinations were detectable, except PFOA + PFBS and PFHxS + PFOS, because of unresolved ion transfer voltammograms. These findings provide a basis for the design of new PFAS sensing strategies based on ion transfer voltammetry.

On-line untargeted metabolomics monitoring of an E. coli succinate fermentation process

The real‐time monitoring of metabolites (RTMet) is instrumental for the industrial production of biobased fermentation products. This study shows the first application of untargeted on‐line metabolomics for the monitoring of undiluted fermentation broth samples taken automatically from a 5 L bioreactor every 5 min via flow injection mass spectrometry. The travel time from the bioreactor to the mass spectrometer was 30 s. Using mass spectrometry allows, on the one hand, the direct monitoring of targeted key process compounds of interest and, on the other hand, provides information on hundreds of additional untargeted compounds without requiring previous calibration data. In this study, this technology was applied in an Escherichia coli succinate fermentation process and 886 different m/z signals were monitored, including key process compounds (glucose, succinate, and pyruvate), potential biomarkers of biomass formation such as (R)‐2,3‐dihydroxy‐isovalerate and (R)‐2,3‐dihydroxy‐3‐methylpentanoate and compounds from the pentose phosphate pathway and nucleotide metabolism, among others. The main advantage of the RTMet technology is that it allows the monitoring of hundreds of signals without the requirement of developing partial least squares regression models, making it a perfect tool for bioprocess monitoring and for testing many different strains and process conditions for bioprocess development.

Online monitoring of small volume reactions using compact liquid chromatography instrumentation

A wide variety of analytical techniques have been employed for monitoring chemical reactions, with online instrumentation providing additional benefits compared to offline analysis. A challenge in the past for online monitoring has been placement of the monitoring instrumentation as close as possible to the reaction vessel to maximize sampling temporal resolution and preserve sample composition integrity. Furthermore, the ability to sample very small volumes from bench-scale reactions allows the use of small reaction vessels and conservation of expensive reagents. In this study, a compact capillary LC instrument was used for online monitoring of as small as 1 mL total volume of a chemical reaction mixture, with automated sampling of nL-scale volumes directly from the reaction vessel used for analysis. Analyses to demonstrate short term (~2 h) and long term (~ 50 h) reactions were conducted using tandem on-capillary ultraviolet absorbance followed by in-line MS detection or ultraviolet absorbance detection alone, respectively. For both short term and long term reactions (10 and 250 injections, respectively), sampling approaches using syringe pumps minimized the overall sample loss to ~0.2% of the total reaction volume.