How do you qualify a working (secondary) reference standard against a pharmacopoeial standard?

Start from a high-purity batch that meets the monograph. Under a pre-approved protocol, confirm identity against the pharmacopoeial standard, assay it against that standard in replicate by the pharmacopoeial method, and assign the mean, with its basis, as its content. Cross-check the value by mass balance. Approve it before first use and requalify it on a written schedule. WHO’s guideline for official secondary standards requires recalibration when the primary lot changes; India’s guidance says re-validation uses only the new lot.

Working standard qualification: protocol, potency, CoA

1Primary, secondary and working standards.

Qualification proves the value a working standard borrows from a primary.

Table 1. Three kinds of reference standard.

Term	What it is	Where its value comes from
Primary standard	A pharmacopoeial or other official standard of high purity¹	Accepted “without requiring comparison with another chemical substance”²
In-house primary	Made when no official standard exists (ICH Q7 11.18)¹	Testing to “establish fully the identity and purity”¹
Secondary or working	Of “established quality and purity, as shown by comparison to a primary reference standard”¹	Calibration against a primary

Neither USP nor the Ph. Eur. gives a qualification procedure. USP “does not provide guidance on the qualification or use of non-USP secondary reference standards, including in-house standards”, and EDQM calls it “beyond the scope of the Ph. Eur.”.³ ⁴

Table 2. Where the requirements sit.⁵ ⁶ ⁷ ⁸ ¹ ⁹ ¹⁰

Rulebook	What it requires	Where
US	Complete records of standardisation; each new batch “qualified/calibrated against the current reference standard”	21 CFR 211.194(c); FDA 2015 guidance, V
EU, UK, PIC/S	Traceability to primaries demonstrated and documented; compendial standards preferred as primaries	EU GMP 6.19 to 6.22; PIC/S PE 009-18, same numbers
APIs (ICH Q7)	Each batch compared with a primary before first use, then requalified under a written protocol	Q7 11.17 to 11.19, reflected in EU GMP Part II
India	Standardised against an official standard, when available, “initially and at regular intervals thereafter”	Schedule M (G.S.R. 922(E), 28 December 2023), Part I, 15.7

Part 211 mentions reference standards only in 211.194(c), and MHRA points to EudraLex Volume 4.¹¹ ¹² Two guidance texts add methods: India’s non-mandatory GD-09 (1 June 2022) and WHO’s 2007 procedure for official secondary standards, which manufacturers can “in principle” follow.¹³ ¹⁴

2Qualification protocol template.

Name one person responsible for standards (TRS 1052, 5.76; Schedule M 15.4).² ¹⁰ Fix the replicates and criteria before testing (TRS 943, B.4.3).¹⁴ Criteria are examples; the last column gives the requirement.

Table 3. A working-standard qualification protocol.¹⁴ ¹ ⁷ ⁵ ³ ¹³

Step	What to do	Example criterion	Requirement
Source batch	Meets the monograph, low in impurities and water, enough for the planned life	Meets every monograph test	WHO 943 B.2.1, B.2.3
Primary standard	The pharmacopoeial lot, with an assigned value for quantitative use	Valid on the day; value on label or certificate	EU GMP 6.20; USP FAQs 12, 22
Identity	IR spectrum recorded beside the primary’s; HPLC retention time	Spectra concordant	ICH Q7 11.19; WHO 943 A.4.1
Assay vs primary	Pharmacopoeial method: six weighings of the candidate, two of the primary	RSD not more than 1.0%; the two primary preparations agree within 99.0 to 101.0%	WHO 943 B.4.3; IPC GD-09
Impurities	Related substances by HPLC, water by Karl Fischer in triplicate, solvents by GC, residue on ignition	Within limits; totals reported	WHO 943 A.3.3
Mass balance	(100 − water − solvents − residue) × (100 − related substances) ÷ 100	Within 0.5 points of the assay mean	WHO 943 A.3.3
Assigned value	Mean assay against the primary, one decimal, basis stated, 95% confidence interval	Half-width not more than 0.3 points	WHO 943 B.4.3, A.6.4
Subdivision	Single-use vials, kept cool and dry	Every vial marked with the ID	WHO 943 A.6.2, B.6; WHO 1052 5.77
Review and approval	Analyst signs, a second person reviews, an authorised approver approves	All raw data attached	21 CFR 211.194(a)(7), (a)(8), (c); ICH Q7 11.19
Retest programme	Interval, tests and the largest allowed change from the assigned value	Re-establish if beyond 0.5 points	WHO 943 B.6; ICH Q7 11.19

GD-09 also sets an injection sequence, and stops the run if the primary preparations disagree or system suitability fails.¹³

3Example: assigning a value to WS-318-26-01.

Invented example: API-318 hydrochloride, primary lot RS-7 and every number are made up.

Batch 26-104 meets the monograph. Primary lot RS-7 is labelled 99.6% as is and was current on the test day, 8 October 2026.

3.1Assay against the primary.

The two primary preparations give 49,872.5 and 49,891.4 area units per mg, a correlation of 99.96%. Their mean, R, is 49,882.0. All solutions are diluted alike.

Table 4. Example. Six weighings of the candidate against primary lot RS-7.

Preparation	Weight (mg)	Peak area	Content (% as is)
WS-1	25.34	1,256,600	99.02
WS-2	24.97	1,243,200	99.41
WS-3	25.23	1,252,800	99.15
WS-4	25.08	1,243,000	98.96
WS-5	24.89	1,237,800	99.30
WS-6	25.15	1,250,000	99.24
Mean			99.18

Content = (area ÷ weight) ÷ R × 99.6. For WS-1: (1,256,600 ÷ 25.34) ÷ 49,882.0 × 99.6 = 99.02%. The standard deviation is 0.17, an RSD of 0.17%. The 95% confidence interval is 99.18 ± 2.571 × 0.17 ÷ √6, where 2.571 is the two-sided 95% t value for five degrees of freedom (six results less one): 99.18 ± 0.18%, or 99.00 to 99.36%. Both pass.

3.2Mass balance check.

The candidate has 0.45% water (Karl Fischer), 0.08% ethanol (800 ppm, GC), 0.05% residue on ignition and 0.32% related substances (HPLC). Mass balance = (100 − 0.45 − 0.08 − 0.05) × (100 − 0.32) ÷ 100 = 99.42 × 0.9968 = 99.10%. The assay mean is 0.08 points higher, inside the 0.5-point limit, so WS-318-26-01 is assigned 99.2% as is.

Purity is a factor in GD-09’s assay formula, so a value 0.5 points high makes every sample read about 0.5% high.¹³ Convert a primary value given on the anhydrous or dried basis first: see potency adjustment. Because WS-318-26-01 comes from production Batch 26-104, it should not be the system suitability standard when Batch 26-104 is tested (FDA Q&A 16).¹⁵

4Working-standard CoA and label.

WHO lists “the certificate of calibration or analysis” among each secondary standard’s records (TRS 1052, 5.78).² The middle column is the example. More in certificate of analysis.

Table 5. A working-standard certificate, with the example’s entries.² ¹⁴ ⁷ ¹ ⁵

Field	Example entry	Requirement
Name and ID	API-318 hydrochloride working standard WS-318-26-01; a new ID for each batch	WHO 1052 5.77
Source and use	Batch 26-104; assay and identification by the monograph methods	WHO 1052 5.78; EU GMP 6.20
Primary standard	Lot RS-7, 99.6% as is, valid on 8 October 2026	EU GMP 6.20; WHO 943 B.4.5
Assay vs primary	99.18%, n = 6, RSD 0.17%, 95% interval 99.00 to 99.36%	WHO 943 B.4.3
Other tests	IR concordant with RS-7; related substances 0.32%; water 0.45%; ethanol 800 ppm; residue 0.05%; mass balance 99.10%	ICH Q7 11.19; 21 CFR 211.194(c); WHO 943 A.3.3
Assigned value	99.2% as is	WHO 943 A.6.4
Storage	2 to 8 °C in single-use vials, protected from moisture	WHO 943 A.6.2, A.6.4
Dates	Approved 15 October 2026; retest by 14 October 2027	WHO 1052 5.78; ICH Q7 11.19
Approval	Analyst, reviewer and approver, each dated; report QR-318-26-01	21 CFR 211.194(a)(7), (a)(8), (c)

Mark each vial with its ID (TRS 1052, 5.77), the preparation and opening dates and the preparer’s signature (EU GMP 6.21).² ⁷ Schedule M’s label adds the batch or lot and control number, shelf-life, potency and storage conditions (15.6).¹⁰

5Biological working reference standards.

Biologics use two tiers. An in-house primary, “prepared from lot(s) representative of production and clinical materials”, should exist at filing; working reference material is calibrated against it, and reference materials against an international or national standard where one is available and appropriate (ICH Q6B 2.2.1).¹⁶ FDA recommends the two tiers “to prevent drift in the quality attributes” (2015 guidance, V).⁶ For each new lot:

Make it like the primary: Q6B’s working reference material is “prepared similarly to the primary reference material”.¹⁶
Characterise it by “routine and beyond routine release testing as described in ICH Q6B”, considering orthogonal methods for potency, purity and impurities (2015 guidance, V).⁶
Assign potency in units of activity against the in-house primary (Q6B 2.1.2), from independent bioassay runs whose number is set by the method’s observed variability. The 483 quoted below faulted a replicate count the variability did not support (observations 2a, 2b).¹⁶ ¹⁷ Mass balance cannot assign units: USP’s own mass balance approach excepts biological standards that “define the Unit of Activity”.³
Requalify it and test its stability under protocols that match the application; a lot qualified after filing follows an FDA-approved protocol and is reported (CP 7346.832M, III.1.A(5)(e)).¹⁸
Report each later lot’s qualification in the annual report (2015 guidance, V).⁶

CP 7346.832M covers CDER-regulated protein products (footnote 2), not CBER’s cell and gene therapies or vaccines.¹⁸ ¹⁹ The 2015 guidance applies to all BLAs. Its line that some products must be released with CBER-authorised standards cites 21 CFR 610.20, which FDA removed in 2016, finding the listed preparations obsolete, unavailable or “described on a product specific basis in BLAs”.⁶ ²⁰

6How long a working standard stays valid.

ICH Q7 and WHO set no period. Q7 asks for periodic requalification “in accordance with a written protocol” (11.19), and WHO ties the interval to the substance’s stability, storage, container and how often it is opened (TRS 1052, 5.80).¹ ² GD-09 allows up to 12 months, extendable on those factors, no more than a month’s use of any vial, and single-use vials for hygroscopic or unstable material.¹³

Some events force a retest early.

The primary lot is replaced. WHO’s guideline for official secondary standards says the secondary “must be recalibrated against the new batch of the primary reference substance” (TRS 943, B.6), and GD-09 says re-validation uses only the new lot.¹⁴ ¹³ ICH Q7, EU GMP chapter 6 and Part 211 do not name this trigger. Recalibrate while the old lot is valid: USP gives a previous lot a valid use date “typically 3-12 months from the date of depletion”, and EDQM generally 6 months.³ ²¹
The assay or related substances test changes substantially (GD-09).¹³
A retest fails. Check the tests run with the standard since its last retest (GD-09), and assess them by risk (TRS 1052, 5.80).¹³ ²
It discolours. WHO says replace it “whether or not the results of subsequent analyses indicate significant degradation” (TRS 943, A.6.3).¹⁴
The source batch’s retest date passes. That date rests on stability data (ICH Q7 11.61), and GD-09 keeps any reassigned validity within the material’s expiry date.¹ ¹³

7Judgement calls.

7.1Assay against the primary, or mass balance?

WHO calls the pharmacopoeial method “essential” for assigning a secondary standard’s value (TRS 943, B.4.3); USP assigns its own standards by mass balance, because assaying against a previous lot “inherently causes greater variability and less precision”.¹⁴ ³ Calibration gives the traceability EU GMP 6.20 asks for, and mass balance catches a degraded primary vial or a weighing error.⁷ Run both, assign one, and fix the agreement limit in advance.

7.2A result above 100%.

GD-09 says an assay above 100.0% “shall be considered and reported as 100.0%w/w”, except for biological standards, which caps the number but explains nothing.¹³ A calibrated 100.3% on a batch with 0.5% impurities is not credible, because water, solvents, inorganic and organic content should total 100% (TRS 943, A.3.3): check the primary’s value and basis, the weighings and the replicate spread.¹⁴ Never assume 100% for the primary either: USP says “A value of 100.0% cannot be assumed for any USP RS without an assigned value”, and EDQM allows it only for impurity standards in related substances tests.³ ²²

7.3A compendial standard for an in-house method.

Calibrating a working standard against a pharmacopoeial standard, by the monograph’s assay, is a use WHO endorses (TRS 1052, 5.75; TRS 943, B.4.3).² ¹⁴ Using the compendial standard in a non-monograph method, or for an attribute its monograph does not cover, is different. EU GMP expects the national competent authority’s authorisation (6.20), and Schedule M says official standards “shall only be used for the purpose described in the appropriate monograph” (15.3).⁷ ¹⁰ WHO discourages such use and leaves it “at the user’s discretion, based on a risk assessment” (TRS 1052, 5.79), and USP puts “the suitability of the RS for a non-USP use” on the user.² ³ Failing that, characterise an in-house primary (ICH Q7 11.18).¹

7.4Other decisions.

Table 6. Other decisions, and the rule behind each.¹⁴ ³ ¹⁵ ⁷

Situation	What to do	Source
Doubtful or disputed result	Repeat with the primary (WHO); for a USP test, only results with the specified USP RS “are conclusive”	WHO 943 introduction; USP FAQ 4
Bought-in secondary	A supplier’s new batch “should be qualified against the primary reference standard”	FDA Q&A 16; EU GMP 6.20
New primary lot	Recheck the basis; USP says it can change between lots	USP FAQ 24

For an out-of-specification result, start with the OOS investigation.

8What inspectors check.

A pre-approval inspection audits the raw data behind the application (CP 7346.832, Objective 3), which should include “qualification test reports and certificates of analysis” for its standards (2015 guidance, V).²³ ⁶ Have these ready:

The qualification report, with raw data and chromatograms, signed and second-person reviewed (21 CFR 211.194(a)(7), (a)(8), (c)).⁵
The primary lot used, proof that it was valid on the test date (USP FAQ 12; EDQM), and records of its own storage and use (ICH Q7 11.17).³ ²¹ ¹
The register entry with the certificate of calibration (TRS 1052, 5.78), and the use log (GD-09).² ¹³
Worksheets quoting the standard’s ID and validity at every use (TRS 1052, 5.77) and cross-referencing its preparation and testing (ICH Q7 6.60).² ¹
System suitability run with a qualified standard, never one from the batch being tested (FDA Q&A 16).¹⁵
The requalification trend, with a root cause for any drift (the 483 below, observation 2c).¹⁷

“Additionally, you failed to determine the suitability of each secondary reference standard against a primary reference standard. For example, you continued to use your 2021 standard for (b)(4) that was never qualified against an official reference standard.” Flowchem Pharma Private Limited, warning letter, 11 March 2026 ²⁴

“Accumulation of (b) (4) requalifications of the (b) (4) standard caused by requalification against itself has accumulated into an underestimated value of the (b) (4) reference standard vs. the true value when calibrated against the WHO standard.” Samsung Biologics Co., Ltd., Form FDA 483, 28 February 2023 ¹⁷

9What has changed since 2024.

WHO’s laboratory guide (TRS 1052, Annex 4, 26 April 2024) revised the 2010 text. It now names pharmacopoeial standards as the primaries against which a manufacturer’s “secondary (working) reference substances can be calibrated” (5.75), and worksheets quote each standard’s validity, not only its ID (5.77).² ²⁵
On 14 April 2026 FDA issued 7346.832M, its pre-approval programme for CDER-regulated biologics, with the checks above.¹⁸
In February 2025 WHO consulted on whether its 2007 reference substance guideline needs revising (QAS/25.972), planning revised drafts for 2026.²⁶ On 8 November 2026 its consultation page still listed only that document: the 2007 text stands.²⁷

10How it runs in Seal.

In Seal, a working standard is a record rather than a logbook line. Its standards and reagents record keeps the source lot, the qualification against a named primary standard, and the assigned value with its unit, basis, uncertainty and effective date, alongside every aliquot, preparation and test use. Test calculations resolve the value in effect at the time of use, so analysts don’t retype potency from a certificate, and configured checks can block an ineligible container before it enters a preparation.

A replacement lot follows a bridging protocol that sets comparators, replicates and acceptance, and observed bias and trends stay visible after the bridge. When a finding such as degradation, a mislabel or a wrong assigned value comes later, it traces forward through aliquots and preparations to the tests, batches, stability studies and certificates that depended on it. In the QC laboratory, standards keep their lot, potency, expiry and storage, and calculations record their inputs.

References

1ICH Q7, Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients, ICH, Step 4, 10 November 2000, sections 6.60, 11.17 to 11.19 and 11.61, and glossary. https://database.ich.org/sites/default/files/Q7%20Guideline.pdf (read 8 November 2026)
2WHO good practices for pharmaceutical quality control laboratories, WHO Technical Report Series No. 1052, Annex 4, WHO, 26 April 2024, glossary and sections 5.74 to 5.81. https://cdn.who.int/media/docs/default-source/medicines/norms-and-standards/guidelines/quality-control/trs1052_annex4.pdf (read 8 November 2026)
3FAQs: Reference Standards, questions 2, 4, 12, 22, 23 and 24, USP. https://www.usp.org/frequently-asked-questions/reference-standards (read 8 November 2026)
4Where can I find advice on how to establish in-house standards, secondary standards and/or working standards?, EDQM FAQs, EDQM. https://faq.edqm.eu/pages/viewpage.action?pageId=23953769 (read 8 November 2026)
521 CFR 211.194, Laboratory records, paragraphs (a)(7), (a)(8) and (c), eCFR. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-C/part-211/subpart-J/section-211.194 (read 8 November 2026)
6Analytical Procedures and Methods Validation for Drugs and Biologics, Guidance for Industry, FDA, July 2015, sections I and V, and footnotes 1 and 13. https://www.fda.gov/media/87801/download (read 8 November 2026)
7EudraLex Volume 4, Part I, Chapter 6: Quality Control, European Commission, in operation from 1 October 2014, sections 6.19 to 6.22. https://health.ec.europa.eu/system/files/2016-11/2014-11_vol4_chapter_6_0.pdf (read 8 November 2026)
8PIC/S GMP Guide PE 009-18, Part I, PIC/S, 24 September 2026, sections 6.19 to 6.22. https://picscheme.org/docview/11332 (read 8 November 2026)
9EudraLex Volume 4, Part II: Basic Requirements for Active Substances used as Starting Materials, European Commission, 13 August 2014, in operation from 1 September 2014, sections 1 and 11.19. https://health.ec.europa.eu/document/download/bd537ccf-9271-4230-bca1-2d8cb655fd83_en?filename=2014-08_gmp_part1.pdf (read 8 November 2026)
10Schedule M, Good Manufacturing Practices and Requirements of Premises, Plant and Equipment for Pharmaceutical Products, substituted by G.S.R. 922(E), Ministry of Health and Family Welfare, Gazette of India, 28 December 2023, Part I, sections 15.3 to 15.7. https://cdsco.gov.in/opencms/resources/UploadCDSCOWeb/2018/UploadGazette_NotificationsFiles/2023.12.28_DR_Final%20G.S.R.%20922%28E%29_Notification%20of%20Schedule%20M%20of.pdf (read 8 November 2026)
1121 CFR Part 211, Current Good Manufacturing Practice for Finished Pharmaceuticals, eCFR, full text searched for “reference standard”. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-C/part-211 (read 8 November 2026)
12Medicines: good manufacturing practice and good distribution practice, MHRA, last updated 13 May 2024, section Overview. https://www.gov.uk/guidance/good-manufacturing-practice-and-good-distribution-practice (read 8 November 2026)
13Guidance Document: Indian Pharmacopoeia Reference Substances, IPC/GD/09, version 1.0, Indian Pharmacopoeia Commission, 1 June 2022, non-mandatory guidance, section Working Standards. https://www.ipc.gov.in/images/GD-09-IP_Reference_Substances.pdf (read 8 November 2026)
14WHO general guidelines for the establishment, maintenance and distribution of chemical reference substances, WHO Technical Report Series No. 943, Annex 3, WHO, 2007, introduction, Part A sections A.3 to A.6 and Part B. https://www.who.int/publications/m/item/trs943-annex3 (read 8 November 2026)
15Questions and Answers on Current Good Manufacturing Practice Requirements: Laboratory Controls, question 16, FDA, 12 August 2019. https://www.fda.gov/drugs/guidances-drugs/questions-and-answers-current-good-manufacturing-practice-requirements-laboratory-controls (read 8 November 2026)
16ICH Q6B, Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products, ICH, Step 4, 10 March 1999, sections 2.1.2 and 2.2.1, and glossary. https://database.ich.org/sites/default/files/Q6B%20Guideline.pdf (read 8 November 2026)
17Form FDA 483, Samsung Biologics Co., Ltd., FEI 3010479596, FDA CBER, inspection 20 to 28 February 2023, issued 28 February 2023, observation 2. https://www.fda.gov/media/177862/download (read 8 November 2026)
18Compliance Program 7346.832M, Prelicense and Preapproval Inspections of CDER-Regulated Biological Product Manufacturers, FDA, issued 14 April 2026, remarks, footnote 2 and Part III.1.A(5)(e). https://www.fda.gov/media/191983/download (read 8 November 2026)
19CBER Product Jurisdiction, FDA, content current as of 13 March 2025. https://www.fda.gov/about-fda/center-biologics-evaluation-and-research-cber/cber-product-jurisdiction (read 8 November 2026)
20Standard Preparations, Limits of Potency, and Dating Period Limitations for Biological Products, direct final rule, 81 FR 26687, FDA, Federal Register, 4 May 2016, effective 16 September 2016, sections I.B and III.A. https://www.federalregister.gov/documents/2016/05/04/2016-10385/standard-preparations-limits-of-potency-and-dating-period-limitations-for-biological-products (read 8 November 2026)
21How can I find out the expiry date of an EDQM reference standard?, EDQM FAQs, EDQM. https://faq.edqm.eu/pages/viewpage.action?pageId=1377133 (read 8 November 2026)
22Where can I find the content assigned to a reference standard used in an assay?, EDQM FAQs, EDQM. https://faq.edqm.eu/pages/viewpage.action?pageId=1377135 (read 8 November 2026)
23Compliance Program 7346.832, Preapproval Inspections, FDA, issued 29 June 2026, Part II, Objective 3. https://www.fda.gov/media/193382/download (read 8 November 2026)
24Warning letter 320-26-51, Flowchem Pharma Private Limited, MARCS-CMS 720719, FDA, 11 March 2026. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/flowchem-pharma-private-limited-720719-03112026 (read 8 November 2026)
25WHO good practices for pharmaceutical quality control laboratories, WHO Technical Report Series No. 957, Annex 1, WHO, 2010, section 11. https://www.who.int/publications/m/item/trs957-annex1 (read 8 November 2026)
26WHO General guidelines for the establishment, maintenance and distribution of chemical reference substances, draft working document QAS/25.972, WHO, February 2025. https://cdn.who.int/media/docs/default-source/medicines/norms-and-standards/current-projects/2025-02-25-referencesubstances-qas25-972.pdf (read 8 November 2026)
27Working documents in public consultation, Norms and standards for pharmaceuticals, WHO. https://www.who.int/teams/health-product-and-policy-standards/standards-and-specifications/pharmaceuticals/working-documents-public-consultation (read 8 November 2026)

AQuestions and answers

Can a working standard be qualified against another working standard?

Not to assign its value. ICH Q7 asks for each batch of secondary standard to be compared with a primary standard before first use. Each comparison against an earlier working standard carries that standard’s error forward, and an FDA inspection found a manufacturer whose standard drifted low after repeated requalification against itself. If no official primary exists, establish an in-house primary and calibrate working standards against it.

Is a working standard the same as a secondary standard?

Usually, yes. Both name a standard whose value comes from comparison with a primary standard, and WHO writes secondary (working) reference substances as one term. Some procedures add a tier below, qualifying working standards against a secondary. That extra link is hard to defend when assigning a value, because ICH Q7 expects each batch to be compared with a primary.

What is the difference between a working standard and a stock standard?

They come from different vocabularies. A working standard is a reference material: a batch of solid substance qualified against a primary standard and given an assigned content. A stock standard is a concentrated solution weighed out from a reference standard, and working standard solutions are its dilutions at the concentration the method uses. A solution made from a working standard carries its own preparation date and preparer, and is used within the period the method’s solution stability data support.

Does a standard used only for identification need full qualification?

It needs less. India’s pharmacopoeia commission says the 99.0% purity desirable for an assay standard may not be necessary where the procedure is not very selective, as in identification tests, system suitability tests and peak markers, and WHO accepts good-quality production material of acceptable purity for identification. Identity must still be shown against the official standard or spectrum and documented. USP itself assigns no value to standards with only qualitative uses.

Can a certified reference material be used instead of a pharmacopoeial standard?

Where an official standard exists, only with justification. EU GMP prefers compendial standards as primaries unless fully justified, India’s Schedule M says official standards shall be used whenever they exist, and in a dispute USP treats only results obtained with the specified USP standard as conclusive. Where none exists, a certified reference material can be the starting material for an in-house primary, tested to establish its identity and purity fully, as ICH Q7 asks.

Does a working standard need a certificate of analysis?

It needs a record that does the same job. US CGMP requires complete records of the testing and standardisation of reference standards, and WHO lists a certificate of calibration or analysis among the records kept for each secondary standard. A certificate that summarises the primary used, the results, the assigned value, storage and dates does that job in one place.