This work was supported by the National Institute of Health (Grant No. R00GM106414 to FFL). We would like to acknowledge the Advanced Mass Spectrometry Facility of Florida International University for their support.

1. Preparation of the Low-energy Water-accommodated Fractions (LEWAF)
<ol>
	<li>Clean 2-L aspirator bottles by rinsing the bottles with methylene chloride in order to remove any potential contaminants.</li>
	<li>Fill bottles with 50&#160;mL of methylene chloride, close them, and agitate for 30 s. Drain them into the appropriate waste container. Repeat for a total of three washes.</li>
	<li>Use one aspirator bottle for the irradiation exposure and the other bottle as a control sample (perform duplicate sets of each if p...

<ol>
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G., Altin, D., Nordtug, T., Daling, P. S., Hansen, B. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+comparison+and+acute+toxicity+of+water+accommodated+fraction+(WAF)+of+source+and+field+collected+Macondo+oils+from+the+Deepwater+Horizon+spill.">Chemical comparison and acute toxicity of water accommodated fraction (WAF) of source and field collected Macondo oils from the Deepwater Horizon spill.</a> Mar Pollut Bull. 91 (1), 222-229 (2015).</li><li>Wang, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biodegradation+of+dispersed+Macondo+crude+oil+by+indigenous+Gulf+of+Mexico+microbial+communities.">Biodegradation of dispersed Macondo crude oil by indigenous Gulf of Mexico microbial communities.</a> Science of The Total Environment. 557-558, 453-468 (2016).</li><li>McKenna, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expansion+of+the+analytical+window+for+oil+spill+characterization+by+ultrahigh+resolution+mass+spectrometry:+beyond+gas+chromatography.">Expansion of the analytical window for oil spill characterization by ultrahigh resolution mass spectrometry: beyond gas chromatography.</a> Environ Sci Technol. 47 (13), 7530-7539 (2013).</li><li>Fernandez-Lima, F. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Petroleum+crude+oil+characterization+by+IMS-MS+and+FTICR+MS.">Petroleum crude oil characterization by IMS-MS and FTICR MS.</a> Anal Chem. 81 (24), 9941-9947 (2009).</li><li>Benigni, P., Marin, R., Fernandez-Lima, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+unsupervised+polyaromatic+hydrocarbons+structural+assignment+from+SA-TIMS-FTMS+data.">Towards unsupervised polyaromatic hydrocarbons structural assignment from SA-TIMS-FTMS data.</a> Int J Ion Mobil Spectrom. 18 (3), 151-157 (2015).</li><li>Benigni, P., Thompson, C. J., Ridgeway, M. E., Park, M. A., Fernandez-Lima, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeted+high-resolution+ion+mobility+separation+coupled+to+ultrahigh-resolution+mass+spectrometry+of+endocrine+disruptors+in+complex+mixtures.">Targeted high-resolution ion mobility separation coupled to ultrahigh-resolution mass spectrometry of endocrine disruptors in complex mixtures.</a> Anal Chem. 87 (8), 4321-4325 (2015).</li><li>Benigni, P., Fernandez-Lima, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oversampling+Selective+Accumulation+Trapped+Ion+Mobility+Spectrometry+coupled+to+FT-ICR+MS:+Fundamentals+and+Applications.">Oversampling Selective Accumulation Trapped Ion Mobility Spectrometry coupled to FT-ICR MS: Fundamentals and Applications.</a> Analytical Chemistry. , (2016).</li><li>Castellanos, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+Screening+of+Polycyclic+Aromatic+Hydrocarbons+using+Trapped+Ion+Mobility+Spectrometry+Mass+Spectrometry.">Fast Screening of Polycyclic Aromatic Hydrocarbons using Trapped Ion Mobility Spectrometry Mass Spectrometry.</a> Anal Methods. 6 (23), 9328-9332 (2014).</li><li>Benigni, P., DeBord, J. D., Thompson, C. 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The authors declare no competing financial interests.

Critical Steps within the Protocol
The chemical complexity of LEWAFs requires accurate preparation in order for the laboratory experiments to accurately reflect what occurs naturally. A valid assessment of the data hinges on three criteria: minimizing the introduction of artifacts throughout sample handling (e.g., preparation of the LEWAF, sampling, extractions, and preparation of the sample for analysis), validating the experimental protocol (i.e., using dark controls for the p...

There are numerous sources of environmental exposure to crude oil, both from natural causes and from anthropogenic exposure. Upon release to the environment, particularly in the ocean, the crude oil can undergo partitioning, with the formation of an oil slick on the surface, a loss of volatile components to the atmosphere, and sedimentation. However, low-energy mixing of the poorly soluble oil and the water does occur, and this mixture, which is not classically solubilized, forms what is referred to as the low-energy water-accommodated fraction (LEWAF). The solubilization of the oil components in the water is typically enhanced during exposure of the oil-water interface to solar radiation. This photo-solubilization of the crude oil in the ocean can undergo significant chemical changes due to this exposure to solar radiation and/or due to enzymatic degradation1,2. Understanding these chemical changes and how they occur in the presence of the bulk matrix (i.e., the crude oil) is fundamental to mitigating the effects this exposure has on the environment.
Previous studies have shown that crude oil undergoes oxygenation, particularly the polycyclic aromatic hydrocarbons (PAHs), which represent a highly toxic source of contamination that harms organisms, undergoes bio-accumulation, and is bioactive3,5,6. Understanding the products of the different oxygenation processes is challenging because they occur only in the presence of the bulk matrix. Therefore, a single, standard analysis may not be representative of the changes occurring in nature. The preparation of the LEWAF must replicate the natural processes that take place in an environmental setting. Of particular interest is the oxygenation of PAHs, which occurs due to solar radiation.
The second challenge in the study of the water-accommodated fraction is the molecular identification of the different chemical constituents in the sample. Due to the complexity of the sample, caused by its high mass and degree of oxygen, the oxygenation products are typically unsuitable for the traditional analysis carried out by gas chromatography combined with MS analysis7,8. An alternative approach is to characterize the changes in the chemical formula of the sample by utilizing ultra-high mass resolution MS techniques (e.g., FT-ICR MS). By coupling TIMS to FT-ICR MS, in addition to the isobaric separation in the MS domain, the ion mobility spectrometry (IMS) dimension provides the separation and characteristic information for the different isomers present in the sample9,10,11. Combined with an atmospheric pressure laser ionization (APLI) source, the analysis can be selective to the conjugated molecules found in the sample, allowing the changes that the PAHs undergo to be accurately characterized12,13.
In this work, we describe a protocol for the preparation of LEWAFs exposed to photo-irradiation in order to study the transformation processes of the oil components. We also illustrate the changes that occur upon photo-irradiation, as well as the procedure for sample extraction. We will also present the use of APLI with TIMS coupled with FT-ICR MS to characterize the PAHs in the LEWAF as a function of the exposure to light.

<table border="0" cellpadding="0" cellspacing="0" width="915">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:228px;">Reagents</td>
			<td style="width:156px;"></td>
			<td style="width:156px;"></td>
			<td style="width:375px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">methylene chloride</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">methanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">toluene</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Na2SO4</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Crude oil</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Instant Ocean&#174;</td>
			<td>Aquarium Systems</td>
			<td></td>
			<td>33 ppt salinity with 0.45 &#956;m pore filtration&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Name&#160;</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Suntext XLS+</td>
			<td>Atlas Chicalo Ill, USA</td>
			<td></td>
			<td>1500 w xeon arc lamp, light intensity of 765 W/m2&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Atmospheric Pressure Laser Ionization</td>
			<td>Bruker Daltonics Inc, MA</td>
			<td></td>
			<td>Note a 266 nm laser is used</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">TIMS-FT-ICR MS Instrument</td>
			<td>Bruker Daltonics Inc, MA</td>
			<td></td>
			<td>The set up we had consisted of a 7T magnet with an infinity cell</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Name&#160;</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DataAnalysis 4.2</td>
			<td>Bruker Daltonics Inc, MA</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Python 2.7</td>
			<td></td>
			<td></td>
			<td>Requires Numpy, Scipy, Pandas, glob, oct2py, and os</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Octave 4.0</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

chemical analysis of water-accommodated fractions of crude oil spills using tims-ft-icr ms

Multiple chemical processes control how crude oil is incorporated into seawater and also the chemical reactions that occur overtime. Studying this system requires the careful preparation of the sample in order to accurately replicate the natural formation of the water-accommodated fraction that occurs in nature. Low-energy water-accommodated fractions (LEWAF) are carefully prepared by mixing crude oil and water at a set ratio. Aspirator bottles are then irradiated, and at set time points, the water is sampled and extracted using standard techniques. A second challenge is the representative characterization of the sample, which must take into consideration the chemical changes that occur over time. A targeted analysis of the aromatic fraction of the LEWAF can be performed using an atmospheric-pressure laser ionization source coupled to a custom-built trapped ion mobility spectrometry&#8211;Fourier transform&#8211;ion cyclotron resonance mass spectrometer (TIMS-FT-ICR MS). The TIMS-FT-ICR MS analysis provides high-resolution ion mobility and ultrahigh-resolution MS analysis, which further allow the identification of isomeric components by their collision cross-sections (CCS) and chemical formula. Results show that as the oil-water mixture is exposed to light, there is significant photo-solubilization of the surface oil into the water. Over time, the chemical transformation of the solubilized molecules takes place, with a decrease in the number of identifications of nitrogen- and sulfur-bearing species in favor of those with a greater oxygen content than were typically observed in the base oil.

LEWAF analysis by TIMS-FT-ICR MS results in a two-dimensional spectrum based on m/z and TIMS trapping voltage. Each of the samples, taken at different time points, can therefore be characterized based on the changing chemical composition, as observed by the distribution of chemical formulas and the isomeric contribution identified by the IMS (see Figure 1). Typically, the m/z information can be utilized to assign elemental formulas to the analyzed peaks....

Watch this Scientific Journal Video about Chemical Analysis of Water-accommodated Fractions of Crude Oil Spills Using TIMS-FT-ICR MS at JoVE.com

Chemical Analysis of Water-accommodated Fractions of Crude Oil Spills Using TIMS-FT-ICR MS

The low-energy water-accommodated fraction (LEWAF) of crude oil is a challenging system to analyze, because over time, this complex mixture undergoes chemical transformations. This protocol illustrates methods for the preparation of the LEWAF sample and for performing photo-irradiation and chemical analysis by trapped ion mobility spectrometry&#8211;FT-ICR MS.

Multiple chemical processes control how crude oil is incorporated into seawater and also the chemical reactions that occur overtime. Studying this system ...

The overall goal of these experiments is to illustrate the analytical advantages of enabling emerging technologies based on TIMS-FT-ICR MS for the molecular characterization of complex mixtures, such as water-accommodated fractions for crude oils. The TIMS-FT-ICR MS coupling combines two of the most comprehensive orthogonal and alluvial techniques for the analysis of complex mixtures. TIMS-FT-ICR MS coupling permits in a single analysis the characterization of thousands of molecular components with mobility resolving powers of over 150, mass resolution of 500, 000, and sub-ppm mass accuracy.TIMS-FT-ICR MS enables the separation, identification, and quantitation at the molecular level of complex mixtures, based on differences in size, charge and mass with minimal sample appropriation. To begin the LEGAF preparation, add 50 milliliters of dicholomethane to a two liter glass aspirator bottle. Close the bottle and agitate the bottle for 30 seconds.Discard the dichloromethane wash, and repeat this process two more times. Wash one more two liter aspirator bottle in this way, then add about 1.6 liters of filtered artificial seawater with a salinity of 33 parts per thousand to each bottle. Add a stir bar, and then use a gas-tight syringe to add sufficient crude oil sample to each bottle to achieve a final concentration of one gram per liter of oil and seawater.Wrap the bottles in aluminum foil to exclude light, and stir the mixtures at approximately 100 RPM for 24 hours to finish preparing the LEWAF. It's important that care is used when first mixing the oil and water to avoid over-mixing the solution. Next, unwrap one of the LEWAF bottles in aluminum foil, leaving one as the dark control.Place the bottles in the solar irradiator with the temperature set to maintain the samples at 25 degrees Celsius. Irradiate the mixtures continuously for the desired experiment length. At set intervals during the experiment, obtain 150 milliliter fractions from each bottle by uncorking the bottle and opening the drain valve.Extract each sample aliquot using 50 milliliters of dichloromethane three times using a separatory funnel. Shake the funnel for two minutes each time, remembering to regularly vent the funnel to avoid pressure buildup. Drain the sample into a flat-bottom flask through a funnel containing sulfate and rinse the sodium sulfate with additional DCM.Concentrate the extract to 15 milliliters using a hot water bath set at 58 degrees Celsius. Transfer the concentrate into a concentration tube, rinsing the flask with DCM. Concentrate each sample to one milliliter under a gentle stream of nitrogen gas.For each concentrated sample, using a glass positive displacement micropipette, add 990 microliters of a one to one by volume mixture of methanol and toluene to a glass vial. Then mix in 10 microliters of the sample. To begin the FTR-ICR MS analysis, set the instrument to Operate mode.Draw a sample into a sample syringe. Set the infusion rate to 200 microliters per hour, the nebulizer pressure to two bar, and the vaporizer temperature to 300 degrees Celsius. Set the dry gas rate to 1.2 liters per minute and the temperature to 220 degrees Celsius.Then set the instrument to Tune mode. Based on the resulting spectrum adjust the instrument parameters and recalibrate the mass spectrometer to improve the ion transmission and detection for the desired range of mass to charge ratios. Once the instrument parameters have been optimized, exit Tune mode.Set the desired number of scans to be average per mass spectrum, and then acquire the spectrum. To begin the trapped ion mobility spectrometry analysis turn on the external breaker to the TIMS instrument to engage TIMS mode. Set the FT-ICR instrument to chromatography mode.Turn on the supplementary roughing pump and set the inlet and outlet pressures to the desired values using the TIMS control valve. Allow the pump to warm up for at least three hours, then perform a fast sweep over a wide voltage range at a low IMS and MS resolution to identify the needed voltage range for the analysis. Once the range has been identified, set the voltage per frame to 0.1 volts.Set the number of frames to cover the entirety of the DeltaV ramp and run the analysis. After performing the analyses, process the data with the appropriate software and scripts to determine the chemical composition and mobility values of identified peaks. After sunlight irradiation of an LEWAF of a crude oil sample, changes in the chemical complexity are observed as a function of exposure time.This complexity was detected and visualized in a 2D spectrum based on mass to charge ratio and ion mobility. The use of APLI resulted in greater analytical sensitivity to molecules with double bonds. Four molecular classes were identified in the sample.Distribution plots of double bond equivalents as a function of the number of carbons were used to monitor changes in the molecular composition over time. Two-dimensional plots of inverse mobility versus carbon number were created, with the double bond equivalents represented as the color of each point. Linear trends were observed for each of the four common molecular classes.After watching this video you should have a good understanding of the basic steps and unique advantages of APLI-TIMS-FT-ICR MS for the analysis of LEWAF samples as well as other complex mixtures. While attempting this procedure it's important to remember that sample integrity, such as reducing sources of contamination, is fundamental for accurate results. The characterization at the molecular level of the water-accommodated fractions of crude oils, the transformation products, and their fate during exposure to sunlight in the ocean is of the utmost environmental importance.Compared to other separation techniques such as liquid chromatography and gas chromatography, TIMS separation occurs in a shorter time scale, and is timing dependent, which permits better coupling with ultra high resolution MS analyzers while providing collision cross sections and chemical formulas in a single analysis. The generation of new comprehensive analytical tools for the analysis of complex mixtures at molecular level, such as TIMS-FT-ICR MS has great implications for our understanding of the chemical transformations and fate of crude oil in the ocean.

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11.0K visualizações.  Florida International University. The overall goal of these experiments is to illustrate the analytical advantages of enabling emerging technologies based on TIMS-FT-ICR MS for the molecular characterization of complex mixtures, such as water-accommodated fractions for crude oils. The TIMS-FT-ICR MS coupling combines two of the most comprehensive orthogonal and alluvial techniques for the analysis of complex mixtures. TIMS-FT-ICR MS coupling permits in a single analysis the characterization of thousands of molecular component...