Capillary‐channeled polymer (C‐CP) fibers are demonstrated as a selective stationary phase for phosphopeptide analysis via LC–MS. Taking advantage of the oxidative self‐polymerization of dopamine under alkaline conditions, a simple system involving a dilute aqueous solution of 0.2% w/v dopamine hydrochloride in 0.15% w/v TRIS buffer, pH 8.5 was utilized to coat polydopamine onto nylon 6 C‐CP fibers. Confirmation of the polydopamine coating on the fibers (nylon‐PDA) was made through attenuated total reflection‐FTIR (ATR‐FTIR) analysis. Imaging using SEM was also performed to examine the morphology and topography of the nylon‐PDA. Subsequent loading of Fe3+to the nylon‐PDA matrix was confirmed by SEM/energy dispersive X‐ray spectroscopy (SEM/EDX). The Fe3+‐bound nylon‐PDA fibers packed in a microbore column format were tested in the off‐line preconcentration of phosphopeptides from a 1:100 mixture of β‐casein/BSA digests for MALDI‐TOF analysis. The packed column was also installed onto an HPLC system as a platform for the online sample clean‐up and enrichment of phosphopeptides from a 1:1000 mixture of β‐casein/BSA protein digests that were determined by subsequent ESI–MS analysis.
We show that
Spontaneous formation of
- NSF-PAR ID:
- 10454595
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Rapid Communications in Mass Spectrometry
- Volume:
- 35
- Issue:
- 5
- ISSN:
- 0951-4198
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Rationale Sulfur isotope analysis of organic sulfur‐containing molecules has previously been hindered by challenging preparatory chemistry and analytical requirements for large sample sizes. The natural‐abundance sulfur isotopic compositions of the sulfur‐containing amino acids, cysteine and methionine, have therefore not yet been investigated despite potential utility in biomedicine, ecology, oceanography, biogeochemistry, and other fields.
Methods Cysteine and methionine were subjected to hot acid hydrolysis followed by quantitative oxidation in performic acid to yield cysteic acid and methionine sulfone. These stable, oxidized products were then separated by reversed‐phase high‐performance liquid chromatography (HPLC) and verified via offline liquid chromatography/mass spectrometry (LC/MS). The sulfur isotope ratios (δ34S values) of purified analytes were then measured via combustion elemental analyzer coupled to isotope ratio mass spectrometry (EA/IRMS). The EA was equipped with a temperature‐ramped chromatographic column and programmable helium carrier flow rates.
Results On‐column focusing of SO2in the EA/IRMS system, combined with reduced He carrier flow during elution, greatly improved sensitivity, allowing precise (0.1–0.3‰ 1 s.d.) δ34S measurements of 1 to 10 μg sulfur. We validated that our method for purification of cysteine and methionine was negligibly fractionating using amino acid and protein standards. Proof‐of‐concept measurements of fish muscle tissue and bacteria demonstrated differences up to 4‰ between the δ34S values of cysteine and methionine that can be connected to biosynthetic pathways.
Conclusions We have developed a sensitive, precise method for measuring the natural‐abundance sulfur isotopic compositions of cysteine and methionine isolated from biological samples. This capability opens up diverse applications of sulfur isotopes in amino acids and proteins, from use as a tracer in organisms and the environment, to fundamental aspects of metabolism and biosynthesis.
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