A comparison of home results against a laboratory result on the same vial

Posting this under the heading it deserves: A comparison of home results against a laboratory result on the same vial Everything below is what sits behind that.

Working through the identity arithmetic and I would like it checked.

tirzepatide has a monoisotopic mass close to 4813.5 Da. On an electrospray instrument I would expect to see the multiply charged series rather than the intact singly charged ion, so for the doubly charged species I calculate (4813.5 + 2 x 1.00728) / 2, and for the triply charged the analogous expression.

The observed values in the report sit within a few ppm of those. My question is what that actually establishes, because I have seen people treat a mass match as a purity result and I do not think it is one.

On the opening post — agreed on the reasoning, with one qualification.

Sample handling matters: if a sample is contaminated or degraded before testing, the test gives you the result for the degraded sample, not for fresh material. That is not a failure of the test; it is the test working correctly.

Picking up post #2: that is the part I would want checked first.

Why third-party testing is stronger: a home test run by the person who made the compound is a self-selected result. The test run by a neutral third party removes obvious sources of bias.

Molecular tests: DNA or RNA tests are not applicable to peptides, which do not contain nucleic acids. Peptide-specific tests rely on protein recognition, not nucleic-acid detection.

Precision of home tests: most consumer-accessible devices are not precise to the level people want ("is this 99% pure or 97% pure"). They give a yes/no or a rough category, not a quantitative number.

This follows post #4 rather than contradicting it.

Colorimetric tests: colour intensity correlates with concentration, but the relationship is non-linear at extremes and the correlation depends on the exact conditions (pH, temperature, timing). Reading the colour visually introduces subjectivity.

I read post #6 twice before replying, because I had assumed the opposite.

Immunoassay limitations: tests that use antibodies have cross-reactivity limitations. An antibody raised to semaglutide will cross-react to some degree with tirzepatide and other structurally similar compounds. The test result conflates them.

post #8 answers the question as asked. The question underneath it is different.

What you can use home tests for: confirmation that a solution contains peptide (as opposed to being saline alone), rough screening for very different compounds (semaglutide versus totally unrelated compound). What you cannot use them for: precise purity assessment or verification that the identity is correct.

Lateral-flow devices: like a rapid COVID test. They have a reagent strip and produce a colour result. They are quick but not precise and not intended for quantitative work.

Coming back to post #9, because the follow-up matters more than the original answer.

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

Picking up post #9: that is the part I would want checked first.

False positives and false negatives: no test has 100% sensitivity and 100% specificity. A negative result does not guarantee absence; a positive result does not guarantee presence. The predictive value depends on prevalence.

Enzyme assays: if you have an enzyme that reacts specifically with your compound, an enzyme-based assay can work. These are sometimes available commercially but are less common than antibody-based tests.

Enzyme assays: if you have an enzyme that reacts specifically with your compound, an enzyme-based assay can work. These are sometimes available commercially but are less common than antibody-based tests.