Ultraviolet Absorbance Detection Research Articles

Overcoming the Strong Sample Solvent Effect for Sustainability Measurement Challenges in Liquid Chromatography. Example for Bisphenol-A.

This paper describes an approach to achieve low parts per billion (ppb) concentration level detection using a reversed-phase ultrahigh-performance liquid chromatographic ultraviolet absorbance detection method with large-volume feed injection (FI) for analytes in dichloromethane (DCM). FI is a novel technology that allows sample injection at a defined speed into the LC mobile phase. We demonstrate this approach for a mixture of bisphenol A and its diglycidyl ether derivatives in DCM. DCM is a very strong injection solvent at reversed-phase LC conditions and is typically immiscible with a starting reversed-phase gradient mobile phase containing a high percentage of water. As a result, reduced separation performance and even peak splitting are seen with classic flow-through injection. The method setup comprised an octyl-bonded core-shell stationary phase (150 × 4.6 mm i.d., 2.7 μm particle size) with a water/acetonitrile mobile phase gradient and an exceptionally high injection volume of 45 μL of DCM solution using FI. Optimization of feed speed (1%) and isocratic hold duration (4 min) was crucial for final separation conditions. FI delivered more than a 20-fold improvement in the limit of detection (LOD) compared to standard flow-through injection while maintaining peak resolution. The LOD of the final method ranged between 1 and 10 ppb in the polymer resin. This methodology has high potential for trace analysis in a large variety of applications that suffer from the "strong solvent effect".

Equinor Leads Project To Turn Ubiquitous Drill Cuttings Into Precious PVT Samples

They were told it wouldn’t work. But in a new study, experts at Equinor and Applied Petroleum Technology (APT) suggest they are on the brink of using contaminated drill cuttings to predict critical reservoir fluid properties. The two Norwegian firms believe their project will soon make it possible to treat cuttings, collected from each well, as if they were pressure/volume/temperature (PVT) samples, which are collected from a significantly smaller share of wells due to the risks and high cost of doing so. Since its inception in 1972, Equinor has drilled over 5,000 offshore wells, from which just over 2,000 PVT samples have been gathered. Given that only two or three good samples are taken from most wells—almost always exploration wells—a significant data gap exists for the remainder, most of which are the subsequent development wells. And each year, Equinor drills around 20 to 25 new wells, mostly near existing platforms. If oil and gas firms could obtain PVT-like results from cuttings alone, they would presumably gain more precise guidance on where to place new wells along with insights on facility/topside design, reservoir management, and eventually on the plugging and abandonment phase. The big obstacle Equinor and APT are trying to surmount centers on how rock cuttings are soaked in oil-based muds (OBMs) as they circulate up the wellbore before being collected from a shale shaker. The oil ends up masking the reservoir’s hydrocarbons, rendering traditional geochemistry methods ineffective. What Equinor has shown in its study is that problem can be circumvented to obtain reliable estimates of API gravity and viscosity, two defining aspects of reservoir fluid quality and flow potential. Several more outputs are in the works. Tao Yang, an industry-recognized reservoir expert and chief professional at Equinor, said when he spoke with geochemists in the company about the project nearly 2 years ago, they were decidedly dubious. “They gave us a warning at the beginning and said that this was a very difficult area, that the cuttings were too dirty, and that we probably wouldn’t get anything out of them,” he said. But what few in the upstream industry knew at the time is that there existed a technology that can overcome the contamination issue—and it has been around for decades. Invented in the 1960s, gel permeation chromatography (GPC) coupled with ultraviolet (UV) absorbance detection, or simply GPC-UV, is used primarily by the chemicals sector for polymer analysis. The GPC aspect separates molecules based on their size as they flow through a gel-filled column. The smaller molecules take the longest to pass through while the larger molecules move more rapidly—the opposite of how most geochemistry assays work. As the molecules move down the column, they are exposed to UV light. Depending on their chemical structure, each molecule will absorb light at varying intensities which in turn can be measured and used to detect the presence of various compounds, including those indicative of oil.

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.

Multi-channel Deep-UV absorbance measurement setup for multi-capillary electrophoresis with two fiber arrays facing each other

We have developed a simple, compact, and robust eight-channel ultraviolet (UV) absorption detection setup featuring two eight-fiber arrays (an irradiation fiber array and a detection fiber array) whose ends face each other across eight capillaries. UV light of a 220-nm wavelength from a single deuterium lamp is stably and evenly split into eight lights by using a thick homogenizing fiber connected to a fiber bundle with eight thin fibers, which make up the irradiation fiber array. Each capillary is directly irradiated with each UV light emitted from the irradiation fiber array and then each of the UV lights transmitted through the capillaries is collected by each fiber of the detection fiber array without using any other optical devices (e.g., a lens) and is detected by each of the eight photodetectors. This setup achieves simultaneous UV absorption measurement for all eight capillaries with the detection limit of 54 μAU, linear dynamic range of four logs or more, and negligible crosstalk of 0.01% or less. We also implemented an eight-capillary electrophoresis system and simultaneously analyzed eight immunoglobulin G samples, separated by capillary electrophoresis sodium dodecyl sulfate.

Observed isavuconazole exposure: 5-year experience of azole TDM from a Spanish reference laboratory.

We aimed to assess patient exposure to isavuconazole (ISZ) from samples received in our laboratory for therapeutic antifungal monitoring. We used liquid chromatography coupled with ultraviolet (UV) absorbance detection adapted from a multiplex-validated method with photodiode array (PDA) detection to monitor the analytes. The latter device allows the characterization of the azoles UV spectra. The method was validated according to international guidelines for efficient ISZ monitoring. The assay exhibited linearity between 0.25 and 16mg/l for ISZ. Accuracy and intra- and inter-day precision were within acceptable ranges, and the method was successfully applied to quantify azoles and major metabolites from clinical samples collected from treated patients. We focus on ISZ blood concentrations and compared them to those of voriconazole, posaconazole, and itraconazole for a period of 5 years (2017-2021). Median ISZ concentration was 2.92mg/l (interquartile range 1.82-5.33mg/l) with 89% of measurements classified as adequate exposure (> 1mg/l). Additionally, 71% of samples reach concentration values > 2mg/l. Different ISZ exposure between adults to children were found. In conclusion, ISZ achieves excellent blood concentrations compared to other azole drugs, they are almost identical to those previously described, they exceed the MICs of most fungi for which its use was recommended and they differ depending on the patient's age. The method we describe for antifungal monitoring is simple, robust, and efficient. It simultaneously analyzes azoles and metabolites, and can be used for tailored interventions, achieve exposures associated with therapeutic success, decrease treatment-related toxicity, and help prevent resistance emergence due to continuous azole sub-optimal concentrations.

Determination of three bioactive holostane-type saponins in Apostichopus japonicus Selenka by matrix solid-phase dispersion - high performance liquid chromatography - ultraviolet absorption detector

Determination of three bioactive holostane-type saponins in Apostichopus japonicus Selenka by matrix solid-phase dispersion - high performance liquid chromatography - ultraviolet absorption detector

Make‐up gas influence on the signal behavior of the Vacuum ultraviolet detector for gas chromatography

AbstractA vacuum ultraviolet absorbance detector features the addition of the make‐up gas whose purpose is to decrease the diffusion of analytes in the flow cell. It has been previously demonstrated that the vacuum ultraviolet detector VGA 100 is a concentration‐sensitive detector for which the signal area is inversely proportional to the total flow in the flow cell. In this work, the signal behavior in the new generation vacuum ultraviolet detector, which features changed configuration for the introduction of make‐up gas, was explored. Contrary to previous instruments, a non‐linear relationship between the detector signal area and the inverse of the total flow in the flow cell (carrier gas flow + make‐up gas flow) was observed. To explain these observations, we have investigated the behavior of the detector in combination with one‐dimensional and two‐dimensional gas chromatography. Based on the results obtained, it was concluded that in these next‐generation instruments, flow in the flow cell cannot be regarded as a simple sum of the gas chromatography column flow and the total make‐up flow. After making modifications to the estimation of the total effective flow in the flow cell, a linear relationship between the signal area and the inverse of the flow in the flow cell was recovered.

Quantification of Hydrocarbons in Gas Oils by GC×GC-VUV: Comparison with Other Techniques

Insight into the composition of middle distillates is essential to meet the requirements for product quality but also in terms of complying with ever more stringent environmental regulations. A newly introduced vacuum ultraviolet absorbance detector (VUV) possesses both quantitative and qualitative abilities and is amenable to hyphenation with comprehensive two-dimensional gas chromatography (GC×GC). It has good selectivity for hydrocarbon species and permits their differentiation even if they are not chromatographically separated. In this study, quantification of hydrocarbons in 14 gas oils coming from different origins was performed to evaluate the benefits of GC×GC-VUV for the analysis of middle distillates. Coelutions between hydrocarbon families were investigated and spectral decomposition was carried out for quantification of coeluted hydrocarbon families. Quantification obtained with GC×GC-VUV was compared with conventional techniques such as GC×GC-FID with prefractionation, MS method based on ASTM D2425, UV spectroscopic analysis, and bromine number. In general, good comparability was obtained between GC×GC-VUV and all the different techniques for major hydrocarbon families, however with a gain in time and/or information when using GC×GC-VUV. This demonstrates that GC×GC-VUV can be considered as a relevant tool for the detailed analysis of middle distillates, regardless of their origin.

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.

Combination of chromatographic and spectroscopic characterization based on primitive ultraviolet absorbance detection to fulfill advanced monitoring of dissolved organic matter in municipal wastewater treatment plant

Effective and affordable monitoring tool for dissolved organic matter (DOM) in municipal wastewater treatment plant (WWTP) is in great need. In this study, high-performance size exclusion chromatography (HPSEC) with ultraviolet absorbance (UVA) detection and ultraviolet (UV) spectrometry were complementarily combined for advanced characterization of DOM in a municipal WWTP. DOM in different process units were chromatographically characterized mainly by UVA at 210 nm (UVA210), 254 nm (UVA254), UVA ratio index (URI, UVA210/UVA254). Differential and derivative UV spectrometry were also used for DOM characterization. HPSEC URI chromatographic analyses helped to acquire rich chemical information of DOM components with primitive UVA detection. Influent HPSEC fractions Ⅰ, Ⅳ, Ⅴ− 2, which were proved to consist of protein and polysaccharides, low molecular weight organic acids and hydrophobic organics respectively, were readily removable. HPSEC fractions Ⅱ and Ⅲ were proved to contain mostly recalcitrant humic substances (HS). Effluent HPSEC fraction Ⅴ− 1 contained nonbiodegradable saturated organics. UV spectrometry complemented HPSEC characterization by revealing that saturated organics generated during sand filtration and second derivative peak height at 295 nm (SDPH295) could be surrogate for biodegradable organics concentration in influent. Measures for DOM control optimization of this WWTP were proposed based on the DOM characteristics revealed. This study proved practicability of achieving advanced DOM monitoring with cheap and convenient but primitive chromatographic and spectroscopic characterization with UVA detection which may provide basis for developing applicable equipment for organic pollutants monitoring of municipal WWTP.

Ion chromatograph with three-dimensional printed absorbance detector for indirect ultraviolet absorbance detection of phosphate in effluent and natural waters.

An ion chromatography system employing a low-cost three-dimensional printed absorbance detector for indirect ultraviolet detection towards portable phosphate analysis of environmental and industrial waters has been developed. The optical detection cell was fabricated using stereolithography three-dimensional printing of nanocomposite material. Chromatographic analysis and detection of phosphate were carried out using a CS5A 4 × 250mm analytical column with indirect ultraviolet detection using a 255nm light-emitting diode. Isocratic elution using a 0.6mM potassium phthalate eluent combined with 1.44mM sodium bicarbonate was employed at a flow rate of 0.75mL/min. A linear calibration range of 0.5 to 30mg/L PO4 3- applicable to environmental and wastewater analysis was achieved. For retention time and peak area repeatability, relative standard deviation values were 0.68 and 4.09%, respectively. Environmental and wastewater samples were analyzed with the optimized ion chromatography platform and the results were compared to values obtained by an accredited ion chromatograph. For the analysis of environmental samples, relative errors of<14 % were achieved. Recovery analysis was also carried out on both freshwater and wastewater samples and recovery results were within the acceptable range for water analysis using standard ion chromatography methods.

Therapeutic drug monitoring of linezolid: HPLC-based assays for routine quantification of linezolid in human serum and cerebrospinal fluid

ObjectiveTherapeutic drug monitoring (TDM) of linezolid can prevent over- and under-dosing in critically ill patients and can be crucial to successful antibiotic treatment. Quick and simple high-performance liquid chromatography (HPLC)...

Investigation of the Experimental Pharmacokinetics of the Bis-Chlorinated Bis-pyridinium Mono-aldoxime Cholinesterase Reactivator K-868 in Rats

Background: The widespread use of organophosphorus compounds in agriculture and their existence in some military arsenals present continuous threats. Quaternary bis-pyridinium aldoximes are potent, highly polar cholinesterase reactivators and the most intensively studied candidate antidotes against poisoning with organophosphorus compounds. Objective: The in vivo experimental pharmacokinetic properties of K-868, a novel bis-chlorinated, bis-pyridinium mono-aldoxime are detailed and put in context with regard to similar compounds described earlier. Methods: Rats received 30 µmol K-868 i.m. and were sacrificed at various time points following treatment. Blood, cerebrospinal fluid and tear were collected, while the brains, eyes, kidneys, livers, lungs and testes were removed, dissected and homogenized. K-868 concentrations were determined using high performance liquid chromatography with ultraviolet absorption detection. Results: K-868 was detected in the eyes, kidneys, lungs and tear within 5 minutes in maximal serum concentrations attained 15 minutes following administration. Elimination was slow for K-868 which remained detectable at 120 minutes in the blood and the kidneys, and at 60 minutes in the eyes, lungs and tear following its administration. Nevertheless, its distribution was overall poor with areas under the 120-minute concentration curves (AUC120) showing close similarity in the blood and the kidneys, while reaching just approximately 5% of serum AUC120 in the eyes and lungs. Conclusion: K-868 is a potent candidate antidote against organophosphate poisoining with a prolonged presence in the circulation.

Green detection of trace cyanuric acid and free chlorine together via ion chromatography

Chlorinated cyanurates (CCAs) are a type of disinfectants currently used worldwide for fight of Coronavirus. However, CCAs upon dosed into water can release not only free chlorine (FC), a strong disinfectant, but also cyanurate (CYA), a persistent compound potentially harmful to human and environment. Therefore, detecting CYA and FC in water are very important not only for ensuring sufficient disinfection but also for monitoring the impacts of FC and CYA on receiving watershed. However, conventional analytical methods for them are mostly based on colorimetric methods, which have high method detection limits (MDLs) and rely on chemical reactions that are likely sensitive to coexisting chemicals. To overcome these issues, we herein proposed a facile and reaction-free method to detect CYA and FC together in just one run by ion chromatography (IC) equipped with both conductivity and ultraviolet absorbance detectors. The method features obvious advantages over colorimetric methods in being lower MDLs (3.6 μg/L for CYA and 9.0 μg/L for FC), environmental-friendly (i.e., no organic solvent involved), and more resistant to alkaline solution. With this method, trace levels of CYA (i.e., 34–44 μg/L), which were nondetectable by conventional method, were found in two river water samples, implying that the local environment was already polluted by CCAs during the pandemic period. Overall, this study demonstrates a robust tool that may assist better understanding and monitoring the fate and transport of trace CCA derivatives in water.

Multi-dimensional plug-and-play liquid chromatography-native ion mobility mass spectrometry method for the analysis of biotherapeutics

A flexible inline size exclusion chromatography (SEC) and ion-exchange chromatography (IEX) method coupled to native mass spectrometry (nMS) method was developed for the analysis of protein aggregates and charge variants in a single run of biotherapeutics. This method can be applied to a broad spectrum of biologics such as human growth hormone and its soluble aggregates, the oligomer state distribution of liraglutide in solutions with different pH, and the native states of homodimers and heterodimers generated during a force stressed study of mixtures of two monoclonal antibodies. Tuning of both orbitrap and time of flight (TOF) mass spectrometers in native MS mode to accommodate this LC system is shown in this work for the analysis of biopharmaceutics. This SEC-IEX -UV-nMS system offers two-dimensional separation and two detection methods (ultraviolet absorbance and mass detection), providing an orthogonal characterization of complicated protein samples in a single method.

Effects of post-veraison irrigation on the phenolic composition of &lt;i&gt;Vitis vinifera&lt;/i&gt; L. cv. ‘Xinomavro’ grapes

‘Xinomavro’ (the second planted red Greek variety behind ‘Agiorgitiko’) generally produces wines that are light in colour but with increased astringency, possibly related to grape flavonoid amount and composition; although irrigation is accepted as an effective means to enhance grape phenolic maturity, its role has not yet been sufficiently studied in the case of Xinomavro. This study aimed to determine the effect of post-veraison irrigation on berry anthocyanin and proanthocyanidin amount and composition, of field-grown Xinomavro vines (Vitis vinifera L.), under the typical summer conditions of Northern Greece. In a 10-year-old Xinomavro vineyard, two post-veraison watering regimes were applied—irrigation starting 20 days after veraison (mid-ripening irrigation, MRI) and irrigation starting immediately after veraison was completed (after veraison irrigation, AVI)—alongside non irrigated vines (NI), and vines irrigated continuously from berry set through harvest (continuous irrigation, CI). Proanthocyanidin composition was determined in both skins and seeds by employing phloroglucinolysis followed by HPLC-UV and MS detection (high-performance liquid chromatographic with tandem mass spectrometric and ultraviolet absorbance detection), and the anthocyanin profile was identified only in the skin extracts by HPLC-UV (high-performance liquid chromatographic with ultraviolet absorbance detection). Post-veraison irrigation increased yield parameters and reduced anthocyanin levels and the proportion of their stable forms (acylated vs. non-acylated, tri-oxygenated and methoxylated on the B-ring vs. di-oxygenated and hydroxylated), compared to NI vines; however, these effects were more pronounced in the case of early post-veraison irrigation (AVI) than late-season irrigation (MRI). Irrigation also increased the mean Degree of Polymerization (mDP) and prodelphinidin percentage of skin tannins and decreased mDP of seed tannins. In the light of the necessity to control the accelerated ripening under the increasingly hotter and drier climatic conditions, late irrigation (MRI) might provide a solution to avoid excessive sugar levels and allow a slightly higher yield without significant reductions in berry phenolic content. The results suggest that the optimisation of the timing of irrigation could provide an effective adaptation strategy to climate change in Mediterranean viticultural areas.

Comparison of ultraviolet and refractive index detections in the HPLC analysis of sugars

Refractive index (RI) detection is the standard approach for quantitatively detecting sugars via high-performance liquid chromatography (HPLC), while ultraviolet (UV) absorbance detection is the most commonly used detection method for general HPLC analysis. We compared the two detection approaches of UV and RI in the HPLC analysis of small sugars to investigate whether UV detection could be an alternative method to RI detection. UV detection was performed using a photodiode array scanning from 190 to 400 nm. We obtained comparable limit of detection (LOD) results for RI and UV detection in the HPLC analysis of monosaccharides, while HPLC-RI provided better LOD results than HPLC-UV in disaccharide analysis. Both HPLC-RI and HPLC-UV methods were applied to analyze a real honey sample, and similar results were obtained in terms of precision and recovery. The study conclusively shows that the UV-based HPLC analysis of sugars offers a sufficient alternative to RI-based HPLC analysis.

Portable analyser using two-dimensional ion chromatography with ultra-violet light-emitting diode-based absorbance detection for nitrate monitoring within both saline and freshwaters

A portable and automated IC system with a dual-capability for the analysis of both fresh and saline environmental waters has been developed. Detection of nitrate in complex matrices such as seawater was achieved by the employment of an automated two-dimensional (heart-cut) IC method utilised in tandem with on-column matrix elimination, using a sodium chloride eluent. The system also demonstrated the capability to switch to a second mode of analysis, whereby direct one-dimensional IC analysis was employed to rapidly detect nitrite and nitrate in freshwater, with direct UV LED based absorption detection in under 3 minutes. Calibration curves using a 195 µL sample loop were generated for both freshwater and artificial seawater samples. For marine analysis, an analytical range of 0.1 mg L−1 – 40 mg L−1 NO3− was possible, while an analytical range (0.1 mg L−1 – 15 mg L−1 NO2−, 0.2 – 30 mg L−1 NO3−) appropriate for freshwater analysis was also achieved. Chromatographic repeatability for both marine and freshwater analysis was verified over 40 sequential runs with RSD values of < 1% demonstrated for both peak area and retention times for each mode of analysis. The selectivity of both methods was demonstrated with interference tests with common anions present in environmental waters. Recovery analysis was carried out on marine samples from Tramore Bay, Co. Waterford, Ireland, and the systems analytical performance was compared with that of an accredited IC following environmental sample analysis.

Airborne measurements of oxygen concentration from the surface to the lower stratosphere and pole to pole

Abstract. We have developed in situ and flask sampling systems for airborne measurements of variations in the O2/N2 ratio at the part per million level. We have deployed these instruments on a series of aircraft campaigns to measure the distribution of atmospheric O2 from 0–14 km and 87∘ N to 86∘ S throughout the seasonal cycle. The National Center for Atmospheric Research (NCAR) airborne oxygen instrument (AO2) uses a vacuum ultraviolet (VUV) absorption detector for O2 and also includes an infrared CO2 sensor. The VUV detector has a precision in 5 s of ±1.25 per meg (1σ) δ(O2/N2), but thermal fractionation and motion effects increase this to ±2.5–4.0 per meg when sampling ambient air in flight. The NCAR/Scripps airborne flask sampler (Medusa) collects 32 cryogenically dried air samples per flight under actively controlled flow and pressure conditions. For in situ or flask O2 measurements, fractionation and surface effects can be important at the required high levels of relative precision. We describe our sampling and measurement techniques and efforts to reduce potential biases. We also present a selection of observational results highlighting the individual and combined instrument performance. These include vertical profiles, O2:CO2 correlations, and latitudinal cross sections reflecting the distinct influences of terrestrial photosynthesis, air–sea gas exchange, burning of various fuels, and stratospheric dynamics. When present, we have corrected the flask δ(O2/N2) measurements for fractionation during sampling or analysis with the use of the concurrent δ(Ar/N2) measurements. We have also corrected the in situ δ(O2/N2) measurements for inlet fractionation and humidity effects by comparison to the corrected flask values. A comparison of Ar/N2-corrected Medusa flask δ(O2/N2) measurements to regional Scripps O2 Program station observations shows no systematic biases over 10 recent campaigns (+0.2±8.2 per meg, mean and standard deviation, n=86). For AO2, after resolving sample drying and inlet fractionation biases previously on the order of 10–100 per meg, independent AO2 δ(O2/N2) measurements over six more recent campaigns differ from coincident Medusa flask measurements by -0.3±7.2 per meg (mean and standard deviation, n=1361) with campaign-specific means ranging from −5 to +5 per meg.

Comparison of headspace solid-phase microextraction high capacity fiber coatings based on dual mass spectrometric and broadband vacuum ultraviolet absorption detection for untargeted analysis of beer volatiles using gas chromatography

Despite the same basic ingredients used in brewing, there is a significant variation in beer styles. With the rapid increase in craft brewing, beer styles have become even more numerous and complex in the recent past. A GC-MS/VUV (post-column split for dual detection) instrument with headspace high capacity SPME was used to investigate 21 different beers which represent three beer styles - India pale ales, blondes, and hefeweizens. Since results from untargeted studies can be affected by the sorbent material used, the extraction performances of three high capacity SPME fibers, i.e., polydimethylsiloxane, polydimethylsiloxane/carbon wide range, and polydimethylsiloxane/carbon wide range/divinylbenzene, were evaluated. Good reproducibility (<10% RSD) was obtained for each high capacity fiber using both detectors. The tandem MS/VUV detection coupled with GC separation proved to be particularly valuable for compound identification, especially for isomers and compounds with similar structures. The evaluation of VUV detection for untargeted analysis led to similar performances as MS detection. Both the VUV and the MS were able to effectively differentiate between beer styles using principal component analysis. In addition, the use of 3 different statistical approaches, one-way ANOVA (p-value < 0.05), partial least square discriminant analysis, and random forest, universally identified 12 of the components most influential in distinguishing the three beer styles (e.g., β-myrcene, linalool, isopentyl acetate, 2,4-di-tert-butylphenol). This is the first reported evaluation of VUV detection and the first comparison of simultaneous VUV and MS detection for untargeted classification of complex mixtures using GC.