Name: using capillary electrophoresis to quantify organic acids from plant tissue: a test case examining coffea arabica seeds
Uploaded: 2016-11-12T14:00:00
Description: Watch this Scientific Journal Video about Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds at JoVE.com

The authors would like to acknowledge the financial support of this project by The J.M. Smucker company.

1. Sample Preparation
<ol>
	<li>Assemble samples for short chain carboxylic acid (SCCA) extraction. Prepare 1.0 g of coffee seed at a time to ensure that enough sample will remain after processing.
	<ol>
		<li>If samples were frozen prior to the grinding process, keep the tissue frozen throughout processing to prevent freeze/thaw damage and sample oxidation. Remove the sample from the freezer or sub-zero storage only as needed for grinding.</li>
		<li>Flash freeze fresh samples in liquid nitrogen immediately prior to s...

<ol>
	<li>Ara&#250;jo, W. L., Nunes-Nesi, A., Nikoloski, Z., Sweetlove, L. J., Fernie, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolic+Control+and+Regulation+of+the+Tricarboxylic+Acid+Cycle+in+Photosynthetic+and+Heterotrophic+Plant+Tissues:+TCA+Control+and+Regulation+in+Plant+Tissues.">Metabolic Control and Regulation of the Tricarboxylic Acid Cycle in Photosynthetic and Heterotrophic Plant Tissues: TCA Control and Regulation in Plant Tissues.</a> Plant Cell Environ. 35 (1), 1-21 (2012).</li><li>Finkemeier, I., Konig, A. C., 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=Transcriptomic+Analysis+of+the+Role+of+Carboxylic+Acids+in+Metabolite+Signaling+in+Arabidopsis+Leaves.">Transcriptomic Analysis of the Role of Carboxylic Acids in Metabolite Signaling in Arabidopsis Leaves.</a> Plant Physiol. 162 (1), 239-253 (2013).</li><li>Doyle, M. P., Buchanan, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Food Microbiology: Fundamentals and Frontiers. , (2013).</li><li>T&#367;ma, P., Samcov&#225;, E., &#352;tul&#236;k, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+Spectrum+of+Low+Molecular+Mass+Organic+Acids+in+Urine+by+Capillary+Electrophoresis+with+Contactless+Conductivity+and+Ultraviolet+Photometric+Detection-An+Efficient+Tool+for+Monitoring+of+Inborn+Metabolic+Disorders.">Determination of the Spectrum of Low Molecular Mass Organic Acids in Urine by Capillary Electrophoresis with Contactless Conductivity and Ultraviolet Photometric Detection-An Efficient Tool for Monitoring of Inborn Metabolic Disorders.</a> Anal Chim Acta. 685 (1), 84-90 (2011).</li><li>L&#243;pez-Bucio, J., Nieto-Jacobo, M. F., Ram&#305;&#769;rez-Rodr&#305;&#769;guez, V., Herrera-Estrella, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organic+Acid+Metabolism+in+Plants:+From+Adaptive+Physiology+to+Transgenic+Varieties+for+Cultivation+in+Extreme+Soils.">Organic Acid Metabolism in Plants: From Adaptive Physiology to Transgenic Varieties for Cultivation in Extreme Soils.</a> Plant Sci. 160 (1), 1-13 (2000).</li><li>Cebolla-Cornejo, J., Valc&#225;rcel, M., Herrero-Mart&#236;nez, J. M., Rosell&#242;, S., Nuez, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Efficiency+Joint+CZE+Determination+of+Sugars+and+Acids+in+Vegetables+and+Fruits:+CE+and+CEC.">High Efficiency Joint CZE Determination of Sugars and Acids in Vegetables and Fruits: CE and CEC.</a> Electrophoresis. 33 (15), 2416-2423 (2012).</li><li>Rosello, S., Galiana-Balaguer, L., Herrero-Martinez, J. M., Maquieira, A., Nuez, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+Quantification+of+the+Main+Organic+Acids+and+Carbohydrates+Involved+in+Tomato+Flavour+Using+Capillary+Zone+Electrophoresis.">Simultaneous Quantification of the Main Organic Acids and Carbohydrates Involved in Tomato Flavour Using Capillary Zone Electrophoresis.</a> J Sci Food Agr. 82 (10), 1101-1106 (2002).</li><li>Wasielewska, M., Banel, A., Zygmunt, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+Electrophoresis+in+Determination+of+Low+Molecular+Mass+Organic+Acids.">Capillary Electrophoresis in Determination of Low Molecular Mass Organic Acids.</a> Int J Environ Sci Dev. 5 (4), 417-425 (2014).</li><li>Galli, V., Garc&#236;a, A., Saavedra, L., Barbas, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+Electrophoresis+for+Short-Chain+Organic+Acids+and+Inorganic+Anions+in+Different+Samples.">Capillary Electrophoresis for Short-Chain Organic Acids and Inorganic Anions in Different Samples.</a> Electrophoresis. 24 (1213), 1951-1981 (2003).</li><li>Klampfl, C. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+Organic+Acids+by+CE+and+CEC+Methods.">Determination of Organic Acids by CE and CEC Methods.</a> Electrophoresis. 28 (19), 3362-3378 (2007).</li><li>Kenney, B. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+Organic+Acids+in+Food+Samples+by+Capillary+Electrophoresis.">Determination of Organic Acids in Food Samples by Capillary Electrophoresis.</a> J Chromatogr A. 546, 423-430 (1991).</li><li>Galli, V., Barbas, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+Electrophoresis+for+the+Analysis+of+Short-Chain+Organic+Acids+in+Coffee.">Capillary Electrophoresis for the Analysis of Short-Chain Organic Acids in Coffee.</a> J Chromatogr A. 1032 (1-2), 299-304 (2004).</li><li>Schmitt-Kopplin, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+Electrophoresis:+Methods+and+Protocols.">Capillary Electrophoresis: Methods and Protocols.</a> Methods in Molecular Biology. , 384 (2008).</li><li>Nollet, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Chromatographic analysis of the environment 3rd ed. , (2006).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ElixerOA Organic Acids/Anions Operating and Instruction Manual, MicroSolv Technology Corperation. , (2001).</li><li>Dahlen, J., Hagberg, J., Karlsson, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+low+molecular+weight+organic+acids+in+water+with+capillary+zone+electrophoresis+employing+indirect+photometric+detection.">Analysis of low molecular weight organic acids in water with capillary zone electrophoresis employing indirect photometric detection.</a> Fresenius J. Anal. Chem. 366 (5), 488-493 (2000).</li><li>Ibanez, A. B., Bauer, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analytical+method+for+the+determination+of+organic+acids+in+dilute+acid+pretreated+biomass+hydrolysate+by+liquid+chromatography-time-of-flight+mass+spectroscopy.">Analytical method for the determination of organic acids in dilute acid pretreated biomass hydrolysate by liquid chromatography-time-of-flight mass spectroscopy.</a> Biotech. For Biofuels. 7 (145), (2014).</li></ol>

As with any analytical technique, there are several critical factors that can significantly impact the quality and reliability of the data generated. First, it is important to process samples efficiently, with a minimum of freeze/thaw cycles. Repeated freezing and thawing can compromise the chemical composition of the sample before processing or analysis. Second, it is critical to apply the steps of this protocol to all samples consistently and evenly. Technical errors arising from inconsistent sample preparation and han...

Carboxylic acids are organic compounds containing one or more terminal carboxyl functional groups, each attached to an R-group containing one or more carbons (R-C[O]OH). Short chain, low molecular weight carboxylic acids (short chain carboxylic acids, SCCAs) containing between one and six carbons, are essential components of cellular respiration, and function in several biochemical pathways necessary for cell growth and development. SCCAs play critical roles in cellular metabolism1, cell signaling2, and organismal responses to the environment (such as antibiosis3). Because of this, SCCAs can serve as useful indicators of disruptions to cellular metabolism, plant stress responses4,5, and fruit quality6,7. To date, SCCAs have been quantified primarily through chromatographic techniques such as high performance liquid chromatography (HPLC) or gas chromatography-mass spectroscopy (GC-MS). While these methods, are capable of achieving very low limits of detection, they can be expensive, require the derivatization of target SCCAs using caustic and/or toxic reagents, and include lengthy separation runs on the GC or HPLC. Because of this, interest in the use of free zonal capillary electrophoresis (CZE), which does not require sample derivatization, to quantify organic acids has steadily increased8.
Free zonal capillary electrophoresis (CZE) is a chromatographic separation methodology that, due to its high number of theoretical plates, speed, and relative ease-of-use, is increasingly replacing both GC-MS and high-pressure liquid chromatography as an analytical method for the quantification (particularly for quality control purposes) of anions, cations, amino acids, carbohydrates, and short chain carboxylic acids (SCCAs)8,9,10. CZE-based separation of small molecules, including SCCAs, is based two primary principles: the electrophoretic movement of charged ions in an electrical field established across the buffer filling the capillary; and the electro-osmotic movement of the entire buffer system from one end of the capillary to the other, generally towards the negative electrode. In this system, small molecules move towards the negative electrode at varying speeds, with the speed of each molecule determined by the ratio of the net charge of the molecule to the molecular mass. As the movement of each individual molecule in this system is dependent on the charge state of the molecule and the overall rate of electro-osmotic flow (which is itself based on the ion content of the buffer used to fill the capillary), the buffer pH and ionic composition heavily impact the degree to which molecules can be efficiently separated using CZE. Because of this, SCCAs, with their relatively high charge-to-mass ratios, are ideal targets for CZE-based separation. Metabolites separated using CZE can be detected using a variety of methods, including UV absorbance, spectral absorbance (which is generally performed using a photo-diode array [PDA]), and/or mass spectroscopy (CE-MS or CE-MS/MS)8. The diversity of separation and detection methods provided by CZE makes it an extremely flexible and adaptable technique. Because of this, CZE has been increasingly applied as a standard method of analysis in the areas of food safety and quality11,12, pharmaceutical research13, and environmental monitoring13,14. 
Capillary electrophoresis has been used to detect and quantify short chain carboxylic acids for nearly two decades13. The resolving power (particularly for small, charged molecules), short run time, and low per sample cost of CZE analyses make CZE an ideal technique for the separation and quantification of SCCAs13. This method presents a protocol to utilize CZE to measure the concentration of organic acids from plant tissues. Example data was generated through the successful implementation of this protocol to measure the change in organic acid levels in coffee seeds following a secondary fermentation treatment. The protocol details the critical steps and common errors of CZE-based separation of SCCAs, and discusses the means by which this protocol can be successfully applied to quantify SCCAs in additional plant tissues.

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	</colgroup>
	<tbody>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">Ceramic Moarter and Pestle</td>
			<td style="width:123px;">Coorstek</td>
			<td style="width:119px;">60310</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">Beckman Coulter P/ACE MDQ CE system</td>
			<td style="width:123px;">Beckman Coulter</td>
			<td style="width:119px;">Various</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">Glass sample vials</td>
			<td style="width:123px;">Fisher Inc.</td>
			<td style="width:119px;">033917D</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">1.5 ml microcentrifuge tubes&#160;</td>
			<td style="width:123px;">Fisher Inc.</td>
			<td style="width:119px;">02-681-5</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:296px;">LC/MS grade water</td>
			<td style="width:123px;">Fisher Inc.</td>
			<td style="width:119px;">W6-1</td>
			<td style="width:247px;">Milli-Q water (18.2 M&#937;.cm) is also acceptable</td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">15 ml glass tube/ Teflon lined cap&#160;</td>
			<td style="width:123px;">Fisher Inc.</td>
			<td style="width:119px;">14-93331A</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">Parafilm M</td>
			<td style="width:123px;">Fisher Inc.</td>
			<td style="width:119px;">13-374-12</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">CElixirOA detection Kit pH 5.4&#160;</td>
			<td style="width:123px;">MicroSolv</td>
			<td style="width:119px;">06100-5.4</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">BD Safety-Lok syringes</td>
			<td style="width:123px;">Fisher Inc.</td>
			<td style="width:119px;">14-829-32</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">17 mm Target Syringe filter, PTFE</td>
			<td style="width:123px;">Fisher Inc.</td>
			<td style="width:119px;">3377154</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">32 Karat, V. 8.0 control software</td>
			<td style="width:123px;">Beckman Coulter</td>
			<td style="width:119px;">285512</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">capillary electrophoresis (CE) sample vials&#160;</td>
			<td style="width:123px;">Beckman Coulter</td>
			<td style="width:119px;">144980</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:296px;">caps for CE vials&#160;</td>
			<td style="width:123px;">Beckman Coulter</td>
			<td style="width:119px;">144648</td>
			<td style="width:247px;"></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:296px;">Liquid Nitrogen</td>
			<td style="width:123px;">N/A</td>
			<td style="width:119px;">N/A</td>
			<td style="width:247px;">Liquid nitrogen is available from most facilities services</td>
		</tr>
	</tbody>
</table>

using capillary electrophoresis to quantify organic acids from plant tissue: a test case examining coffea arabica seeds

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic acids containing three to six carbons), such as malate and citrate, are critical to the proper functioning of many biological systems, where they function in cellular respiration and can serve as indicators of cell health. In foods, organic acid content can have significant impact on taste, with increased SCCA levels resulting in a sour or &#34;acid&#34; taste. Because of this, methods for the rapid analysis of organic acid levels are of particular interest to the food and beverage industries. Unfortunately, however, most methods used for SCCA quantification are dependent on time-consuming protocols requiring the derivatization of samples with hazardous reagents, followed by costly chromatographic and/or mass spectrometric analyses. This method details an alternate method for the detection and quantification of organic acids from plant material and food samples using free zonal capillary electrophoresis (CZE), sometimes simply referred to as capillary electrophoresis (CE). CZE provides a cost-effective method for measuring SCCAs with a low limit of detection (0.005 mg/ml). This article details the extraction and quantification of SCCAs from plant samples. While the method provided focuses on measurement of SCCAs from coffee beans, the method provided can be applied to multiple plant-based food materials.

This protocol has been successfully utilized to measure the effects of seed treatments on the SCCA content of green coffee seeds. In this experiment, the six treatments were: a saturated microbial suspension of Leuconostoc pseudomesenteroides strain GCP674 in its growth medium (1), an aqueous suspension of GCP674 microbes in water (2), an aqueous solution of acetic and lactic acids (0.15 and 0.4 mg/ml respectively) (3), a spent M1 growth medium treatment (4), dH2O wate...

Watch this Scientific Journal Video about Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds at JoVE.com

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

This article presents a method for the detection and quantification of organic acids from plant material using free zonal capillary electrophoresis. An example of the potential application of this method, determining the effects of a secondary fermentation on organic acid levels in coffee seeds, is provided.

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic ...

The overall goal of this procedure is to quantify the levels of organic acids present in plant tissues. This method can be used to answer questions in plant biochemistry and physiology, such as the impact of environmental stimuli on root growth, crop development, and food or beverage quality. The main advantages of this method are that sample preparation is minimal, the method is high throughput, and capillary electrophoresis is more cost effective than mass spectrometry.Though this method is used to elucidate plant physiological responses, it can also be applied to food science and food quality, where organic acids critically impact flavor, safety, and stability. To begin, assemble samples for short chain carboxylic acid, or SCCA, extraction. Prepare one gram of coffee seed at a time to ensure that enough sample will remain after processing.To attain a uniform particle size for maximal SCCA extraction efficiency, first pre-chill a mortar and pestle with liquid nitrogen. Add the sample to a small volume of liquid nitrogen in the mortar. Using a ladle, add enough liquid nitrogen to the mortar to completely submerge the sample.Add hard-to-grind samples, such as raw coffee seeds, to the liquid nitrogen. Allow them to freeze for 10 to 30 seconds before grinding. Break the tissue into smaller fragments using a vertical crushing motion.Then, complete tissue grinding using a circular grinding motion. Repeat the freezing and grinding steps twice more so that samples are ground the total of three times. Typically, three successive rounds of grinding will reduce samples to a powder with a flour-like consistency.Transfer the powder to glass vials or 1.5 ml micro-centrifuge tubes. Initiate downstream processing immediately after grinding or store samples at 80 degrees Celsius until samples are ready for extraction. Assemble authentic standards for the SCCAs of interest to create external and internal standard solutions for use in determining SCCA concentrations.For coffee samples, include citric, malic, acetic, and lactic acid as acids of interest, and adipic acid as the internal standard. Create a 10 milligram per milliliter stock solution by adding 100 milligrams of standard to a 10 milliliter volumetric flask. Fill the volumetric flask to the 10 milliliter line with ultra pure water to dissolve the acid.Transfer each stock solution to a clean 15 milliliter glass tube, with a polytetrafluoroethylene lined cap, and seal with plastic paraffin film. Stock solutions can be stored in sealed tubes at four degrees Celsius for one week. Prepare 50 milliliters of the SCCA extraction solution by diluting the internal standard stock solution to 0.05 milligrams per milliliter in ultra pure water.Do this by adding 250 microliters of the internal standard stock solution to 49.75 milliliters of water. Next, prepare standard curve samples for SCCAs of interest. Use a minimum of at least five points with concentrations in the linear response range that span the expected SCCA concentrations in the samples.Dilute each SCCA to the determined concentration in new micro-centrifuge tubes using ultra pure water to a volume of one milliliter. Ensure that each concentration point contains all four acid standards and the internal standard at the correct concentration. Remove samples to be extracted from storage, and place them on ice.Weigh out 100 milligrams of sample for the SCCA extraction. Measure an amount of sample as close to the target mass as possible, to reduce variability. After weighing each sample, transfer the tissue to a clean 1.5 milliliter micro-centrifuge tube.Keep track of the mass of each sample measured, as the amounts of SCCAs detected will be normalized using the sample mass. After weighing all samples, add one milliliter of exaction solution to each of the sample tubes. Keep the ratio of extraction solution to tissue mass the same across all extractions.Mix well by vortexing for 10 seconds. Allow the samples to sit at room temperature for one hour. During this hour, mix each tube every 15 minutes by vortexing for 10 seconds.After one hour of extraction, mix the samples one final time and transfer the sample tubes to a micro-centrifuge. Centrifuge the samples at four degrees Celsius, 10, 000 times G for 10 minutes, to precipitate the solid material. To filter the samples, prepare syringe-mounted disc filters, ensuring that each filter is correctly attached to the syringe.Prepare one syringe equipped with a disc filter for each sample to be analyzed, including the standard curve samples. Filter the supernatants directly into a clean micro-centrifuge tube. After filtering, close the tube containing the filtrate, and discard the syringe filter apparatus.Transfer one milliliter of sample to each capillary electrophoresis, or CE vial, taking care to avoid splashing the sample into the neck of the vial. After transferring the sample, place a CE cap on each vial. Set up the SCCA detection run as described in the text protocol.Load the vials containing the standard curve points and the vials containing the samples to assayed into the inlet sample tray, as described in the manufacturer's instructions. Note the position of each vial for auto-sampler programming. After conditioning as described in the text protocol, initiate sample separation by opening the Control menu in the software, and selecting Run Sequence.Monitor the photodiode array, or PDA trays, to ensure proper separation. Observe the first trace and ensure that it has a flat baseline, and cleanly resolve individual acid peaks. To integrate sample peaks, open the first file and set the automatic integration steps to exclude the first three minutes of the run.In the same menu, set peak selection criteria to a minimum peak width of 50 units, and a peak area of 100 units, to provide a moderately high level of selectivity, separating acid peaks from background noise in the trace. Perform data analysis as described in the text protocol. Shown here, is a comparison of PDA traces highlighting an overloaded sample.As analyte concentration increases, individual peak geometry may begin to become asymmetric. At 0.05 milligrams per milliliter, acetic acid presents a well defined bilaterally symmetrical peak. As the concentration of acetic acid increases to 0.07 or 0.10 milligrams per milliliter, the peak becomes asymmetrical, and a peak tail forms.This peak tailing is a good indication that the sample is overloaded. Displayed here are example PDA traces showing organic acids in green coffee samples. Green coffee samples were dilution 1:10 before loading into CE vials.Acids of interest include acetic acid, citric acid, lactic acid, malic acid, and the internal standard, adipic acid. While attempting this procedure, it's important to remember to grind samples to uniform consistency, and pipette samples carefully, to maximize reproducibility and minimize experimental error. After watching this video, you should have a good understanding of how to quantify organic acids from plant samples using capillary electrophoresis, or CE.You should be able to grind plant samples, extract organic acids, and prepare plant extracts for downstream CE analysis.

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Chemistry

Qualitative Identification of Carboxylic Acids, Boronic Acids, and Amines Using Cruciform Fluorophores

Molecular cruciforms are X-shaped systems in which two conjugation axes intersect at a central core. If one axis of these molecules is substituted with electron-donors, and the other with electron-acceptors, cruciforms&#39; HOMO will localize along the electron-rich and LUMO along the electron-poor axis. This spatial isolation of cruciforms&#39; frontier molecular orbitals (FMOs) is essential to their use as sensors, since analyte binding to the cruciform invariably changes its HOMO-LUMO gap and the associated optical properties. Using this principle, Bunz and Miljani&#263; groups developed 1,4-distyryl-2,5-bis(arylethynyl)benzene and benzobisoxazole cruciforms, respectively, which act as fluorescent sensors for metal ions, carboxylic acids, boronic acids, phenols, amines, and anions. The emission colors observed when these cruciform are mixed with analytes are highly sensitive to the details of analyte&#39;s structure and - because of cruciforms&#39; charge-separated excited states - to the solvent in which emission is observed. Structurally closely related species can be qualitatively distinguished within several analyte classes: (a) carboxylic acids; (b) boronic acids, and (c) metals. Using a hybrid sensing system composed from benzobisoxazole cruciforms and boronic acid additives, we were also able to discern among structurally similar: (d) small organic and inorganic anions, (e) amines, and (f) phenols. The method used for this qualitative distinction is exceedingly simple. Dilute solutions (typically 10-6 M) of cruciforms in several off-the-shelf solvents are placed in UV/Vis vials. Then, analytes of interest are added, either directly as solids or in concentrated solution. Fluorescence changes occur virtually instantaneously and can be recorded through standard digital photography using a semi-professional digital camera in a dark room. With minimal graphic manipulation, representative cut-outs of emission color photographs can be arranged into panels which permit quick naked-eye distinction among analytes. For quantification purposes, Red/Green/Blue values can be extracted from these photographs and the obtained numeric data can be statistically processed.

Cross-conjugated cruciform fluorophores based on 1,4-distyryl-2,5-bis(arylethynyl)benzene and benzobisoxazole nuclei can be used to qualitatively identify diverse Lewis acidic and Lewis basic analytes. This method relies on the differences in emission colors of the cruciforms that are observed upon analyte addition. Structurally closely related species can be distinguished from each other.

Molecular cruciforms are X-shaped systems in which two conjugation axes intersect at a central core. If one axis of these molecules is substituted with ...

Thin-layer Chromatographic (TLC) Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds

A common screen for plant antimicrobial compounds consists of separating plant extracts by paper or thin-layer chromatography (PC or TLC), exposing the chromatograms to microbial suspensions (e.g. fungi or bacteria in broth or agar), allowing time for the microbes to grow in a humid environment, and visualizing zones with no microbial growth.&#160;The effectiveness of this screening method, known as bioautography, depends on both the quality of the chromatographic separation and the care taken with microbial culture conditions.&#160;This paper describes standard protocols for TLC and contact bioautography&#160;with a novel application to amino acid-fermenting bacteria. The extract is separated on flexible (aluminum-backed) silica TLC plates, and bands are visualized under ultraviolet (UV) light.&#160;Zones are cut out and incubated face down onto agar inoculated with the test microorganism.&#160;Inhibitory bands are visualized by staining the agar plates with tetrazolium red.&#160;The method is applied to the separation of red clover (Trifolium pratense cv. Kenland) phenolic compounds and their screening for activity against Clostridium sticklandii, a hyper ammonia-producing bacterium (HAB) that is native to the bovine rumen.&#160;The TLC methods apply to many types of plant extracts&#160;and other bacterial species (aerobic or anaerobic), as well as fungi, can be used as test organisms if culture conditions are modified to fit the growth requirements of the species.

Thin-layer Chromatographic TLC Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds

Methods are described for thin-layer chromatographic (TLC) separation of plant extracts and contact bioautography to identify antibacterial metabolites. The methods are applied to the screening of red clover phenolic compounds inhibiting hyper&#160;ammonia-producing bacteria (HAB) native to the bovine rumen.

A common screen for plant antimicrobial compounds consists of separating plant extracts by paper or thin-layer chromatography (PC or TLC), exposing the ...

The Use of Gas Chromatography to Analyze Compositional Changes of Fatty Acids in Rat Liver Tissue during Pregnancy

Gas chromatography (GC) is a highly sensitive method used to identify and quantify the fatty acid content of lipids from tissues, cells, and plasma/serum, yielding results with high accuracy and high reproducibility. In metabolic and nutrition studies GC allows assessment of changes in fatty acid concentrations following interventions or during changes in physiological state such as pregnancy. Solid phase extraction (SPE) using aminopropyl silica cartridges allows separation of the major lipid classes including triacylglycerols, different phospholipids, and cholesteryl esters (CE). GC combined with SPE was used to analyze the changes in fatty acid composition of the CE fraction in the livers of virgin and pregnant rats that had been fed various high and low fat diets. There are significant diet/pregnancy interaction effects upon the omega-3 and omega-6 fatty acid content of liver CE, indicating that pregnant females have a different response to dietary manipulation than is seen among virgin females.

Pregnancy leads to significant changes to the fatty acid composition of maternal tissues. Lipid profiles can be obtained via gas chromatography to allow identification and quantification of fatty acids in individual lipid classes among rats fed various high and low fat diets during pregnancy.

Gas chromatography (GC) is a highly sensitive method used to identify and quantify the fatty acid content of lipids from tissues, cells, and plasma/serum, ...

Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The analysis of volatile and oxidation sensitive compounds by mass spectrometry is not easily achieved, as all state-of-the-art mass spectrometric methods require at least one sample preparation step, e.g., dissolution and dilution of the analyte (electrospray ionization), co-crystallization of the analyte with a matrix compound (matrix-assisted laser desorption/ionization), or transfer of the prepared samples into the ionization source of the mass spectrometer, to be conducted under atmospheric conditions. Here, the use of a sample inlet system is described which enables the analysis of volatile metal organyls, silanes, and phosphanes using a sector field mass spectrometer equipped with an electron impact ionization source. All sample preparation steps and the sample introduction into the ion source of the mass spectrometer take place either under air-free conditions or under vacuum, enabling the analysis of compounds highly susceptible to oxidation. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes, which have to be handled using inert conditions, such as the Schlenk technique. The principle of operation is presented in this video.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes which have to be handled using inert conditions, such as the Schlenk technique.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The ...

Capillary Electrophoresis to Monitor Peptide Grafting onto Chitosan Films in Real Time

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. Compared to other analytical separation techniques, such as chromatography, CE is cheap, robust and effectively requires no sample preparation (for a number of complex natural matrices or polymeric samples). CE is fast and can be used to follow the evolution of mixtures in real time (e.g., chemical reaction kinetics), as the signals observed for the separated compounds are directly proportional to their quantity in solution.
Here, the efficiency of CE is demonstrated for monitoring the covalent grafting of peptides onto chitosan films for subsequent biomedical applications. Chitosan&#39;s antimicrobial and biocompatible properties make it an attractive material for biomedical applications such as cell growth substrates. Covalently grafting the peptide RGDS (arginine - glycine - aspartic acid - serine) onto the surface of chitosan films aims at improving cell attachment. Historically, chromatography and amino acid analysis have been used to provide a direct measurement of the amount of grafted peptide. However, the fast separation and absence of sample preparation provided by CE enables equally accurate yet real-time monitoring of the peptide grafting process. CE is able to separate and quantify the different components of the reaction mixture: the (non-grafted) peptide and the chemical coupling agents. In this way the use of CE results in improved films for downstream applications.
The chitosan films were characterized through solid-state NMR (nuclear magnetic resonance) spectroscopy. This technique is more time-consuming and cannot be applied in real time, but yields a direct measurement of the peptide and thus validates the CE technique.

Free solution capillary electrophoresis is a fast, cheap and robust analytical method that enables the quantitative monitoring of chemical reactions in real time. Its utility for rapid, convenient and precise analysis is demonstrated here through analysis of covalent peptide grafting onto chitosan films for improved cell adhesion.

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. ...

Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a free-radical polymerization strategy to enable the modulation of the nanotube surface properties and produce supramolecular self-assembly of the nanostructures. First, a selective hydroxylation of the pristine nanotubes through a biphasic catalytically mediated oxidation reaction creates superficially distributed reactive sites at the sidewalls. The latter reactive sites are subsequently modified with methacrylic moieties using a silylated methacrylic precursor to create polymerizable sites. Those polymerizable groups can address further polymerization of styrene to produce a hybrid nanomaterial containing PS chains grafted to the nanotube sidewalls. The polymer-graft content, amount of silylated methacrylic moieties introduced and hydroxylation modification of the nanotubes are identified and quantified by Thermogravimetric Analysis (TGA). The presence of reactive functional groups hydroxyl and silylated methacrylate are confirmed by Fourier Transform Infrared Spectroscopy (FT-IR). Polystyrene-grafted carbon nanotube solutions in tetrahydrofuran (THF) provide wall-to-wall collinearly self-assembled nanotubes when cast samples are analyzed by transmission electron microscopy (TEM). Those self-assemblies are not obtained when suitable blanks are similarly cast from analogous solutions containing non-grafted counterparts. Therefore, this method enables the modification of the nanotube anisotropic patchiness at the sidewalls which results into spontaneous auto-organization at the nanoscale.

A procedure for the synthesis of polystyrene-grafted multiwalled carbon nanotubes using successive chemical modification steps to selectively introduce the polymer chains to the sidewalls and their self-assembly via anisotropic patchiness is presented.

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a ...

Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance (EPR) or ultraviolet-visible and near-infrared (UV-Vis-NIR) spectroscopies, we obtain useful information such as electron affinity, ionization potential, band-gap energies, the type of charge carriers, and degradation information that can be used to synthesize stable organic electronic devices. In this study, we present electrochemical and spectroelectrochemical methods to analyze the processes occurring in active layers of an organic device as well as the generated charge carriers.

In this article, we describe electrochemical, electron paramagnetic resonance, and ultraviolet-visible and near-infrared spectroelectrochemical methods to analyze organic compounds for application in organic electronics.

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance ...

Microprobe Capillary Electrophoresis Mass Spectrometry for Single-cell Metabolomics in Live Frog (Xenopus laevis) Embryos

The quantification of small molecules in single cells raises new potentials for better understanding the basic processes that underlie embryonic development. To enable single-cell investigations directly in live embryos, new analytical approaches are needed, particularly those that are sensitive, selective, quantitative, robust, and scalable to different cell sizes. Here, we present a protocol that enables the in situ analysis of metabolism in single cells in freely developing embryos of the South African clawed frog (Xenopus laevis), a powerful model in cell and developmental biology. This approach uses a capillary microprobe to aspirate a defined portion from single identified cells in the embryo, leaving neighboring cells intact for subsequent analysis. The collected cell content is analyzed by a microscale capillary electrophoresis electrospray ionization (CE-ESI) interface coupled to a high-resolution tandem mass spectrometer. This approach is scalable to various cell sizes and compatible with the complex three-dimensional structure of the developing embryo. As an example, we demonstrate that microprobe single-cell CE-ESI-MS enables the elucidation of metabolic cell heterogeneity that unfolds as a progenitor cell gives rise to descendants during development of the embryo. Besides cell and developmental biology, the single-cell analysis protocols described here are amenable to other cell sizes, cell types, or animal models.

Microprobe Capillary Electrophoresis Mass Spectrometry for Single-cell Metabolomics in Live Frog Xenopus laevis Embryos

We describe steps that enable fast in situ sampling of a small portion of an individual cell with high precision and minimal invasion using capillary-based micro-sampling, to facilitate chemical characterization of a snapshot of metabolic activity in live embryos using a custom-built single cell capillary electrophoresis and mass spectrometry platform.

The quantification of small molecules in single cells raises new potentials for better understanding the basic processes that underlie embryonic ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Large-scale Top-down Proteomics Using Capillary Zone Electrophoresis Tandem Mass Spectrometry

Capillary zone electrophoresis-electrospray ionization-tandem mass spectrometry (CZE-ESI-MS/MS) has been recognized as a useful tool for top-down proteomics that aims to characterize proteoforms in complex proteomes. However, the application of CZE-MS/MS for large-scale top-down proteomics has been impeded by the low sample-loading capacity and narrow separation window of CZE. Here, a protocol is described using CZE-MS/MS with a microliter-scale sample-loading volume and a 90-min separation window for large-scale top-down proteomics. The CZE-MS/MS platform is based on a linear polyacrylamide (LPA)-coated separation capillary with extremely low electroosmotic flow, a dynamic pH-junction-based online sample concentration method with a high efficiency for protein stacking, an electro-kinetically pumped sheath flow CE-MS interface with extremely high sensitivity, and an ion trap mass spectrometer with high mass resolution and scan speed. The platform can be used for the high-resolution characterization of simple intact protein samples and the large-scale characterization of proteoforms in various complex proteomes. As an example, a highly efficient separation of a standard protein mixture and a highly sensitive detection of many impurities using the platform is demonstrated. As another example, this platform can produce over 500 proteoform and 190 protein identifications from an Escherichia coli proteome in a single CZE-MS/MS run.

A detailed protocol is described for the separation, identification, and characterization of proteoforms in protein samples using capillary zone electrophoresis-electrospray ionization-tandem mass spectrometry (CZE-ESI-MS/MS). The protocol can be used for the high-resolution characterization of proteoforms in simple protein samples and the large-scale identification of proteoforms in complex proteome samples.