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c/hplc·posted 2 years ago by u/hana_lehtinen

[Results] 87 weeks, 36kg, and purity was the hard part

Correction Well Actually ×5 Clean Column ×3 Long Haul ×3

Long-ish post, sorry. tl;dr at the bottom.

I have been tracking LC-MS against eGFR for 29 weeks because I could not find anyone who had. The correlation is weaker than I expected, which is itself mildly interesting given how confidently people link the two in here.

Caveats up front: one person, one lab, one assay, no control, and I changed my training in the middle of it, which was stupid.

tl;dr: probably real, definitely smaller than the threads imply, and not worth reorganising your week around.

4,455 up / 1,101 down80% upvoted55 commentsid 1p4rcg11 Jan 2024

55 comments

30 in this archive, depth 5

best — the order this archive was captured in

u/marisol_frisk309 points·2 years ago

No. This is the kind of confident post that gets copied into a screenshot and repeated for years. Where is the evidence.

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u/sig_figs_samMOD226 points·2 years ago

Tracking number removed. It identifies both ends of a shipment.

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[deleted]165 points·2 years ago

[deleted]

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u/hana_lehtinenOP-31 points·2 years ago

integration decision on a shoulder changes your number by half a point on its own

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u/gustav_solberg1 point·2 years ago

area% and mass% are not the same and this whole post conflates them

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u/marit_mwangi1 point·2 years ago

the detector wavelength matters more than people think

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u/isabela_nilsen117 points·2 years ago

Injection volume and flow rate? Those affect resolution.

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u/aksel_kjaer73 points·2 years ago

two labs, two different baselines, two different purity numbers, both honest

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u/kofi_ferreira69 points·2 years ago

Strongly agree. Largest single impurity tells a different story than total purity.

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u/cagrilintide_enthusiast51 points·2 years ago

co-elution is real and method development is usually not enough to resolve it

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u/nabila_espinoza67 points·2 years ago

state the method: column, gradient, detection wavelength, injection volume

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u/downvote_magnet30 points·2 years ago

The confident tone is doing a lot of work that the evidence is not.

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u/santiago_villalobos17 points·2 years ago

axis labels included, always

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u/nnt_nate25 points·2 years ago

axis labels included, always

Counter-anecdote: opposite result, same dose. Which mostly tells us the variance is huge.

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u/hana_lehtinenOP7 points·2 years ago

Gradient goblin mode: changed the solvent composition 5 times, finally got good resolution on a integration peak.

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u/mariam_cabrera28 points·2 years ago

What was the column and what gradient?

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u/bilal_adebayo6 points·2 years ago

instrument quality is less important than analyst consistency

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u/rasmus_kimani2 points·2 years ago

This is the correct method framing. Column and gradient are load-bearing fields.

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u/medutest_mel1 point·2 years ago

area% and mass% are not the same and this whole post conflates them

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u/canada_coverage20 points·2 years ago

What was the column and what gradient?

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u/honest_syringe_pls14 points·2 years ago

Did they post the raw trace or just the summary?

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u/rasmus_petrescu6 points·2 years ago

the detector wavelength matters more than people think

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u/micro_bump_mick11 points·2 years ago

Did they post the raw trace or just the summary?

Adding to this: method development is doing more work than the comment implies.

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u/aksel_kjaer6 points·2 years ago·edited

co-elution is real and LC-MS is usually not enough to resolve it

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u/liv_okafor5 points·2 years ago

a round-robin on baseline integration would be genuinely useful

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u/two_mil_or_one4 points·2 years ago

Small correction: the trial was 24 weeks, not 6. Does not change your point but people will quote it.

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u/fatima_yildiz3 points·2 years ago·edited

Small correction: the trial was 24 weeks, not 6.

Disagree on that part. 98.7% and 98.7% on the same vial is normal.

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u/canada_coverage14 points·2 years ago

Strongly agree. Largest single impurity tells a different story than total purity.

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About c/hplc

The analytical deep end: RP-HPLC methods, gradient design, integration decisions, LC-MS confirmation, amino-acid analysis, water content, and why two labs can report 98.1% and 96.4% on the same vial and both be right. Post the chromatogram, not the summary line.

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