🧪 Formaldehyde in Water
In short
Spectrophotometric determination of formaldehyde in water by acetylacetone method (Hantzsch). The test is performed according to PN-EN ISO 12460-5:2016; 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-EN ISO 12460-5:2016
- 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.
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-EN ISO 12460-5:2016
- Title (PL)
- Oznaczanie formaldehydu w wodzie — Metoda spektrofotometryczna z acetyloacetonem
- Title (EN)
- Determination of formaldehyde in water — Spectrophotometric method with acetylacetone
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-EN ISO 12460-5:2016 — “Determination of formaldehyde in water — Spectrophotometric method with acetylacetone”.
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-ISO 12460.