Albert Robbat

High-performance liquid chromatography retention index and detection of nitrated polycyclic aromatic hydrocarbons

Abstract Based on reversed-phase isocratic experiments and gradient optimization modeling, acetonitrile was found to provide optimum separation of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs). A 31-min linear gradient between 24% and 80% acetonitrile in water at 35°C and 0.5 ml/min flow-rate was established. Nitro-PAH retention indices, I, were measured under these conditions. It was found that retention index values varied with changing column temperature and/or mobile phase compositions. Diode-array, fluorescence (FD) and chemiluminescence (CD) detection were studied for nitro-PAHs. Diode-array detection responded linearly with detection limits between 2 and 12 ng/compound injected. In addition, dual-wavelength UV absorbance ratio (A230/A254, A330/A254 and A230/A330) measurements at these wavelength pairs were reported. Fluorescence and chemiluminescence provided increased selectivity and sensitivity. Four orders of magnitude linear range were found for both detection methods with detection limits between 10 and 15 pg and 50 pg (on an NO2/compound mole basis), respectively.

Total alkylated polycyclic aromatic hydrocarbon characterization and quantitative comparison of selected ion monitoring versus full scan gas chromatography/mass spectrometry based on spectral deconvolution

Quantitative information of alkylated PAH is frequently used in forensic investigations to characterize petroleum releases and fate in the environment. Interference from a complex matrix often obviates target compound quantitation. Using single ion SIM or a single mass spectral pattern to analyze these homologs should result in either over- or underestimating their concentration. To confirm this hypothesis, a library of C(1)-C(4) alkylated PAH fragmentation patterns were made from automated sequential two-dimensional GC-GC/MS data and the Ion Signature deconvolution software. Based on these patterns, 1D GC/MS data was compared using single ion extraction and one fragmentation pattern per homolog against data obtained from those peaks whose scans met the spectral deconvolution criteria. Significant overestimation occurs when a single ion is used to extract peak signal for C(4)-naphthalene, C(1)-fluorene, and the C(1)- to C(3)-dibenzothiophenes. In contrast, C(2)-naphthalene, C(2)-fluorene, C(3)-phenanthrene, and C(1)-dibenzothiophene were underestimated by >50% when one fragmentation pattern per homolog was used. The Ion Signature deconvolution software makes it easy to interpret mass spectrometry data, especially in complex environmental samples like diesel fuel.

Comprehensive profiling of coal tar and crude oil to obtain mass spectra and retention indices for alkylated PAH shows why current methods err.

Investigators use C(1) to C(4) substituted polycyclic aromatic hydrocarbons (PAH) to assess ecological risk and to track fossil fuels and related pollutants in the environment. To quantify these compounds gas chromatography/mass spectrometry (GC/MS) is used. This work demonstrates single ion monitoring (SIM) or extraction (SIE) of full scan data produces inaccurate and imprecise concentration estimates due to incorrect homologue peak assignments. Profiling of coal tar and crude oil by automated sequential GC-GC/MS provided the retention windows and spectral patterns for each homologue to correctly quantify these compounds. Simultaneous pulsed flame photometric (sulfur-specific) detection differentiated PAH from polycyclic aromatic sulfur heterocycles and their alkylated homologues when they eluted within the same retention windows and had common ions. Differences between SIE and spectral deconvolution of GC/MS data based on multiple fragmentation patterns per homologue ranged from a few percent for C(1) compounds to hundreds of percent for the higher alkylated homologues. Findings show current methods produce poor quality data adversely affecting forensic investigations, risk assessments, and weathering studies.

Effect of temperature and organic modifier on the isocratic retention characteristics of nitrated polycyclic aromatic hydrocarbons on a reversed-phase octadecylsilane column

Abstract Nitrated polycyclic aromatic hydrocarbon (nitro-PAH) retention behavior was evaluated on a reversed-phase polymeric octadecylsilane column under isocratic conditions as a function of organic modifier and temperature. Several conclusions can be drawn from the retention and organic modifier study ( viz. , methanol and acetonitrile—water). First, the logarithm of the capacity factor (log k ′) was linearly dependent on organic—water volume fraction (ϕ). Second, nitro-PAH k ′ values increased with decrease in organic modifier concentration. Third, the slopes of log k ′ vs. ϕ plots were solvent-dependent. Larger slope values were found for nitro-PAHs in methanol—water than in acetonitrile—water mixtures for a particular compound. Fourth, slope values were dependent on the molecular structure of individual nitro-PAHs. Nitro-PAH retention times decreased with increase in column temperature. A linear dependence of log k ′ on the reciprocal of the absolute column temperature, the Van `t Hoff plott, was observed for both organic modifiers over the temperature range studied. The standard enthalpic range (Δ H 0 ) for nitro-PAH transfer from the mobile to the stationary pahse was determined. Δ H 0 was dependent on organic modifier tupe and composition as well as solute structure. The enthalpy—entropy compensation effect was evaluated by plotting log k ′ vs. — Δ H 0 and used to interpret nitro-PAH retention mechanisms. A compensation effect was found for some mononitrated PAHs for both organic modifiers. The compensation temperatures were within the accepted range described for reversed-phase high-performance liquid chromatography systems.

Toward the accurate analysis of C1-C4 polycyclic aromatic sulfur heterocycles.

Polycyclic aromatic sulfur heterocycles (PASH) are sulfur analogues of polycyclic aromatic hydrocarbons (PAH). Alkylated PAH attract much attention as carcinogens, mutagens, and as diagnostics for environmental forensics. PASH, in contrast, are mostly ignored in the same studies due to the conspicuous absence of gas chromatography/mass spectrometry (GC/MS) retention times and fragmentation patterns. To obtain these data, eight coal tar and crude oils were analyzed by automated sequential GC-GC. Sample components separated based on their interactions with two different stationary phases. Newly developed algorithms deconvolved combinatorially selected ions to identify and quantify PASH in these samples. Simultaneous detection by MS and pulsed flame photometric detectors (PFPD) provided additional selectivity to differentiate PASH from PAH when coelution occurred. A comprehensive library of spectra and retention indices is reported for the C(1)-C(4) two-, three-, and four-ring PASH. Results demonstrate the importance of using multiple fragmentation patterns per homologue (MFPPH) compared to selected ion monitoring (SIM) or extraction (SIE) to identify isomers. Since SIM/SIE analyses dramatically overestimate homologue concentrations, MFPPH should be used to correctly quantify PASH for bioavailability, weathering, and liability studies.

Effects of Extreme Climate Events on Tea (Camellia sinensis) Functional Quality Validate Indigenous Farmer Knowledge and Sensory Preferences in Tropical China

Climate change is impacting agro-ecosystems, crops, and farmer livelihoods in communities worldwide. While it is well understood that more frequent and intense climate events in many areas are resulting in a decline in crop yields, the impact on crop quality is less acknowledged, yet it is critical for food systems that benefit both farmers and consumers through high-quality products. This study examines tea (Camellia sinensis; Theaceae), the worlds most widely consumed beverage after water, as a study system to measure effects of seasonal precipitation variability on crop functional quality and associated farmer knowledge, preferences, and livelihoods. Sampling was conducted in a major tea producing area of China during an extreme drought through the onset of the East Asian Monsoon in order to capture effects of extreme climate events that are likely to become more frequent with climate change. Compared to the spring drought, tea growth during the monsoon period was up to 50% higher. Concurrently, concentrations of catechin and methylxanthine secondary metabolites, major compounds that determine tea functional quality, were up to 50% lower during the monsoon while total phenolic concentrations and antioxidant activity increased. The inverse relationship between tea growth and concentrations of individual secondary metabolites suggests a dilution effect of precipitation on tea quality. The decrease in concentrations of tea secondary metabolites was accompanied by reduced farmer preference on the basis of sensory characteristics as well as a decline of up to 50% in household income from tea sales. Farmer surveys indicate a high degree of agreement regarding climate patterns and the effects of precipitation on tea yields and quality. Extrapolating findings from this seasonal study to long-term climate scenario projections suggests that farmers and consumers face variable implications with forecasted precipitation scenarios and calls for research on management practices to facilitate climate adaptation for sustainable crop production.

Fast Gas Chromatography/Mass Spectrometry Analysis in Support of Risk-Based Decisions

A new data analysis software system (Ion Fin- gerprint DetectionTM) has been developed to provide fast mass spectral data analysis. Methods have been devel- oped that can provide screening to quantitative gas chro- matography/mass spectrometry (GC/MS) data in 30 s to minutes. Compound selectivity is provided through a unique set of algorithms rather than GC separation. The data quality produced for volatile and semivolatile or- ganic contaminants under fast GC/MS conditions during dynamic site investigations carried out at Hanscom Air Force Base (Bedford, MA) and Joliet Army Ammunition Plant (Joliet, IL) are discussed. More than 800 samples were analyzed in each project, with state and federal reg- ulators accepting the data to complete remedial investi- gation/feasibility (RI/FS) studies. Q 1999 John Wiley & Sons, Inc. Field Analyt Chem Technol 3:55-66, 1999

Electrocatalytic decomposition of hydrogen sulfide

The recently discovered phenomenon of nonfaradaic electrochemical modification of catalytic activity (NEMCA) was explored for the electrocatalytic decomposition of H2S to H2 and S2 over Pt electrodes at 600–750 °C and 1 atm. It was found that upon applying a potential to Pt supported on a O2− conducting yttria-stabilized zirconia disk, the decompoition of H2S significantly increased up to a factor of 11 at 600 °C. The results appear to verify several aspects of NEMCA including the phenomenon that the electrolyte needs not to conduct reaction-specific species and that the degree of rate enhancement is related to the working electrode polarization. In addition, results indicate that separate chambers are not always required for electrocatalysis.

A more accurate analysis of alkylated PAH and PASH and its implications in environmental forensics

The accurate measurement of polycyclic aromatic hydrocarbons (PAH), polycyclic aromatic sulfur heterocycles (PASH), and their alkylated homologues is essential at all levels of risk assessment and remedial decision-making. In the field of environmental forensics, diagnostic ratios of these compounds are used to delineate fossil fuel-based sources from one another and to assess the degree of weathering occurring on-site. Fresh and weathered coal tar and crude oil samples from different locations were analysed by gas chromatography/mass spectrometry. The same files were analysed by selected ion extraction of one-ion and two-ion signals from full-scan data and compared to a new data analysis method using spectral information from homologous isomers. Findings showed that using too few ions produced false positives and concentrations much higher than those found using the homologous isomer spectral method, which adversely affected the corresponding diagnostic ratios used by forensic scientists.

Metabolite profiling of Camellia sinensis by automated sequential, multidimensional gas chromatography/mass spectrometry reveals strong monsoon effects on tea constituents.

Seasonal variation in tea (Camellia sinensis (L.) Kuntze; Theaceae) chemistry was investigated using automated sequential, multidimensional gas chromatography/mass spectrometry (GC-GC/MS). Metabolite libraries were produced for teas harvested from the Bulang Mountains in Yunnan, China before and after the onset of the East Asian Monsoon. A total of 201 spring and 196 monsoon metabolites were identified, with 169 common and 59 seasonally unique compounds. An additional 163 metabolites were detected but their identity could not be confirmed. Spectral deconvolution of GC/MS data was used to measure the relative concentrations in the teas. Within each family individual metabolite concentrations increased, decreased and stayed the same. The major constituents in both teas were linalool (28%), geraniol (13%), α-terpineol (10%), hotrienol (4%) and nerol (3%). This work provides the foundation to monitor seasonal variations of tea chemistry.