Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235nm / 280 nm UV Absorbance Ratio

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1 an ABC Laboratories white paper Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235nm / 280 nm UV Absorbance Ratio A. Sen, R. Dunphy, L. Rosik Analytical Bio-Chemistry Laboratories

2 Copyright Notice Copyright Analytical Bio-Chemistry Laboratories, Inc All Rights Reserved. Unless otherwise indicated, all materials on these pages are copyrighted by ABC Laboratories. No part of this publication may be reproduced for commercial use without ABC Laboratories express consent. Copying tables, figures, or excerpts with proper attribution is permitted for noncommercial use, on the condition that proper attribution of the source in all copies is provided; however, this does not grant permission to publish. In referencing this work, please observe the following preferred citation: A.Sen, R. Dunphy, and L. Rosik. Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldahyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio. ABC Laboratories, Analytical Bio-Chemistry Laboratories, Inc. i Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

3 Table of Contents Abstract... Introduction... Experimental... Results and Discussion... Conclusions... References ii Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

4 Abstract The 235 nm/280 nm UV absorbance ratio (UV Ratio) is widely used as a measure of the degree of polymerization of glutaraldehyde. Conventional practice is to measure the UV absorbance of bulk material at 235 nm (C=C absorption) and at 280 nm (C=O absorption). Gel permeation chromatography of preparations of heat-treated glutaraldehyde (HTGA) did not have sufficient mass discrimination to explain the variation in the UV Ratio of HTGA. Preparations of HTGA were analyzed by direct infusion ion trap mass spectrometry (IT-MS) and time of flight mass spectrometry (TOF-MS). Structures were assigned to the masses found. The structures of the UV-absorbing species were used to calculate absorbance contributions from each species found in the preparations at greater than 5% relative abundance. The contributions were weighted and summed. A MS-based UV Ratio was calculated and compared to the experimentally determined UV Ratio for the HTGA preparations. A very good correlation was obtained. 1 Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

5 Introduction Polymerized glutaraldehyde has been used as a fixative agent for electron microscopy and to immobilize proteins for decades (1-5). The solution chemistry of glutaraldehyde has been reviewed (2). The UV Ratio is a parameter that has been used classically to describe the extent of polymerization of the material (3,4,7,8). An additional analytical method was developed to better characterize the polymeric mixture and correlate to this absorbance ratio. Development data from a low molecular weight SEC method resulted in nearly the same molecular weight values for all four of the HTGA samples examined (Mp = 377 to 384 Da) which had UV Ratios of from 2 to 20. This suggested that the UV Ratio (degree of polymerization) was not simply molecular weight dependent but was also dependent on the structures of the oligomers present. The existing literature seems to support this (1,3,6-9). Direct infusion mass spectra of the HTGA preparations were acquired. A simple weighted average molecular weight was calculated for the samples (based on the masses seen and their relative abundances in each sample) and was found to not correlate to the UV Ratio, as was seen for the SEC results. From the MS data the structures were assigned for the various types of oligomers present. Based on these structures and the published values for the mass extinction coefficients of the chromophores (1) in the oligomers a MSbased UV Ratio was calculated for the bulk HTGA. 2 Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

6 Experimental The HTGA samples were prepared in water and heat treated. The samples had varying degrees of polymerization as indicated by their UV Ratio, as shown in Table 1. The HTGA samples were diluted 1:1 with a 0.1% formic acid aqueous solution for mass spectrometric analysis. Table 1: HTGA Samples The diluted samples were analyzed on a Thermo Fleet Ion Trap Mass Spectrometer by direct infusion into the electrospray ionization (ESI) source using the onboard syringe pump at a flow rate ~ 15 µl/ min. Data was collected for the range of m/z 50 to 1000 for two minutes and the data from the entire infusion was averaged. Earlier SEC work with these samples had indicated that the vast majority of the sample would be below 1000 Da. The MS thus obtained for 74, 78-2, 78-1, and 78-3 are shown in Figure 1, Figure 2, Figure 3, and Figure 4 respectively. The majority of the structures could be assigned from this data. Note that due to the sodium content of the samples the ions seen are sodiated cations that are +23 u from the actual neutral masses of the oligomers of interest. Some peaks seen were not readily assigned based on these spectra. The samples were also analyzed by Waters Micromass LCT Premier Time of Flight Mass Spectrometer in order to obtain empirical formulae for the ions of interest and thus allow complete structural assignments. Direct infusion into the electrospray ionization (ESI) source using a syringe pump at a flow rate ~ 15 µl/min. Data was collected for the range of m/z 50 to 1000 for two minutes and the data from the entire infusion was averaged. 3 Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

7 Experimental (cont) Figure 1: Mass Spectrum of Sample 74 Figure 2: Mass Spectrum of Sample Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

8 Experimental (cont) Figure 3: Mass Spectrum of Sample 78-1 Figure 4: Mass Spectrum of Sample Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

9 Results and Discussion The acetal family of oligomers were the most predominant series of compounds seen in the aqueous samples. Their general structure is shown in Figure 5 along with the mass assignments and two example structures. These oligomers have no chromophores and so do not contribute to the UV Ratio. This is why the UV Ratio does not correlate to the average molecular weight of the sample. These compounds therefore were not included in the calculation. Figure 5: The Acetal Family of Oligomers The aldol condensation family of oligomers were also seen in the samples. Their general structure is shown in Figure 6 along with the mass assignments and two example structures. Figure 6: The Aldol Condensation Family of Oligomers 6 Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

10 Results and Discussion (cont) The aldol condensation family of oligomers shown above in Figure 6 can also undergo the elimination of water to give compounds with some of the aldol linkages dehydrated to yield unsaturated aldehydes. Their general structure is shown in Figure 7 and Table 2, along with the mass assignments and two example structures. Figure 7: The Partially Dehydrated Aldol Condensation Family of Oligomers Table 2 The aldol condensation oligomers shown in Figure 6 have suffered aerobic oxidation to the diacids. Their general structure is shown in Figure 8 along with the mass assignments and two example structures. 7 Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

11 Results and Discussion (cont) The aldol condensation family of oligomers shown above in Figure 6 can also undergo the elimination of water to give compounds with some of the aldol linkages dehydrated to yield unsaturated aldehydes. Their general structure is shown in Figure 7 and Table 2, along with the mass assignments and two example structures. Figure 8: The Oxidized Aldol Condensation Family of Oligomers The above assignments are in agreement with previous UV, IR, and NMR studies (1,2,6,9). There were no significant peaks found in the sample spectra that corresponded to oxidized and partially dehydrated oligomers. This was also the case for mono-oxidized and partially dehydrated species. Calculation of the MS-Based 235 nm/280 nm UV Absorbance Ratio The structural assignments are in agreement with previous UV, IR, and NMR studies (1,2,6,9). Once the structures for all of the significant peaks have been assigned then the UV absorbance contributions for each molecule can be calculated. The aldehydes moieties absorb at 280 nm and the carbon-carbon double bond absorbs at 235 nm. The mass extinction coefficients for the unconjugated aldehyde group, the conjugated aldehyde group, and the conjugated carbon-carbon double bond have been given as 0.042, 0.41, and 18.6 L/g cm (1). Therefore, for each relevant mass (structure that has a UV absorbance) the number of each kind of contributing chromophore can be determined by inspection. Those contributions to the 280 nm or the 235 nm absorptions can then be summed. These summed contributions can then be weighted with the relative abundance of the peak in the MS to give weighted 280 nm and 235 nm absorptions. The weighted absorptions can then be summed9 for all the relevant molecules in a sample and the UV Ratio calculated. The MS-based UV Ratio can then be correlated to the experimentally determined UV Ratio by regression. Summaries of this calculation for the samples 3.5% HTGA, 15% HTGA-1, 15% HTGA-2, and 15% HTGA-3 are shown in Figure 9, Figure 10, Figure 11, and Figure 12 respectively. A co-efficient of determination (R 2 ) value of was obtained and is show in Figure Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

12 Results and Discussion (cont) Figure 9: MS-Based UV Ratio of Sample 74 Figure 10: MS-Based UV Ratio of Sample Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

13 Results and Discussion (cont) Figure 11: MS-Based UV Ratio of Sample 78-1 Figure 12: MS-Based UV Ratio of Sample Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

14 Results and Discussion (cont) Figure 13: Correlation of Experimental UV Ratio to the MS-Based UV Ratio 11 Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

15 Conclusions Preparations of HTGA were analyzed by direct infusion MS and structures were assigned to the masses found. The structures of the UV-absorbing species were used to calculate absorbance contributions from each species found in the preparations at greater than 5% relative abundance. The contributions were weighted and summed and a MS-based UV Ratio was calculated and compared to the experimentally determined UV Ratio for the HTGA preparations. Very good correlation was obtained. 12 Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

16 References 1. Margel S. and Rembaum A., Macromolecules 1980, 13, Mignealt I. et al., BioTechniques 2004, 37, Prento P., Histochemical Journal 1995, 27, Jones G.J., Journal of Histochemistry and Cytochemistry 1974, 22, Goff C.W. and Oster M.O., Journal of Histochemistry and Cytochemistry 1974, 22, Aso C. and Aito Y., Die Makromolekulare Chemie 1962, 58, Anderson P.J., Journal of Histochemistry and Cytochemistry 1967, 15, Frigerio N.A. and Shaw M.J., Journal of Histochemistry and Cytochemistry 1969, 17, Hardy P.M. et al., Chemical Communications 1969, Correlation of the Mass Spectrometric Analysis of Heat-Treated Glutaraldehyde Preparations to Their 235 nm/280 nm UV Absorbance Ratio

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