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    "title": "Why one mass number can’t prove your peptide is pure",
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    "url": "https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure",
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    "tldr": "A mass spectrometer only measures the combined weight of the peptide backbone, glycan and sialic acid, so one mass number can't prove a glycopeptide is pure.",
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            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "title",
            "value": "Why one mass number can’t prove your peptide is pure",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "published",
            "value": "2026-08-06",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "id": "why-one-mass-number-can-t-prove-peptide-pure:author",
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            "value": "PreppinPeppers Editorial Team",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "topics",
            "value": "peptide research, Research, study",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "category": "content",
            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "summary",
            "value": "A mass spectrometer only measures the combined weight of the peptide backbone, glycan and sialic acid, so one mass number can't prove a glycopeptide is pure.",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure"
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        {
            "id": "why-one-mass-number-can-t-prove-peptide-pure:section-1",
            "category": "content",
            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "section",
            "value": "What these molecules are",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure"
        },
        {
            "id": "why-one-mass-number-can-t-prove-peptide-pure:section-2",
            "category": "content",
            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "section",
            "value": "What a sugar-coated peptide actually is",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure"
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            "category": "content",
            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "section",
            "value": "Why these molecules are so hard to identify",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure"
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            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "section",
            "value": "What the numbers actually showed",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure"
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            "category": "content",
            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "section",
            "value": "What the research community gets wrong here",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure"
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            "entity": "Why one mass number can’t prove your peptide is pure",
            "attribute": "cites",
            "value": "this coverage at bioRxiv → - www.biorxiv.org",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://www.biorxiv.org/content/10.64898/2026.08.05.743002v1?rss=1"
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            "attribute": "cites",
            "value": "D'Hondt et al., J Pharm Biomed Anal 2014: Related impurities in peptide medicines - pubmed.ncbi.nlm.nih.gov",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
            "evidence": "https://pubmed.ncbi.nlm.nih.gov/25044089/"
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            "value": "Thacker et al., Front Immunol 2022: Detection of innate immune response modulating impurities (IIRMI) in therapeutic peptides and proteins: Impact of excipients - pmc.ncbi.nlm.nih.gov",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "value": "Badgujar et al., Chirality 2024: Enantiomeric purity of synthetic therapeutic peptides: A review - pubmed.ncbi.nlm.nih.gov",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "value": "Gansulin Pen · Reusable Click-Dial, 3 ml (1-60 Units)",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "value": "Gansulin-Compatible 3 ml Glass Cartridge for Pens (10-Pack)",
            "source": "Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-one-mass-number-can-t-prove-peptide-pure)",
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            "q": "What is a sialylated N-glycopeptide?",
            "a": "It's a small piece of a protein (a peptide) that still carries an attached sugar chain (a glycan) ending in a sialic acid cap, attached at an asparagine amino acid."
        },
        {
            "q": "Why is mass spec bad at reading these directly?",
            "a": "The sugar chain tends to break off before the peptide backbone during fragmentation, and one site can carry dozens of glycan shapes, so a single spectrum often can't confirm the underlying peptide sequence."
        },
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            "q": "Does a matching mass prove a peptide's identity or purity?",
            "a": "No. Different peptide-glycan combinations can produce nearly identical masses, so fragment-level evidence like Y-ions and oxonium ions is needed, not just a matching precursor mass."
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            "description": "A mass spectrometer only measures the combined weight of the peptide backbone, glycan and sialic acid, so one mass number can't prove a glycopeptide is pure."
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