🌿 Tetraphosphorus decaoxide (P₄O₁₀) in workplace air — spectrophotometric method with phosphomolybdenum blue

Environment PN-Z-04073-1

Overview

What the standard concerns. The catalogue card describes the scope thus: "This standard gives a method for determining tetraphosphorus decaoxide (CAS No 1314-56-3) in workplace air using absorption spectrophotometry in visible light. The method is used in the control of sanitary and hygienic conditions. The method is not used in the presence in the air tested of other phosphorus(V) compounds, of arsenic and its compounds. The smallest concentration of tetraphosphorus decaoxide that can be determined under the conditions of air sampling and of carrying out the determination described in the standard is about 0.1 mg/m³".

TWO EXCLUSIONS THAT DECIDE THE FITNESS OF THE METHOD: it is not used in the presence of other phosphorus(V) compounds or of arsenic and its compounds. The method measures the phosphate formed by hydrolysis, so any other source of phosphorus(V) in the air gives a positive result, and arsenic forms an analogous complex with molybdate and likewise overstates the result. A laboratory accepting a commission must know what else occurs at the workplace.

RELATION TO THE LIST OF MAXIMUM ADMISSIBLE CONCENTRATIONS — the standard is written for an item of the list, though differently from nickel: there the proof of it (the exclusion of the tetracarbonyl) vanished from the list, whereas here the name of the substance and the CAS number still agree with the list exactly. The Regulation of the Minister of Family, Labour and Social Policy of 12 June 2018 (Journal of Laws 2018 item 1286) names tetraphosphorus decaoxide [1314-56-3] with the values MAC 1 mg/m³ and short-term MAC 2 mg/m³. A NOTE ON THE ITEM NUMBER: in the original 2018 wording it was item 133, but Annex No 1 was given a new wording in its entirety twice, and in the list in force (Journal of Laws 2026 item 447, in force 02-04-2026) the same substance stands at item 142. The values themselves have not changed. The number of the item in the list is therefore not a permanent identifier and must not be given without indicating the wording of the annex (status checked 11 September 2026). The name of the substance and the CAS number agree exactly with the scope of the standard.

WHY 0.1 mg/m³ IS NOT MERELY AN ANALYTICAL PARAMETER — and this is the most important thing in this entry. A limit of determination of about 0.1 mg/m³ against a MAC of 1 mg/m³ is exactly 1/10 of the limit value, and the 1/10 threshold has a legal consequence — the entitled party, however, being the EMPLOYER and not the laboratory. Under § 7 of the Regulation of the Minister of Health on tests and measurements of harmful agents (consolidated text, Journal of Laws 2025 item 949): if the results of the TWO most recent tests and measurements, made at an interval of at least two years (and for agents with a carcinogenic or mutagenic action and for reprotoxic substances — at least six months), have not exceeded 0.1 of the MAC value, "the employer may refrain from carrying out tests and measurements". The laboratory therefore supplies the result that makes this possible, but does not itself exercise that entitlement. The previous edition of the standard did NOT reach the 1/10 threshold. In the paper describing the revision of the method (PiMOŚP 2013 No 1(75), E. Gawęda) we read: the method from PN-78/Z-04073.01 "is characterised by a limit of determination at the level of 1/5 of the value presently in force, that is 0.2 mg/m³, and not 1/10 of the MAC value, which in accordance with the regulation of the minister of health (Journal of Laws 2011, No 33, item 166) would allow exemption from carrying out measurements to be obtained". The difference between the 1978 edition and the 2014 edition therefore does not lie in accuracy — it lies in WHETHER THE MEASUREMENT HAS TO BE MADE AT ALL. Whoever gives both figures without that sentence makes the reader take the older one for simply a worse version of the same thing, whereas it was the basis of a different decision. A second reason for the revision, given in the same paper: the 1978 method "is also not adapted to making measurements in accordance with the principles of personal dosimetry set out in the standard PN-Z-04008-7:2002".

TWO PARALLEL NUMBERINGS IN THE SAME SERIES — and this is a trap that does not catch the eye. The PKN catalogue holds SIDE BY SIDE the old series with a TWO-DIGIT element: PN-Z-04073-00:1978, -01:1978, -03:1991, -04:1991, -05:1988, and the new one with a ONE-DIGIT element: PN-Z-04073-1:2014-08, -3:2013-08, -4:2013-08 (checked 11 September 2026). "PN-Z-04073-3" and "PN-Z-04073-03" are THEREFORE TWO DIFFERENT DOCUMENTS, differing by a single zero — and a difference of thirty years in the date of issue is not visible in the number itself. This entry concerns exclusively part 1 in the NEW numbering (PN-Z-04073-1:2014-08); the predecessor it superseded is PN-Z-04073-01:1978 (Polish version), that is part "zero-one" of the old numbering, cited in the literature also as PN-78/Z-04073.01.

WHAT DID NOT CHANGE: the technique remained the same. The paper on the revision states that the determination is carried out "using absorption spectrophotometry at a wavelength of 825 nm, that is as in the standard PN-78/Z-04073/01"; what changed was the concentration range.

What this entry does not contain. The working steps OF THE STANDARD ITSELF the entry does not give, because we did not have the text of the standard — PKN supplies it for a fee and we did not obtain the preview (checked 11 September 2026). The principle of the method given below comes from the PAPER ON THE REVISION in PiMOŚP 2013, that is from a document describing the work on the basis of which the standard was revised — and not from the standard itself. We have not compared the text of the article with the text of the standard and we do not claim that they are identical. We therefore do not give: the volume and flow rate of the air drawn through, the composition of the solution in the impinger, the concentrations of ammonium molybdate and ascorbic acid, the time for the colour to develop, or the way of preparing the calibration curve. The regulation on maximum admissible concentrations does not contain those parameters — it gives only the limit values, so with air methods there is no superior document from which the procedure could be reconstructed.

A note on the English title: the PKN catalogue card gives the Polish title only; the title in the English field is our reconstruction.

Method principle

THE DESCRIPTION COMES FROM THE PAPER ON THE REVISION (PiMOŚP 2013 No 1(75)), not from the text of the standard. A known volume of the air tested is drawn through an impinger containing water; the tetraphosphorus decaoxide hydrolyses in it to phosphoric(V) acid. The determination consists in forming a complex — phosphomolybdenum blue — by acting on the solution from the impinger with ammonium molybdate and ascorbic acid. The intensity of the colour of the solution formed is the basis of the spectrophotometric determination at a wavelength of 825 nm. The result is converted into the concentration of tetraphosphorus decaoxide in the air by relating the mass of phosphorus determined to the volume of the sample taken.

Applications

• Control of sanitary and hygienic conditions where tetraphosphorus decaoxide is formed — in the burning of white phosphorus
• Production of phosphoric(V) acid by the thermal route
• Manufacture of plant protection products and phosphorus additives
• Production and use of drying agents based on P₄O₁₀
• Measurements for assessing occupational exposure made under the strategy of PN-EN 689+AC:2019-06 (the strategy for the number and choice of measurements; the requirements for the measurement procedure itself are set by PN-EN 482)

Key parameters

Standard

Standard number

PN-Z-04073-1:2014-08

Title (PL)

Ochrona czystości powietrza -- Badania zawartości fosforu i jego związków -- Część 1: Oznaczanie dekatlenku tetrafosforu na stanowiskach pracy metodą spektrofotometryczną

Title (EN)

Air purity protection — Determination of phosphorus and its compounds — Part 1: Determination of tetraphosphorus decaoxide at workplaces by spectrophotometric method (tytuł angielski odtworzony z polskiego — karta katalogowa PKN podaje wyłącznie polski)

Step-by-step procedure

1. Taking the air sample through the impinger (description from PiMOŚP 2013, not from the text of the standard)

   Draw a known volume of the air tested through an impinger containing water. WE GIVE NEITHER THE VOLUME, NOR THE FLOW RATE, NOR THE SAMPLING TIME — they are in the standard, whose text we did not have.

2. Hydrolysis to phosphoric(V) acid (description from PiMOŚP 2013)

   The tetraphosphorus decaoxide hydrolyses in the absorbing solution to phosphoric(V) acid. The step takes place of itself in the impinger.

3. Formation of phosphomolybdenum blue (description from PiMOŚP 2013)

   Act on the solution from the impinger with ammonium molybdate and ascorbic acid. WE GIVE NEITHER THE CONCENTRATIONS OF THE REAGENTS, NOR THE ORDER OF ADDITION, NOR THE TIME FOR THE COLOUR TO DEVELOP — they are neither on the catalogue card nor in the regulation on maximum admissible concentrations.

4. Spectrophotometric measurement at 825 nm (description from PiMOŚP 2013)

   Measure the absorbance of the solution formed at a wavelength of 825 nm. The same wavelength as in the 1978 edition — the technique did not change, the concentration range did.

5. Conversion to the concentration in air

   Relate the mass of phosphorus determined to the volume of the sample taken and express the result as the concentration of tetraphosphorus decaoxide in mg/m³.

6. Comparison with the limit values (Journal of Laws 2018 item 1286, Annex No 1 item 142 as worded by Journal of Laws 2026 item 447) — STEP FROM THE LEGISLATION

   Compare the result with the MAC of 1 mg/m³ and the short-term MAC of 2 mg/m³. The values have not changed since the original wording; the number of the item in the list changed (133 → 142), because Annex No 1 was given a new wording in its entirety.

7. Report

   Give the EDITION OF THE STANDARD — with this method that is not a formality: the 2014 edition has a limit of determination of 1/10 of the MAC and the 1978 edition had 1/5, and the possibility of exemption from measurements depends on it. Note also that the determination is invalid in the presence of other phosphorus(V) compounds or of arsenic — if their presence at the workplace has not been excluded, the result settles nothing.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Tetraphosphorus decaoxide is the anhydride of phosphoric(V) acid — it is corrosive, and it reacts violently with water, evolving heat.
• The substance is absorbed through the respiratory tract and the digestive tract; work only under a fume hood, in gloves and safety goggles.
• Transport impingers with absorbing solution tightly closed — the solution is acidic.
• When sampling at a workplace the same protective measures apply as to the worker: the person sampling stands in the exposure zone.
• Ammonium molybdate is harmful if swallowed and is an irritant — weigh it out under a fume hood.

Frequently asked questions