20 categories

Analytics

Analytical chemistry: chromatography, mass spectrometry, certificates of analysis, impurity profiles and method validation. The most technical part of the site.

178 topics8,388 posts59 solved Moderators: j.mwangi, KLindqvist About this category

HPLC & UHPLC 35 Mass spectrometry 30 COA interpretation 33 Impurities & related substances 30 Method validation 28 Home & field testing 22

178 topics · page 5 of 6

Topic	Participants	Replies	Views	Activity
When a tidy document is a signal and when it is decoration Analytics › COA interpretation certificate of analysis reference standards batch & lot numbers amino acid analysis When a tidy document is a signal and when it is decoration I have a specific reason for asking rather than idle curiosity, and the context is below. What changes if the standard account of tidy document is…	+6	10	20k	10mo
Deconvolution of a multiply charged envelope Analytics › Mass spectrometry MALDI-TOF charge states mass error (ppm) counter-ion content Closed Deconvolution of a multiply charged envelope — setting out what I have, and where I think it stops being reliable. Working through the identity arithmetic and I would like it checked. tirzepatide has a…		2	63	10mo
Revisiting: Why I ask for the gradient before I discuss the number Analytics › HPLC & UHPLC UV & DAD detection data table peak integration system suitability Posting this under the heading it deserves: Revisiting: Why I ask for the gradient before I discuss the number Everything below is what sits behind that. I would like to understand what this number means…	+15	19	43k	10mo
Coming back to: Oxidation and deamidation mass shifts, tabulated Analytics › Mass spectrometry LC-MS charge states MALDI-TOF high-resolution MS Oxidation and deamidation mass shifts, tabulated — setting out what I have, and where I think it stops being reliable. Reading back through what has been written here about Oxidation and deamidation mass…	+34	38	4.8k	10mo
Column chemistry choices for a 40-residue peptide Analytics › HPLC & UHPLC gradient method system suitability HPLC peak integration Column chemistry choices for a 40-residue peptide — setting out what I have, and where I think it stops being reliable. Collecting what is known about column chemistry choices in one place, because it is…	+39	43	1.1k	10mo
Second pass at: LOD and LOQ: definitions people get wrong Analytics › Method validation recovery precision & repeatability linearity LOD & LOQ Posting this under the heading it deserves: Second pass at: LOD and LOQ: definitions people get wrong Everything below is what sits behind that. Something about LOD and LOQ does not reconcile and I would like…	+47	51	40k	10mo
Reflectance and photometric devices: precision in practice Analytics › Home & field testing third-party testing documentation quality LOD & LOQ Solved On the subject in the title: Reflectance and photometric devices: precision in practice Working notes rather than a conclusion. I was wrong about reflectance and photometric devices in a thread last spring…		2	2.2k	10mo
[2026 update] A certificate with no method stated: what can you conclude? Analytics › COA interpretation reference standards certificate of analysis documentation quality batch & lot numbers Solved A certificate with no method stated: what can you conclude? — that is the question, and I have not found it answered plainly anywhere I have looked. I would like to understand what this number means before I…		2	82	11mo
System suitability injections: if they failed, the run did not happen Analytics › HPLC & UHPLC peak integration HPLC data table gradient method Posting this under the heading it deserves: System suitability injections: if they failed, the run did not happen Everything below is what sits behind that. Proposing that system suitability injections…	+23	27	6k	11mo
MALDI versus ESI for a quick identity check Analytics › Mass spectrometry high-resolution MS charge states mass error (ppm) MALDI-TOF Closed On the subject in the title: MALDI versus ESI for a quick identity check Working notes rather than a conclusion. I was wrong about MALDI versus ESI in a thread last spring and I would like to correct it…		2	2k	11mo
Distinguishing a deletion sequence by mass alone — the long version Analytics › Mass spectrometry high-resolution MS mass error (ppm) charge states MALDI-TOF On the subject in the title: Distinguishing a deletion sequence by mass alone — the long version Working notes rather than a conclusion. A narrow question about Distinguishing a deletion sequence,…	+38	44	60k	11mo
When a tidy document is a signal and when it is decoration — does this still hold? Analytics › COA interpretation reference standards amino acid analysis documentation quality certificate of analysis Solved Asking directly, because I could not find a straight answer: When a tidy document is a signal and when it is decoration — does this still hold? Tidy document keeps being re-asked here and I think that is…	+3	7	22k	11mo
Second pass at: What a reversed-phase purity number actually is Analytics › HPLC & UHPLC peak integration UV & DAD detection system suitability On the subject in the title: Second pass at: What a reversed-phase purity number actually is Working notes rather than a conclusion. I would like to understand what this number means before I repeat it…		2	7.4k	11mo
Counter-ion content and its effect on measured mass Analytics › Mass spectrometry high-resolution MS charge states MALDI-TOF LC-MS Solved On the subject in the title: Counter-ion content and its effect on measured mass Working notes rather than a conclusion. Something about counter-ion content does not reconcile and I would like a second pair…	+100	108	45k	12mo
Why quantitation is the hard part, not detection Analytics › Home & field testing LOD & LOQ third-party testing ELISA Why quantitation is the hard part, not detection I have a specific reason for asking rather than idle curiosity, and the context is below. Collecting what is known about quantitation in one place, because it…	+11	15	27k	12mo
A field-by-field walk through a certificate of analysis Analytics › COA interpretation documentation quality amino acid analysis certificate of analysis batch & lot numbers Solved Posting this under the heading it deserves: A field-by-field walk through a certificate of analysis Everything below is what sits behind that. I have spent a fortnight trying to pin field-by-field walk…	+136	147	1.8k	12mo
Forced degradation studies: designing one that is informative — does this still hold? Analytics › Method validation stability-indicating method precision & repeatability LOD & LOQ system suitability Solved The question in the title: Forced degradation studies: designing one that is informative — does this still hold? I will give what I have already checked below so nobody repeats it. The question about Forced…	+37	41	1.2k	12mo
Reading a chromatogram someone posted without axes Analytics › HPLC & UHPLC HPLC UV & DAD detection gradient method data table Reading a chromatogram someone posted without axes — setting out what I have, and where I think it stops being reliable. Posting a small dataset on reading a chromatogram. It is mine, it is uncontrolled, and…	+47	55	9.4k	13mo
Repeatability versus intermediate precision Analytics › Method validation precision & repeatability recovery LOD & LOQ linearity Solved Repeatability versus intermediate precision — setting out what I have, and where I think it stops being reliable. Trying to establish the boundary conditions on repeatability versus intermediate precision.…	+119	134	34k	13mo
Area percent versus weight percent: the confusion that causes most arguments — what changed since Analytics › HPLC & UHPLC gradient method data table HPLC Area percent versus weight percent: the confusion that causes most arguments — what changed since Writing it up because I had to work it out twice and would rather nobody else did. What changes if the…	+30	34	40k	13mo
Reading an MS report that only gives you a single number Analytics › Mass spectrometry counter-ion content mass error (ppm) charge states On the subject in the title: Reading an MS report that only gives you a single number Working notes rather than a conclusion. I would like to understand what this number means before I repeat it anywhere. A…	+100	113	48k	13mo
Relative retention time as a better inter-laboratory comparator Analytics › Method validation linearity recovery precision & repeatability stability-indicating method On the subject in the title: Relative retention time as a better inter-laboratory comparator Working notes rather than a conclusion. What changes if the standard account of relative retention time is wrong? I…	+7	11	28k	14mo
Particulates in a reconstituted solution: identifying the likely source — what changed since Analytics › Impurities & related substances water content HPLC forced degradation counter-ion content Particulates in a reconstituted solution: identifying the likely source — what changed since — setting out what I have, and where I think it stops being reliable. What changes if the standard account of…		2	129	14mo
Water content on a certificate and why it changes the arithmetic Analytics › COA interpretation certificate of analysis reference standards batch & lot numbers Closed Water content on a certificate and why it changes the arithmetic — setting out what I have, and where I think it stops being reliable. Water content: setting out the arithmetic in full, because I have had to…	+19	23	24k	14mo
Residual solvents and scavengers: what is looked for Analytics › Impurities & related substances counter-ion content HPLC data table forced degradation Solved On the subject in the title: Residual solvents and scavengers: what is looked for Working notes rather than a conclusion. I would like to know what people here actually do about residual solvents and…	+19	23	39k	14mo
Coming back to: Oxidation pathways for methionine and tryptophan Analytics › Impurities & related substances HPLC counter-ion content water content data table Oxidation pathways for methionine and tryptophan Writing it up because I had to work it out twice and would rather nobody else did. Reading back through what has been written here about Oxidation pathways for…	+1	5	36k	15mo
Deamidation and the close-eluting pair it produces Analytics › Impurities & related substances forced degradation HPLC water content data table Deamidation and the close-eluting pair it produces Writing it up because I had to work it out twice and would rather nobody else did. Something about deamidation does not reconcile and I would like a second…	+33	37	46k	15mo
Certificates issued by the seller versus by a laboratory Analytics › COA interpretation amino acid analysis certificate of analysis documentation quality Posting this under the heading it deserves: Certificates issued by the seller versus by a laboratory Everything below is what sits behind that. I would like to understand what this number means before I…	+58	65	1.2k	15mo
Adducts: sodium, potassium, and the peak you did not expect Analytics › Mass spectrometry LC-MS MALDI-TOF mass error (ppm) Wiki Adducts: sodium, potassium, and the peak you did not expect Writing it up because I had to work it out twice and would rather nobody else did. Adducts keeps being re-asked here and I think that is because the…	+70	77	3.5k	15mo
When to suspect the method rather than the sample Analytics › Method validation recovery stability-indicating method linearity system suitability Solved When to suspect the method rather than the sample — that is the question, and I have not found it answered plainly anywhere I have looked. Two reports on the same lot, and I would like help deciding whether…	+109	115	63k	15mo