🌿 4,4′-Methylenediphenyl diisocyanate (MDI; in the standard "4,4-diisocyanatodiphenylmethane") in workplace air — hydrolysis to methylenedianiline, diazotisation, coupling with R-acid sodium salt, colorimetric (spectrophotometric) determination; NDS for diisocyanates as NCO group; PN-Z-04131-02:1981 (withdrawn 17-10-2011)

Environment PN-Z-04131-02

Overview

WHAT THE STANDARD COVERS. Scope from the PKN card, in full: "A method has been established consisting in the hydrolysis of MDI to methylenedianiline, diazotisation of the amine formed and coupling with R-acid sodium salt. The coloured solution is the basis of the colorimetric determination. General guidelines, apparatus and instruments, reagents and solutions, preparation of the calibration curve and of the standard solutions are given" (our translation; on the card without a full stop at the end). The card gives neither the sampling method nor the lowest determinable concentration. We did not have the text of the standard (2 pages); the CIOP index of methods from 2000–2017 lists no article on MDI (searched on 04.10.2026 — it lists only cyclohexyl isocyanate, methyl isocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate and toluylene diisocyanate).

NDS VALUES (regulation of 26 March 2026, Journal of Laws 2026 item 447). In the annex, item 177: "Diisocyanates – as NCO group" with footnotes 14 and 16 — NDS 0.006 mg/m³, NDSCh 0.012 mg/m³, "skin" notation; footnote 14: the substance "may have a sensitising effect on the skin and the respiratory system", footnote 16: exposure is assessed "on the basis of the sum of concentrations of the isocyanate functional groups of diisocyanate compounds" in the air. Transitional provisions (§ 2): until 8 April 2026 separate values applied — for 2,2′- and 2,4′-methylenediphenyl diisocyanate, their isomer mixture and methylenebis(phenyl isocyanate) an NDS of 0.03 mg/m³ and an NDSCh of 0.09 mg/m³ — and the value as NCO group was not applied; from 9 April 2026 to 31 December 2028 the NDS for diisocyanates as NCO group is 0.01 mg/m³ and the NDSCh 0.02 mg/m³; from 1 January 2029 — the values from the annex.

STATUS (card as of 04.10.2026). The card of PN-Z-04131-02:1981 (Polish version) has the heading "Withdrawn": published 25-04-1981, withdrawal date 17-10-2011, 2 pages, price group A, Health, Environment and Medicine Sector, KT 159 Chemical and Dust Hazards in the Working Environment, ICS 13.040.30; the card does not name a replacing standard. The PKN search for "PN-Z-04131" (04.10.2026) shows the series "Tests for isocyanate content": labelled "Withdrawn" — parts 00:1981 (general provisions), 01:1981 (toluylene diisocyanate, colorimetry), 02:1981 and 10:1993 (TDI and MDI vapours and their hydrolysis products), and 5:2008 (cyclohexyl isocyanate) — "Withdrawn and replaced by PN-Z-04560:2025-04"; without the label — 3:2001 (hexane-1,6-diyl diisocyanate), 4:2008 (methyl isocyanate) and 6:2008 (3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate). The search term "metylenodifenylu" returns no standard, and "diizocyjanianu" only PN-Z-04490:2017-10 (TDI, a separate entry of this database) and PN-Z-04131-3:2001; the search shows no current standard for MDI at workplaces.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data load up to 17.09.2026, read on 04.10.2026). The number 04131-02 (with a hyphen, full stop or slash before the part number) appears in 4 records at 4 laboratories; in the current PCA documents (read on 03.10.2026; issues from 04.09.2025 to 18.08.2026 — all issued after the withdrawal of the standard) — in 4 rows at the same laboratories; a search of all PCA documents downloaded from the BIP found no laboratories outside the database copy; no item is suspended, and no document repeats pages. The form "PN-81/Z-04131/02" — AB 647 and AB 1287; "PN-81/Z-04131.02" — AB 340; "PN-Z-04131-02:1981" — AB 935. The "Laboratories" tab: "PN-81/Z-04131/02" shows 2 laboratories, "PN-Z-04131-02" — 1, "PN-81/Z-04131.02" — 1, 4 in total, the same in the copy and on the labcoda.pl production server (tab queries of 04.10.2026). Part 01 (TDI, colorimetry, also withdrawn 17-10-2011) is cited in the copy by one laboratory — AB 935.

WHAT THE LABORATORIES TEST (database copy and PCA documents). AB 340 — working environment, "4,4'-diisocyanatodiphenylmethane as NCO group", 0.0014–0.056 mg/m³; AB 647 — air samples collected on filters, "methylenebis(phenyl isocyanate)", 0.0017–0.83 mg/m³ and 0.62–12.5 µg per sample; AB 1287 — working environment, "methylenebis(phenyl isocyanate)", 0.003–0.25 mg/m³ and 0.0019–0.15 mg per sample; AB 935 — object "Waste gases", "isocyanates – MDI", 0.0052–0.208 mg/m³ and 0.625–25 µg per sample. Technique: spectrophotometric method — all 4 laboratories.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — the reference value: from 9 April 2026 there is no separate NDS for MDI — the value for the sum of diisocyanates as NCO group applies; only AB 340 reports the result as NCO, the others as MDI, which has to be converted and summed with other diisocyanates; comparison with the former 0.03 and 0.09 mg/m³ is out of date. Second — status: the standard has been withdrawn since 17-10-2011, and PKN shows no current standard for MDI; 4 laboratories have it in scopes issued since September 2025. Third — object: AB 935 applies the "at workplaces" standard to waste gases, i.e. an emission measurement, for which the NDS is not a reference value. Fourth — principle: according to the card the amine formed by hydrolysis of MDI is measured; whether the standard takes into account methylenedianiline present in the air before hydrolysis does not follow from the card. Fifth — determinability: the card does not give it, and the laboratories' bottom limits (0.0014–0.0052 mg/m³) have to be related to the NDS as NCO.

WHAT WE DO NOT GIVE. We did not have the text of the standard, and the card gives neither sampling nor determinability — we do not give the sampler and absorbing solution, the air volume, the hydrolysis and diazotisation conditions, the wavelength or calculations; we do not convert results to the NCO group. We do not claim that another standard has replaced PN-Z-04131-02:1981 — PKN names none.

Method principle

MDI from workplace air is hydrolysed to methylenedianiline, the amine is diazotised and coupled with R-acid sodium salt, and the coloured solution is determined colorimetrically (PKN card). From 9.04.2026 to 31.12.2028 the result is assessed against the NDS of 0.01 mg/m³ and the NDSCh of 0.02 mg/m³ for diisocyanates as NCO group (sum). The standard is withdrawn (17-10-2011); WE DO NOT GIVE details — we did not have the text of the standard.

Applications

• Workplace air — MDI (methylenebis(phenyl isocyanate)) — in the current scopes of 3 laboratories, and at a fourth — waste gases; despite the withdrawal of the standard
• Assessment of occupational exposure to diisocyanates as NCO group — from 9.04.2026 to 31.12.2028 NDS 0.01 mg/m³, NDSCh 0.02 mg/m³ (Journal of Laws 2026 item 447, § 2(2); in the annex, item 177: 0.006 and 0.012 mg/m³)

Key parameters

Standard

Standard number

PN-Z-04131-02:1981

Title (PL)

Ochrona czystości powietrza — Badania zawartości izocyjanianów — Oznaczanie 4,4-dwuizocyjanianodwufenylometanu na stanowiskach pracy metodą kolorymetryczną

Title (EN)

Air purity protection — Tests for isocyanate content — Determination of 4,4-diisocyanatodiphenylmethane at workplaces by colorimetric method

Step-by-step procedure

1. Status

   PN-Z-04131-02:1981 withdrawn 17-10-2011, with no successor named (card as of 04.10.2026).

2. Sampling

   WE DO NOT GIVE the method — the card does not give it; in the AB 647 scope — filters.

3. Hydrolysis and colour reaction

   Hydrolysis of MDI to methylenedianiline, diazotisation, coupling with R-acid sodium salt (PKN card); WE DO NOT GIVE the conditions.

4. Result and assessment

   Colorimetric measurement and calibration curve (PKN card); for assessment — conversion to the NCO group and sum of diisocyanates against the NDS of 0.01 mg/m³ and the NDSCh of 0.02 mg/m³ (§ 2(2), until 31.12.2028).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Diisocyanates — "skin" notation and possible sensitisation of the skin and respiratory system (footnote 14 of the list); standards in a fume hood, with gloves
• TECHNICAL NOTE: standard withdrawn 17-10-2011; from 9.04.2026 assessment against the NDS for the sum of diisocyanates as NCO, not against the former value for MDI

Frequently asked questions