Automated method using direct-immersion solid-phase microextraction and on-fiber derivatization coupled with comprehensive two-dimensional gas chromatography high-resolution mass spectrometry for profiling naphthenic acids in produced water.

Naphthenic acids (NAs) are naturally occurring organic acids in petroleum and are found in waste waters generated during oil production (produced water, PW). Profiling this class of compounds is important due to flow assurance during oil exploration. Compositional analysis of PW is also relevant for waste treatment to reduce negative impacts on the environment. Here, comprehensive two-dimensional gas chromatography coupled with high-resolution mass spectrometry (GC×GC-HRMS) was applied as an ideal platform for qualitative analysis of NAs by combining the high peak capacity of the composite system with automated scripts for group-type identification based on accurate mass measurements and fragmentation patterns. To achieve high-throughput profiling of NAs in PW samples, direct-immersion solid phase microextraction (DI-SPME) was selected for extraction, derivatization and preconcentration. A fully automated DI-SPME method was developed to combine extraction, fiber rinsing and drying, and on-fiber derivatization with N-methyl-N­tert-butyldimethylsilyltrifluoroacetamide (MTBSTFA). Data processing was based on filtering scripts using the Computer Language for Identifying Chemicals (CLIC). The method successfully identified up to 94 NAs comprising carbon numbers between 6 and 18 and hydrogen deficiency values ranging from 0 to -4. The proposed method demonstrated wider extraction coverage compared to traditional liquid-liquid extraction (LLE) - a critical factor for petroleomic investigations. The method developed also enabled quantitative analysis, exhibiting detection limits of 0.5 ng L-1 and relative standard deviation (RSD) at a concentration of NAs of 30 µg L-1 ranging from 4.5 to 25.0%.

Miniaturized systems for gas chromatography: Developments in sample preparation and instrumentation.

An important field of research is the miniaturization of analytical systems for laboratory applications and on-field analysis. In particular, gas chromatography (GC) has benefited from the recent advances in enabling technologies like photolithography, micromachining, hot embossing, and 3D-printing to improve sampling and sample preparation, microcolumn technologies, and detection. In this article, the developments and applications reported since 2015 were reviewed and summarized. Important applications using benchtop instruments, portable GCs, and micro-GCs (µGCs) were showcased to illustrate the current challenges associated with each miniaturized interfaces and systems. For instance, portable instruments need to be energy-efficient and ideally depend on renewable sources for carrier gas generation. Lastly, multidimensional separations were addressed using miniaturized systems to effectively improve the peak capacity of portable systems.

Naphthenic Acids: Formation, Role in Emulsion Stability, and Recent Advances in Mass Spectrometry-Based Analytical Methods.

Naphthenic acids (NAs) are compounds naturally present in most petroleum sources comprised of complex mixtures with a highly variable composition depending on their origin. Their occurrence in crude oil can cause severe corrosion problems and catalysts deactivation, decreasing oil quality and consequently impacting its productivity and economic value. NAs structures also allow them to behave as surfactants, causing the formation and stabilization of emulsions. In face of the ongoing challenge of treatment of water-in-oil (W/O) or oil-in-water (O/W) emulsions in the oil and gas industry, it is important to understand how NAs act in emulsified systems and which acids are present in the interface. Considering that, this review describes the properties of NAs, their role in the formation and stability of oil emulsions, and the modern analytical methods used for the qualitative analysis of such acids.

Practical Considerations in Method Development for Gas Chromatography-Based Metabolomic Profiling.

This chapter discusses the fundamentals of gas chromatography (GC) to improve method development for metabolic profiling of complex biological samples. The selection of column geometry and phase ratio impacts analyte mass transfer, which must be carefully optimized for fast analysis. Stationary phase selection is critical to obtain baseline resolution of critical pairs, but such selection must consider important aspects of metabolomic protocols, such as derivatization and dependence of analyte identification on existing databases. Sample preparation methods are also addressed depending on the sample matrix, including liquid-liquid extraction and solid-phase microextraction.

Profiling naphthenic acids in produced water using hollow fiber liquid-phase microextraction combined with gas chromatography coupled to Fourier transform Orbitrap mass spectrometry.

In this study, we describe the development of an analytical method to profile naphthenic acids (NAs) from produced water (PW). The NAs were isolated by hollow fiber liquid-phase microextraction (HF-LPME). A microwave-assisted methylation method was used to convert the free acids into its corresponding naphthenic methyl esters (NAMEs). The best reaction conditions were ascertained using central composite design. The optimized sample preparation method exhibited an improved analytical eco-scale value (80 vs. 61) compared to conventional liquid-liquid extraction. Although the primary goal was qualitative analysis of NAMEs (e.g., group-type separation) in produced water, the quantitative performance was also evaluated for future investigations. The instrumental detection and quantification limits were 0.10 ng mL-1 and 0.16 ng mL-1, respectively, using full spectrum data acquisition. The accuracy and precision of the proposed method ranged from 90.4 to 96.6 % and 3.3 to 13.1 %, respectively, using matrix-matched working solutions (0.1, 0.5, and 1.0 µg mL-1). The monoisotopic masses of the adduct ions ([M+H]+) and its corresponding fine isotopic patterns were used to determine the elemental composition of the NAMEs in the PW samples. Qualitative analysis indicated the O2 class as the predominant class in all samples with carbon numbers ranging from C5 to C19 and double bond equivalent (DBE) values of 1 to 8. Additional classes of polar compounds, i.e., O3, O4 and nitrogen-containing classes, are reported for the first time by gas chromatography coupled to Fourier transform Orbitrap mass spectrometry and chemical ionization.

Simple and cost-effective determination of polychlorinated biphenyls in insulating oils using an ionic liquid-based stationary phase and flow modulated comprehensive two-dimensional gas chromatography with electron capture detection.

In this article we describe a method using flow-modulated comprehensive two-dimensional gas chromatography with electron capture detector (FM-GC×GC-ECD) for the determination of polychlorinated biphenyls (PCBs) in complex transformer oils bypassing the need for sample preparation. A two-fold improvement in method development was attained. First, the solvation parameter model (SPM) was used to guide column selection. A highly cohesive ionic liquid-based phase (low l system constant), namely 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethanesulfonyl)imide, was used in the primary stage leading to negligible retention of interfering aliphatic hydrocarbons, which are eluted in the first upper quadrant of the chromatogram. The resulting separation space was used to resolve the critical class of compounds, namely, PCBs and polyaromatic hydrocarbons. Second, a unique combination of column geometries and phase ratios enabled highly efficient reverse fill/flush flow modulation using very low pressure for auxiliary gas flow. The proof of concept method described herein exhibited linearities ranging from 0.990 to 0.994, limits of quantitation (LOQ) from 2.23 and 6.85 µg mL-1, precision below 5% relative standard deviation (RSD), and accuracy from 84.2% to 108.9% showcasing the potential of FM-GC×GC for routine analysis.

Characterization of the aroma profile of novel Brazilian wines by solid-phase microextraction using polymeric ionic liquid sorbent coatings.

In this study, a series of polymeric ionic liquid (PIL) sorbent coatings is evaluated for the extraction of polar volatile organic compounds (VOCs) from Brazilian wines using headspace solid-phase microextraction (HS-SPME), including samples from 'Isabella' and 'BRS Magna' cultivars-the latter was recently introduced by the Brazilian Agricultural Research Corporation - National Grape & Wine Research Center. The structurally tuned SPME coatings were compared to the commercial SPME phases, namely poly(acrylate) (PA) and divinylbenzene/carboxen/poly(dimethylsiloxane) (DVB/CAR/PDMS). The separation, detection and identification of the aroma profiles were obtained using comprehensive two-dimensional gas chromatography mass spectrometry (GC×GC-MS). The best performing PIL-based SPME fiber, namely 1-hexadecyl-3-vinylimidazolium bis[(trifluoromethyl)sulfonyl]imide with 1,12-di(3-vinylimidazolium)dodecane dibis[(trifluoromethyl)sulfonyl]imide incorporated cross-linker supported on an elastic nitinol wire, exhibited superior performance to DVB/CAR/PDMS regarding the average number of extracted peaks and extracted more polar analytes providing additional insight into the aroma profile of 'BRS Magna' wines. Four batches of wine were evaluated, namely 'Isabella' and 'BRS Magna' vintages 2015 and 2016, using highly selective PIL-based SPME coatings and enabled the detection of 350+ peaks. Furthermore, this is the first report evaluating the aroma of 'BRS Magna' wines. A hybrid approach that combined pixel-based Fisher ratio and peak table-based data comparison was used for data handling. This proof-of-concept experiment provided reliable and statistically valid distinction of wines that may guide regulation agencies to create high sample throughput protocols to screen wines exported by Brazilian vintners. Graphical abstract Highly selective extraction of wine aroma using polymeric ionic liquid.

Incidence and growth of Salmonella enterica on the peel and pulp of avocado (Persea americana) and custard apple (Annona squamosa).

The aim of this study was to assess the incidence and to estimate the growth kinetic parameters (maximum growth rate, µ; lag time, λ; and maximum population, κ) of Salmonella on the peel and pulp of avocado (Perseaamericana var. americana) and custard apple (Annona squamosa L.) as affected by temperature (10-30°C). The incidence of Salmonella was assessed on the peel and pulp of the fruits (n=200 of each fruit), separately, totalizing 800 analyses. Only three samples of custard apple pulp were positive for Salmonella enterica and the three isolates recovered belonged to serotype S. Typhimurium. Salmonella was not recovered from avocado and custard apple peels and from avocado pulp. Generally, the substrate (pulp or peel) of growth did not affect µ values of S. enterica (p>0.05). Very similar µ values were found for S. enterica inoculated in custard apple and avocado. S. enterica presented the highest λ in the peel of the fruits. The growth of S. enterica resulted in larger λ in custard apple in comparison to avocado. For example, the λ of S. enterica in the pulp of custard apple and avocado were 47.0±0.78h and 10.0±3.78h, respectively. The lowest values of κ were obtained at the lower storage temperature conditions (10°C). For instance, κ values of 3.7±0.06log CFU/g and 2.9±0.03log CFU/g were obtained from the growth of S. enterica in avocado and custard apple pulps at 10°C (p<0.05), respectively. On the other hand, at 30°C, κ values were 6.5±0.25log CFU/g and 6.5±0.05log CFU/g, respectively. Significantly higher κ were obtained from the growth of S. enterica in the pulp than in the peel of the fruits (p<0.05). For instance, the growth of S. enterica in the pulp of avocado led to a κ value of 6.5±0.25log CFU/g, while in the peel led to a κ value of 4.6±0.23log CFU/g (p<0.05). In general, growth kinetic parameters indicated that avocado comprises a better substrate than custard apple for the growth of S. enterica. The square root model fitted to the data obtained in this study and to the growth data available in the literature for other tropical low acid fruits indicated high variability in µ and λ of Salmonella. The results obtained in this study show that whole low acid tropical fruits can harbor Salmonella, and that this foodborne pathogen can not only survive but also grow both on the peel and pulp of low acid tropical fruits, such as avocado and custard apple.