Purpose
The urban sedimentary system is attracting increasing interest because of its role in influencing air and water quality. A large amount of road-deposited sediment (RDS) lies on the road ...network of Prince George, a city of about 80,000 people, in British Columbia, Canada. The objectives of this study were: (1) to determine the total mass of RDS within the city, and how this varied over time and space; and (2) to determine the temporal and spatial variations in the particle-size fractions of the RDS.
Materials and methods
Samples of RDS were collected using a grid network during two different time periods in the snow-free season in 2009. Composite samples for each grid (
n
= 46) were fractionated into five grain-size classes (>500, 250–500, 125–250, 63–125, <63 μm) using stainless steel sieves. Fractionated sediment samples were weighed to obtain a mass for each size class for each grid cell.
Results and discussion
The total amount of RDS (all particle-size fractions) in the city of Prince George was estimated to be 746 × 10
3
and 204 × 10
3
kg for the summer and fall 2009 sampling periods, respectively. Based on a total road length of 1,030 km within the sampled area of the city, this equates to an average of 724 and 198 kg per km of road, for the summer and fall sampling periods, respectively. The RDS was dominated by the >500-μm fraction, and there was a trend of decreasing amounts (by mass) for the finer particle-size fractions. In terms of the most important particle-size fraction from an air and water quality perspective, the <63-μm particle-size fraction accounted for, on average, 6.5% and 4.8% of the total RDS mass for the summer and fall 2009 sampling periods, respectively; it is estimated that an additional approximately 2% was lost to the air during sample collection, and thus values may be closer to 9% and 7%, respectively. This equates to averages of between 47–61 and 10–13 kg per km of road for the summer and fall periods, respectively. Total amounts of RDS were greatest in the city centre, compared to the outlying areas, reflecting the greater density of roads in the former, although there were some hotspots which may reflect land use activities such as light-industry and pulp and paper mills.
Conclusions
These findings have implications for air and water quality in the city and surrounding area, including the role of RDS in contributing to airborne fine particulates (i.e. PM
10
and PM
2.5
) and the fine-grained sediment (<63 μm) transported within storm sewers to receiving waterways, such as the Fraser and Nechako Rivers.
New insight into the role of solubility in the sample preparation process for MALDI MS is reported. Reversed-phase gradient HPLC conditions were developed that enable the analysis of a broad range of ...analyte polarities with a single method. This HPLC method was used to establish a relative polarity scale for a series of 15 MALDI matrix materials, a set of example peptides, and a series of model polymer materials with a broad range of polarity. Examples of each polymer type within the range of 6000−10 000 were analyzed with six matrixes that cover a broad range of polarity using MALDI TOFMS. With regard to polymer signal-to-noise ratio, the matrix and polymer combinations that had a close match of HPLC retention time produced the best MALDI spectra. Conversely, the matrix and polymer combinations that have a large difference in HPLC retention time produced poor MALDI spectra. The results suggest that there is a relationship between polarity (solubility) and effective MALDI sample preparation. The relative HPLC retention time of an unknown polymer can serve as a starting point for predicting the matrix (or range of matrixes) that would be most effective.
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.
The development of reliable sample preparation methods has been critical to the success of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry experiments. Good MALDI sample ...preparation for polymers involves choosing the solvent system, the matrix, and the ionization agent correctly, and combining them in a manner that will lead to a sample that will produce the desired ions. The vast diversity of chemistry available in industrial polymers has challenged our ability to design reliable sample preparation methods. In the experiments reported here, we show that matrix-enhanced secondary ion mass spectrometry (MESIMS) is an effective analytical technique to explore sample segregation in solid phase MALDI samples. Qualitative comparison of MESIMS and MALDI results for polymer samples prepared with multiple matrices aids our investigation of the solid-phase solubility of a variety of low molecular weight polymer materials. Including the solid-phase solubility with the liquid-phase solubility of the polymer samples and the matrices enables the construction of a relative solubility chart, which shows the best solubility matches between the polymer and matrix materials for MALDI experiments.
Potential difficulties associated with background silver salt clusters during matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of nonpolar polymers are reported. Silver salt ...cluster ions were observed from
m/z 1500 to 7000 when acidic, polar matrices, such as 2,5-dihydroxybenzoic acid (DHB),
all-trans-retinoic acid (RTA) or 2-(4-hydroxyphenylazo)benzoic acid (HABA), were used for the analysis of nonpolar polymers. These background signals could be greatly reduced or eliminated by the use of nonpolar matrices such as anthracene or pyrene. Representative examples of these background interferences are demonstrated during the analysis of low molecular weight nonpolar polymers including polybutadiene and polystyrene. Nonpolar polymers analyzed with acidic, polar matrices (e.g., RTA) and silver cationization reagents can yield lower quality mass spectral results when interferences due to silver clusters are present. Replacing the polar matrices with nonpolar matrices or the silver salts with copper salts substantially improved the quality of the analytical results. In addition, it was found that silver contamination cannot be completely removed from standard stainless steel sample plates, although the presence of silver contamination was greatly reduced after thorough cleaning of the sample plate with aluminum oxide grit. Carry-over silver may cationize polymer samples and complicate the interpretation of data obtained using nonpolar matrices in the absence of added cationization reagents.
Improved PSD and CID on a MALDI TOFMS Hoteling, Andrew J; Owens, Kevin G
Journal of the American Society for Mass Spectrometry,
04/2004, Letnik:
15, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The influence of several instrument-operating parameters on the product-ion resolution and mass accuracy in matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) post-source decay ...(PSD) and collision-induced dissociation (CID) experiments is reported. Voltages commonly applied to the reflectron for PSD and CID experiments were found to be non-ideal; optimization of these voltages resulted in better resolution across each segment of the measured PSD spectrum. Mass resolution, calculated as M/ΔM (FWHM) for the product-ion peaks, was as high as 2500. Additionally, precursor-ion selection and segment mass range setup were each found to have dramatic influences on product-ion mass accuracy. An understanding of the influence of these variables aided in the interpretation of (a-NH
3) and (b − NH
3) ions observed in the PSD/CID spectra of a number of peptides. In addition, product ions resulting from coincidence peaks in the precursor-ion selection window were found to be a general problem. With the improvements to resolution and optimization of these mass accuracy variables, the mass accuracy of product ions from MALDI TOF PSD and CID experiments was tested with several reference materials, including the peptides Substance P, bradykinin, angiotensin I, and angiotensin II and the synthetic polymers poly(methyl methacrylate) and polystyrene. The absolute error (Da) for each test material was, on average, below 0.1 Da, demonstrating a significant improvement in mass accuracy using the improved operational parameters and an extension of the use of poly(ethylene glycol) (PEG) as a mass calibrant for the PSD/CID spectra.
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