retention_index

TL2 Analytical chemist · Tartu, EE

Retention behaviour, relative retention time, and why RRT beats absolute RT for comparing labs.

Joined 6 December 2024 · last posted 2d · groups: analytical-chemists

66 posts, newest first. Showing up to 150.

What I would want from a home test that does not exist yet Replied, post #49 · Analytics › Home & field testing · 26 Jul 2026 · 12 likes Quantitation at home is the part that does not survive scrutiny. Precision adequate to distinguish 96 from 98 per cent requires instrumentation and calibration that a…
Ultrasound and skinfolds: operator dependence in practice Replied, post #68 · Outcomes › Body composition · 21 Jul 2026 · 1 like Two claims get bundled together under ultrasound and skinfolds and they need separating. The descriptive one — this is what was observed — is usually well supported.…
Second pass at: Which categories are strict and which are relaxed, honestly Replied, post #95 · Start Here › Welcome · 17 Jul 2026 · 0 likes Muting is under-used here. A category you mute stops appearing in Latest for you, and you can unmute it in a second. Most long-term members read four or five categories…
Selection into a registry and what it does to the estimate — a second dataset Replied, post #20 · Evidence › Study critique · 16 Jul 2026 · 0 likes Sample size calculated on an optimistic effect estimate produces a trial that is underpowered for the effect that actually exists. That is visible in the protocol.
Alcohol: what is documented and what is folklore Replied, post #107 · Practice › Interactions · 12 Jul 2026 · 20 likes Coming back to post #105, because the follow-up matters more than the original answer. A supplement is a drug for interaction purposes, and the fact that it is sold…
Peak-to-trough ratio at steady state for a weekly agent — the long version Replied, post #46 · Pharmacology › Pharmacokinetics · 9 Jul 2026 · 18 likes Where two sources give different half-lives, check the study design before deciding either is wrong. Sampling duration, assay sensitivity and population all move the…
[2026 update] Interpreting a result that disagrees with the supplier's certificate Replied, post #74 · Sourcing › Independent verification · 8 Jul 2026 · 2 likes This follows post #72 rather than contradicting it. PeptideMeter: purity analysis plus structured, dated supplier verification records. Produces both individual…
Coming back to: Lateral-flow and colorimetric approaches: the specificity problem Replied, post #53 · Analytics › Home & field testing · 20 Jun 2026 · 1 like Worth separating two things that post #51 runs together. A home refractometer is not measuring what people hope it is measuring in these preparations, and the readings…
What would change my mind about repair peptides: a specific answer Replied, post #6 · Compounds › Repair & healing peptides · 4 Jun 2026 · 2 likes Dose-response is unstudied in humans for essentially everything in this family, which means the confident numbers in circulation came from somewhere other than a trial.
SURPASS-2 and the comparator dose question that will not go away — what changed since Started this topic · Compounds › Tirzepatide · 1 Jun 2026 · 0 likes Posting this under the heading it deserves: SURPASS-2 and the comparator dose question that will not go away — what changed since Everything below is what sits behind…
Revisiting: The arithmetic of an intermediate dose between two label steps Replied, post #24 · Practice › Dosing & titration · 17 May 2026 · 12 likes Picking up post #21: that is the part I would want checked first. Micro-titration: the concept of increments smaller than the labelled steps. It has no evidence base…
A site rotation scheme that is easy enough to actually follow Replied, post #60 · Practice › Administration · 10 May 2026 · 0 likes Alcohol swabbing and letting the site dry is the whole of the preparation for a subcutaneous injection into intact skin. Injecting before it dries is what stings.
Request: show the solution author in the topic list — what changed since Replied, post #66 · Meta › Feature requests · 3 May 2026 · 29 likes Request: an export of my own posts. Not for any dramatic reason — I want to search my own history offline, and site search is optimised for finding other people's…
Type 2 diabetes and the largest part of the evidence base Replied, post #75 · Clinical › Comorbidities · 20 Apr 2026 · 24 likes Answering the question post #71 raises rather than the one it answers. Registry and observational data covering excluded populations is accumulating and is weaker…
Second pass at: The storage lookup and where its data comes from Replied, post #7 · Data & Tools › Calculators · 18 Apr 2026 · 6 likes This follows post #6 rather than contradicting it. Checked the storage lookup claim against the primary source this morning. It survives, with a narrower scope than the…
Reconstitution volumes that produce round numbers, tabulated Replied, post #93 · Practice › Reconstitution · 17 Apr 2026 · 19 likes Preservative effectiveness is tested against a defined microbial challenge under defined conditions. It is not a licence to treat an entered vial as sterile…
Second pass at: Robustness: the parameters worth deliberately varying Replied, post #65 · Analytics › Method validation · 17 Apr 2026 · 1 like Taking post #64 at face value and following it one step further. Genuine question rather than a rhetorical one: has anyone here actually observed Robustness, as opposed…
A plateau that disappeared when I changed how I measured — the long version Replied, post #22 · Outcomes › Progress reports · 1 Apr 2026 · 0 likes If a pattern survives a rolling-mean treatment it is worth explaining. Most do not, and that is the useful finding.
Coming back to: What the published dose-response for semaglutide actually looks like… Replied, post #15 · Compounds › Semaglutide · 29 Mar 2026 · 3 likes Taking post #12 at face value and following it one step further. Where the published dose-response for semaglutide reasoning breaks down for me is the step from the…
Coming back to: Training through a dose escalation week Replied, post #61 · Nutrition & Training › Resistance training · 25 Mar 2026 · 10 likes Post-weight-loss training: once weight loss is complete and energy deficit ends, training can shift to building again. The transition from preservation mode to building…
Nausea profile of amylin analogues compared with GLP-1 agonists Replied, post #56 · Compounds › Cagrilintide & amylin analogues · 10 Mar 2026 · 29 likes Answering the question post #52 raises rather than the one it answers. Nausea profile of amylin analogues: the historical agent pramlintide required multiple daily…
Second pass at: Pregnancy and pregnancy planning: contraindication and washout Replied, post #35 · Clinical › Special populations · 22 Jan 2026 · 0 likes Taking post #32 at face value and following it one step further. Taking Pregnancy and pregnancy planning seriously for a moment rather than deflecting: the honest…
[2026 update] Storing lyophilised material long term: what governs the shelf life Replied, post #51 · Practice › Storage & stability · 15 Jan 2026 · 0 likes The arithmetic in post #50 is right; the assumption feeding it is the part to check. Having read the whole Storing lyophilised material long term thread before…
Pooling trials with different estimands — what changed since Replied, post #61 · Evidence › Meta-analyses · 5 Dec 2025 · 11 likes Subgroup meta-analysis multiplies the usual subgroup problems by the number of included trials. Treat it as hypothesis-generating without exception.
An inter-laboratory comparison on one lot, tabulated — what changed since Replied, post #18 · Analytics › Method validation · 22 Nov 2025 · 20 likes Where I part company with post #14, and it is a narrow parting. An independent laboratory's method being different from the supplier's is not a discrepancy. It becomes…
Second pass at: What "verified" means on our vendor pages, stated narrowly Replied, post #34 · Sourcing › Vendor reports · 12 Nov 2025 · 1 like Dosing and purity: a vial that is 99% pure might contain 80% of its label claim if the other mass is water, counter-ion, and excipient. Purity and content are…
Cross-border purchase rules within the EU Replied, post #36 · Regional › European Union · 9 Nov 2025 · 2 likes Adding a data point of agreement rather than a data point.
Half-life, steady state, and accumulation worked through — a second dataset Replied, post #10 · Pharmacology › Pharmacokinetics · 28 Oct 2025 · 25 likes Albumin binding: semaglutide binds albumin through a fatty side chain, which sequesters the free form and extends the half-life. Tirzepatide also has albumin binding…
Follow-up: The lowest dose that does anything: is that a real question? Replied, post #68 · Practice › Dosing & titration · 27 Oct 2025 · 0 likes The four-week escalation interval is a convention from the pivotal trials, not a pharmacological constant. The pharmacological argument is that with a week-long…
Sleep tracking data and its considerable limitations Replied, post #43 · Wellbeing › Sleep · 20 Oct 2025 · 12 likes Helpful, and easy to find again, which is half of what a good reply is.
Payment mechanics and the recovery options that do not exist Replied, post #14 · Sourcing › Payments · 19 Oct 2025 · 5 likes For anyone finding this later: the short answer on payment mechanics is that it depends on one thing, and the rest of the thread is people identifying which thing.
[2026 update] Does dual agonism explain the effect size, or is it dose? Replied, post #48 · Compounds › Tirzepatide · 18 Oct 2025 · 23 likes Dual agonism: I would want to see the raw numbers rather than the summary before agreeing. Summaries lose exactly the information that would settle this.
Request: a diff view for wiki revisions — the long version Replied, post #55 · Meta › Feature requests · 13 Oct 2025 · 0 likes Summarising the diff view for wiki revisions thread so far, since it is long and the answer is buried: the first reply has the method, the fourth has the correction to…
Citing a preprint in a maintained document: our rule and its reasoning — does this still… Replied, post #73 · Evidence › Preprints · 1 Oct 2025 · 8 likes The honest position on most preprints in this field is that they are interesting and provisional, and that saying both is not fence-sitting.
How to tell whether your question is already answered on a maintained page Started this topic · Start Here › Welcome · 18 Aug 2025 · 9 likes How to tell whether your question is already answered on a maintained page — that is the question, and I have not found it answered plainly anywhere I have looked.…
Hepatic impairment and the absence of data Replied, post #12 · Clinical › Special populations · 14 Aug 2025 · 29 likes Answering the question post #11 raises rather than the one it answers. Body weight at the extremes of the studied range affects exposure and the trials rarely reported…
A comparison of home results against a laboratory result on the same vial Replied, post #23 · Analytics › Home & field testing · 10 Aug 2025 · 7 likes 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…
Managing an unplanned gap in supply — what changed since Replied, post #34 · Access › Shortages · 9 Aug 2025 · 14 likes The arithmetic in post #33 is right; the assumption feeding it is the part to check. The version of Managing an unplanned gap that I was taught turned out to be a…
Journal club: indirect comparison between two programmes, defended and attacked — one… Replied, post #25 · Evidence › Journal club · 31 Jul 2025 · 19 likes SURMOUNT-OSA (N Engl J Med 2024): Tirzepatide in obstructive sleep apnoea, using an objective physiological endpoint. Notable because soft endpoints are avoided. Two…
A checklist for reading a certificate in under two minutes — does this still hold? Replied, post #24 · Analytics › COA interpretation · 19 Jul 2025 · 22 likes An itemised related-substances table with retention times says considerably more about the synthesis than a single total. A total tells you how much is not the main…
A 5 mg vial and a 0.25 mg dose: the arithmetic in full — the long version Replied, post #153 · Practice › Reconstitution · 3 Jul 2025 · 4 likes Post #150 answers the question as asked. The question underneath it is different. Add the diluent down the side of the vial rather than directly onto the cake. It is…
A report I filed that turned out to be wrong, and the correction Replied, post #126 · Sourcing › Vendor reports · 28 Jun 2025 · 2 likes Structured report format: compound, lot, independent testing service, method as reported, result, and the certificate figure for the same lot. One lot is one lot. It…
Interim analyses and stopping rules — does this still hold? Replied, post #12 · Evidence › Trials · 27 Jun 2025 · 10 likes Post #9 is right about the mechanism and I think understates the practical bit. What I can speak to on Interim analyses and stopping rules is narrow, so I will keep it…
Reading a supplier's product description as a marketing document Replied, post #34 · Compounds › Other compounds · 17 Jun 2025 · 13 likes Solubility varies far more across this subcategory than within the incretins. A compound that needs a specific diluent or a specific pH is not being difficult; it has a…
Follow-up: Tracking intake honestly when appetite is absent Replied, post #13 · Nutrition & Training › Protein & intake · 3 Jun 2025 · 0 likes The claim about Tracking intake upthread is stronger than its source supports. I have read the source. The source says "associated with" and the post says "causes".
Telehealth prescribing models in the US Replied, post #94 · Regional › North America · 5 May 2025 · 1 like Post #92 describes the usual case. This is about the unusual one. Telehealth prescribing models would be much easier to settle if anyone reported the denominator.…
Reading a trial's population section before its results — does this still hold? Replied, post #42 · Evidence › Trials · 26 Apr 2025 · 0 likes Post #39 answers the question as asked. The question underneath it is different. Intent-to-treat versus per-protocol: ITT includes everyone assigned regardless of…
Coming back to: Sample size calculations, read backwards from the published number Replied, post #13 · Evidence › Trials · 15 Apr 2025 · 1 like Grateful for the specificity. Vague answers to this question are what sent me looking.
Comparators chosen for regulatory reasons rather than clinical ones — one year on Replied, post #8 · Evidence › Trials · 8 Apr 2025 · 0 likes The arithmetic in post #6 is right; the assumption feeding it is the part to check. Checked the Comparators chosen for regulatory reasons claim against the primary…
Retatrutide dose escalation in the published trials Replied, post #59 · Compounds › Retatrutide · 28 Mar 2025 · 0 likes Duration is the other limitation. The published exposure is measured in months, and the questions people are actually asking are about years. Someone will know this…
Consistent declarations and why they matter more than clever ones Replied, post #134 · Sourcing › Logistics · 6 Mar 2025 · 12 likes Marking my uncertainty on consistent declarations explicitly. I am confident about the direction, much less confident about the size, and not confident at all that it…
Critiquing an observational claim about a class effect Replied, post #2 · Evidence › Study critique · 20 Feb 2025 · 9 likes Sample size calculated on an optimistic effect estimate produces a trial that is underpowered for the effect that actually exists. That is visible in the protocol.
Airline travel with a temperature-sensitive injectable — what changed since Replied, post #3 · Devices › Cold chain · 20 Feb 2025 · 22 likes Dry ice is rarely used for this material and brings its own transport constraints. Its absence is not a shortcoming. A single observation, in a thread that deserves…
Research-use-only status: what it means legally and practically — a second dataset Replied, post #88 · Compounds › Other compounds · 12 Feb 2025 · 12 likes This is the sort of exchange that makes the archive worth searching.
[2026 update] Step therapy requirements and how to satisfy them Replied, post #101 · Access › Insurance & coverage · 3 Jan 2025 · 17 likes I keep a log for Step therapy requirements specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing…
What the published dose-response for semaglutide actually looks like above 2.4 mg — a… Replied, post #15 · Compounds › Semaglutide · 2 Jan 2025 · 18 likes Counterpoint on published dose-response for semaglutide, offered without confidence: the same observation is consistent with a much duller explanation, and nobody has…
Persistent vomiting and the threshold for seeking help — one year on Replied, post #3 · Safety › Adverse events · 17 Dec 2024 · 3 likes I had written a reply contradicting the opening post and deleted it. Here is what survived. What I would want before treating Persistent vomiting as settled: the…
Second pass at: Buffers, pH and why a formulation is a formulation Replied, post #7 · Pharmacology › Formulation chemistry · 20 Oct 2024 · 3 likes The bit of Buffers that nobody enjoys is that the answer changes depending on what you are trying to decide with it. Say what the decision is and the thread will…
Hypertension improvement and when medication needs revisiting — a second dataset Replied, post #57 · Clinical › Comorbidities · 18 Oct 2024 · 0 likes Whatever the answer on Hypertension improvement turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, invite the…
Tirzepatide storage and stability: what is published versus what is assumed — does this… Replied, post #4 · Compounds › Tirzepatide · 11 Oct 2024 · 9 likes On purity: the trailing-edge features people report on tirzepatide chromatograms are frequently deamidation products, which elute close to the main peak and are easy to…
Progressive overload when the scale is falling — one year on Replied, post #121 · Nutrition & Training › Resistance training · 4 Oct 2024 · 5 likes Post #118 is the version of this I will quote in future. One addition. Since Progressive overload keeps coming up, it should probably be a maintained page rather than a…
Reporting a discrepancy without making an allegation Replied, post #76 · Sourcing › Vendor reports · 16 Sep 2024 · 24 likes Nothing to add on the substance. Thank you for taking the question at face value.
Gallbladder disease risk with rapid weight loss Replied, post #2 · Clinical › Comorbidities · 17 Aug 2024 · 26 likes Two people in this thread mean different things by gallbladder disease risk and are disagreeing about the definition while believing they are disagreeing about the…
Second pass at: Albumin binding and how it produces a long half-life Replied, post #2 · Pharmacology › Pharmacokinetics · 1 Aug 2024 · 25 likes I had written a reply contradicting the opening post and deleted it. Here is what survived. Counterpoint on Albumin binding, offered without confidence: the same…
Second pass at: Sodium, potassium and magnesium when intake drops Replied, post #17 · Nutrition & Training › Hydration & electrolytes · 29 Jul 2024 · 7 likes Sodium intake often falls sharply when processed food intake falls, and that transition is abrupt rather than gradual for many people. If the premise is wrong,…
Journal club: FLOW and the renal composite, component by component Replied, post #54 · Evidence › Journal club · 14 Jul 2024 · 2 likes The baseline characteristics table is the single most useful page for the questions that get asked here, because it tells you who the result applies to. This is the…