🌿 Sulphur dioxide in workplace air — pararosaniline method, PN-Z-04015-12

Environment PN-Z-04015-12

Overview

WHAT THIS STANDARD DESCRIBES. The scope from the PKN catalogue card: "Metoda polega na zaabsorbowaniu dwutlenku siarki w płuczce z roztworem czterochlorortęcianu potasu. Do otrzymanego roztworu dodawane są pararozanilina oraz formaldehyd. W wyniku reakcji powstaje związek barwy czerwonofioletowej, który jest podstawą oznaczania spektrofotometrycznego. Najmniejsze stężenie dwutlenku siarki jakie można oznaczyć wynosi 0,32 mg/m3" [The method consists in absorbing sulphur dioxide in an impinger with a potassium tetrachloromercurate solution. Pararosaniline and formaldehyde are added to the resulting solution. The reaction produces a red-violet compound, which is the basis of the spectrophotometric determination. The lowest concentration of sulphur dioxide that can be determined is 0.32 mg/m3]. The standard was published on 21 March 1996 in a Polish-language version, has four pages, is maintained by KT 159 and replaced PN-Z-04039:1968. The card has neither a "Withdrawn" header nor a "Withdrawal date" row (checked on 23.09.2026).

TWO NAMES FOR THE SAME SUBSTANCE — AND BOTH ARE OFFICIAL. The title of the standard speaks of **"dwutlenek siarki"**, while the list of maximum admissible concentrations carries the same substance under the name **"ditlenek siarki"** (item 203) — both mean sulphur dioxide. The difference is purely one of nomenclature: "ditlenek" is the name in line with the current systematic nomenclature, "dwutlenek" — the traditional name, established in documents from before the reform. Both refer to SO₂ and both stand in official documents, only in different ones. **For a laboratory this has a practical consequence: searching the list by the name from the standard will not find the item**, because the list knows only the other form. This is the same class as our distorted prefixes, only on the side of the substance name rather than the standard number.

A LIMIT OF QUANTIFICATION TWO AND A HALF TIMES ABOVE THE REQUIREMENT. The limit value for sulphur dioxide is **NDS 1.3 mg/m³ (0.5 ppm) and NDSCh 2.7 mg/m³ (1 ppm)** — item 203 of the list in the wording given by the regulation of 26 March 2026 (Journal of Laws 2026 item 447). The lowest determinable concentration is 0.32 mg/m³, i.e. **0.25 of the limit value — one quarter**. PN-EN 482 requires the method to cover the range from one tenth; this one starts two and a half times higher. This ratio is worse than for pentane (PN-Z-04318, a separate entry in this database), where it is 0.15. **A result "below the limit of quantification" means here "below 25 % of the limit value"**, which is sufficient for the assessment of exposure, but not for demonstrating compliance with the one-tenth threshold.

A MERCURY REAGENT — SOMETHING THAT WEIGHS MORE TODAY THAN IN 1996. The absorbent is a solution of potassium tetrachloromercurate, i.e. a mercury compound. The pararosaniline method was created at a time when this was a standard solution — today it means three things at once for a laboratory: obligations arising from the regulations on particularly hazardous substances, the cost of disposing of the spent solutions as mercury waste, and restrictions on trade in mercury reagents. **This is the reason why some laboratories are switching to instrumental methods** — ion chromatography or analysers with fluorescence detection — even though this standard remains valid and has no successor in the PN collection.

AMENDMENT Ap1:2001 AND FIVE WAYS OF ATTACHING IT. In accreditation scopes the standard is cited almost half with and half without the amendment: "PN-Z-04015-12:1996" 9 times, "PN-Z-04015-12:1996+Ap1:2001" 8. The amendment itself is written in FIVE ways: with a plus without spaces (8), with a slash after the number without the year of the standard (2), with a plus with spaces (2), with a slash after the year (1) and with a plus with an addition about an exclusion (1). We recall here a finding of this database: **a plus before the element means a CONSOLIDATED edition, a slash — a separate amendment sheet**, and laboratories do not preserve this distinction. The form of the amendment is recognised from the catalogue card, never from the notation in the scope.

SCALE OF CITATIONS (reading of 23.09.2026, copy of the database of accreditation scopes). Matching by the BEGINNING of the notation: 21 entries at 18 laboratories; across all forms of the core "04015-12" — the same number of entries, 25 occurrences in seven forms. The difference between the number of entries and the number of occurrences arises because four entries carry the designation TWICE — once with the amendment, once without — in two separate elements of the reference-document field.

Method principle

Air from the workplace is drawn through an impinger with a potassium tetrachloromercurate solution, in which sulphur dioxide is bound in the form of a dichlorosulphitomercurate complex — stable enough for the sample to be transported to the laboratory. Pararosaniline and formaldehyde are added to the solution; red-violet pararosaniline methylsulphonic acid is formed, and its absorbance is measured spectrophotometrically. The colour intensity is proportional to the amount of SO₂ bound, and the concentration in air is calculated from the volume of air drawn and the volume of the absorption solution.

Applications

• Periodic measurements of occupational exposure required by the regulation of the Minister of Health on tests and measurements of agents harmful to health in the working environment
• Boiler houses and combined heat and power plants fired with sulphur-containing fuels
• Non-ferrous metal smelters — roasting of sulphide ores
• Food plants using sulphur dioxide as a preservative, and wineries

Key parameters

Standard

Standard number

PN-Z-04015-12:1996 (wersja polska)

Title (PL)

Ochrona czystości powietrza -- Badania zawartości siarki i jej związków -- Oznaczanie dwutlenku siarki na stanowiskach pracy metodą spektrofotometryczną z pararozaniliną

Title (EN)

Air purity protection — Testing for content of sulphur and its compounds — Determination of sulphur dioxide at workplaces by spectrophotometric method with pararosaniline

Step-by-step procedure

1. Sampling

   Draw a known volume of air from the worker's breathing zone through an impinger with a potassium tetrachloromercurate solution.

2. Colour reaction

   Add pararosaniline and formaldehyde to the solution after absorption; wait for the time provided for in the procedure for the colour to develop.

3. Measurement

   Measure the absorbance of the solution spectrophotometrically at the wavelength appropriate for the red-violet product.

4. Calculation

   Read the SO₂ content from the calibration curve and calculate the concentration in air from the volume of air drawn.

5. Reference to the limit values

   Compare the exposure index for the work shift with the NDS of 1.3 mg/m³, and the results of short-term measurements with the NDSCh of 2.7 mg/m³. State in the report that the limit of quantification is one quarter of the limit value.

6. Handling of waste

   The spent solutions contain mercury — collect them separately and hand them over as hazardous waste; do not discharge them into the sewer.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Potassium tetrachloromercurate contains mercury — work only in a fume hood, in gloves, with a register of particularly hazardous substances; collect waste separately
• Formaldehyde is a category 1B carcinogen and a skin sensitiser — work in a fume hood
• Sulphur dioxide irritates the respiratory tract; when sampling at workplaces with high concentrations, use respiratory protection

Frequently asked questions