Nonpolar Analytes Research Articles

Determination of multiple restricted and prohibited ingredients in hair dyes using a novel 3D stationary phase coupled with gas chromatography-mass spectrometry

Hair dyes (HDs) are mainly composed of various benzene series, amines, and phenolic compounds. These ingredients are well known to have allergenic, teratogenic, and carcinogenic properties. As such, the presence of these ingredients in HDs has received increased attention in recent years. At present, the applications of traditional analytical and detection methods and commercial chromatographic columns are limited by problems such as poor qualitative analysis and inaccurate quantification. Thus, the development of new analytical and detection technologies and stationary phases is an urgent endeavor. Moreover, HDs contain complex compounds and exhibit significant matrix interference. Hence, appropriate sample pretreatment methods are necessary to analyze HDs. In this study, the 3D nonpolar rigid structure of triptycene (TP) was combined with the polar flexible chains of polyethylene glycol (PEG) to design and synthesize a TP derivative, TP-PEG, as a stationary phase for chromatographic columns. The stationary phase enabled the expansion of the selection range for polar and nonpolar analytes. Subsequently, gas chromatography-mass spectrometry (GC-MS) was used to quantitatively analyze 22 ingredients in HDs. The experimental results demonstrated that analytes with different polarities exhibited sharp and symmetrical peak shapes on the stationary phase, and all 22 analytes achieved baseline separation on the chromatographic column. The 22 ingredients in HDs showed good linear relationships within their respective ranges, with correlation coefficients greater than 0.9985. The average recovery rates at three spiked levels were in the range of 89.2%-103.2%, and RSDs were less than 5%. Compared with traditional methods, the proposed method has higher efficiency and better accuracy, thus verifying the excellent separation performance of the new stationary phase and the effectiveness of the established GC-MS detection method. The findings indicated the applicability of the developed method to the detection and analysis of various compounds in HDs.

High-temperature liquid chromatography-isotope ratio mass spectrometry methodology for carbon isotope ratio determination of anabolic steroids in urine

BackgroundGas Chromatography Isotope Ratio Mass Spectrometry (GC-C-IRMS) has long been used in routine laboratories to determine the δ13C values of anabolic steroids in urine, differentiating between, e.g., endogenous and synthetic testosterone (T) in sports doping control. Until now, liquid chromatography (LC-IRMS) has not been used. The LC-IRMS setup doesn't allow organic solvents or modifiers in the mobile phase for δ13C determinations. Mid-to non-polar analytes such as steroids can be analysed in water heated to High Temperatures (HT, up to 200 °C) because at 200 °C has a similar polarity as 80/20 methanol/water at ambient temperature. In this work, we developed a method for steroids in urine, extending the application of the LC-IRMS to non-polar analytes in complex matrices. ResultAn HT-LC-IRMS method capable of determining the δ13C values of four steroids (i.e., testosterone (T), 5α-androstane-3α,17β-diol (ααβ), 5β-androstane-3α,17β-diol (βαβ) and pregnanetriol (PT)) in urine was developed and validated. Accuracy ranged from 0.23 ‰ (ααβ and βαβ) to 0.49 ‰ (T), and the detection limit was set at 10 ng mL−1 (T, ααβ+βαβ). The validation data and a comparison of authentic urine samples analysed with HT-LC-IRMS and GC-C-IRMS indicated a comparable performance between HT-LC-IRMS and GC-C-IRMS. SignificanceHT-LC-IRMS can be used to determine δ13C values of anabolic steroids, extending the applicability of both HT-LC and LC-IRMS to non-polar substances determined in a complex matrix in routine laboratory practice.

Chemical Characterization of Terpene-Based Hydrophobic Eutectic Solvents and Their Application for Pb(II) Complexation during Solvent Extraction Procedure.

Solvents prepared from natural terpenes (menthol and thymol), as H-bond acceptors, and a series of organic acids (chain lengths of 8, 10, and 14 C atoms), as H-bond donors, were characterized and tested as reaction media for liquid-liquid extraction purposes. Due to their high hydrophobicity, they seem to be promising alternatives to conventional (nonpolar and toxic) solvents, since they possess relatively less toxic, less volatile, and consequently, more environmentally friendly characteristics. Assuming that the equilibrium is established between solvent and analyte during a ligandless procedure, it can be concluded that those nonpolar solvents can efficiently extract nonpolar analytes from the aqueous environment. Previous investigations showed a wide range of applications, including their use as solvents in extractions of metal cations, small molecules, and bioactive compounds for food and pharmaceutical applications. In this work, hydrophobic solvents based on natural terpenes, which showed chemical stability and desirable physicochemical and thermal properties, were chosen as potential reaction media in the liquid-liquid extraction (LLE) procedure for Pb(II) removal from aqueous solutions. Low viscosities and high hydrophobicities of prepared solvents were confirmed as desirable properties for their application. Extraction parameters were optimized, and chosen solvents were applied. The results showed satisfactory extraction efficiencies in simple and fast procedures, followed by low solvent consumption. The best results (98%) were obtained by the thymol-based solvent, thymol-decanoic acid (Thy-DecA) 1:1, followed by L-menthol-based solvents: menthol-octanoic acid (Men-OctA) 1:1 with 97% and menthol-decanoic acid (Men-DecA) 1:1 with 94.3% efficiency.

Synergistic Interface Platforms: Designing Superhydrophilic Conductive Nanoparticle‐Decorated Nanofibrous Membranes

AbstractIn today's technological landscape, advancing methods for producing conductive membranes that simplify and streamline the development of advanced interface materials is crucial. This study introduces a versatile and innovative method for fabricating superhydrophilic, conductive nanofibrous membranes based on the in situ synthesis of polypyrrole nanoparticles on poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) electrospun fibers. The composite membranes morphologically exhibit a particle‐decorated nanofibrous configuration, with polypyrrole nanoparticles distributed along the individual fibers' surface. The nanoparticle‐nanofiber configuration shows distinctive properties; electrochemically, the electrospun mats demonstrate excellent inherent electrical conductivity, good cyclic and high electrochemical stability, and low resistance. Furthermore, the amphiphilic and superhydrophilic behavior, achieved through nanotopography, porosity and interactions between the intrinsically conductive polymer and the PVDF‐HFP fibers, enables efficient uptake of polar and nonpolar analytes. The membranes also demonstrate good in vitro cell viability of both murine and human fibroblasts. Given its efficient interaction with liquids and omnidirectional 360‐degree conductivity, this material emerges as an excellent candidate for use as a biocompatible, multifunctional interface layer. The produced nanoparticle‐nanofibrous membrane materials offer a promising platform for interface applications, featuring enhanced spatiotemporal configurations and wide‐ranging applicability.

Reversible solvent interactions with UiO-67 metal-organic frameworks.

The utility of UiO-67 Metal-Organic Frameworks (MOFs) for practical applications requires a comprehensive understanding of intermolecular host-guest MOF-analyte interactions. To investigate intermolecular interactions between UiO-67 MOFs and complex molecules, it is useful to evaluate the interactions with simple polar and non-polar analytes. This problem is approached by investigating the interactions of polar (acetone and isopropanol) and non-polar (n-heptane) molecules with functionalized UiO-67 MOFs via temperature programmed desorption mass spectrometry and temperature programmed Fourier transform infrared spectroscopy. We find that isopropanol, acetone, and n-heptane bind reversibly and non-destructively to UiO-67 MOFs, where MOF and analyte functionality influence relative binding strengths (n-heptane ≈ isopropanol > acetone). During heating, all three analytes diffuse into the internal pore environment and directly interact with the μ3-OH groups located within the tetrahedral pores, evidenced by the IR response of ν(μ3-OH). We observe nonlinear changes in the infrared cross sections of the ν(CH) modes of acetone, isopropanol, and n-heptane following diffusion into UiO-67. Similarly, acetone's ν(C=O) infrared cross section increases dramatically when diffused into UiO-67. Ultimately, this in situ investigation provides insights into how individual molecular functional groups interact with UiO MOFs and enables a foundation where MOF interactions with complex molecular systems can be evaluated.

Utilizing a Metal Inlet Coiled with Copper Wire as the Ion Source for Ambient Ionization Mass Spectrometry.

In ambient ionization mass spectrometry (MS), a customized metal inlet is typically adapted to the orifice of the mass spectrometer for ease of introduction of the sample. We herein explore that the metal inlet coiled with a copper wire (∼50 μm) can be directly used as an ion source to induce corona discharge-like processes for ionization of analytes in the gas phase. When the metal inlet is subjected to a high voltage in the mass spectrometer, the electric field provided by the mass spectrometer enables the generation of corona discharge to ionize volatile/semivolatile analytes derived from the sample in the condensed phase. The limit of detection for azulene derived from the aqueous sample was as low as ∼1 pM. Moreover, we also demonstrated the feasibility of coupling ultraviolet-visible absorption spectroscopy with MS by using the metal inlet coiled with a thin copper wire as the interface. Integration of these two techniques enables the simultaneous acquisition of spectra from both instruments for quantitative and qualitative analysis of the sample. Furthermore, we showed that polar and nonpolar analytes in a mixture can be acquired in the same mass spectrum by simply depositing a sample droplet (∼20 μL) on a dielectric substrate near the copper wire-coiled metal inlet of the mass spectrometer. The ionization processes involved both electrospray ionization and corona discharge. To demonstrate the applicability of our method for detecting nonpolar and polar analytes in complex samples, we spiked a nonpolar analyte, benzo[a]pyrene, to a spice sample and successfully detected analytes with different polarities using our approach.

Comprehensive two-step supercritical fluid extraction for green isolation of volatiles and phenolic compounds from plant material

A comprehensive two-step supercritical extraction using green solvents allows the extraction of non-polar and polar analytes within one run in two consecutive steps.

Development of a column switching for direct online enrichment and separation of polar and nonpolar analytes from aqueous matrices

Trace substances in surface waters may threaten health and pose a risk for the aquatic environment. Moreover, separation and detection by instrumental analysis is challenging due to the low concentration and the wide range of polarities. Separation of polar and nonpolar analytes can be achieved by using stationary phases with different selectivity. Lower limits of detection of trace substances can be obtained by offline enrichment on solid phase materials. However, these practices require substantial effort and are time consuming and costly. Therefore, in this study, a column switching was developed to enrich and separate both polar and nonpolar analytes by an on-column large volume injection of aqueous samples. The column switching can significantly reduce the effort and time for analyzing trace substances without compromising on separation and detection. A reversed phase (RP) column is used to trap the nonpolar analytes. The polar analytes are enriched on a porous graphitized carbon column (PGC) coupled serially behind the RP column. A novel valve switching system is implemented to enable elution of the nonpolar analytes from the RP column and, subsequently, elution of polar analytes from the PGC column and separation on a hydrophilic interaction liquid chromatography (HILIC) column. To enable separation of polar analytes dissolved in an aqueous matrix by HILIC, the water plug that is flushed from the PGC column is diluted by dosing organic solvent directly upstream of the HILIC column. The developed method was tested by applying target analysis and non-target screening, highlighting the advantage to effectively separate and detect both polar and nonpolar compounds in a single chromatographic run. In the target analysis, the analytes, with a logD at pH 3 ranging from -2.8 to + 4.5, could be enriched and separated. Besides the 965 features in the RP phase, 572 features from real wastewater were observed in the HILIC phase which would otherwise elute in the void time in conventional one-dimensional RP methods.

Novel Models for Accurate Estimation of Air-Blood Partitioning: Applications to Individual Compounds and Complex Mixtures of Neutral Organic Compounds.

The air-blood partition coefficient (Kab) is extensively employed in human health risk assessment for chemical exposure. However, current Kab estimation approaches either require an extensive number of parameters or lack precision. In this study, we present two novel and parsimonious models to accurately estimate Kab values for individual neutral organic compounds, as well as their complex mixtures. The first model, termed the GC×GC model, was developed based on the retention times of nonpolar chemical analytes on comprehensive two-dimensional gas chromatography (GC×GC). This model is unique in its ability to estimate the Kab values for complex mixtures of nonpolar organic chemicals. The GC×GC model successfully accounted for the Kab variance (R2 = 0.97) and demonstrated strong prediction power (RMSE = 0.31 log unit) for an independent set of nonpolar chemical analytes. Overall, the GC×GC model can be used to estimate Kab values for complex mixtures of neutral organic compounds. The second model, termed the partition model (PM), is based on two types of partition coefficients: octanol to water (Kow) and air to water (Kaw). The PM was able to effectively account for the variability in Kab data (n = 344), yielding an R2 value of 0.93 and root-mean-square error (RMSE) of 0.34 log unit. The predictive power and explanatory performance of the PM were found to be comparable to those of the parameter-intensive Abraham solvation models (ASMs). Additionally, the PM can be integrated into the software EPI Suite, which is widely used in chemical risk assessment for initial screening. The PM provides quick and reliable estimation of Kab compared to ASMs, while the GC×GC model is uniquely suited for estimating Kab values for complex mixtures of neutral organic compounds. In summary, our study introduces two novel and parsimonious models for the accurate estimation of Kab values for both individual compounds and complex mixtures.

Development of a universal sol–gel sorbent for fabric phase sorptive extraction and its application in tandem with high performance liquid chromatography-ultraviolet detection for the analysis of phthalates in environmental and drinking water samples

Most sorbent-based sample preparation methods are designed to interact with a class of analytes i.e., a polar sorbent for polar analytes, a non-polar sorbent for non-polar analytes, an ion-exchange sorbent for ionized compounds. A big challenge surfaces when making a choice of an appropriate sorbent when there is a mixture of compounds of varying polarities and ionization states in the complex sample matrices. Hence, the aim of this study was to develop a universal sol–gel sorbent coating for fabric phase sorptive extraction that would effectively and simultaneously extract polar, nonpolar, organic acids and bases via different intermolecular/interionic interactions. The universal sol–gel sorbent coated fabric phase sorptive extraction membrane was created by exploiting sol–gel surface coating technology to implant different functional moieties, ion exchanging ligands and an organic polymer that results in a 3-D organic–inorganic hybrid structure on the fabric substrate with a high level of selectivity/affinity for the target compounds. The preconcentrated extracts containing the isolated phthalates after the fabric phase sorptive extraction procedure were injected into the high-performance liquid chromatography-ultraviolet detection (HPLC-UV) system for the quantification. The FPSE-HPLC-UV method demonstrated a linear range between 50 and 1000 ng/mL for dimethyl phthalate, diethyl phthalate, dipropyl phthalate, diallyl phthalate, benzyl butyl phthalate, 1–10000 ng/mL for di-n-heptyl phthalate, 1–5000 ng/mL for di-n-heptyl phthalate, 10–5000 ng/mL for di-n-ethyl hexyl phthalate and 100–7500 ng/mL di-n-octyl phthalate. The intra-day and inter-day reproducibility (in terms of percentage relative standard deviation, %RSD) did not exceed 13.6. This method proves to be a selective, accurate, reproducible, cheap, and fast analytical approach for the quantitative and qualitative determination of the phthalates which is useful in crafting regulations for phthalates content in beverages and juices as well as in environmental monitoring.

Quality Control in Targeted GC-MS for Amino Acid-OMICS.

Gas chromatography-mass spectrometry (GC-MS) is suitable for the analysis of non-polar analytes. Free amino acids (AA) are polar, zwitterionic, non-volatile and thermally labile analytes. Chemical derivatization of AA is indispensable for their measurement by GC-MS. Specific conversion of AA to their unlabeled methyl esters (d0Me) using 2 M HCl in methanol (CH3OH) is a suitable derivatization procedure (60 min, 80 °C). Performance of this reaction in 2 M HCl in tetradeutero-methanol (CD3OD) generates deuterated methyl esters (d3Me) of AA, which can be used as internal standards in GC-MS. d0Me-AA and d3Me-AA require subsequent conversion to their pentafluoropropionyl (PFP) derivatives for GC-MS analysis using pentafluoropropionic anhydride (PFPA) in ethyl acetate (30 min, 65 °C). d0Me-AA-PFP and d3Me-AA-PFP derivatives of AA are readily extractable into water-immiscible, GC-compatible organic solvents such as toluene. d0Me-AA-PFP and d3Me-AA-PFP derivatives are stable in toluene extracts for several weeks, thus enabling high throughput quantitative measurement of biological AA by GC-MS using in situ prepared d3Me-AA as internal standards in OMICS format. Here, we describe the development of a novel OMICS-compatible QC system and demonstrate its utility for the quality control of quantitative analysis of 21 free AA and metabolites in human plasma samples by GC-MS as Me-PFP derivatives. The QC system involves cross-standardization of the concentrations of the AA in their aqueous solutions at four concentration levels and a quantitative control of AA at the same four concentration levels in pooled human plasma samples. The retention time (tR)-based isotope effects (IE) and the difference (δ(H/D) of the retention times of the d0Me-AA-PFP derivatives (tR(H)) and the d3Me-AA-PFP derivatives (tR(D)) were determined in study human plasma samples of a nutritional study (n = 353) and in co-processed QC human plasma samples (n = 64). In total, more than 400 plasma samples were measured in eight runs in seven working days performed by a single person. The proposed QC system provides information about the quantitative performance of the GC-MS analysis of AA in human plasma. IE, δ(H/D) and a massive drop of the peak area values of the d3Me-AA-PFP derivatives may be suitable as additional parameters of qualitative analysis in targeted GC-MS amino acid-OMICS.

A composite hydrogel modified silica stationary phase for mixed‑mode liquid chromatography

A novel composite hydrogel functionalized silica core-shell stationary phase was prepared by the surface modification of silica sphere. The successful synthesis of the new stationary phase (T-Sil@PAM/SA/UiO-66-NH2) was proven by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), etc. Due to the coexistence of amide, hydroxyl, long carbon chain and UiO-66-NH2 in composite hydrogel shell, the obtained stationary phase can be used in hydrophilic/reversed-phase liquid chromatography with multiple retention mechanisms, such as hydrophilic, hydrophobic and π - π interactions. The chromatographic retention behavior of T-Sil@PAM/SA/UiO-66-NH2 demonstrated that the new stationary phase showed excellent separation performance for both polar analytes (such as alkaloids, saccharides, etc.) and nonpolar analytes (such as substituted benzene and polycyclic aromatic hydrocarbon (PAHs), etc.). Furthermore, compared with NH2 column and commercial C18 column, the T-Sil@PAM/SA/UiO-66-NH2 exhibited a certain superiority. Moreover, the relative standard deviation (RSD) of PAHs’ retention time with eight replicates consecutive elution was found to range from 0.03% to 0.17%. Therefore, the successful use of T-Sil@PAM/SA/UiO-66-NH2 in mixed‑mode liquid chromatography expanded the potential applications of hydrogels in the field of separation.

Ultrahigh Sensitivity PTR-MS Instrument with a Well-Defined Ion Chemistry.

Proton-transfer-reaction mass spectrometry (PTR-MS) is widely used for measuring organic trace gases in air. In traditional PTR-MS, both nonpolar and polar analytes are ionized with unit efficiency, as predicted from ion-molecule collision theories. This well-defined ion chemistry allows for direct quantification of analytes without prior calibration and therefore is an important characteristic of PTR-MS. In an effort to further increase the sensitivity, recently developed ultrahigh sensitivity chemical ionization mass spectrometry (CIMS) analyzers have, however, been reported to have sacrificed unit ionization efficiency for selected analytes or classes of analytes. We herein report on the development of a novel ultrasensitive PTR-MS instrument, the FUSION PTR-TOF 10k, which exhibits the same universal unit response as conventional PTR-MS analyzers. The core component of this analyzer is the newly designed FUSION ion-molecule reactor, which is a stack of concentric ring electrodes generating a static longitudinal electric field superimposed by a focusing transversal radiofrequency (RF) field. The FUSION PTR-TOF 10k instrument is equipped with an improved ion source, capable of switching between different reagent ions (H3O+, O2+, NO+, NH4+) in less than one second. The improved time-of-flight mass spectrometer analyzes m/z signals with a mass resolution in the 10000-15000 range. FUSION PTR-TOF 10k achieves sensitivities up to 80000 cps ppbV-1 and detection limits down to 0.5 pptV for a 1 s measurement time. We show time-series of naphthalene and 13C-napthalene as measured in ambient air in Innsbruck for demonstrating the sub-pptV detection capability of this novel FUSION PTR-TOF 10k.

Evaluation of Solvent Compatibilities for Headspace-SIFT-MS Analysis of Pharmaceutical Products

Procedures for determination of the residual solvent and volatile impurity content in pharmaceutical products usually rely on dissolution in a solvent, followed by headspace-gas chromatography (HS-GC) analysis. Whereas chromatographic systems can utilize a wide variety of solvents, direct-injection mass spectrometry (DIMS) techniques have fewer solvent options, because elimination of the chromatographic column means that the instrument is more susceptible to saturation. Since water has the lowest impact, it has almost always been the default solvent for DIMS. In this study, selected ion flow tube mass spectrometry (SIFT-MS)—a DIMS technique—was applied to the systematic evaluation of the proportion of solvent that can be utilized (with aqueous diluent) without causing instrument saturation and while maintaining satisfactory analytical performance. The solvents evaluated were N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), methanol, and triacetin. All solvents are compatible with headspace-SIFT-MS analysis at 5% (min) in water, while DMI, DMAC, and DMSO can be used at higher concentrations (50, 100, and 25%, respectively), though suffering substantial diminution of the limit of quantitation for non-polar analytes at higher proportions of non-aqueous solvent. Analytical performance was also evaluated using linearity, repeatability, and recovery measurements. This work demonstrates that organic solvents diluted in water can be utilized with headspace-SIFT-MS and provide an approach for evaluation of additional diluent solvents.

Sequential Solid-Phase Microextraction with Biocompatible Coating Materials to Address Displacement Effects in the Quantitative Analysis

Solid-phase microextraction (SPME) is a simple and effective sample-preparation technique for the analysis of complex samples. However, sample matrices containing high concentrations of nonpolar substances or spiked analytes in free form can cause swelling, saturation, and/or competition phenomena in the coating material. This results in a displacement effect wherein polar analytes with low affinities for the solid coating material are displaced by nonpolar substances in the matrix or spiked analytes with a high affinity. Therefore, the quantitative analysis of polar analytes can be challenging, as the displacement effect causes non-linearity in the calibration curves. This paper presents a comprehensive investigation of the conditions under which the displacement effect occurs and how it influences the quantitative analysis of polar analytes. To remedy this issue, a sequential SPME strategy using two SPME blades with different selectivities is applied. SPME blades offer a large surface area and coating volume─and thus, greater extraction capacity─which may mitigate the displacement effect. In addition, the biocompatible coatings on the SPME blades are comprised of small amounts of sorbent particles embedded by a polyacrylonitrile (PAN) binder, which allows them to be directly immersed into complex matrixes such as biological and food samples, as the PAN acts as a barrier that prevents the adsorption of large macromolecules (e.g., cells and proteins). As such, a C18/PAN-coated blade was applied for the first extraction step, which significantly decreased the concentrations of nonpolar compounds in the sample. In the second step, a hydrophilic-lipophilic balanced (HLB)/PAN-coated blade was employed to extract the polar analytes and any remaining nonpolar analytes. The proposed sequential SPME strategy successfully enabled the quantitative determination of polar and nonpolar drugs of abuse with log P values ranging from 0.16 to 4.98 in biological matrices while also providing good linearities.

The Improved Non-Polar Gas Sensing Performance of Surface-Modified Porous Silicon-Based Gas Sensors

The present article studied gas sensor sensing characteristics based on surface-modified porous silicon (PS) by depositing the metal oxide semiconductor layer. The PS layer was prepared through the electrochemical etching of crystalline silicon in an HF-based solution. DC magnetron sputtering technology was used to obtain the p-CuO layer on the surface of the p-PS. The obtained material’s structural, morphological, and sensing behavior were investigated using SEM, XRD, Raman spectra, and the current–voltage characteristics. For the detection of toluene and chloroform vapors, a planar structure was used. The sensing response value revealed that the CuO/PS-based gas sensors have good sensitivity for toluene and chloroform vapors. The sensing mechanism is explained using schematic energy band diagrams. Therefore, this approach is helpful for the development of a simple, cost-effective sensor for detecting non-polar chemical analytes.

CCQM Key Comparison track A CCQM-K168: Non-polar analytes in high carbohydrate food matrix: trans-zearalenone in maize powder

Main textDemonstrating competency and equivalence for the measurement capacity of contaminants and nutrients in primary foodstuffs is a priority of the OAWG 10-year strategy for Track A core comparisons. Such measurements have posed significant challenges for reference material producers and calibration service providers. This key comparison (KC), under the topic of "non- polar analyte in high carbohydrate food matrix: trans-Zearalenone (trans-ZEN) in maize powder", was a sector of the model system selected to align with this class within the OAWG strategy. Evidence of successful participation in formal, relevant international comparisons is needed to demonstrate the Calibration and Measurement Capabilities (CMCs) of National Metrology Institutes (NMIs) and Designated Institutes (DIs).17 NMIs and DIs participated in the Track A KC CCQM-K168 "non-polar analyte in high carbohydrate food matrix: trans-ZEN in maize powder". Participants were requested to evaluate the mass fraction (μg/kg) of trans-ZEN in maize powder material. Methods like liquid-liquid extraction and SPE were applied in the pre-treatment, and HPLC-MS/MS and HPLC-FLD were used for detection by the participants. The mass fractions for trans-ZEN were in the range of (91.8 to 169) μg/kg with standard uncertainties of (1.5 to 24.7) μg/kg, and corresponding relative standard uncertainties from 1.5% to 14.6%. Two laboratories, INTI and BAM were excluded from the key comparison reference value (KCRV) evaluation. INTI result was identified as an outlier and confirmed their method had insufficient specificity. For BAM the calibration approach they used does not meet the CIPM traceability requirements. The other 15 laboratories included in the calculation of the consensus KCRV all agreed within their standard uncertainties. Hierarchical Bayes was used as estimators in calculating KCRV and standard uncertainty.Successful participation in CCQM-K168 demonstrates the measurement capabilities in determining mass fraction of organic compounds, with molecular mass of 100 g/mol to 500 g/mol, having low polarity pKow < -2, in mass fraction range from 1 μg/kg to 1000 μg/kg in a high carbohydrate food matrix.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Does High Polarity Mean High Retention on Stationary Phases in Gas Chromatography?

Stationary phase chemistry, polarity, and selectivity have been of ongoing interest since the inception of gas chromatography (GC) in the 1950s. In the early days when most analyses were performed on packed columns, there were hundreds of stationary phase materials available. Today, with modern capillary columns, most GC analyses are performed with a few stationary phases, with a wide array of choices for specialty applications. Stationary phases are often classified using the broad term polarity, with polar stationary phases recommended for separating polar analytes and nonpolar stationary phases recommended for nonpolar analytes. In this installment, we examine the idea of stationary phase polarity. We examine the assumptions inherent in the most popular stationary phase polarity evaluating systems—McReynolds constants and the polarity scale. We see that high polarity does not always mean greater retention or higher selectivity.

Reliable prediction of sensory irritation threshold values of organic compounds using new models based on linear free energy relationships and GC×GC retention parameters

The human sensory irritation threshold (SIT) is an important biochemical parameter for the exposure assessment of organic air pollutants. First, we recalibrated the Abraham solvation models (ASMs) for 9 SIT endpoints by curating 720 individual experimental SIT values to find an accurate and parsimonious ASM variant, which exhibited root mean square error (RMSE) = 0.174–0.473 log unit. Second, we report linear free energy relationships — henceforth called partition models (PMs) — which exploit the correlations of 9 SIT endpoints with the linear combinations of partition coefficients for octanol-water and air-water systems showing RMSE = 0.221–0.591 log unit. These PMs can easily be integrated into widely used EPI-Suite™ screening tool. The explanatory and predictive performance of PMs were like parameter-intensive ASMs. Third, we present GC × GC models that are based on the retention times of the nonpolar analytes on the comprehensive two-dimensional gas chromatography (GC × GC), which successfully described the SIT variance (R2=0.959−0.996) and depicted a strong predictive power (RMSE = 0.359–0.660 log unit) for an independent set of nonpolar analytes. Taken together, PMs allow easy SIT screening of organic chemicals compared to ASMs. Unlike ASMs, our GC × GC models can be applied to estimate SIT of complex nonpolar mixtures.

IR-MALDI Mass Spectrometry Imaging with Plasma Post-Ionization of Nonpolar Metabolites.

Ambient mass spectrometry imaging (MSI) methods come with the advantage of visualizing biomolecules from tissues with no or minimal sample preparation and operation under atmospheric-pressure conditions. Similar to all other MSI methodologies, however, ambient MSI modalities suffer from a pronounced bias toward either polar or nonpolar analytes due to the underlying desorption and ionization mechanisms of the ion source. In this study, we present the design, construction, testing, and application of an in-capillary dielectric barrier discharge (DBD) module for post-ionization of neutrals desorbed by an ambient infrared matrix-assisted laser desorption/ionization (IR-MALDI) MSI source. We demonstrate that the DBD device enhances signal intensities of nonpolar compounds by up to 104 compared to IR-MALDI without affecting transmission of IR-MALDI ions. This allows performing MSI experiments of mouse tissue and Danaus plexippus caterpillar tissue sections, visualizing the distribution of sterols, fatty acids, monoglycerides, and diglycerides that are not detected in IR-MALDI MSI experiments. The pronounced signal enhancement due to IR-MALDI-DBD compared to IR-MALDI MSI enables mapping of nonpolar analytes with pixel resolutions down to 20 μm in mouse brain tissue and to discern the spatial distribution of sterol lipids characteristic for histological regions of D. plexippus.