Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is an important technique to characterize many different materials, including synthetic polymers. MALDI mass spectral data can be used to determine the polymer average molecular weights, repeat units, and end groups. The development of solvent-free sample preparation methods has enabled MALDI to analyze insoluble materials and, interestingly, can provide higher-quality mass spectral data. Although the utility of solvent-free sample preparation for MALDI has been demonstrated, the reasons for its success are only now being discovered. In this study, we use microscopy tools to image samples prepared using solvent-free methods to examine the morphology of these samples. The samples are prepared using a simple vortex method. Our results show that the average particle size of typical MALDI matrices is reduced from their original tens to hundreds of micrometers to hundreds of nanometers. This size reduction of the matrix occurs in one minute using the vortex method. We also observe remarkably smooth and homogeneous sample morphologies for the laser to interrogate, especially considering the relatively crude methods used to prepare our samples. [5][6][7][8][9][10]. MALDI can generate important data on the telomer repeat units, end groups, and average molecular weights of these materials. MALDI methods have been developed to address a broad variety of different polymer materials containing different chemistries. One of the key issues in traditional MALDI sample preparation is making true solutions of the analyte and the matrix [9]. Many interesting polymeric analytes are either completely insoluble or present significant challenges in making analytically useful solutions. To address these issues, solvent-free sample preparation methods have been developed. While several groups investigated solventfree sample preparation methods at nearly the same time, the methods developed by Trimpin, Räder, and coworkers have gained widespread use [11][12][13][14][15]. To make the sample preparation step easier, less time consuming, and reduce the risk of cross-contamination, we developed a simple version of the solvent-free sample preparation method, now called the vortex method [16]. Although the utility of solvent-free sample preparation for MALDI has been clearly demonstrated, the investigations into why it works and what impact these data have on our overall understanding of the MALDI process have only recently begun [17,18].To develop increased understanding of the utility of the solvent-free MALDI sample preparation method, we have investigated the morphology of these samples using different imaging experiments-optical imaging [19], scanning electron microscopy (SEM) [20], atomic force microscopy (AFM) [21], and time-of-flight secondary ion mass spectrometry (ToF-SIMS) [22]. Previous work has shown the utility of investigating MALDI sample morphology using imaging methods. We have used SEM to investigate the morphology of electrospray deposited samples [23] ...
In the interest of a more thorough understanding of the relationship between sample deposition technique and the quality of data obtained using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, details of the electrospray (ES) process of sample deposition are investigated using a number of techniques. Sample morphology was observed with scanning electron microscopy (SEM) and atomic force microscopy (AFM), while matrix-enhanced secondary ion mass spectrometry (MESIMS) monitored surface coverage. Electrospray deposition reduces the analyte segregation that can occur during traditional dried droplet deposition for MALDI. We attribute statistically significant improvements in the reproducibility of signal intensity and MALDI average molecular mass measurements to the ES sample deposition technique.
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is an important technique to characterize many different materials, including synthetic polymers. MALDI mass spectral data is used to determine the polymer average molecular weights, repeat units, and end groups. The development of the vortex method of solvent-free sample preparation showed that remarkably short mixing times could prepare samples that yielded high quality MALDI mass spectra. In this paper, we use microscopy images and MALDI mass spectra to evaluate the mixing time required by the vortex method to produce mass spectra for low molecular mass polymer samples. Our results show that mixing times of as little as 10 s can generate homogeneous thin films that produce high quality mass spectra with S/N ϳ 100. In addition, ultrashort mixing times of only 2 s still produce samples with mostly smooth morphology and mass spectra with S/N ϳ 10. [5][6][7][8][9][10]. MALDI generates important data on telomer repeat units, end groups, and average molecular weights of these materials. MALDI methods have been developed to address a broad variety of different polymer materials containing different chemistries and different molecular weight ranges. To address issues with solubility and matrix compatibility, solvent-free sample preparation methods have been developed. While several groups investigated solvent-free sample preparation methods at nearly the same time, the methods developed by Trimpin, Räder, and coworkers have gained widespread use [11][12][13][14]. To make the sample preparation step easier, less time consuming, and reduce the risk of cross contamination, we developed a simple version of the solvent-free sample preparation method, now called the vortex method [15]. Previously, we examined the morphology of solvent-free prepared samples using powerful microscopy tools, such as atomic force microscopy (AFM), scanning electron microscopy (SEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) [16].To further understand the vortex method of solventfree MALDI sample preparation, we have studied samples prepared with different vortex mixing times. The previous work showed that 60 s vortex mixing times produced remarkably homogenous thin films, and that the thin films were composed of submicron features [16]. In this paper, we search for the minimum vortex time required to create these homogenous thin films. We expect that this research will further illuminate the vortex method and enable greater efficiency of preparing these samples by showing that shorter vortexing times create equivalent MALDI mass spectra.We will characterize the different samples with both MALDI and SEM. MALDI will be the critical method to determine if the sample preparation has been successful, and SEM will be used to learn more about the sample morphology and what changes in the morphology can tell us about the MALDI process.
Controlled studies of the effect of moisture content on the corrosivity of normalHBr toward common materials of construction were performed. Coupons of EP316L stainless steels, two types of stainless steel welds, and Hastelloy C‐22 were exposed to normalHBr containing 0.5, 10, 100, and 1000 ppm moisture. The coupons were exposed to normalHBr for 10 days, then the normalHBr was thoroughly purged from the reactor. The samples were then transferred under nitogen into a scanning electron microscope and analyzed by scanning electron microscopy (SEM), and energy dispersive x‐ray spectroscopy (EDS). The corrosion products were then removed by washing and the coupons analyzed by atomic force microscopy (AFM) and ion chromatography. The SEM and EDS data showed little reaction between EP316L stainless steels and normalHBr with 0.5 ppm moisture. The two welded samples showed minor bromide incorporation into the weld bead at this moisture level. Exposure to normalHBr with 10 ppm moisture caused a thin deposit to form on the surface of the stainless steels and both welded samples. The EDS spectra at this moisture level showed 1 atom percent false(normala/normalofalse) bromide incorporation over a sampling depth of about 1 μm, indicating the onset of corrosion. normalHBr with 100 ppm moisture formed corrosion pits on EP316L. normalHBr with 1000 ppm moisture caused a dense bromide scale to form on all the stainless steel samples, and the samples showed 11 atom percent bromide incorporation (EDS) over a sampling depth of about 1 μm. From the SEM images, it appeared that the Hastelloy C‐22 was unaffected at all moisture levels, but the Hastelloy showed bromide incorporation by EDS after exposure to normalHBr with 1000 ppm moisture. The AFM experiments showed that the root mean squared ampitude (rms) of the surface roughness for EP316L stainless steel was 1, 2, 7, and 16 nm for samples exposed to normalHBr containing 0.5, 0, 100, and 1000 ppm moisture, respectively. Existing dew point data for normalHBr/normalmoisture are analyzed. Interpolation of the data suggests that a moisture concentration of about 200 to 500 ppm would give a room temperature dew point at 1 atmosphere normalHBr pressure. The trends in the corrosion data are related to the dew point curve and are consistent with a change in corrosion mechanism at the dew point concentration.
Progress is reported in developing reliable methodology for imaging silicon surfaces with the atomic force microscope (AFM). A new form of AFM, known as tapping mode AFM, has been found to provide the best quality data for surface roughness determinations. Commercially available colloidal gold spheres have been used to fabricate tip characterization standards and are used to report tip size with roughness data. Power spectral density calculations are shown to provide a useful roughness calculation based on lateral wavelength.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.