🍎 Potassium iodide in salt (sodium chloride) — photocolorimetric method: iodides are oxidised with bromine to iodates, excess bromine is bound with phenol, the iodates are converted to iodine in an acidic medium, and the iodine is determined as the blue complex with starch at 590 nm; PN-C-84081-35:1980 (withdrawn standard)

Food chemistry PN-80/C-84081.35

Overview

WHAT THE STANDARD COVERS. The "Scope" field of the PKN card, in full: "A method has been established consisting in the oxidation of iodides with bromine to iodates, binding of the excess bromine with phenol and conversion of the iodates into iodine in an acidic medium, followed by photocolorimetric determination of the iodine in the form of the blue complex with starch at a wavelength of 590 nm. The apparatus, reagents, method of preparing the standard solutions and the calibration curve are given. The precision of the method is specified" (our translation; no full stop at the end on the card). We did not have the text of the standard (2 pages).

STATUS (cards as of 13.10.2026). The card of PN-C-84081-35:1980 (Polish version) bears the heading "Withdrawn": publication 10-06-1980, "Withdrawal date: 30-09-2011", 2 pages, price group A, Chemistry Sector, technical body RS SCH (Sector Council of the Chemistry Sector), "Replaces: PN-G-92002:1954 - Polish version", ICS 71.060.50; there is no "Replaced by" field. The sheet belongs to the PN-C-84081 series "Salt (sodium chloride)"; sheet 00 "General provisions and scope of the standard" (with a list of the sheets and requirements for the purity of reagents) was withdrawn on the same day, 30-09-2011. The PKN search under "PN-C-84081" (12.10.2026) returns 45 items of the series; only PN-C-84081-1:1999 "Salt (sodium chloride) — Classification and designation" has no withdrawal note. The neighbouring sheet PN-C-84081-34:1980 "Determination of potassium iodide content by the iodometric method" has also been withdrawn. We do not name a standard that would replace this sheet.

IN THE REGULATION. Regulation of the Minister of Health of 13 March 2024 on fortifying substances added to food (Journal of Laws 2024 item 420; status "in force" in the Sejm ELI database, entry into force 04.04.2024, amended by the regulation of 16 March 2026, Journal of Laws 2026 item 371, which does not concern the provision on salt), § 2 point 2: to salt intended for direct human consumption "potassium iodide or potassium iodate is added, so that 100 g of table salt contains 2.3 (±0.77) mg of iodine, which corresponds to 30 (±10) mg of potassium iodide or 39 (±13) mg of potassium iodate per 1 kg of table salt" (our translation). The regulation does not specify a method of determination.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database from the production server, refreshed on 12.10.2026). Number 84081-35 appears in 8 records at 8 laboratories; in the current PCA documents (read on 12–13.10.2026; issues from 24.11.2025 — AB 451, AB 562 — to 21.08.2026 — AB 552) — in 8 rows at the same laboratories; a search of all downloaded PCA documents found no laboratories outside the database copy, no row with the number is set in bold italics, and no pages are repeated in any document. Notations: "PN-80/C-84081.35" — 5 laboratories (AB 451, AB 515, AB 537, AB 539, AB 552); "PN-C-84081.35:1980" — 3 (AB 343, AB 486, AB 562). The "Laboratories" tab looks for notations BEGINNING with the search term: "PN-80/C-84081.35" — 5 laboratories, "PN-C-84081.35" — 3 — checked with the tab query on the labcoda.pl production server on 13.10.2026; this page searches with "PN-80/C-84081.35", so the tab shows 5 of the 8 laboratories.

WHAT THE LABORATORIES TEST (database copy and PCA documents). Test object: salt — AB 486, AB 537, AB 539; salt (sodium chloride) — AB 343, AB 451; salt intended for human consumption — AB 515; table salt — AB 552; edible salt — AB 562. Characteristic: potassium iodide content; potassium iodate calculated — AB 343, AB 515 (also iodine), AB 537, AB 562. Technique: spectrophotometric method — all. Potassium iodide ranges: 3.3–52.3 mg/kg — AB 562; 3.3–65.4 mg/kg — AB 515; 5.0–750 mg/kg — AB 552; 5.2–65.0 mg/kg — AB 539; 6.54–100.00 mg/kg — AB 343; 8–65 mg/kg — AB 537; 10–100 mg/kg — AB 486; 0.0006–0.0065 % (i.e. 6–65 mg/kg) — AB 451.

ALONGSIDE THIS STANDARD. No other document stands in the entries with this standard. Iodine in salt is determined by 16 laboratories in the database copy (entries with iodine in the test description or parameters and with salt or sodium chloride as the test object): this standard is cited by 8, sheet PN-C-84081-34 (iodometric method) by 3 (AB 438, AB 509, AB 601), PN-EN 15111:2008 by AB 545, in-house procedures by AB 311, AB 435, AB 486 (alongside this standard, in another entry), AB 519, AB 520.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — form of the result: the regulation gives the same iodine content as 30 (±10) mg of potassium iodide or 39 (±13) mg of potassium iodate per kilogram of salt, while the standard — according to its title — determines potassium iodide; four laboratories calculate potassium iodate from the result, one also iodine — when comparing with the regulation, the same form (iodine, iodide or iodate) must be compared: the regulation requires 20–40 mg of potassium iodide or 26–52 mg of potassium iodate per kilogram of salt (the lower limits of the laboratories' ranges are from 3.3 to 10 and the upper limits from 52.3 to 750 mg/kg of iodide — each range covers this interval). Second — status: the sheet has been withdrawn since 2011 without a successor being named, as have the neighbouring iodometric sheet and the general provisions of the series. Third — tab: because of the two notations of the number, the "Laboratories" tab of this page shows 5 of the 8 laboratories.

WHAT WE DO NOT GIVE. We did not have the text of the standard — we do not give the sample mass, the concentrations of bromine, phenol and starch, the preparation of the standard solutions and the calibration curve, or the precision. We do not state how the method behaves with salt iodised with potassium iodate — the card does not say.

Method principle

Iodides from the salt sample are oxidised with bromine to iodates, excess bromine is bound with phenol, the iodates are converted to iodine in an acidic medium, and the iodine is determined photocolorimetrically as the blue complex with starch at a wavelength of 590 nm, using a calibration curve (PKN card). WE DO NOT GIVE concentrations or details — we did not have the text of the standard.

Applications

• Salt (sodium chloride), table salt and edible salt — potassium iodide content (withdrawn sheet in the current accreditation scopes of 8 laboratories)
• Control of the iodisation of salt intended for direct consumption — 30 (±10) mg of potassium iodide or 39 (±13) mg of potassium iodate per 1 kg (Journal of Laws 2024 item 420, § 2 point 2)

Key parameters

Standard

Standard number

PN-C-84081-35:1980

Title (PL)

Sól (chlorek sodowy) — Oznaczanie zawartości jodku potasowego metodą fotokolorymetryczną

Title (EN)

Salt (sodium chloride) — Determination of potassium iodide content by the photocolorimetric method

Step-by-step procedure

1. Oxidation of iodides

   Iodides are oxidised with bromine to iodates (PKN card). PN-C-84081-35:1980 withdrawn on 30-09-2011 (card as of 13.10.2026).

2. Removal of excess bromine

   Excess bromine is bound with phenol (PKN card).

3. Liberation of iodine

   The iodates are converted to iodine in an acidic medium (PKN card).

4. Measurement and result

   Blue iodine–starch complex at 590 nm, calibration curve (PKN card); result as potassium iodide, when comparing with the regulation the same form (iodine, KI or KIO3).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Bromine and phenol — safety rules of a chemical laboratory and the safety data sheets of the substances
• SUBJECT-MATTER NOTE: the regulation also gives the iodine content as potassium iodide or potassium iodate — the numbers in these forms are different

Frequently asked questions