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Identification and structural elucidation of ozonation transformation products of estrone.

Segura PA, Kaplan P, Yargeau V - Chem Cent J (2013)

Bottom Line: A control compare trend experiment consisting in the comparison of a control sample to several samples having been exposed to decreasing concentrations of O3(aq) indicated that 593 peaks could be associated with OTPs.After applying various filters to remove background noise, sample contaminants and signal spikes, this data set was reduced to 16 candidate peaks.Structures for these two compounds were proposed based on their MSn spectra.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, McGill University, 3610 University, Montreal, QC, H3A 2B2, Canada. viviane.yargeau@mcgill.ca.

ABSTRACT

Background: Quantitative methods for the analysis of contaminants of emerging concern (CECs) are abundant in the scientific literature. However, there are few reports on systematic methods of identification and structural identification of transformation products. For this reason, a new method based on high-resolution mass spectrometry and differential analysis was developed in order to facilitate and accelerate the process of identification and structural elucidation of transformation products CECs. This method was applied to the study of ozonation transformation products (OTPs) of the natural hormone estrone (E1).

Results: A control compare trend experiment consisting in the comparison of a control sample to several samples having been exposed to decreasing concentrations of O3(aq) indicated that 593 peaks could be associated with OTPs. After applying various filters to remove background noise, sample contaminants and signal spikes, this data set was reduced to 16 candidate peaks. By inspection of the shape of these peaks, only two compounds OTP-276 (m/z 275.12930) and OTP-318 (m/z 317.14008) were considered as good candidates for further study. Multi-stage tandem mass spectrometry (MSn) experiments of SPE extracts of the ozonated samples of E1 and of a deuterium-labeled analogue (E1-d4) showed that OTP-276 and OTP-318 had carboxylic acid and hydroxyl functional groups, as previously reported for OTPs of other hormones. Structures for these two compounds were proposed based on their MSn spectra.

Conclusion: These results indicate that the method proposed is a systematic and rapid approach to study transformation products of CECs.

No MeSH data available.


Related in: MedlinePlus

Fragmentation tree of OTP-276 showing the most probable elemental composition of the main MSn product ions.
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Figure 2: Fragmentation tree of OTP-276 showing the most probable elemental composition of the main MSn product ions.

Mentions: Following these results, MSn (n=3-4) experiments were performed with the precursor ion at m/z 275 in order to further confirm the proposed molecular structure of OTP-276. The fragmentation tree of m/z 275 showing the formulas of the observed MSn product ions can be seen in Figure 2. The presence of the second generation (MS3) product ion at m/z 214 is particularly puzzling since it does not follow the nitrogen rule. Therefore this ion must be odd-electron, meaning that m/z 214 violates the even-electron rule which states that even-electron ions do not lose a radical to form an odd-electron ion [39]. However, such deviations of the even-electron rule have been previously reported after CID of even-electron ions [38,40]. The loss of 17 u was thus interpreted as the loss of H• + CH4. The minor MS3 product ions observed in the full scan CID spectrum of m/z 231 at m/z 213.09290 (C14H13O2-, Δmmu=0.797), m/z 199.07718 (C13H11O2-, Δmmu=0.727), m/z 135.0826 (C9H11O-, Δmmu=0.722) and m/z 133.06660 (C9H9O-, Δmmu=0.712) indicate neutral losses of CH6, C2H8, C6H8O and C6H10O, respectively. Since the loss H2 and CH4 is a common pattern of fragmentation for negative even-electron ions [32], the neutral loss of CH6 was interpreted as the combined loss H2 + CH4, and that of C2H8 as 2CH4. Losses of CH4 can be explained by the dissociation in stepwise elimination mechanisms [32] of the methyl group from C-13 (the C atom numbering of E1 is preserved to facilitate the identification of the fragmentation sites) and the methylene group from C-5. However, the precise mechanism that could yield H2 and CH4 losses from m/z 231 remains unclear. Additionally, the formation of ions at m/z 135 and m/z 133 is also difficult to elucidate, however they are likely the consequence of stepwise elimination reactions and internal nucleophilic displacements [32]. The elemental compositions of the second generation product ions formed during the MS3 experiments were confirmed using the E1-d4 ozonated SPE extract (Additional file 1: Figure S2). The results of these experiments showed that a D atom was lost during the fragmentation of m/z 234.15759 (C15H16D3O2-, Δmmu=−0.293) to form m/z 201.08897 (C13H9D2O2-, Δmmu=−0.246). This D atom was most likely located in the methylene group on C-5. The third generation (MS4) product ion scan experiment (m/z 275 → m/z 231 → m/z 214 ↗ m/z 50–300) with NCE=50 resulted in the presence of only one ion at m/z 199.07631. This third generation product ion was likely formed by dissociation of •CH3.


Identification and structural elucidation of ozonation transformation products of estrone.

Segura PA, Kaplan P, Yargeau V - Chem Cent J (2013)

Fragmentation tree of OTP-276 showing the most probable elemental composition of the main MSn product ions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3643888&req=5

Figure 2: Fragmentation tree of OTP-276 showing the most probable elemental composition of the main MSn product ions.
Mentions: Following these results, MSn (n=3-4) experiments were performed with the precursor ion at m/z 275 in order to further confirm the proposed molecular structure of OTP-276. The fragmentation tree of m/z 275 showing the formulas of the observed MSn product ions can be seen in Figure 2. The presence of the second generation (MS3) product ion at m/z 214 is particularly puzzling since it does not follow the nitrogen rule. Therefore this ion must be odd-electron, meaning that m/z 214 violates the even-electron rule which states that even-electron ions do not lose a radical to form an odd-electron ion [39]. However, such deviations of the even-electron rule have been previously reported after CID of even-electron ions [38,40]. The loss of 17 u was thus interpreted as the loss of H• + CH4. The minor MS3 product ions observed in the full scan CID spectrum of m/z 231 at m/z 213.09290 (C14H13O2-, Δmmu=0.797), m/z 199.07718 (C13H11O2-, Δmmu=0.727), m/z 135.0826 (C9H11O-, Δmmu=0.722) and m/z 133.06660 (C9H9O-, Δmmu=0.712) indicate neutral losses of CH6, C2H8, C6H8O and C6H10O, respectively. Since the loss H2 and CH4 is a common pattern of fragmentation for negative even-electron ions [32], the neutral loss of CH6 was interpreted as the combined loss H2 + CH4, and that of C2H8 as 2CH4. Losses of CH4 can be explained by the dissociation in stepwise elimination mechanisms [32] of the methyl group from C-13 (the C atom numbering of E1 is preserved to facilitate the identification of the fragmentation sites) and the methylene group from C-5. However, the precise mechanism that could yield H2 and CH4 losses from m/z 231 remains unclear. Additionally, the formation of ions at m/z 135 and m/z 133 is also difficult to elucidate, however they are likely the consequence of stepwise elimination reactions and internal nucleophilic displacements [32]. The elemental compositions of the second generation product ions formed during the MS3 experiments were confirmed using the E1-d4 ozonated SPE extract (Additional file 1: Figure S2). The results of these experiments showed that a D atom was lost during the fragmentation of m/z 234.15759 (C15H16D3O2-, Δmmu=−0.293) to form m/z 201.08897 (C13H9D2O2-, Δmmu=−0.246). This D atom was most likely located in the methylene group on C-5. The third generation (MS4) product ion scan experiment (m/z 275 → m/z 231 → m/z 214 ↗ m/z 50–300) with NCE=50 resulted in the presence of only one ion at m/z 199.07631. This third generation product ion was likely formed by dissociation of •CH3.

Bottom Line: A control compare trend experiment consisting in the comparison of a control sample to several samples having been exposed to decreasing concentrations of O3(aq) indicated that 593 peaks could be associated with OTPs.After applying various filters to remove background noise, sample contaminants and signal spikes, this data set was reduced to 16 candidate peaks.Structures for these two compounds were proposed based on their MSn spectra.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, McGill University, 3610 University, Montreal, QC, H3A 2B2, Canada. viviane.yargeau@mcgill.ca.

ABSTRACT

Background: Quantitative methods for the analysis of contaminants of emerging concern (CECs) are abundant in the scientific literature. However, there are few reports on systematic methods of identification and structural identification of transformation products. For this reason, a new method based on high-resolution mass spectrometry and differential analysis was developed in order to facilitate and accelerate the process of identification and structural elucidation of transformation products CECs. This method was applied to the study of ozonation transformation products (OTPs) of the natural hormone estrone (E1).

Results: A control compare trend experiment consisting in the comparison of a control sample to several samples having been exposed to decreasing concentrations of O3(aq) indicated that 593 peaks could be associated with OTPs. After applying various filters to remove background noise, sample contaminants and signal spikes, this data set was reduced to 16 candidate peaks. By inspection of the shape of these peaks, only two compounds OTP-276 (m/z 275.12930) and OTP-318 (m/z 317.14008) were considered as good candidates for further study. Multi-stage tandem mass spectrometry (MSn) experiments of SPE extracts of the ozonated samples of E1 and of a deuterium-labeled analogue (E1-d4) showed that OTP-276 and OTP-318 had carboxylic acid and hydroxyl functional groups, as previously reported for OTPs of other hormones. Structures for these two compounds were proposed based on their MSn spectra.

Conclusion: These results indicate that the method proposed is a systematic and rapid approach to study transformation products of CECs.

No MeSH data available.


Related in: MedlinePlus