🍎 Sulphur dioxide in fruit and vegetable products — iodometric (routine) and distillation (reference) method, PN-A-75101-23

Food Chemistry PN-90/A-75101/23

Overview

WHAT THE STANDARD COVERS. The scope from the PKN catalogue card, quoted in full: "Two methods of determination are established: iodometric and distillation. The iodometric method is the routine method. It consists in determining the content of free sulphur dioxide and then of bound sulphur dioxide by direct titration with iodine solution. The distillation method is the reference method and consists in releasing sulphur dioxide from the sample with hydrochloric acid, distilling it off and collecting it in a 3(m/m) hydrogen peroxide solution, and then determining the sulphuric acid formed by titration with a standard sodium hydroxide solution. Contains 2 figures: apparatus for titration of dark liquids and distillation set." The notation "3(m/m)" stands on the card without a percent sign. The reference method is the one whose result decides when a result of the routine method is disputed. Amendment Az2:2002 according to its own card: "The wording in point b) of chapter 1 of standard PN-90/A-75101.23 […] was changed" — what this point concerns, the card does not say.

STATUS (state of the cards on 28 September 2026). The card of the standard carries the heading "Withdrawn" and the withdrawal date 02-12-2011; there is no "Superseded by" field. "Supersedes: PN-A-75022:1962, PN-A-75108:1986"; "Introduces: ISO 5521:1981 [EQV], ISO 5522:1981 [IDT], ISO 5523:1981 [IDT]". Edition: published 24-05-1990, 4 pages, PKN technical committee KT 38 (Fruit and Vegetable Products), ICS 67.080.01. Amendment PN-A-75101-23:1990/Az2:2002: published 10-12-2002, 1 page, heading "Withdrawn", withdrawal date 02-12-2011. The PKN search for "PN-A-75101-23" shows only these two cards — the catalogue has no amendment Az1 to this sheet, although AB 486 writes "+Az1:2002 + Az2:2002".

EUROPEAN STANDARDS FOR SULPHITES IN FOOD. The PKN catalogue contains two valid parts of PN-EN 1988 (both cards without the heading "Withdrawn" and without a withdrawal date, read on 29 September 2026): PN-EN 1988-1:2001 "Foodstuffs — Determination of sulphite — Part 1: Optimized Monier-Williams method" — according to the card "a distillation method for determining the sulphite content, expressed as sulphur dioxide content, in foodstuffs containing not less than 10 mg/kg of sulphite" (introduces EN 1988-1:1998) — and PN-EN 1988-2:2001 "Part 2: Enzymatic method" (introduces EN 1988-2:1998). The card of PN-A-75101-23 indicates neither of them as a successor. Four of the 19 laboratories citing this standard also have PN-EN 1988-1:2001 in their scope: AB 519 for dried fruit (10–4460 mg/kg), AB 540 for fruit and vegetable products (5.0–3000 mg/kg or mg/l — a lower limit below the 10 mg/kg of the PN-EN 1988-1 card), AB 565 for mushrooms, vegetables and fruit and their products (10–2300 mg/kg or mg/l) and AB 583 together with its own procedure (10–100 mg/kg).

REGULATION: THE LABELLING THRESHOLD. Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex II ("Substances or products causing allergies or intolerances"), point 12: "Sulphur dioxide and sulphites at concentrations of more than 10 mg/kg or 10 mg/litre in terms of the total SO2 which are to be calculated for products as proposed ready for consumption or as reconstituted according to the instructions of the manufacturers". Point 12 has not been amended: of the five acts amending the regulation (list from the CELLAR database of the EU Publications Office, read on 29 September 2026), two amend Annex II — Delegated Regulation (EU) No 78/2014 (point 1) and (EU) 2024/2512 (point 10). The threshold refers to the product ready for consumption or reconstituted according to the manufacturer’s instructions — a result for a concentrate or a dried product has to be related to that. The regulation does not specify a method.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17 September 2026, read on 28 September 2026). All records of number 75101 with sheet 23: 28 entries at 19 laboratories. The "Laboratories" tab searches for records BEGINNING with "PN-90/A-75101/23" and will show 12 laboratories in 20 entries. It will not show the other seven: AB 343, AB 519, AB 583 and AB 601 (form "PN-A-75101-23:1990"; AB 343 in its second entry "PN-A-75101/23:1990"), AB 379 and AB 486 ("PN-A-75101.23:1990") and AB 565 ("PN-90/A-75101.23"). 13 laboratories add amendment Az2:2002. Current scopes on the PCA website (read on 29 September 2026, issues from 3 November 2025 to 1 September 2026): all 28 entries stand in the valid issues with the same range as in the copy, and none is suspended.

WHICH OF THE TWO METHODS. Clause 3 of the standard is cited by eight laboratories (AB 343, AB 381, AB 438, AB 515, AB 521, AB 560, AB 562, AB 601), clause 2 by AB 451 and AB 521 (for vinegar only), and AB 519 cites the standard "excluding clause 2.3.a and 3". AB 343 writes "Distillation method" next to clause 3 in one of its entries — so the scopes indicate that clause 3 is the distillation method and clause 2 the iodometric one; we did not have the text of the standard and cannot confirm this numbering otherwise. Nine laboratories cite the standard without a clause number: AB 370 ("Titrimetric method (after distillation)"), AB 379, AB 444 and AB 583 ("distillation-titrimetric") and AB 079, AB 486, AB 528, AB 540 and AB 565 ("Titrimetric method"). Both methods end with a titration, so for the last five the scope does not show which method is used to determine sulphur dioxide.

TEST OBJECTS AND RANGES. The title of the standard speaks of fruit and vegetable products; in their scopes the laboratories also apply it to vinegar (AB 451, AB 521, AB 540, AB 560), mustards and sauces (AB 343, AB 451, AB 521, AB 560), alcoholic beverages (AB 343, AB 451, AB 565), fish and seafood (AB 438, AB 451), spices and herbs (AB 438, AB 451, AB 540), confectionery (AB 343, AB 451, AB 540), cereal products (AB 540), and AB 381 to gelatine, starch, potato flour and desiccated coconut. Lower limits: from 1.0 mg/kg (AB 562, dried fruit) to 12 mg/kg (AB 519); upper limits from 120 mg/kg (AB 438, mushrooms) to 4000 mg/kg (AB 343, AB 381, AB 486, AB 540, AB 560). Against the 10 mg/kg threshold: 18 laboratories start their range at 10 mg/kg or lower, so a result "below the range" is enough to state that the threshold is not exceeded; AB 519 starts at 12 mg/kg (vegetable products, PCA scope issue 26 of 26 November 2025) and cannot demonstrate a result between 10 and 12 mg/kg.

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN sells it (4 pages). We do not give the sample mass and its preparation, the concentrations of the iodine and sodium hydroxide solutions, the indicators, the distillation conditions, how the sum of free and bound SO₂ is calculated, or the precision; we do not know what AB 519 excludes with clause 2.3.a.

Method principle

According to the card of the standard: in the iodometric (routine) method free and then bound sulphur dioxide are determined by titrating the sample directly with iodine solution; in the distillation (reference) method sulphur dioxide is released from the sample with hydrochloric acid, distilled off and collected in hydrogen peroxide solution, and the sulphuric acid formed is titrated with a standardised sodium hydroxide solution (on the card: "standard"). The result in mg SO₂ per kg or per litre of product is compared with the allergen labelling threshold — more than 10 mg/kg or 10 mg/l in terms of total SO₂ (Regulation (EU) No 1169/2011). We DO NOT GIVE the working conditions — we did not have the text of the standard.

Applications

• Fruit and vegetable products (title of the standard); in accreditation scopes also dried fruit, mushrooms, vinegar, mustards and sauces, alcoholic beverages, fish and seafood, spices, confectionery
• Allergen labelling: whether SO₂ in terms of total content exceeds 10 mg/kg or 10 mg/l (Regulation (EU) No 1169/2011, Annex II, point 12)
• Settling disputes about a result — according to the card, the distillation method is the reference method

Key parameters

Standard

Standard number

PN-A-75101-23:1990 (wersja polska) ze zmianą PN-A-75101-23:1990/Az2:2002

Title (PL)

Przetwory owocowe i warzywne — Przygotowanie próbek i metody badań fizykochemicznych — Oznaczanie zawartości dwutlenku siarki

Title (EN)

Fruit and vegetable products — Preparation of samples and methods of physicochemical testing — Determination of sulphur dioxide content

Step-by-step procedure

1. Status of the document and choice of method

   PKN card: standard and amendment Az2:2002 withdrawn on 02-12-2011, no successor (state of the cards on 28 September 2026). The iodometric method is the routine one, the distillation method the reference one; the report should state the clause of the standard, because "titrimetric method" alone does not say which method was used.

2. Sample preparation

   Sample mass and preparation NOT GIVEN — we did not have the text of the standard.

3. Iodometric method

   Direct titration with iodine solution: first free, then bound sulphur dioxide (from the card). For dark liquids the standard has a separate titration apparatus.

4. Distillation method

   Sulphur dioxide is released from the sample with hydrochloric acid, distilled off and collected in hydrogen peroxide solution; the sulphuric acid formed is titrated with standardised sodium hydroxide solution (from the card).

5. Result and assessment

   Result in mg SO₂/kg or mg/l. Against the labelling threshold — more than 10 mg/kg or 10 mg/l of total SO₂ for the product ready for consumption or reconstituted according to the manufacturer’s instructions (Regulation (EU) No 1169/2011).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Hydrochloric acid and sodium hydroxide are corrosive, and sulphur dioxide released from the acidified sample irritates the respiratory tract — distillation is carried out in a fume cupboard
• TECHNICAL NOTE: both methods of the standard end with a titration — "Titrimetric method" without a clause number does not say whether the result comes from the routine or the reference method

Frequently asked questions