The authors have no acknowledgements.

1. Sample Plate Preconditioning
<ol>
	<li>Cleaning of the sample plate
	<ol>
		<li>Wear nitrile gloves to avoid contamination of the sample plate during cleaning.</li>
		<li>Hand-wash the sample plate with 100.0 mL of detergent solution (1.0 mg/mL).</li>
		<li>Hand-wash the sample plate with distilled-deionized water (DDW).</li>
		<li>Rinse the sample plate surface with 30.0 mL of MeOH.</li>
		<li>Put the sample plate in a 600 mL beaker and fill with DDW until the sample plate is fully immersed in water.</li>
		<li>Put the beaker in an ultrasonic bath (see Table of Materials) and sonicate the sample plate for 15 min (200 W, 40 kHz).</li>
		<li>Take out the sample plate and blow off water drops using pressurized nitrogen.</li>
		<li>Deposit 0.2 &#181;L of MeOH on the sample plate to check whether MeOH spreads to other spots. 
		Note: If MeOH merges with other spots, repeat steps 1.1.3-1.1.5; if not, proceed to the next step.</li>
	</ol>
	</li>
	<li>Regulation of drying chamber temperature
	<ol>
		<li>Use a drying chamber under steady conditions to dry droplets, as described previously11,12,13. In particular, use the detailed procedure described in steps 2.1-2.5 of Ou, Y.-M. et al. 201612. Briefly:
		<ol>
			<li>Purge the drying chamber by room temperature nitrogen at a constant flow rate to maintain a low relative humidity environment.</li>
			<li>Keep the sample plate temperature constant at regular- (25 &#176;C) or fast-drying conditions (50 &#176;C), regulated by a temperature-controlled copper block in the drying chamber.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Preparation of matrix and analyte solutions
	<ol>
		<li>Preparation of matrix solutions
		<ol>
			<li>Dissolve DHB in 50% acetonitrile (ACN):50% DDW to prepare a 0.1 M solution.</li>
		</ol>
		</li>
		<li>Preparation of carbohydrate analytes
		<ol>
			<li>Dissolve SLeA in DDW to prepare a 10-4 M solution.</li>
			<li>Dissolve MH in DDW to prepare a 10-4 M solution.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Sample Deposition and Recrystallization
Note: The optimized procedures for analyzing small and regular amounts of samples are described here. Ensure that the sample plate temperature is stabilized at the desired temperature before depositing the solutions. If the sample spreads over a large area to cover other sample spots during recrystallization, prepare a new sample or repeat step 1.1.
<ol>
	<li>For analysis of a small amount (0.1 &#181;L) of sample 
	Note: The following steps have been developed for minimizing sample and time consumption. It is suitable for quantitative analysis of real samples with a limited amount or quick IMS for quantification analysis.
	<ol>
		<li>Premix 0.25 &#181;L of DHB solution and 0.25 &#181;L of SLeA or MH solution in a microcentrifuge tube.</li>
		<li>Vortex the mixed solution using a vortex mixer for 3 s.</li>
		<li>Spin down the mixed solution in a mini centrifuge for 2 s (2000 x g).</li>
		<li>Use a pipette to draw out 0.1 &#181;L of the premixed solution and immediately deposit it on the sample plate. 
		Note: When depositing a small amount of sample, DO NOT keep the premixed solution in the tip of pipette for over 10 s.</li>
		<li>Wait for the sample to dry out. Typical drying times are listed in Table 1.</li>
		<li>Use a pipette to deposit 0.2 &#181;L of MeOH right onto the dried sample spot. The sample will get wet and dry out immediately. 
		Note: Ensure that the deposition procedure is finished in 3 s to avoid significant evaporation loss of MeOH.</li>
		<li>Examine the sample using a microscope. If the crystal morphologies are not as expected (see Figure 1 for example of desired results), repeat steps 2.1.1-2.1.6 to prepare a new sample.</li>
		<li>Wear nitrile gloves and carefully take out the sample plate from the drying chamber.</li>
	</ol>
	</li>
	<li>For analysis of a regular amount (1 &#181;L) of sample 
	Note: The following steps are developed for maximizing the homogeneity of carbohydrate samples with typically utilized MALDI sample amount. The process is suitable for routine and quantitative analyses. The recrystallization process redistributes samples and matrixes evenly to larger areas.
	<ol>
		<li>Premix 2.5 &#181;L of DHB solution and 2.5 &#181;L SLeA or MH solution in a microcentrifuge tube.</li>
		<li>Vortex the premixed solution with a vortex mixer for 5 s.</li>
		<li>Spin down the mixed solution in a mini centrifuge for 2 s (2000 x g).</li>
		<li>Use a pipette to draw out 1.0 &#181;L of the premixed solution and immediately deposit it on the sample plate. 
		Note: DO NOT use the remaining premixed solution again after depositing the samples.</li>
		<li>Wait for the sample to dry out. Typical drying times are listed in Table 1.</li>
		<li>Use a pipette to deposit 1.5 &#181;L of MeOH right onto the dried sample spot. The sample will get wet and dry out immediately. 
		Note: In cases with high sample plate temperature (50 &#176;C), the recrystallization step should be done within 5 s to minimize evaporation of MeOH in pipette tip.</li>
		<li>Examine the sample using a microscope. If the crystal morphologies are not as expected (see Figure 1 for example of desired results), repeat steps 2.2.1-2.2.6 to prepare a new sample.</li>
		<li>Wear nitrile gloves and carefully take out the sample plate from the drying chamber.</li>
	</ol>
	</li>
</ol>
3. Mass Spectrometry Data Acquisition and Analysis
Note: The analysis is performed using a commercial time-of-flight mass spectrometer (Table of Materials) equipped with a MALDI ion source. The instrument is operated by specific control software (Table of Materials) with pre-optimized extraction delay and laser energy. Spectra are recorded in linear mode with a mass range of m/z = 0 &#8211; 1500. The sample plate potential is &#177;25 keV and every spectrum averages 10 laser shots. Users should conduct instrument optimization and sample analysis using compatible software and follow instrument manufacturer&#39;s instructions.
<ol>
	<li>Open the instrument control software (see Table of Materials).</li>
	<li>Insert the sample plate into the mass spectrometer.</li>
	<li>Select the pre-optimized data acquisition method in the software.</li>
	<li>Register the whole sample region for IMS using the imaging software (see Table of Materials). 
	Note: Skip this step if not doing IMS.</li>
	<li>Start data acquisition in the batch mode of the control software.</li>
	<li>Plot the ion images using the imaging software after data acquisition is complete.</li>
	<li>Analyze mass spectra using analysis software (see Table of Materials) if the data is recorded without an ion image.</li>
</ol>

<ol>
	<li>Holme, D. J., Peck, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Analytical Biochemistry. , (1998).</li><li>Costello, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time,+life+...+and+mass+spectrometry+-+New+techniques+to+address+biological+questions.">Time, life ... and mass spectrometry - New techniques to address biological questions.</a> Biophysical Chemistry. 68 (1-3), 173-188 (1997).</li><li>Caroff, M., Karibian, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+of+bacterial+lipopolysaccharides.">Structure of bacterial lipopolysaccharides.</a> Carbohydrate Research. 338 (23), 2431-2447 (2003).</li><li>Marvin, L. F., Roberts, M. A., Fay, L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrix-assisted+laser+desorption/ionization+time-of-flight+mass+spectrometry+in+clinical+chemistry.">Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in clinical chemistry.</a> Clinica Chimica Acta. 337 (1), 11-21 (2003).</li><li>Harvey, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrix-assisted+laser+desorption/ionization+mass+spectrometry+of+carbohydrates.">Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates.</a> Mass Spectrometry Reviews. 18 (6), 349-450 (1999).</li><li>Ciucanu, I., Kerek, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+and+rapid+method+for+the+permethylation+of+carbohydrates.">A simple and rapid method for the permethylation of carbohydrates.</a> Carbohydrate Research. 131 (2), 209-217 (1984).</li><li>Lamari, F. N., Kuhn, R., Karamanos, N. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Derivatization+of+carbohydrates+for+chromatographic,+electrophoretic+and+mass+spectrometric+structure+analysis.">Derivatization of carbohydrates for chromatographic, electrophoretic and mass spectrometric structure analysis.</a> Journal of Chromatography B. 793 (1), 15-36 (2003).</li><li>Nishikaze, T., Amano, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reverse+thin+layer+method+for+enhanced+ion+yield+of+oligosaccharides+in+matrix-assisted+laser+desorption/ionization.">Reverse thin layer method for enhanced ion yield of oligosaccharides in matrix-assisted laser desorption/ionization.</a> Rapid Communications in Mass Spectrometry. 23 (23), 3787-3794 (2009).</li><li>Williams, T. I., Saggese, D. A., Wilcox, R. J., Martin, J. D., Muddiman, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+matrix+crystal+structure+on+ion+abundance+of+carbohydrates+by+matrix-assisted+laser+desorption/ionization+Fourier+transform+ion+cyclotron+resonance+mass+spectrometry.">Effect of matrix crystal structure on ion abundance of carbohydrates by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry.</a> Rapid Communications in Mass Spectrometry. 21 (5), 807-811 (2007).</li><li>Nicola, A. J., Gusev, A. I., Proctor, A., Jackson, E. K., Hercules, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+the+fast-evaporation+sample+preparation+method+for+improving+quantification+of+angiotensin+II+by+matrix-assisted+laser+desorption/ionization.">Application of the fast-evaporation sample preparation method for improving quantification of angiotensin II by matrix-assisted laser desorption/ionization.</a> Rapid Communications in Mass Spectrometry. 9 (12), 1164-1171 (1995).</li><li>Lai, Y. H., 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=Reducing+Spatial+Heterogeneity+of+MALDI+Samples+with+Marangoni+Flows+During+Sample+Preparation.">Reducing Spatial Heterogeneity of MALDI Samples with Marangoni Flows During Sample Preparation.</a> Journal of the American Society for Mass Spectrometry. 27 (8), 1314-1321 (2016).</li><li>Ou, Y. -. 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=Preparation+of+Homogeneous+MALDI+Samples+for+Quantitative+Applications.">Preparation of Homogeneous MALDI Samples for Quantitative Applications.</a> Journal of Visualized Experiments. (116), e54409 (2016).</li><li>Lee, H., 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=Enhancing+carbohydrate+ion+yield+by+controlling+crystalline+structures+in+matrix-assisted+laser+desorption/ionization+mass+spectrometry.">Enhancing carbohydrate ion yield by controlling crystalline structures in matrix-assisted laser desorption/ionization mass spectrometry.</a> Analytica Chimica Acta. , 49-55 (2017).</li><li>Allwood, D. A., Perera, I. K., Perkins, J., Dyer, P. E., Oldershaw, G. 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The authors have nothing to disclose.

Sample heterogeneity is a crucial problem in MALDI-MS. DD is the most commonly used sample preparation method, but the resultant crystals are highly heterogeneous. Such samples show poor shot-to-shot and sample-to-sample signal reproducibility. Therefore, searching for &#34;sweet spots&#34; in sample areas during data acquisition is a common procedure in MALDI experiments. Such heterogeneous samples are unsuitable for quantification in routine analyses.
In the current study, MALDI sample morph...

Carbohydrate analysis is an important and challenging subject. Carbohydrates and their derivatives play important roles in living organisms1,2,3. These molecules have complicated structures and are prone to decompose. Many of them cannot be clearly characterized due to difficulties in separation and detection. Although matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) has been applied to analysis of a wide range of biomolecules, due to its sensitivity and comprehensible results4, analyzing carbohydrates using MALDI-MS continues to be a major challenge due to the low ionization efficiency of such molecules5. Chemical derivatization is a common way to improve ionization efficiency of carbohydrates6,7, but such procedures are time and sample consuming. Besides, the ionization efficiency of derivatized carbohydrates is still lower than that of proteins. Thus, the development of methods to improve carbohydrate signal in MALDI-MS without complicated procedures is necessary.
The application of MALDI-MS to quantitative analysis is another challenging subject. A major problem of MALDI-MS is that its sensitivity and data reproducibility relies critically on sample preparation protocols and experimental parameters. In many cases, quantitative analysis by MALDI-MS is unreliable due to heterogeneous sample morphologies and analyte distribution. A well-known example is samples prepared with a 2,5-dihydroxybenzoic acid (DHB) MALDI matrix. When DHB is crystallized slowly under ambient environment, the extent of analyte incorporation into matrix crystals is unpredictable, because resultant samples show irregular morphologies. Such samples normally consist of large needle-shaped and fine crystals. When DHB is prepared using a volatile solvent and/or a heated sample plate, a fast drying process results in more homogeneous fine crystals and better quantitative results8,9,10. This technique is known as &#34;recrystallization&#34; of MALDI samples. The improvement is attributed to better incorporation of analytes into fine matrix crystals during the fast crystallization process. We have also demonstrated that adjusting the sample preparation environment reduced the heterogeneity of carbohydrate signal and improved quantitative results11,12. The findings in these works suggest that sample morphology is a critical factor in determining carbohydrate signal quality. To develop a general strategy for daily analysis, an efficient sample reformation method providing improved carbohydrate sensitivity is required.
We have systematically examined the correlation between sample morphology and carbohydrate sensitivity in MALDI-MS in a recent report13. The results obtained using several important carbohydrates and matrixes show that the best signal enhancement is fulfilled by recrystallizing dried MALDI samples. The morphology of samples prepared using the conventional dried droplet (DD) method is reformed by fast recrystallization with methanol (MeOH). The detailed sample preparation protocols are demonstrated here. The protocol consists of three main steps, including sample plate preconditioning, sample deposition and recrystallization, and mass spectrometry analysis. The utilized carbohydrates include sialyl-lewis A (SLeA) and maltoheptaose (MH). DHB is used as a model matrix. The results show that carbohydrate signal intensity and spatial distribution improved markedly after recrystallization. Such a method can be applied to samples with other popular matrixes, including 2,4,6-trihydroxyacetophenone (THAP) and &#945;-cyano-4-hydroxycinnamic acid. This method serves as a general approach that can be easily integrated in the laboratory routine for carbohydrate analysis.

<table border="0" cellpadding="0" cellspacing="0" width="816">
	<tbody>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Reagent</td>
			<td style="width:157px;"></td>
			<td style="width:137px;"></td>
			<td style="width:191px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Detergent powder</td>
			<td style="width:157px;">Alconox</td>
			<td style="width:137px;">242985</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Methanol</td>
			<td style="width:157px;">Merck</td>
			<td style="width:137px;">106009</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Acetonitrile</td>
			<td style="width:157px;">Merck</td>
			<td style="width:137px;">100003</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">2,5-dihydroxybenzoic acid (DHB)</td>
			<td style="width:157px;">Alfa Aesar</td>
			<td style="width:137px;">A11459</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">sialyl-lewis A (SLeA)</td>
			<td style="width:157px;">Sigma-Aldrich</td>
			<td style="width:137px;">S1782</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">Maltoheptaose</td>
			<td style="width:157px;">Sigma-Aldrich</td>
			<td style="width:137px;">M7753</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Pipette tips</td>
			<td style="width:157px;">Mettler Toledo</td>
			<td style="width:137px;">17005091</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Microcentrifuge tube</td>
			<td style="width:157px;">Axygen</td>
			<td style="width:137px;">MCT-150-C</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Equipment</td>
			<td style="width:157px;"></td>
			<td style="width:137px;"></td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Milli-Q water purification system</td>
			<td style="width:157px;">Millipore</td>
			<td style="width:137px;">ZMQS6VFT1</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">Powder-free nitrile gloves</td>
			<td style="width:157px;">Microflex</td>
			<td style="width:137px;">SU-690</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">600 mL beaker</td>
			<td style="width:157px;">Duran</td>
			<td style="width:137px;">2110648</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Ultrasonic cleaner</td>
			<td style="width:157px;">Delta</td>
			<td style="width:137px;">DC300H</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Hygrometer</td>
			<td style="width:157px;">Wisewind</td>
			<td style="width:137px;">5330</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Nitrogen gas flowmeter</td>
			<td style="width:157px;">Dwyer</td>
			<td style="width:137px;">RMA-6-SSV</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">K-type thermocouples</td>
			<td style="width:157px;">Digitron</td>
			<td style="width:137px;">311-1670</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Vortex mixer</td>
			<td style="width:157px;">Scientific Industries</td>
			<td style="width:137px;">&#160;SI-0236</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Mini centrifuge</td>
			<td style="width:157px;">Select BioProducts</td>
			<td style="width:137px;">Force Mini&#160;</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Pipette</td>
			<td style="width:157px;">Rainin</td>
			<td style="width:137px;">pipet-lite XLS</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Stereomicroscope</td>
			<td style="width:157px;">Olympus</td>
			<td style="width:137px;">SZX16</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Temperature controllable drying chamber</td>
			<td style="width:157px;">This lab</td>
			<td style="width:137px;"></td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Ultraflex II TOF/TOF mass spectrometer</td>
			<td style="width:157px;">Bruker Daltonics</td>
			<td style="width:137px;"></td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">MTP 384 target plate polished steel BC</td>
			<td style="width:157px;">Bruker Daltonics</td>
			<td style="width:137px;">8280781</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Flexcontrol Version 3.4</td>
			<td style="width:157px;">Bruker Daltonics</td>
			<td style="width:137px;"></td>
			<td>Control software</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Fleximaging Version 2.1</td>
			<td style="width:157px;">Bruker Daltonics</td>
			<td style="width:137px;"></td>
			<td>Imaging software</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:332px;">Flexanalysis Version 3.4</td>
			<td style="width:157px;">Bruker Daltonics</td>
			<td style="width:137px;"></td>
			<td>Analysis software</td>
		</tr>
	</tbody>
</table>

an efficient sample preparation method to enhance carbohydrate ion signals in matrix-assisted laser desorption/ionization mass spectrometry

Sample preparation is a critical process in mass spectrometry (MS) analysis of carbohydrates. Although matrix-assisted laser desorption/ionization (MALDI) MS is the method of choice in carbohydrate analysis, poor ion signal and data reproducibility of carbohydrate samples continue to be severe problems. For quantitative analysis of carbohydrates, an effective analytical protocol providing superior data quality is necessary. This video demonstrates sample preparation protocols to improve signal intensity and minimize data variation of carbohydrates in MALDI-MS. After drying and crystallization of sample droplets, the crystal morphology is reformed by methanol before mass spectrometric analysis. The enhancement in carbohydrate signal is examined with MALDI imaging mass spectrometry (IMS). Experimental results show that crystal reformation adjusts crystalline structures and redistributes carbohydrate analytes. In comparison with the dried droplet preparation method in conventional MALDI-MS, reforming carbohydrate crystal morphologies with methanol shows significantly better signal intensity, ion image distribution, and data stability. Since the protocols demonstrated herein do not involve changes in sample composition, they are generally applicable to various carbohydrates and matrixes.

Representative SEM images of SLeA mixed with DHB prepared using DD and recrystallization methods are shown in Figure 1. A typical DHB morphology as prepared by the DD method is large needle-shaped crystals at the rim and fine crystalline structures in the center of sample spots. The typical lengths of such needle-shaped crystals are ~100 &#181;m. After recrystallization by MeOH, the sample has a larger area covered evenly with fine flake-like cryst...

Watch this Scientific Journal Video about An Efficient Sample Preparation Method to Enhance Carbohydrate Ion Signals in Matrix-assisted Laser Desorption/Ionization Mass Spectrometry at JoVE.com

An Efficient Sample Preparation Method to Enhance Carbohydrate Ion Signals in Matrix-assisted Laser Desorption/Ionization Mass Spectrometry

A protocol for enhancing carbohydrate ion signals in MALDI mass spectrometry by reforming crystalline structures during sample preparation processes is demonstrated.

Sample preparation is a critical process in mass spectrometry (MS) analysis of carbohydrates. Although matrix-assisted laser desorption/ionization (MALDI) ...

an-efficient-sample-preparation-method-to-enhance-carbohydrate-ion

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7.0K Views.  Academia Sinica. A protocol for enhancing carbohydrate ion signals in MALDI mass spectrometry by reforming crystalline structures during sample preparation processes is demonstrated.

Video: An Efficient Sample Preparation Method to Enhance Carbohydrate Ion Signals in Matrix-assisted Laser Desorption/Ionization Mass Spectrometry

Untargeted Metabolomics from Biological Sources Using Ultraperformance Liquid Chromatography-High Resolution Mass Spectrometry (UPLC-HRMS)

Here we present a workflow to analyze the metabolic profiles for biological samples of interest including; cells, serum, or tissue. The sample is first separated into polar and non-polar fractions by a liquid-liquid phase extraction, and partially purified to facilitate downstream analysis. Both aqueous (polar metabolites) and organic (non-polar metabolites) phases of the initial extraction are processed to survey a broad range of metabolites. Metabolites are separated by different liquid chromatography methods based upon their partition properties. In this method, we present microflow ultra-performance (UP)LC methods, but the protocol is scalable to higher flows and lower pressures. Introduction into the mass spectrometer can be through either general or compound optimized source conditions. Detection of a broad range of ions is carried out in full scan mode in both positive and negative mode over a broad m/z range using high resolution on a recently calibrated instrument. Label-free differential analysis is carried out on bioinformatics platforms. Applications of this approach include metabolic pathway screening, biomarker discovery, and drug development.

Untargeted Metabolomics from Biological Sources Using Ultraperformance Liquid Chromatography-High Resolution Mass Spectrometry UPLC-HRMS

Untargeted metabolomics provides a hypothesis generating snapshot of a metabolic profile. This protocol will demonstrate the extraction and analysis of metabolites from cells, serum, or tissue. A range of metabolites are surveyed using liquid-liquid phase extraction, microflow ultraperformance liquid chromatography/high-resolution mass spectrometry (UPLC-HRMS) coupled to differential analysis software.

Here we present a workflow to analyze the metabolic profiles for biological samples of interest including; cells, serum, or tissue. The sample is first ...

Matrix-assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) Mass Spectrometric Analysis of Intact Proteins Larger than 100 kDa

Effectively determining masses of proteins is critical to many biological studies (e.g. for structural biology investigations). Accurate mass determination allows one to evaluate the correctness of protein primary sequences, the presence of mutations and/or post-translational modifications, the possible protein degradation, the sample homogeneity, and the degree of isotope incorporation in case of labelling (e.g. 13C labelling).
Electrospray ionization (ESI) mass spectrometry (MS) is widely used for mass determination of denatured proteins, but its efficiency is affected by the composition of the sample buffer. In particular, the presence of salts, detergents, and contaminants severely undermines the effectiveness of protein analysis by ESI-MS. Matrix-assisted laser desorption/ionization (MALDI) MS is an attractive alternative, due to its salt tolerance and the simplicity of data acquisition and interpretation. Moreover, the mass determination of large heterogeneous proteins (bigger than 100 kDa) is easier by MALDI-MS due to the absence of overlapping high charge state distributions which are present in ESI spectra.
Here we present an accessible approach for analyzing proteins larger than 100 kDa by MALDI-time of flight (TOF). We illustrate the advantages of using a mixture of two matrices (i.e. 2,5-dihydroxybenzoic acid and &#945;-cyano-4-hydroxycinnamic acid) and the utility of the thin layer method as approach for sample deposition. We also discuss the critical role of the matrix and solvent purity, of the standards used for calibration, of the laser energy, and of the acquisition time. Overall, we provide information necessary to a novice for analyzing intact proteins larger than 100 kDa by MALDI-MS.

Matrix-assisted Laser Desorption/Ionization Time of Flight MALDI-TOF Mass Spectrometric Analysis of Intact Proteins Larger than 100 kDa

Accurate mass measurement represents an important step during the investigation of proteins. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) can be used for such determination and its key advantage is the tolerance to salts, detergents and contaminants. Here we illustrate an accessible approach for the analysis of proteins larger than 100 kDa by MALDI-MS.

Effectively determining masses of proteins is critical to many biological studies (e.g. for structural biology investigations). Accurate mass ...

Improved In-gel Reductive &#946;-Elimination for Comprehensive O-linked and Sulfo-glycomics by Mass Spectrometry

Separation of proteins by SDS-PAGE followed by in-gel proteolytic digestion of resolved protein bands has produced high-resolution proteomic analysis of biological samples. Similar approaches, that would allow in-depth analysis of the glycans carried by glycoproteins resolved by SDS-PAGE, require special considerations in order to maximize recovery and sensitivity when using mass spectrometry (MS) as the detection method. A major hurdle to be overcome in achieving high-quality data is the removal of gel-derived contaminants that interfere with MS analysis. The sample workflow presented here is robust, efficient, and eliminates the need for in-line HPLC clean-up prior to MS. Gel pieces containing target proteins are washed in acetonitrile, water, and ethyl acetate to remove contaminants, including polymeric acrylamide fragments. O-linked glycans are released from target proteins by in-gel reductive &#946;-elimination and recovered through robust, simple clean-up procedures. An advantage of this workflow is that it improves sensitivity for detecting and characterizing sulfated glycans. These procedures produce an efficient separation of sulfated permethylated glycans from non-sulfated (sialylated and neutral) permethylated glycans by a rapid phase-partition prior to MS analysis, and thereby enhance glycomic and sulfoglycomic analyses of glycoproteins resolved by SDS-PAGE.

In order to comprehensively explore the diversity of O-linked glycans, a new procedure for in-gel reductive &#946;-elimination, combined with permethylation and a rapid phase-partition method, is applied to the analysis of O-linked glycans directly released from glycoproteins resolved by SDS-PAGE and amenable to subsequent glycomic analysis by mass spectrometry.

Separation of proteins by SDS-PAGE followed by in-gel proteolytic digestion of resolved protein bands has produced high-resolution proteomic analysis of ...

An HS-MRM Assay for the Quantification of Host-cell Proteins in Protein Biopharmaceuticals by Liquid Chromatography Ion Mobility QTOF Mass Spectrometry

The analysis of low-level (1-100 ppm) protein impurities (e.g., host-cell proteins (HCPs)) in protein biotherapeutics is a challenging assay requiring high sensitivity and a wide dynamic range. Mass spectrometry-based quantification assays for proteins typically involve protein digestion followed by the selective reaction monitoring/multiple reaction monitoring (SRM/MRM) quantification of peptides using a low-resolution (Rs ~1,000) tandem quadrupole mass spectrometer. One of the limitations of this approach is the interference phenomenon observed when the peptide of interest has the "same" precursor and fragment mass (in terms of m/z values) as other co-eluting peptides present in the sample (within a 1-Da window). To avoid this phenomenon, we propose an alternative mass spectrometric approach, a high selectivity (HS) MRM assay that combines the ion mobility separation of peptide precursors with the high-resolution (Rs ~30,000) MS detection of peptide fragments. We explored the capabilities of this approach to quantify low-abundance peptide standards spiked in a monoclonal antibody (mAb) digest and demonstrated that it has the sensitivity and dynamic range (at least 3 orders of magnitude) typically achieved in HCP analysis. All six peptide standards were detected at concentrations as low as 0.1 nM (1 femtomole loaded on a 2.1-mm ID chromatographic column) in the presence of a high-abundance peptide background (2 &#181;g of a mAb digest loaded on-column). When considering the MW of rabbit phosphorylase (97.2 kDa), from which the spiked peptides were derived, the LOQ of this assay is lower than 50 ppm. Relative standard deviations (RSD) of peak areas (n = 4 replicates) were less than 15% across the entire concentration range investigated (0.1-100 nM or 1-1,000 ppm) in this study.

Here, we describe a chromatographic assay coupled with the ion mobility separation of peptide precursors followed by the high-resolution (~30,000) MS-detection of peptide fragments for the quantification of spiked peptide standards in a monoclonal antibody digest.

The analysis of low-level (1-100 ppm) protein impurities (e.g., host-cell proteins (HCPs)) in protein biotherapeutics is a challenging assay requiring ...

Characterization of Synthetic Polymers via Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) Mass Spectrometry

There are many techniques that can be employed in the characterization of synthetic homopolymers, but few provide as useful of information for end group analysis as matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). This tutorial demonstrates methods for optimization of the sample preparation, spectral acquisition, and data analysis of synthetic polymers using MALDI-TOF MS. Critical parameters during sample preparation include the selection of the matrix, identification of an appropriate cationization salt, and tuning the relative proportions of the matrix, cation, and analyte. The acquisition parameters, such as mode (linear or reflector), polarization (positive or negative), acceleration voltage, and delay time, are also important. Given some knowledge of the chemistry involved to synthesize the polymer and optimizing both the data acquisition parameters and the sample preparation conditions, spectra should be obtained with sufficient resolution and mass accuracy to enable the unambiguous determination of the end groups of most homopolymers (masses below 10,000) in addition to the repeat unit mass and the overall molecular weight distribution. Though demonstrated on a limited set of polymers, these general techniques are applicable to a much wider range of synthetic polymers for determining mass distributions, though end group determination is only possible for homopolymers with narrow dispersity.

Characterization of Synthetic Polymers via Matrix Assisted Laser Desorption Ionization Time of Flight MALDI-TOF Mass Spectrometry

A protocol for the matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) characterization of synthetic polymers is described including the optimization of sample preparation, spectral acquisition, and data analysis.

There are many techniques that can be employed in the characterization of synthetic homopolymers, but few provide as useful of information for end group ...

Imaging Corrosion at the Metal-Paint Interface Using Time-of-Flight Secondary Ion Mass Spectrometry

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS), illustrating that SIMS is a suitable technique to study the chemical distribution at a metal-paint interface. The painted Al alloy coupons are immersed in a salt solution or exposed to air only. SIMS provides chemical mapping and 2D molecular imaging of the interface, allowing direct visualization of the morphology of the corrosion products formed at the metal-paint interface and mapping of the chemical after corrosion occurs. The experimental procedure of this method is presented to provide technical details to facilitate similar research and highlight pitfalls that may be encountered during such experiments.

Time-of-flight secondary ion mass spectrometry is applied to demonstrate the chemical mapping and corrosion morphology at the metal-paint interface of an aluminum alloy after being exposed to a salt solution compared with a specimen exposed to air.

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass ...

Ion Mobility-Mass Spectrometry Techniques for Determining the Structure and Mechanisms of Metal Ion Recognition and Redox Activity of Metal Binding Oligopeptides

Electrospray ionization (ESI) can transfer an aqueous-phase peptide or peptide complex to the gas-phase while conserving its mass, overall charge, metal-binding interactions, and conformational shape. Coupling ESI with ion mobility-mass spectrometry (IM-MS) provides an instrumental technique that allows for simultaneous measurement of a peptide&#8217;s mass-to-charge (m/z) and collision cross section (CCS) that relate to its stoichiometry, protonation state, and conformational shape. The overall charge of a peptide complex is controlled by the protonation of 1) the peptide&#8217;s acidic and basic sites and 2) the oxidation state of the metal ion(s). Therefore, the overall charge state of a complex is a function of the pH of the solution that affects the peptides metal ion binding affinity. For ESI-IM-MS analyses, peptide and metal ions solutions are prepared from aqueous-only solutions, with the pH adjusted with dilute aqueous acetic acid or ammonium hydroxide. This allows for pH dependence and metal ion selectivity to be determined for a specific peptide. Furthermore, the m/z and CCS of a peptide complex can be used with B3LYP/LanL2DZ molecular modeling to discern binding sites of the metal ion coordination and tertiary structure of the complex. The results show how ESI-IM-MS can characterize the selective chelating performance of a set of alternative methanobactin peptides and compare them to the copper-binding peptide methanobactin.

Ion mobility-mass spectrometry and molecular modeling techniques can characterize the selective metal chelating performance of designed metal-binding peptides and the copper-binding peptide methanobactin. Developing new classes of metal chelating peptides will help lead to therapeutics for diseases associated with metal ion misbalance.

Electrospray ionization (ESI) can transfer an aqueous-phase peptide or peptide complex to the gas-phase while conserving its mass, overall charge, ...

Analysis of Complex Molecules and Their Reactions on Surfaces by Means of Cluster-Induced Desorption/Ionization Mass Spectrometry

Desorption/Ionization Induced by Neutral SO2 Clusters (DINeC) is employed as a very soft and efficient desorption/ionization technique for mass spectrometry (MS) of complex molecules and their reactions on surfaces. DINeC is based on a beam of SO2 clusters impacting on the sample surface at low cluster energy. During cluster-surface impact, some of the surface molecules are desorbed and ionized via dissolvation in the impacting cluster; as a result of this dissolvation-mediated desorption mechanism, low cluster energy is sufficient and the desorption process is extremely soft. Both surface adsorbates and molecules of which the surface is composed of can be analyzed. Clear and fragmentation-free spectra from complex molecules such as peptides and proteins are obtained. DINeC does not require any special sample preparation, in particular no matrix has to be applied. The method yields quantitative information on the composition of the samples; molecules at a surface coverage as low as 0.1 % of a monolayer can be detected. Surface reactions such as H/D exchange or thermal decomposition can be observed in real-time and the kinetics of the reactions can be deduced. Using a pulsed nozzle for cluster beam generation, DINeC can be efficiently combined with ion trap mass spectrometry. The matrix-free and soft nature of the DINeC process in combination with the MSn capabilities of the ion trap allows for very detailed and unambiguous analysis of the chemical composition of complex organic samples and organic adsorbates on surfaces.

Neutral SO2 clusters of low kinetic energy (&#60; 0.8 eV/constituent) are used to desorb complex surface molecules such as peptides or lipids for further analysis by means of mass spectrometry using an ion trap mass spectrometer. No special sample preparation is required, and real-time observation of reactions is possible.

Desorption/Ionization Induced by Neutral SO2 Clusters (DINeC) is employed as a very soft and efficient desorption/ionization technique for mass ...

3D Depth Profile Reconstruction of Segregated Impurities Using Secondary Ion Mass Spectrometry

The presented protocol combines excellent detection limits (1 ppm to 1 ppb) using secondary ion mass spectrometry (SIMS) with reasonable spatial resolution (~1 &#181;m). Furthermore, it describes how to obtain realistic three-dimensional (3D) distributions of segregated impurities/dopants in solid state materials. Direct 3D depth profile reconstruction is often difficult to achieve due to SIMS-related measurement artifacts. Presented here is a method to identify and solve this challenge. Three major issues are discussed, including the i) nonuniformity of the detector being compensated by flat-field correction; ii) vacuum background contribution (parasitic oxygen counts from residual gases present in the analysis chamber) being estimated and subtracted; and iii)&#160;performance of all steps within a stable timespan of the primary ion source. Wet chemical etching is used to reveal the position and types of dislocation in a material, then the SIMS result is superimposed on images obtained via scanning electron microscopy (SEM). Thus, the position of agglomerated impurities can be related to the position of certain defects. The method is fast and does not require sophisticated sample preparation stage; however, it requires a high-quality, stable ion source, and the entire measurement must be performed quickly to avoid deterioration of the primary beam parameters.

The presented method describes how to identify and solve measurement artifacts related to secondary ion mass spectrometry as well as obtain realistic 3D distributions of impurities/dopants in solid state materials.

The presented protocol combines excellent detection limits (1 ppm to 1 ppb) using secondary ion mass spectrometry (SIMS) with reasonable spatial ...

Thermochemical Studies of Ni(II) and Zn(II) Ternary Complexes Using Ion Mobility-Mass Spectrometry

This article describes an experimental protocol using electrospray-ion mobility-mass spectrometry (ES-IM-MS) and energy-resolved threshold collision-induced dissociation (TCID) to measure the thermochemistry of the dissociation of negatively-charged [amb+M(II)+NTA]- ternary complexes into two product channels: [amb+M(II)] + NTA or [NTA+M(II)]-&#160;+ amb, where M = Zn or Ni and NTA is nitrilotriacetic acid. The complexes contain one of the alternative metal binding (amb) heptapeptides with the primary structures acetyl-His1-Cys2-Gly3-Pro4-Tyr5-His6-Cys7 or acetyl-Asp1-Cys2-Gly3-Pro4-Tyr5-His6-Cys7, where the amino acids&#39; Aa1,2,6,7 positions are the potential metal-binding sites. Geometry-optimized stationary states of the ternary complexes and their products were selected from quantum chemistry calculations (presently the PM6 semi-empirical Hamiltonian) by comparing their electronic energies and their collision cross-sections (CCS) to those measured by ES-IM-MS. From the PM6 frequency calculations, the molecular parameters of the ternary complex and its products model the energy-dependent intensities of the two product channels using a competitive TCID method to determine the threshold energies of the reactions that relate to the 0 K enthalpies of dissociation (&#916;H0). Statistical mechanics thermal and entropy corrections using the PM6 rotational and vibrational frequencies provide the 298 K enthalpies of dissociation (&#916;H298). These methods describe an EI-IM-MS routine that can determine thermochemistry and equilibrium constants for a range of ternary metal ion complexes.

Thermochemical Studies of NiII and ZnII Ternary Complexes Using Ion Mobility-Mass Spectrometry

This article describes an experimental protocol using electrospray-ion mobility-mass spectrometry, semi-empirical quantum calculations, and energy-resolved threshold collision-induced dissociation to measure the relative thermochemistry of the dissociation of related ternary metal complexes.