Adsorption of Nickel Ions on the γ-Alumina Surface: Competitive Effect of Protons and Its Impact on Concentration Profiles.

Mesoporous γ-alumina is used as an adsorbent in the decontamination of water from heavy metals (e.g., nickel and cobalt) and as a support for heterogeneous catalysts prepared by impregnation. In these cases, alumina extrudates are in contact with aqueous solutions containing precursors of the active metal phase to be deposited. The proton concentration (or pH) in the metal solution in contact with alumina can impact the adsorption efficiency of decontamination processes and the activities of catalysts. Yet, it is difficult to quantify the effect of the pH inside the pores since protons are not detected by classical imaging techniques. In this article, the effect of protons on nickel adsorption on alumina is evaluated using a novel technique coupling liquid analysis (pH, conductivity, and UV/vis) and laser-induced breakdown spectroscopy (or LIBS) analysis of concentration gradients inside the solid. Both methods are in excellent agreement. The results show a slow diffusion of protons inside alumina pores (diffusion continues even after 940 min), yielding high proton concentration gradients. On the other hand, the nickel species penetrate the extrudates faster but are slowly displaced by protons under certain operating conditions. As a result, different metal concentration profiles are obtained, depending on the initial pH and contact time. These findings are interesting in catalysis since they prove the possibility of controlling the deposition of the active metal on catalysts by regulating the operating conditions of impregnation. For typical industrial impregnation times (a few minutes to 1 to 2 h), protons do not have enough time to deeply penetrate inside extrudates, so the initial pH of the metal solution will have nearly no effect on the metal distribution. Conversely, decontamination processes have much longer contact times; therefore, lower initial pH values should have negative impacts on the adsorption efficiency due to the protons displacing the adsorbed nickel.

Profiling of Organic Compounds in Bioethanol Samples of Different Nature and the Related Fractions.

Forty-one bioethanol real samples and related fractions, together with a biobutanol sample, have been analyzed with gas chromatography coupled to either mass spectrometry (GC-MS) or flame ionization detection (GC-FID). Bioethanol with different water contents, samples originated from several sources of biomass, first- as well as second-generation specimens, distillation fractions, samples stocked in containers made of four different materials, and, finally, a biobutanol sample have been analyzed. The number of the compounds found through GC-MS has been 130, including alcohols, aldehydes, ketones, esters, ethers, nitrogen compounds, organic acids, furane derivates as well as other species (e.g., limonene). Afterward, a quantitative determination of major components of bioethanol has been carried out. The achieved results have revealed that, besides ethanol and, in some cases, water, species such as acetaldehyde, methanol, and higher alcohols, as well as 1,1-diethoxyethane, may be present at concentrations above 500 mg L-1. While the source of bioethanol (nature of the raw material, ethanol generation, or water content) has a direct impact on its volatile organic compound (VOC) profile, the material of the container where the biofuel has been stored does not play a significant role. Finally, the results have demonstrated that, for a given production process, different distillation fractions contain unequal VOC profiles.

Comprehensive two-dimensional liquid chromatography with inductively coupled plasma mass spectrometry detection for the characterization of sulfur, vanadium and nickel compounds in petroleum products.

The petroleum industry is increasingly concerned with the conversion of vacuum residues as a consequence of decreased conventional crude oil availability. The compositional analysis of heavy oil products has become a key step in conversion processes, but the complexity of these oil matrices tends to increase with their boiling point. In this study, comprehensive two-dimensional liquid chromatography (LCxLC) coupled to inductively coupled mass spectrometry (ICP-MS/MS) is considered with a view to meet new requirements and to bring additional information regarding the species present in these matrices. In search for a high degree of orthogonality, two separation techniques involving two different retention mechanisms were evaluated: Size Exclusion Chromatography (SEC) and Reverse Phase Liquid Chromatography (RPLC). In SEC, the analytes are separated according to their molecular weight while according to their hydrophobicity in RPLC. The separation power of both individual separation techniques was first evaluated. Off-line and on-line LCxLC were compared on the basis of an optimization approach. It is shown that off-line SECxRPLC can provide, for the same analysis time of 150 min, a higher peak capacity (2600 vs 1700) than on-line RPLCxSEC while a similar dilution factor (close to 30) but also requires far fewer fractions to be analyzed (12 vs 400). Asphaltenes which constitute the heaviest fraction of crude oils (obtained from petroleum industry) were analyzed by the developed off-line SECxRPLC method. The resulting 2D-contour plots show that co-elutions could be removed leading, for the first time, to new information on high molecular weight species containing sulfur and vanadium.

Suitable interface for coupling liquid chromatography to inductively coupled plasma-mass spectrometry for the analysis of organic matrices. 2 Comparison of Sample Introduction Systems.

Liquid chromatography (LC) coupled with a specific detection such as inductively coupled plasma-mass spectrometry (ICP-MS/MS) is a technique of choice for elementary speciation analysis for complex matrices. The analysis of organic matrices requires the introduction of volatile solvents into the plasma which is an analytical challenge for this coupling technique. Detection sensitivity can be significantly affected by instrumental limitations. Among those, we were interested in the solute dispersion into the interface located between LC and ICP-MS/MS. This interface consists in both a Sample Introduction System (SIS) and a possible flow splitter. This study, divided into two parts, investigated the analytical performance (in terms of sensitivity and efficiency) generated by the coupling of LC and ICP-MS in the specific case of organic matrices. In Part I [1], we previously discussed the impact of extra column dispersion on the performance of LC-ICP-MS, first from a theoretical point of view and next, by assessing extra-column dispersion in 55 published studies on LC-ICP-MS. It was shown that SIS was rarely optimized with respect to its contribution to extra-column band broadening. The critical impact of flow splitting on extra-column dispersion was also pointed out. The present Part II is dedicated to the experimental comparison of commercially available SIS by assessing extra-column band broadening and hence the contribution of SIS to the loss in both efficiency and sensitivity. It is shown that the peak variance, due to SIS, can vary from 10 to 8000 µL² depending on the combination of both nebulizer and spray chamber. Whereas the highest values (i.e. > 2000 µL²) are much too high in high performance liquid chromatography (HPLC), even the lowest values (i.e. < 100 µL²) can be inappropriate in ultra-high pressure liquid chromatography (UHPLC) as highlighted in this study. In light of these results, it appears that nebulizer and spray chamber have to be chosen together with respect to the chromatographic technique (HPLC or UHPLC) and that both peak dispersion and peak intensity depend on key parameters including SIS device geometry, flow rate entering the interface or spray chamber temperature.

Suitable interface for coupling liquid chromatography to inductively coupled plasma-mass spectrometry for the analysis of organic matrices. 1 Theoretical and experimental considerations on solute dispersion.

Liquid chromatography (LC) hyphenated to a specific detection such as inductively coupled plasma-mass spectrometry (ICP-MS) is a technique of choice for elemental speciation analysis. However, various instrumental limitations may considerably reduce the expected sensitivity of the technique. Among those, we were interested by the solute dispersion into the interface located between LC and ICP-MS. The interface consists of a Sample Introduction System (SIS) and a possible flow-splitter prior to SIS. Flow splitting can be required in case of organic matrices to reduce the organic solvent amount entering plasma which may lead to plasma instabilities. Although extra-column dispersion is usually well taken into account with conventional UV detection it has been little studied in the context of LC-ICP-MS and moreover never quantified. Our objective is to assess the loss in column plates and hence in both separation quality and sensitivity which may be generated by the coupling of LC and ICP-MS in the specific case of organic matrices. In this first study, this is done (1) from a theoretical approach; (2) from 55 experimental studies reported in LC-ICP-MS and (3) from our experimental results highlighting the critical impact of the flow splitter on extra-column dispersion depending on both flow-rate and split ratio. It turns out by evaluating the 55 reported studies by means of theoretical calculations, that the loss in plates due to extra-column dispersion was most of the time beyond 50% and even often beyond 90%. Moreover, from our experiments, it has been shown that a very low split ratio (1:50) could generate an additional variance around 200 µL² which induces a loss in theoretical plate of 90% for ultra-high performance LC (UHPLC) column (5 cm × 2.1 mm, 1.7 µm).

Development of heart-cutting multidimensional gas chromatography coupled to time of flight mass spectrometry for silicon speciation at trace levels in gasoline samples.

To improve the understanding of hydrotreatment (HDT) catalyst poisoning by silicon species, these molecules must be characterized in petroleum products using powerful analytical systems. Heart-cutting gas chromatography coupled to time of flight mass spectrometry (GC-GC/TOFMS) method equipped with a Deans switch (DS) system was developed for the direct characterization of target silicon compounds at trace level (µg kg(-1)) in gasoline samples. This method was performed to identify silicon compounds never characterized before. After the selection of the second dimension column using GC-GC-FID, GC-GC/TOFMS was performed. The calibration curves obtained by the GC-GC/TOFMS method were linear up to 1,000 µg kg(-1). Limits of detection (LOD) were ranging from 5 to 33 µg kg(-1) in spiked gasoline. The method provided sufficient selectivity and sensitivity to characterize known silicon compounds thanks to their specific ions and their retention times. The analysis of a naphtha sample by GC-GC/TOFMS has shown the presence of cyclic siloxanes (D(n)) as major compounds of PDMS thermal degradation with the occurrence of linear siloxanes, especially hexamethyldisiloxane (L(2)), which was never characterized in petroleum products but already known as severe poison for catalyst.

Combining Fourier transform-ion cyclotron resonance/mass spectrometry analysis and Kendrick plots for silicon speciation and molecular characterization in petroleum products at trace levels.

A new method combining FT-ICR/MS analysis and Kendrick plots for the characterization of silicon species at trace levels in light petroleum products is presented. The method provides efficient instrumental detection limits ranging from 80 ng/kg to 5 µg/kg and reliable mass accuracy lower than 0.50 ppm for model silicon molecules in spiked gasoline. More than 3000 peaks could be detected in the m/z 50-500 range depending on the nature of the gasoline sample analyzed. An in-house software program was used to calculate Kendrick plots. Then, an algorithm searched, selected, and represented silicon species classes (O(2)Si, O(3)Si, and O(4)Si classes) in Kendrick plots by incorporating model molecules' information (i.e., exact mass and intensity). This procedure allowed the complete characterization of more than 50 new silicon species with different degrees of unsaturation in petroleum products.

Silicon speciation by gas chromatography coupled to mass spectrometry in gasolines.

A method for the speciation of silicon compounds in petroleum products was developed using gas chromatography coupled to mass spectrometry (GC-MS). Prior to analysis, several precautions about storage and conservation were applied for all samples. In spiked gasoline samples, limits of detection between 24 and 69 µg kg(-1) for cyclic siloxanes (D(4)-D(6)) and between 1 and 7 µg kg(-1) for other species were obtained. In this study, cyclic siloxanes (D(n)) and one ethoxysilane were quantified for the first time in petroleum products by a specific method based on response factor calculation to an internal standard. This method was applied to four samples of naphthas and gasolines obtained from a steam cracking process. Cyclic siloxanes were predominant in four investigated samples with concentrations ranging between 101 and 2204 µg kg(-1). Cyclic siloxane content decreased with an increase in their degree of polymerization. During a steam cracking process, silicon concentrations determined by GC-MS SIM (single ion monitoring) significantly increase. This trend was confirmed by ICP-OES (inductively coupled plasma optical emission spectroscopy) measurements but a difference on the total silicon content was observed, certainly highlighting the presence of unknown silicon species. GC-MS SIM method gives access to the chemical nature of the silicon species, which is crucial for the understanding of hydrotreatment catalyst poisoning in the oil and gas industry.

Sensitivity improvement in ICP MS analysis of fuels and light petroleum matrices using a microflow nebulizer and heated spray chamber sample introduction.

Reasons for signal suppression during the analysis of light petroleum matrices by inductively coupled plasma mass spectrometry (ICP MS) were examined. A decrease of the ionization efficiency of the plasma was found to be the principal factor responsible for this loss of sensitivity. Consequently, an interface based on a total consumption micronebulizer and a heated spray chamber was constructed to alleviate this problem. A method based on flow-injection ICP MS using this interface was developed for the direct multielement analysis of undiluted fuels (gasoline, kerosene) and gas condensates offering an increase in sensitivity by at least a factor of 3-4 in comparison with the existing setups.

Capillary electrophoresis monitoring of halide impurities in ionic liquids.

Quantification of impurities in ionic liquids is a crucial task in assessing the reliability of physical constants and solvent properties: taking into account the particularities of the ionic matrix, a simple routine method using capillary electrophoresis (CE) is developed to determine the halide content at the ppm level in water-immiscible ionic liquids.

Evidence for a dynamic cycle between Mn and Co in the water column of a stratified lake.

The geochemical behavior of Co in aquatic systems has often been related to the presence of Fe and Mn particles. A few studies have shown that Co is exclusively associated with particulate Mn, but the dynamics of Co and Mn cycling have never been determined in real time under natural conditions. In this study, we used a combination of analytical techniques to study the temporal and spatial evolution of Mn microparticles (MnOx) over 2 weeks in the water column of a shallow stratified lake (Paul Lake, MI). We report a temporal accumulation of dissolved Mn at the oxic-anoxic transition, and we show that this accumulation is due to the reductive dissolution of Mn particles. The reductant has not been identified, but abiotic reduction by sigmaH2S and ferrous iron is excluded because they are produced below the zone of MnOx reduction. Hybridization of RNA isolated from Paul Lake with oligonucleotide probes targeting the delta proteobacteria, which include metal-reducing species, suggests that their activity is greatest at and just below the oxic-anoxic transition, so that Mn reduction may be influenced by bacterial activity. Mn-oxidizing bacteria were isolated from this zone as well. We also demonstrate that the dynamic evolution of MnOx has a direct influence on the distribution of Co in the water column of this lake: dissolved Co is released during the reductive dissolution of MnOx and accumulates at the redox interface.