Jacqueline M.R. Bélanger

Microwave-assisted process (MAP™): a new tool for the analytical laboratory

Abstract This article describes the latest advances in a patented microwave-assisted extraction process. The fundamental physical phenomena at play are reviewed and discussed in terms of their role in methods development work. The process offers new sample preparation techniques for matrices such as plant and animal tissues, soils, water, consumer products, cosmetics, and others. Two main areas of extractions are discussed, namely liquid-phase and gas-phase extraction.

Influence of solvent, matrix dielectric properties, and applied power on the liquid-phase microwave-assisted processes (MAP™) extraction of ginger (Zingiber officinale)

Abstract The present work reports on an assessment of the relative importance of the nature of solvent and the applied power on the liquid-phase microwave-assisted processes (MAP) extraction of ginger ( Zingiber officinale ). The dielectric properties of the matrix was also modified in a controlled fashion by the addition of strongly absorbing substances that do not alter the quality of the extract and that do not involve supplementary steps for the recovery of the extract while allowing greater yield in much reduced extraction times when compared to conventional Soxhlet procedures. These results show the potential value of controlling the energy density of the system and the possibility of using a benign chemical such as water as a “lens” to enhance microwave-assisted processes such as the extraction of natural products from plant material.

Microwave-assisted Extraction of Phenolic Compounds from Grape Seed

Abstract A microwave-assisted extraction technique was developed to optimize the extraction of phenolic compounds from grape seeds. The microwave power (300-150W) and time of extraction (20-200s) were varied during the optimization process. The polyphenol content of the resulting extracts were measured as mg of tannic acid equivalent per gram of crude extract (mg TAE/g of crude extract), using a Folin-Ciocalteau reagent. In general, neither the time nor the power had a significant effect on the overall % yield (average of 13.5%) and on the polyphenol content (392 mg TAE/g of crude extract) of the extracts. However, when the solvent polarity was changed by the addition of 10% water, the yield increased to 15.2% and the polyphenol content increased to 429 mg TAE/g of crude extract.

Evaluation of supercritical fluid extraction, microwave-assisted extraction and sonication in the determination of some phenolic compounds from various soil matrices

Abstract Extraction methods using supercritical fluid extraction (SFE) and microwave-assisted process (MAP) techniques, with or without a one-step in situ derivatisation, were evaluated for the extraction of phenol, o-cresol, m-cresol and p-cresol from soils. Five artificially spiked soil matrices were prepared; three of them were prepared by adding various amounts of activated charcoal in order to increase the degree of analyte–matrix interaction. We also applied the methods to a real phenol contaminated soil with a high carbon content (18%). To provide a basis for comparison, all the soils were extracted using an US Environmental Protection Agency-approved sonication protocol. The extracts obtained were analyzed on a GC–MS system without any preliminary clean-up or concentration steps. The results showed that SFE and MAP are more efficient than sonication with at least twice the recovery in all the soils tested. MAP and MAP-derivatisation showed the best recoveries (>80%) for the five spiked matrices studied with the exception of o-cresol in soils with activated charcoal content higher than 5%. In these specific soils, SFE showed very low recoveries for the four phenols. However, recoveries were significantly improved when a derivatisation step was combined to SFE. In the real soil tested, the recoveries using derivatisation–extraction process were lower than the recoveries using extraction process. In general, derivatisation–extractions perform better and do not require extreme extraction conditions.

Phenol and methylphenol isomers determination in soils by in-situ microwave-assisted extraction and derivatisation

A simultaneous microwave-assisted extraction-derivatisation procedure was developed and optimised for phenol and methyl phenol isomers from soil samples. Both spiked and real soil samples (carbon content of 18%) were irradiated with microwaves in a closed-vessel system while immersed in hexane that had been previously doped with acetic anhydride and pyridine so as to effect an in situ catalytic acetylation of the target phenolic compounds. Spiked samples were prepared at least 20 days before treatment to simulate natural weathering processes and allow for the formation of analyte-matrix interactions. Optimization of the method was achieved by using a factorial design approach on parameters such as the volume of solvent, the quantity of acetic anhydride and the extraction temperature. Comparison with ultrasonic extraction procedures indicated that microwave-assisted methods gave superior recoveries (ca. two-fold) and greater precision in addition to being characterised by shorter extraction times. The procedure using microwaves yielded samples that could be analyzed directly on a GC-MS system without any preliminary clean-up or concentration steps. The detection limit of this novel method was found to be in the low-ppb range.

High Performance Liquid Chromatography Determination Following Microwave Assisted Extraction of 3-Nitro-4-Hydroxyphenylarsonic Acid from Swine Liver, Kidney, and Muscle

Abstract A simple and rapid analytical method is described for the determination of 3-nitro-4-hydroxyphenylarsonic acid (roxarsone, 3-nitro) in tissues. It involves extraction of 3-nitro from swine tissues by microwave-assisted process (MAP™) followed by high performance liquid chromatography using a PRP-1 column. The compound is detected in visible region at 410 nm after post-column reaction with 0.15 N sodium hydroxide. The detection limit is estimated to be 0.25 μg g−1 for 3-nitro, equivalent to about 0.2 μg g−1 of arsenic. Official tolerances for arsenic in liver and muscle are set at 2.0 μg g−1 and 0.5 μg g−1, respectively. The method was employed to detect 3-nitro residues in incurred tissue samples from pigs fed 150 mg kg−1 of 3-nitro for a 28-d period.

RemaRks on VaRious applications of micRowaVe eneRgy

Microwave energy is an alternative energy source that is receiving a considerable amount of attention from researchers for a wide spectrum of applications. The fundamentally different method of transferring energy from the source to the sample is the main benefit of utilizing microwave energy; by directly delivering energy to microwave-absorbing materials, conventional issues such as long heating periods, thermal gradients, and energy lost to the system environment can be minimized or avoided. Furthermore, the penetrating capacity of microwave allows volumetric heating of samples. These attributes of microwave energy make utilizing it very attractive for industrial applications as an alternative to conventional processing methods. The reality is otherwise however, and limited literature is found in any given area of work. Despite the lack of focus, in most published cases, the utilization of microwave energy has produced improved results compared to conventional methods with reduced heating times or reaction temperatures. This review provides a general overview of reported applications of microwave energy in the open literature. It also attempts to summarize the results obtained for various common uses and highlights some applications that have not gathered as much attention as anticipated.

Microwave-assisted PEGylation of Merrifield resins

Modification of insoluble polymers through covalent attachment of short chain soluble polymers can produce hybrids that combine some of the advantages of both types of polymers such as physical stability and solvent-like characteristics. A convenient microwave-assisted PEGylation method of Merrifield resin (MR) was developed using focused microwave irradiation under atmospheric pressure conditions. The effect of molecular weight of PEG, % cross-link and chloride load of MR on the yield of the hybrid polymer was investigated and compared with yields obtained under conventional heating. The data indicated that the yield decreased with increasing the molecular weight of PEG and increasing chloride load of MR and that the highest yield (92.6%) was obtained with PEG molecular weight of 200 and MR (2% cross-link) with 1.25 mequiv./g of chloride. Thermal degradation observed of the grafted PEG increased with increasing heating time under conventional heating conditions.

Microwave-Assisted Process (MAPTM) for the Extraction of Contaminants from Soil

Laboratory-scale tests were performed to evaluate the use of Environment Canadas patented Microwave-Assisted Process (MAPTM) for the extraction of petroleum hydrocarbons from contaminated soil. The purpose of these tests was to determine the potential for using the process for large-scale processing of contaminated soil. Tests were performed using three soil types: a certified sediment and certified soil, both contaminated with polycyclic aromatic hydrocarbons (PAHs), and spiked peat soil contaminated with long-chain petroleum hydrocarbons. The test methods used were based on existing MAP techniques that have been proven for the sample preparation of contaminated soils for analytical purposes. The parameters evaluated concentrated on those that are amenable to a continuous large-scale process running at atmospheric pressures. This meant using solvents that are inexpensive and readily available in large volumes, low solvent to material ratios, and optimized energy inputs. In general, it was found that mic...

Emissions from mesoscale in situ oil fires: the mobile 1991 experiments

A series of 14 mesoscale burns were conducted in 1991 to study various aspects of oil burning in situ. Extensive sampling and monitoring of these burns were conducted to determine the emissions. This was done at two downwind ground stations, one upwind ground station and in the smoke plume using a blimp and a remote-controlled helicopter. Particulate samples in air were taken and analyzed for polycyclic aromatic hydrocarbons (PAHs). PAHs were found to be lower in the soot than in the starting oil. Metals in the oil were found concentrated in the residue and could not be measured in soot samples using conventional industrial hygiene sampling techniques. Particulates in the air were measured by several means and found to be greater than recommended exposure levels only up to 150 m downwind at ground level. Combustion gases including carbon dioxide, sulphur dioxide and carbon monoxide did not reach exposure level maximums. These gases were emitted over a broad area around the fire and are not directly associated with the plume trajectory. Volatile organic compound (VOCs) emissions are extensive from fires, but the levels are less than those emitted from a non-burning test spill. Over 50 compounds were identified and quantified, several at possible levels of concern up to 200 m downwind. Water under the burns was analyzed; no analytes of concern could be found at the detection levels of the methods. The burn residue was analyzed for the same compounds as the air particulate samples. The residue contained elevated amounts of metals. PAHs were at a lower concentration in the residue than in the starting oil, however there is a slight differential concentration increase in some higher molecular weight species. Overall, indications from these mesoscale trials are that emissions from in situ burning are low in comparison to other sources of emissions and result in concentrations of air contaminants that are below exposure limits beyond 500 m downwind.