This work was funded through U.S. Department of Energy, Office of Science.

1. Laser System
<ol>
	<li>Use laser pulses produced by a Q-switched Nd:YAG laser operating at 1,064 nm and at 10 Hz.</li>
	<li>Focus the laser pulses onto the sample with a 75 mm focal length lens.</li>
	<li>Collect the plasma light with an optical fiber pointed at and placed near the plasma formed on the sample.</li>
	<li>Use an Echelle spectrograph/ICCD to spectrally resolve and record the LIBS spectrum.</li>
	<li>Operate the ICCD in both non-gated and gated modes using a gain of 125.</li>
	<li>Use a 0 &#956;sec time delay (td) in non-gated mode and a 1 &#956;sec td in gated mode.</li>
	<li>For both modes, use a gate width (tb) of 20 &#956;sec with a 3 sec exposure (integrating the plasma light on the ICCD camera chip); this will result in 30 individual laser shots being added to produce each spectrum.</li>
	<li>Record a total of 5 such spectra for each sample analyzed.</li>
	<li>Use a digital delay generator to control the timing between the laser and the ICCD gate pulse. The experimental set up is shown in Figure 1.</li>
	<li>Verify the timing with an oscilloscope.</li>
	<li>Operate the laser at pulse energies of 10, 25, 50, and 100 mJ using both non-gated and gated detection.</li>
	<li>Continually monitor the laser energy and adjust to correct for drift, if necessary.</li>
	<li>Safety Consideration: The Nd:YAG laser is a Class IV laser; wear appropriate laser safety goggles at all times when operating the laser and establish room interlocks in conjunction with the room door and laser.14</li>
</ol>
2. Samples and Sample Preparation
<ol>
	<li>Use synthetic silicate certified reference materials with known element concentrations as samples; these mimic common soil samples with minor and trace amounts of selected elements spanning a range of concentrations.</li>
	<li>Concentrations of the trace elements ranged from a few ppm to 10,000 ppm. Table 1 lists the elements monitored here including their line types and wavelengths used for analysis. The line types labeled as I and II signify neutral atoms or a singly ionized atoms, respectively. The common base composition of each silicate sample is SiO2 (72%), Al2O3 (15%), Fe2O3 (4%), CaMg(CO3)2 (4%), Na2SO4 (2.5%), and K2SO4 (2.5%).</li>
	<li>Press the samples into 31 mm diameter pellets using a hydraulic press to create a smooth surface for LIBS analysis. The smooth surface helps to create consistency with the LIBS results.</li>
	<li>Analyze a new sample spot for each spectrum recorded.</li>
	<li>Safety consideration: The synthetic silicate samples contain a wide variety of elements at various concentrations; wear gloves during handling.</li>
</ol>
3. Preparing Calibration Curves
<ol>
	<li>Prepare calibration curves for the various elements in both gated and non-gated detection over the range of laser energies tested.</li>
	<li>Make these curves by plotting the peak area or the ratioed peak area (y-axis) against element concentration (x-axis).</li>
	<li>Use a linear trend line to fit the calibration curve. [screen shot 1]</li>
	<li>Calculate detection limits using 3&#963; detection as defined by IUPAC.15 [calculation 1]</li>
</ol>
4. Plasma Temperature Determination
<ol>
	<li>Measure plasma temperatures from Boltzmann plots.</li>
	<li>Use a set of iron lines [Fe(I)] between wavelengths of 371-408 nm to create Boltzmann plots using: ln(I&#955;/gA) = -Eu/kT - ln(4&#961;Z/hcN0) (Eq. 1) where I is the intensity of the transition as determined from the peak area, &#955; is the wavelength, A is the transition probability, g is the degeneracy of the transition, Eu is the upper state for emission, k is the Boltzmann constant, T is the temperature, Z is the partition function, h is Planck&#39;s constant, c is the speed of light, N0 is the total species population.</li>
	<li>Chose Fe lines that have known Eu, g, and A values.</li>
</ol>
<ul>
	<li>The Fe(I) lines used here are 371.99, 374.56, 382.04, 404.58, 406.36 nm.</li>
	<li>The Eu, g, and A values can be found on this website (<a href="http://physics.nist.gov/PhysRefData/ASD/lines_form.html" target="_blank">http://physics.nist.gov/PhysRefData/ASD/lines_form.html</a>)</li>
	<li>Make sure to select the option to show the &#34;g&#34; under additional criteria labeled as level information.</li>
	<li>Use the Ek and gk values.</li>
</ul>
<ol start="4">
	<li>To determine temperature, plot ln(I&#955;/gA) against Eu and fit the data with a linear trend line; the slope is equals to -1/kT.16,17 [screen shot 2]</li>
</ol>
5. Electron Density Determination
<ol>
	<li>To measure the electron density, use the full width at half maximum (FWHM) of the hydrogen line at 656.5 nm.</li>
	<li>Take this data using td=0.5 &#956;sec and tb= 4.5 &#956;sec on the ICCD.</li>
	<li>Measure the FWHM of the hydrogen line. [screen shot 3]</li>
	<li>Calculate the electron density using: Ne = 8.02 x 1012[&#916;&#955;1/2/&#945;1/2]3/2 (Eq. 2) where Ne is the electron density, &#916;&#955;1/2 is the measured FWHM of the hydrogen line, and &#945;1/2 is the reduced wavelength which is a function of the temperature and the electron density. The values for the reduced wavelengths are provided in Griem&#39;s Appendix IIIa.16-18</li>
	<li>Calculate the electron density using a temperature of 10,000 K (this was the close to the average temperature of the plasma). [screen shot 4]</li>
</ol>
6. Work up All Data Using a Program that Can Determine the Peak Areas and/or Microsoft Excel

<ol>
	<li>Song, K., Lee, Y., Sneddon, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+developments+in+instrumentation+for+laser+induced+breakdown+spectroscopy.">Recent developments in instrumentation for laser induced breakdown spectroscopy.</a> Appl. Spec. Rev. 37 (1), 89-117 (2002).</li><li>Yamamoto, K. Y., Cremers, D. A., Foster, L. E., Ferris, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+Metals+in+the+Environment+Using+a+Portable+Laser-Induced+Breakdown+Spectroscopy+Instrument.">Detection of Metals in the Environment Using a Portable Laser-Induced Breakdown Spectroscopy Instrument.</a> Appl. Spec. 50 (2), 222-233 (1996).</li><li>Cu&#241;at, J., Fortes, F. J., Cabal&#237;n, L. M., Carrasco, F., Sim&#243;n, M. D., Laserna, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Man-Portable+Laser-Induced+Breakdown+Spectroscopy+System+for+in+Situ+Characterization+of+Karstic+Formations.">Man-Portable Laser-Induced Breakdown Spectroscopy System for in Situ Characterization of Karstic Formations.</a> Appl. Spec. 62 (11), 1250-1255 (2008).</li><li>Munson, C. A., Gottfried, J. L., Gibb-Snyder, E., DeLucia, F. C., Gullett, B., Miziolek, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+indoor+biological+hazards+using+the+man-portable+laser+induced+breakdown+spectrometer.">Detection of indoor biological hazards using the man-portable laser induced breakdown spectrometer.</a> Appl. Opt. 47 (31), G48-G57 (2008).</li><li>Multari, R. A., Foster, L. E., Cremers, D. A., Ferris, M. J. <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+Sampling+Geometry+on+Elemental+Emissions+in+Laser-Induced+Breakdown+Spectroscopy.">Effect of Sampling Geometry on Elemental Emissions in Laser-Induced Breakdown Spectroscopy.</a> Appl. Spec. 50 (12), 1483-1499 (1996).</li><li>Harmon, R. S., DeLucia, F. C., McManus, C. E., McMillan, N. J., Jenkins, T. F., Walsh, M. E., Miziolek, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-induced+breakdown+spectroscopy+-+An+emerging+chemical+sensor+technology+for+real-time+field-portable,+geochemical,+mineralogical,+and+environmental+applications.">Laser-induced breakdown spectroscopy - An emerging chemical sensor technology for real-time field-portable, geochemical, mineralogical, and environmental applications.</a> Appl. Geochem. 21 (5), 730-747 (2006).</li><li>Schill, A. W., Heaps, D. A., Stratis-Cullum, D. N., Arnold, B. R., Pellegrino, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+near-infrared+low+energy+ultra-short+laser+pulses+for+portable+applications+of+laser+induced+breakdown+spectroscopy.">Characterization of near-infrared low energy ultra-short laser pulses for portable applications of laser induced breakdown spectroscopy.</a> Opt. Express. 15 (21), 14044-14056 (2007).</li><li>Fortes, F. J., Laserna, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+development+of+fieldable+laser-induced+breakdown+spectrometer:+No+limits+on+the+horizon.">The development of fieldable laser-induced breakdown spectrometer: No limits on the horizon.</a> Spectrochim. Acta Part B. 65 (12), 975-990 (2010).</li><li>Leis, F., Sdorra, W., Ko, J. B., Niemax, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Basic+Investigations+for+Laser+Microanalysis:+I.+Optical+Emission+Spectrometry+of+Laser-Produced+Sample+Plumes.">Basic Investigations for Laser Microanalysis: I. Optical Emission Spectrometry of Laser-Produced Sample Plumes.</a> Mikrochim. Acta II. 98, 185-199 (1989).</li><li>Lida, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+atmosphere+on+laser+vaporization+and+excitation+processes+of+solid+samples.">Effects of atmosphere on laser vaporization and excitation processes of solid samples.</a> Spectrochim. Acta Part B. 45 (12), 1353-1367 (1990).</li><li>Radziemski, L. J., Loree, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-induced+breakdown+spectroscopy:+Time-integrated+applications.">Laser-induced breakdown spectroscopy: Time-integrated applications.</a> J. Plasma Chem. Plasma Proc. 1 (3), 281-293 (1981).</li><li>Mueller, M., Gornushkin, I. B., Florek, S., Mory, D., Panne, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Approach+to+Detection+in+Laser-Induced+Breakdown+Spectroscopy.">Approach to Detection in Laser-Induced Breakdown Spectroscopy.</a> Anal. Chem. 79 (12), 4419-4426 (2007).</li><li>Fan, C., Longtin, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+Optical+Breakdown+in+Dielectrics+During+Ultrafast+Laser+Processing.">Modeling Optical Breakdown in Dielectrics During Ultrafast Laser Processing.</a> Appl. Opt. 40 (18), 3124-3131 (2001).</li><li>ANSI Z-136.5. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> American National Standard for Safe Use of Lasers in Educational Institutions. , (2009).</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> Compendium of Chemical Terminology. , (1997).</li><li>Cremers, D. A., Radziemski, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Handbook of Laser-Induced Breakdown Spectroscopy. , (2006).</li><li>Griem, H. 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> Spectral Line Broadening by Plasmas. , (1974).</li><li>Ashkenazy, J., Kipper, R., Caner, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectroscopic+Measurements+of+Electron+Density+of+Capillary+Plasma+Based+on+Stark+Broadening+of+Hydrogen+Lines.">Spectroscopic Measurements of Electron Density of Capillary Plasma Based on Stark Broadening of Hydrogen Lines.</a> Phys. Rev. A. 43 (10), 5568-5574 (1991).</li></ol>

The authors do not have anything to disclose.

When comparing non-gated and gated detection modes, the detection limit data show that the gated detection mode allowed for detection of all of the elements including those that were not seen using higher laser energies in non-gated detection mode. Using gated detection, the initial high background from the formation of the plasma is not observed and the background is decreased showing the elemental emission better resolved. Furthermore, the detection limits were slightly lower using gated detection.
<p class="jove_c...

Laser-induced breakdown spectroscopy (LIBS) is a simple method of elemental analysis that uses a laser-generated spark as the excitation source. The laser pulse is focused onto a surface that heats, ablates, atomizes and ionizes the surface material resulting in the formation of plasma. The plasma light is spectrally resolved and detected and elements are identified by their spectral signatures. If properly calibrated, LIBS can provide quantitative results. LIBS can analyze solids, gases, and liquids with little or no sample preparation.1 These characteristics make it ideal for analyses that cannot be carried out in the laboratory.
Currently, LIBS is being studied for many different applications especially those that require field-based measurements for quantification.1-8 This requires the development of LIBS instrumentation using rugged and compact components suitable for a field-based system. In most cases, these components will not have the full capabilities of laboratory-based instrumentation, thereby compromising the analysis performance. LIBS results are dependent on laser pulse parameters and other measurement conditions that include sampling geometry, surrounding atmosphere, and the use of gated or non-gated detection.9-12 For field-based LIBS instrumentation, two important factors to consider are the pulse energy and the use of gated versus non-gated detection. These two factors determine to a large extent the cost, size, and complexity of the LIBS instrument. Small, ruggedly built lasers that can generate pulses from 10-50 mJ at repetition rates of 0.3-10 Hz are commercially available and would be highly advantageous to use. Therefore, it is important to know what, if any, loss in detection capabilities will result from the use of these lasers. The pulse energy is a key parameter for LIBS as it determines the amount of material ablated and vaporized and the excitation characteristics of the plasma. In addition, the use of gated detection can increase the cost of the LIBS system; as a result, it is imperative to determine the differences between spectra and detection capabilities using gated and non-gated detection.
Recently, a study was performed comparing gated detection to non-gated detection for minor elements found in steel. The results showed that the detection limits were comparable if not better for non-gated detection.12 One important characteristic of LIBS is that the technique experiences physical and chemical matrix effects. An example of the former is that the laser pulse couples more efficiently with conducting/metal surfaces than non-conducting surfaces.13 For this study, we wanted to determine the effects of pulse energy and timing parameters for non-conducting materials like soil simulants.
Although, field portable LIBS instruments have been developed and used for some applications, a comprehensive study on the detection capabilities has not been performed comparing higher energy and gated systems to lower energy and non-gated systems using soil simulants. This study focuses on laser pulse energy and timing parameters for determination of trace elements in complex matrices. The laser pulse energy ranged from 10 to 100 mJ to obtain a comparison between lower and higher energies. A comparison of the use of gated versus non-gated detection was also performed over the same energy range.

<table border="1">
		<tbody>
		 <tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Equipment</td>
		 </tr>
		 <tr>
			<td>Nd:YAG laser</td>
			<td>Continuum</td>
			<td>Surelite II</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Echelle spectrograh/ICCD</td>
			<td>Catalina/Andor</td>
			<td>SE200/iStar</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Digital delay generator</td>
			<td>BNC</td>
			<td>Model 575-4C</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Hydraulic Press</td>
			<td>Carver</td>
			<td>Model-C</td>
			<td></td>
		 </tr>
		 <tr>
			<td>31-mm pellet die</td>
			<td>Carver</td>
			<td>3902</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Power meter indictor model</td>
			<td>Scientech, Inc.</td>
			<td>Model number: AI310D</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Power meter detector model</td>
			<td>Scientech, Inc.</td>
			<td>Model number: AC2501S</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Oscilloscope</td>
			<td>Tektronix</td>
			<td>MSO 4054</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Optical fiber</td>
			<td>Ocean Optics</td>
			<td>QP1000-2-UV-VIS</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Lens kit (this kit contains the 75 mm f.l. lens)</td>
			<td>CVI Optics</td>
			<td>LK-24-C-1064</td>
			<td></td>
		 </tr>
		 <tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Reagent/Material list</td>
		 </tr>
		 <tr>
			<td>Synthetic silicate sample</td>
			<td>Brammer Standard Company</td>
			<td>GBW 07704 </td>
			<td></td>
		 </tr>
		 <tr>
			<td>Synthetic silicate sample</td>
			<td>Brammer Standard Company</td>
			<td>GBW 07705 </td>
			<td></td>
		 </tr>
		 <tr>
			<td>Synthetic silicate sample</td>
			<td>Brammer Standard Company</td>
			<td>GBW 07706</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Synthetic silicate sample</td>
			<td>Brammer Standard Company</td>
			<td>GBW 07708</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Synthetic silicate sample</td>
			<td>Brammer Standard Company</td>
			<td>GBW 07709</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Aluminum caps (for pressing synthetic silicate samples)</td>
			<td>SCP Science</td>
			<td>040-080-001</td>
			<td></td>
		 </tr>
		</tbody>
 </table>

dependence of laser-induced breakdown spectroscopy results on pulse energies and timing parameters using soil simulants

The dependence of some LIBS detection capabilities on lower pulse energies (&lt;100 mJ) and timing parameters were examined using synthetic silicate samples. These samples were used as simulants for soil and contained minor and trace elements commonly found in soil at a wide range of concentrations. For this study, over 100 calibration curves were prepared using different pulse energies and timing parameters; detection limits and sensitivities were determined from the calibration curves. Plasma temperatures were also measured using Boltzmann plots for the various energies and the timing parameters tested. The electron density of the plasma was calculated using the full-width half maximum (FWHM) of the hydrogen line at 656.5 nm over the energies tested. Overall, the results indicate that the use of lower pulse energies and non-gated detection do not seriously compromise the analytical results. These results are very relevant to the design of field- and person-portable LIBS instruments.

Effect of laser pulse energy and detection modes on detection capabilities. LIBS spectra of the synthetic silicate samples were recorded using gated and non-gated detection over the range of laser pulse energies tested. Over 100 calibration curves were constructed from these data to evaluate the effect of the laser pulse energy. Calibration curves were prepared by (1) using the area under the analyte peak and (2) by ratioing the area of the analyte peak to the area of the iron peak at 405.58 nm. The iron...

Watch this Scientific Journal Video about Dependence of Laser-induced Breakdown Spectroscopy Results on Pulse Energies and Timing Parameters Using Soil Simulants at JoVE.com

Dependence of Laser-induced Breakdown Spectroscopy Results on Pulse Energies and Timing Parameters Using Soil Simulants

LIBS detection capabilities on soil simulants were tested using a range of pulse energies and timing parameters. Calibration curves were used to determine detection limits and sensitivities for different parameters. Generally, the results showed that there was not a significant reduction in detection capabilities using lower pulse energies and non-gated detection.

The  dependence of some LIBS detection capabilities on lower pulse energies (&lt;100  mJ) and timing parameters were examined using synthetic silicate ...

dependence-laser-induced-breakdown-spectroscopy-results-on-pulse

Research

JoVE Journal

Chemistry

11.3K vues.  Alvernia University.  Capacités de détection LIBS sur des simulateurs de sol ont été testés en utilisant une gamme d'énergies d'impulsions et les paramètres de synchronisation. Les courbes d'étalonnage ont été utilisés pour déterminer les limites de détection et les sensibilités des paramètres différents. En général, les résultats ont montré qu'il n'y avait pas de réduction significative de la capacité de détection à l'aide des énergies d'i...

Vidéo: Dependence of Laser-induced Breakdown Spectroscopy Results on Pulse Energies and Timing Parameters Using Soil Simulants

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 ...

Transport of Surface-modified Carbon Nanotubes through a Soil Column

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs. The transport and retention of CNTs in both natural and artificial media have been reported in literature, but the findings widely vary and are thus not conclusive. There are a number of physical and chemical parameters responsible for variation in retention and transport. In this study, a complete procedure of selected multiwalled carbon nanotubes (MWCNTs) is presented starting from their surface modification to a complete set of laboratory column experiments at critical physical and chemical scenarios. Results indicate that the stability of the commercially available MWCNTs are critical with their attached surface functional group which can also influence the transport and retention of MWCNT through the surrounding medium.

Surface properties of a nanoparticle are important for their interaction with the surrounding medium. Therefore the surface modification of carbon nanotubes can be critical for their transport and retention through porous media. Here, lab scale column experiments are used to understand the possible transport and retention of these nanoparticles.

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, ...

Construction of Models for Nondestructive Prediction of Ingredient Contents in Blueberries by Near-infrared Spectroscopy Based on HPLC Measurements

Nondestructive prediction of ingredient contents of farm products is useful to ship and sell the products with guaranteed qualities. Here, near-infrared spectroscopy is used to predict nondestructively total sugar, total organic acid, and total anthocyanin content in each blueberry. The technique is expected to enable the selection of only delicious blueberries from all harvested ones. The near-infrared absorption spectra of blueberries are measured with the diffuse reflectance mode at the positions not on the calyx. The ingredient contents of a blueberry determined by high-performance liquid chromatography are used to construct models to predict the ingredient contents from observed spectra. Partial least squares regression is used for the construction of the models. It is necessary to properly select the pretreatments for the observed spectra and the wavelength regions of the spectra used for analyses. Validations are necessary for the constructed models to confirm that the ingredient contents are predicted with practical accuracies. Here we present a protocol to construct and validate the models for nondestructive prediction of ingredient contents in blueberries by near-infrared spectroscopy.

We present here a protocol to construct and validate models for nondestructive prediction of total sugar, total organic acid, and total anthocyanin content in individual blueberries by near-infrared spectroscopy.

Nondestructive prediction of ingredient contents of farm products is useful to ship and sell the products with guaranteed qualities. Here, near-infrared ...

Insights into the Interactions of Amino Acids and Peptides with Inorganic Materials Using Single-Molecule Force Spectroscopy

The interactions between proteins or peptides and inorganic materials lead to several interesting processes. For example, combining proteins with minerals leads to the formation of composite materials with unique properties. In addition, the undesirable process of biofouling is initiated by the adsorption of biomolecules, mainly proteins, on surfaces. This organic layer is an adhesion layer for bacteria and allows them to interact with the surface. Understanding the fundamental forces that govern the interactions at the organic-inorganic interface is therefore important for many areas of research and could lead to the design of new materials for optical, mechanical and biomedical applications. This paper demonstrates a single-molecule force spectroscopy technique that utilizes an AFM to measure the adhesion force between either peptides or amino acids and well-defined inorganic surfaces. This technique involves a protocol for attaching the biomolecule to the AFM tip through a covalent flexible linker and single-molecule force spectroscopy measurements by atomic force microscope. In addition, an analysis of these measurements is included.

Here we present a protocol to measure the force of interactions between a well-defined inorganic surface and either peptides or amino acids by single-molecule force spectroscopy measurements using an atomic force microscope (AFM). The information obtained from the measurement is important to better understand the peptide-inorganic material interphase.

The interactions between proteins or peptides and inorganic materials lead to several interesting processes. For example, combining proteins with minerals ...

Real-time Breath Analysis by Using Secondary Nanoelectrospray Ionization Coupled to High Resolution Mass Spectrometry

Exhaled volatile organic compounds (VOCs) have aroused considerable interest, since they can serve as biomarkers for disease diagnosis and environmental exposure in a non-invasive manner. In this work, we present a protocol to characterize the exhaled VOCs in real time by using secondary nanoelectrospray ionization coupled to high resolution mass spectrometry (Sec-nanoESI-HRMS). The homemade Sec-nanoESI source was readily set up based on a commercial nanoESI source. Hundreds of peaks were observed in the background-subtracted mass spectra of exhaled breath, and the mass accuracy values are -4.0-13.5 ppm and -20.3-1.3 ppm in the positive and negative ion detection modes, respectively. The peaks were assigned with accurate elemental composition according to the accurate mass and isotopic pattern. Less than 30 s is used for one exhalation measurement, and it takes approximately 7 min for six replicated measurements.

A protocol for characterizing chemical composition of exhaled breath in real time by using secondary nanoelectrospray ionization coupled to high resolution mass spectrometry is demonstrated.

Exhaled volatile organic compounds (VOCs) have aroused considerable interest, since they can serve as biomarkers for disease diagnosis and environmental ...

Obtaining 3D Chemical Maps by Energy Filtered Transmission Electron Microscopy Tomography

Energy filtered transmission electron microscopy tomography (EFTEM tomography) can provide three-dimensional (3D) chemical maps of materials at a nanometric scale. EFTEM tomography can separate chemical elements that are very difficult to distinguish using other imaging techniques. The experimental protocol described here shows how to create 3D chemical maps to understand the chemical distribution and morphology of a material. Sample preparation steps for data segmentation are presented. This protocol permits the 3D distribution analysis of chemical elements in a nanometric sample. However, it should be noted that currently, the 3D chemical maps can only be generated for samples that are not beam sensitive, since the recording of filtered images requires long exposure times to an intense electron beam. The protocol was applied to quantify the chemical distribution of the components of two different heterogeneous catalyst supports. In the first study, the chemical distribution of aluminum and titanium in titania-alumina supports was analyzed. The samples were prepared using the swing-pH method. In the second, the chemical distribution of aluminum and silicon in silica-alumina supports that were prepared using the sol-powder and mechanical mixture methods was examined.

This paper describes a protocol to achieve 3D chemical maps combining energy filtered imaging and electron tomography. The chemical distribution of two catalyst supports formed by elements that are difficult to distinguish by other imaging techniques was studied. Each application consists of mapping overlapped chemical elements - respectively spaced-ionization edges.

Energy filtered transmission electron microscopy tomography (EFTEM tomography) can provide three-dimensional (3D) chemical maps of materials at a ...

The MPLEx Protocol for Multi-omic Analyses of Soil Samples

Mass spectrometry (MS)-based integrated metaproteomic, metabolomic, and lipidomic (multi-omic) studies are transforming our ability to understand and characterize microbial communities in environmental and biological systems. These measurements are even enabling enhanced analyses of complex soil microbial communities, which are the most complex microbial systems known to date. Multi-omic analyses, however, do have sample preparation challenges, since separate extractions are typically needed for each omic study, thereby greatly amplifying the preparation time and amount of sample required. To address this limitation, a 3-in-1 method for the simultaneous extraction of metabolites, proteins, and lipids (MPLEx) from the same soil sample was created by adapting a solvent-based approach. This MPLEx protocol has proven to be both simple and robust for many sample types, even when utilized for limited quantities of complex soil samples. The MPLEx method also greatly enabled the rapid multi-omic measurements needed to gain a better understanding of the members of each microbial community, while evaluating the changes taking place upon biological and environmental perturbations.

A protocol is presented for simultaneously extracting metabolites, proteins, and lipids from a single soil sample, allowing reduced sample preparation times and enabling multi-omic mass spectrometry analyses of samples with limited quantities.

Mass spectrometry (MS)-based integrated metaproteomic, metabolomic, and lipidomic (multi-omic) studies are transforming our ability to understand and ...

A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy

Fluorination has become an effective tool to optimize physicochemical properties of bioactive compounds. One of the applications of fluorine introduction is to modulate the lipophilicity of the compound. In our group, we are interested in the study of the impact of fluorination on lipophilicity of aliphatic fluorohydrins and fluorinated carbohydrates. These are not UV-active, resulting in a challenging lipophilicity determination. Here, we present a straightforward method for the measurement of lipophilicity of fluorinated compounds by 19F NMR spectroscopy. This method requires no UV-activity. Accurate solute mass, solvent and aliquot volume are also not required to be measured. Using this method, we measured the lipophilicities of a large number of fluorinated alkanols and carbohydrates.

A New Straightforward Method for Lipophilicity logP Measurement using 19F NMR Spectroscopy

A novel and straightforward variation of the shake-flask method was developed for accurate lipophilicity measurement of fluorinated compounds by 19F NMR spectroscopy.

Fluorination has become an effective tool to optimize physicochemical properties of bioactive compounds. One of the applications of fluorine introduction ...

Performing Spectroscopy on Plasmonic Nanoparticles with Transmission-Based Nomarski-Type Differential Interference Contrast Microscopy

Differential interference contrast (DIC) microscopy is a powerful imaging tool that is most commonly employed for imaging microscale objects using visible-range light. The purpose of this protocol is to detail a proven method for preparing plasmonic nanoparticle samples and performing single particle spectroscopy on them with DIC microscopy. Several important steps must be followed carefully in order to perform repeatable spectroscopy experiments. First, landmarks can be etched into the sample substrate, which aids in locating the sample surface and in tracking the region of interest during experiments. Next, the substrate must be properly cleaned of debris and contaminants that can otherwise hinder or obscure examination of the sample. Once a sample is properly prepared, the optical path of the microscope must be aligned, using Kohler Illumination. With a standard Nomarski style DIC microscope, rotation of the sample may be necessary, particularly when the plasmonic nanoparticles exhibit orientation-dependent optical properties. Because DIC microscopy has two inherent orthogonal polarization fields, the wavelength-dependent DIC contrast pattern reveals the orientation of rod-shaped plasmonic nanoparticles. Finally, data acquisition and data analyses must be carefully performed. It is common to represent DIC-based spectroscopy data as a contrast value, but it is also possible to present it as intensity data. In this demonstration of DIC for single particle spectroscopy, the focus is on spherical and rod-shaped gold nanoparticles.

The goal of this protocol is to detail a proven approach for the preparation of plasmonic nanoparticle samples and for performing single particle spectroscopy on them with differential interference contrast (DIC) microscopy.

Differential interference contrast (DIC) microscopy is a powerful imaging tool that is most commonly employed for imaging microscale objects using ...

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy

Lewis acid-activation of carbonyl-containing substrates is a fundamental basis for facilitating transformations in organic chemistry. Historically, characterization of these interactions has been limited to models equivalent to stoichiometric reactions. Here, we report a method utilizing in situ infrared spectroscopy to probe the solution interactions between Lewis acids and carbonyls under synthetically relevant conditions. Using this method, we were able to identify 1:1 complexation between GaCl3 and acetone and a highly ligated complex for FeCl3 and acetone. The impact of this technique on mechanistic understanding is illustrated by application to the mechanism of Lewis acid-mediated carbonyl-olefin metathesis in which we were able to observe competitive binding interactions between substrate carbonyl and product carbonyl with the catalyst.

Here, we present a method for the observation of solution interactions between Lewis acids and bases by employing in situ infrared spectroscopy as a detector for titration under synthetically relevant conditions. By examining solution interactions, this method represents a complement to X-ray crystallography, and provides an alternative to NMR spectroscopy.

Lewis acid-activation of carbonyl-containing substrates is a fundamental basis for facilitating transformations in organic chemistry. Historically, ...