🧪 Formaldehyde in Water
In short
Spectrophotometric determination of formaldehyde in water by acetylacetone method (Hantzsch). The test is performed according to PN-C-04593:1971 (PN-71/C-04593); Measurement range: 10–5,000 µg/L (with dilution). The procedure comprises 10 steps (about 3 h 20 min in total); it is used for: Drinking water quality control — formaldehyde monitoring, Industrial wastewater testing (chemical plants, sawmills, resin production), Monitoring by-products of water ozonation.
At a glance
- Standard: PN-C-04593:1971 (PN-71/C-04593)
- Category: Physicochemistry
- Procedure steps: 10
- Total time of stages: 3 h 20 min
- Measurement wavelength: 410 nm
- Measurement range: 10–5,000 µg/L (with dilution)
- Limit of quantification (LOQ): 10–50 µg/L (1–5 cm cuvette)
Overview
Formaldehyde (HCHO) is the simplest aldehyde, occurring in water as industrial pollution (resin, glue, textile production), by-product of water ozonation, and natural product of organic matter decomposition. It is classified by IARC as group 1 carcinogen. The permissible formaldehyde concentration in drinking water is 50 µg/L according to WHO.
The acetylacetone method (Nash/Hantzsch method) is a classic colorimetric technique based on condensation reaction of formaldehyde with acetylacetone and ammonium ion in acetic acid medium. The reaction product is 3,5-diacetyl-1,4-dihydrolutidine (DDL) — a yellow dye with absorption maximum at 410 nm. Color intensity is proportional to formaldehyde concentration in sample.
The method has good selectivity — other aldehydes (acetaldehyde, propionaldehyde) do not interfere at typical concentrations found in water. The limit of quantification is 10–50 µg/L depending on cuvette path length. The method is routinely used in water and wastewater laboratories.
Alternatively, formaldehyde in water can be determined by HPLC with DNPH derivatization (more sensitive, LOD ~1 µg/L) or enzymatic method. However, the spectrophotometric method remains the simplest and cheapest in routine laboratory practice.
THE ENTRY CITED THE WRONG STANDARD — CORRECTED AND CONFIRMED BY THE CATALOGUE CARD (23.09.2026). Until now the full designation field read "PN-EN ISO 12460-5:2016", and the standard title — "Oznaczanie formaldehydu w wodzie — Metoda spektrofotometryczna z acetyloacetonem" [Determination of formaldehyde in water — Spectrophotometric method with acetylacetone]. THIS TITLE DOES NOT BELONG TO ANY STANDARD: the PKN catalogue card for PN-EN ISO 12460-5:2016-02 (read on 23.09, sklep.pkn.pl) gives "Płyty drewnopochodne — Oznaczanie emisji formaldehydu — Część 5: Metoda ekstrakcyjna (zwana metodą perforatora)" [Wood-based panels — Determination of formaldehyde release — Part 5: Extraction method (called the perforator method)], 28 pages, publication date 23-02-2016. It is a standard on the EMISSION OF FORMALDEHYDE FROM WOOD-BASED PANELS tested by the perforator method — a different test object, a different matrix and a different technique from the acetylacetone method for water described in this entry. THE CORRECT REFERENCE DOCUMENT IS PN-C-04593:1971 — PKN card (read on 23.09): "Woda i ścieki — Oznaczanie zawartości aldehydu mrówkowego" [Water and wastewater — Determination of formaldehyde content], Polish version, publication date 06-11-1971, 3 pages, technical body KT 122 for Water Quality — Chemical Testing — Organic Substances. "Aldehyd mrówkowy" is the old Polish name for formaldehyde, hence the method described in this entry and this standard are the same thing. THE ACCREDITATION SCOPES CONFIRM THIS AND ALSO SETTLE THE FORM OF THE KEY: the record "PN-71/C-04593" occurs 3 times at THREE laboratories (AB 176, AB 199, AB 663), while the form in the new convention, "PN-C-04593", DOES NOT OCCUR EVEN ONCE. The key has been set to the old form — the tab now shows three laboratories instead of none ("PN-ISO 12460" gave 0 entries at 0 laboratories, because no such designation exists in the scopes at all). HOW THE DEFECT CAME TO LIGHT: not from reading the entry, but from comparing the key field with the full designation field in the same record. The key read "PN-ISO 12460", the full designation "PN-EN ISO 12460-5:2016" — the former was not the beginning of the latter, which for a field meant to be an abbreviation of the designation is a signal in itself. The screening was built to look for keys that are TOO BROAD; what it found with it was an entry with a standard on someone else's test object.
Method principle
Formaldehyde reacts with acetylacetone (2,4-pentanedione) and ammonium ion (from ammonium acetate) in Hantzsch reaction, forming 3,5-diacetyl-1,4-dihydrolutidine (DDL). This is a condensation reaction leading to yellow dye with absorption maximum at λ = 410 nm. The reaction proceeds at 40°C for 30 minutes or at room temperature for 60 minutes. Absorbance is measured with UV-Vis spectrophotometer in 1 cm or 5 cm cuvette. Formaldehyde concentration is calculated from calibration curve prepared from formaldehyde standard solutions.
Applications
- Drinking water quality control — formaldehyde monitoring
- Industrial wastewater testing (chemical plants, sawmills, resin production)
- Monitoring by-products of water ozonation
- Swimming pool water control
- Surface water testing around industrial facilities
- Process water analysis in textile and paper industry
Key parameters
| Parameter | Value |
|---|---|
| Measurement wavelength | 410 nm |
| Measurement range | 10–5,000 µg/L (with dilution) |
| Limit of quantification (LOQ) | 10–50 µg/L (1–5 cm cuvette) |
| Reaction temperature | 40°C / 30 min or 20°C / 60 min |
| Precision (CV) | 3–8% |
| Selectivity | High — no interference from C2–C4 aldehydes |
Standard
- Standard number
- PN-C-04593:1971 (PN-71/C-04593)
- Title (PL)
- Woda i ścieki — Oznaczanie zawartości aldehydu mrówkowego
- Title (EN)
- Water and wastewater — Determination of formaldehyde content
Step-by-step procedure
-
Nash reagent preparation
Dissolve 150 g ammonium acetate in ~800 mL deionized water. Add 3 mL glacial acetic acid and 2 mL acetylacetone. Make up to 1 L. Store in dark bottle at 4°C (stable 1 month).
-
Standard preparation
From formaldehyde standard (37%) prepare working solution 100 mg/L. Prepare calibration series: 0, 0.05, 0.1, 0.25, 0.5, 1.0, 2.0, 5.0 mg/L in 25 mL volumetric flasks.
-
Color reaction — standards
To each standard (10 mL) add 2 mL Nash reagent. Mix. Place in water bath at 40°C for 30 minutes.
-
Cooling
Remove tubes from water bath. Cool to room temperature in darkness (30 min). DDL dye is stable for 2 hours.
-
Absorbance measurement — calibration
Measure absorbance of standards at 410 nm against blank (water + Nash reagent). Plot calibration curve A = f(c).
-
Sample preparation
To 10 mL water sample add 2 mL Nash reagent. Mix. Incubate 40°C / 30 min, cool 30 min (same as standards).
-
Absorbance measurement — samples
Measure sample absorbance at 410 nm in 1 cm cuvette (or 5 cm for low concentrations). Read concentration from calibration curve.
-
Calculations
HCHO concentration [µg/L] = reading from curve × dilution factor. Account for blank and control sample correction.
-
Quality control
Control sample (CRM or spike 0.5 mg/L) — recovery 90–110%. Blank < LOQ. Duplicate: RSD < 10%.
-
Cleaning
Rinse cuvettes with deionized water and ethanol. Store Nash reagent at 4°C in darkness. Collect waste in organic waste container.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| UV-Vis spectrophotometer | Hach DR 6000, Shimadzu UV-1900i, Agilent Cary 60 | 15,000–80,000 PLN |
| Glass/quartz cuvettes 1–5 cm | Hellma, Starna, borosilicate/quartz optical cuvettes | 100–500 PLN/pc |
| Water bath | Memmert WNB 10, Julabo TW 12, PolyScience WB05 | 3,000–10,000 PLN |
| Automatic pipettes | Eppendorf Research Plus 100–1000 µL, 1–5 mL | 800–2,000 PLN |
| Class A volumetric flasks | 25, 50, 100, 250 mL, borosilicate glass class A | 30–80 PLN/pc |
| Analytical balance | Mettler Toledo XPR205, Sartorius Quintix 224 | 8,000–25,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Acetylacetone (2,4-pentanedione) | 123-54-6 | Analytical grade, 2 mL per 1 L Nash reagent |
| Ammonium acetate (CH₃COONH₄) | 631-61-8 | 150 g per 1 L Nash reagent — NH₄⁺ ion source |
| Glacial acetic acid (CH₃COOH) | 64-19-7 | 3 mL per 1 L Nash reagent — pH adjustment ~6 |
| Formaldehyde standard solution | 50-00-0 | 37% formaldehyde stabilized with methanol, for calibration curve preparation |
| Deionized water | — | Resistivity >18.2 MΩ·cm, for dilutions and blanks |
Health and safety (OHS)
- Formaldehyde 37% — carcinogenic (cat. 1), mutagenic, sensitizing — work exclusively in fume hood!
- Acetylacetone — flammable, irritant to respiratory tract, use under fume hood
- Glacial acetic acid — corrosive, causes skin and eye burns, acid-resistant gloves
- Safety glasses, lab coat, and nitrile gloves mandatory
- Dispose formaldehyde waste as hazardous waste
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-C-04593:1971 (PN-71/C-04593) — “Water and wastewater — Determination of formaldehyde content”.
How does this method work?
Formaldehyde reacts with acetylacetone (2,4-pentanedione) and ammonium ion (from ammonium acetate) in Hantzsch reaction, forming 3,5-diacetyl-1,4-dihydrolutidine (DDL). This is a condensation reaction leading to yellow dye with absorption maximum at λ = 410 nm.
What is the measuring range and accuracy?
Measurement wavelength: 410 nm; Measurement range: 10–5,000 µg/L (with dilution); Limit of quantification (LOQ): 10–50 µg/L (1–5 cm cuvette); Reaction temperature: 40°C / 30 min or 20°C / 60 min.
How long does the test take?
The times given for the individual stages add up to approximately 3 h 20 min. The procedure comprises 10 steps.
What equipment is required?
UV-Vis spectrophotometer, Glass/quartz cuvettes 1–5 cm, Water bath, Automatic pipettes, Class A volumetric flasks, Analytical balance. Indicative cost of the core instrument (UV-Vis spectrophotometer): 15,000–80,000 PLN.
Where is this test used?
Drinking water quality control — formaldehyde monitoring; Industrial wastewater testing (chemical plants, sawmills, resin production); Monitoring by-products of water ozonation; Swimming pool water control; Surface water testing around industrial facilities; Process water analysis in textile and paper industry.
What safety precautions apply?
Formaldehyde 37% — carcinogenic (cat. 1), mutagenic, sensitizing — work exclusively in fume hood!; Acetylacetone — flammable, irritant to respiratory tract, use under fume hood; Glacial acetic acid — corrosive, causes skin and eye burns, acid-resistant gloves; Safety glasses, lab coat, and nitrile gloves mandatory; Dispose formaldehyde waste as hazardous waste.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-71/C-04593.