🔬 UV Absorbance at 254 nm
In short
Measurement of water absorbance at wavelength 254 nm as an indicator of organic matter content (aromatic and unsaturated compounds). The test is performed according to PN-EN ISO 7887:2012; Wavelength: 254 nm (UV). The procedure comprises 10 steps (about 50 min in total); it is used for: Monitoring of water treatment processes — coagulation and filtration effectiveness, Assessment of potential for formation of disinfection by-products (DBP — THM, HAA), Fast control of drinking water quality — operational parameter.
At a glance
- Standard: PN-EN ISO 7887:2012
- Category: Physicochemistry
- Procedure steps: 10
- Total time of stages: 50 min
- Wavelength: 254 nm (UV)
- Result: Absorbance [cm⁻¹] or SAC254 [m⁻¹]
- Cuvette: Quartz, 1 cm (standard) or 5 cm (low absorbance)
Overview
UV absorbance at 254 nm (UV254, SAC254 — Spectral Absorption Coefficient) is a fast, simple and non-invasive parameter used to assess dissolved organic matter (DOM — Dissolved Organic Matter) content in water. Organic compounds containing aromatic rings and unsaturated bonds (C=C, C=O, C=N) strongly absorb ultraviolet radiation at 254 nm.
UV254 is a valuable operational parameter in water treatment processes — it correlates with total organic carbon (TOC/DOC) content, potential for formation of disinfection by-products (trihalomethanes — THM, haloacetic acids — HAA during chlorination) and effectiveness of organic matter removal in coagulation, filtration and sorption on activated carbon processes. The SUVA result (Specific UV Absorbance = UV254/DOC × 100) informs about hydrophobicity and aromaticity of organic matter.
The method is described in standard PN-EN ISO 7887:2012 as method D (color measurement by spectrophotometric method in UV range) and consists of measuring absorbance of filtered water sample in quartz cuvette with optical path length 1 cm (or 5 cm for waters with low absorbance) at wavelength 254 nm relative to ultrapure water as reference.
UV254 is a fast and cheap parameter to perform — measurement takes several seconds, requires no chemical reagents and can be performed continuously (on-line) using immersion spectrophotometric probes. Therefore it is widely used for process monitoring in water treatment plants.
THE STANDARD CITED IN THIS ENTRY CONCERNS COLOUR, NOT THIS PARAMETER — CORRECTION (23.09.2026). The entry describes absorbance at 254 nm (UV254, SAC254), and the reference document given for it is PN-EN ISO 7887:2012. The PKN catalogue card gives the scope of this standard in full: "Four methods of examining colour are presented: a method of examining apparent colour by visual observation of a water sample in a bottle; a method of determining the true colour of a water sample using optical instruments; a method of determining the true colour of a water sample using optical instruments and comparison with the hexachloroplatinate concentration at a wavelength of 410 nm; a method of determining colour by visual comparison with hexachloroplatinate standard solutions". THE WAVELENGTH 254 nm DOES NOT APPEAR IN IT EVEN ONCE — the wavelength given is 410 nm, i.e. measurement against the platinum-cobalt scale. ACCREDITATION SCOPES CONFIRM THIS, AND UNAMBIGUOUSLY: PN-EN ISO 7887 is cited in them **265 times by 222 laboratories when matching the beginning of the value (267 by 224 when matching the core of the number with a boundary on both sides) and EVERY TIME against the methodology "Barwa" (colour)** ("Barwa" alone 214 times, the rest with ranges in mg/l Pt), with ranges given in mg/l Pt. NOT ONE laboratory determines absorbance at 254 nm according to this standard — those that have this parameter in their scope cite in-house procedures ("PB-P/06", "PWL-28", "PWL-29", "P/19/IB-19") or the German document "ASU L 00.00-170:2020-05". WHAT THIS MEANS FOR THE "LABORATORIES" TAB: the key of this entry shows more than two hundred and twenty laboratories that determine COLOUR — not UV absorbance. The number is true, the list is true, and it answers a different question from the one asked. This is the same class as in the entries on ether extract and on formaldehyde in water: the tab is neither silent nor empty, it SPEAKS CORRECTLY ABOUT SOMETHING ELSE — which is why no count of laboratories could have detected it. THE SITUATION CANNOT BE REMEDIED BY CHANGING THE KEY, BECAUSE THERE IS NO STANDARD FOR THIS PARAMETER IN THE PN COLLECTION. Absorbance at 254 nm is an operational indicator described in guidelines and in the literature (method 5910 B in Standard Methods, the German DIN 38404-3), not in a Polish Standard. A laboratory that has this parameter in its accreditation scope must therefore base it on an in-house procedure with demonstrated validation — and this is exactly what each of those that declare it does.
Method principle
UV radiation with wavelength 254 nm is passed through a quartz cuvette containing filtered water sample (0.45 µm filter). Organic compounds containing aromatic structures (e.g., humic substances, fulvic acids, phenols, ligno-cellulose compounds) and other chromophores (C=C, C=O bonds) absorb part of the radiation. The detector on the other side of the cuvette measures the intensity of transmitted radiation. Absorbance is calculated from Lambert-Beer law: A = -log₁₀(I/I₀), where I — transmitted intensity, I₀ — incident intensity. Result expressed as SAC254 in m⁻¹ or absorbance in cm⁻¹.
Applications
- Monitoring of water treatment processes — coagulation and filtration effectiveness
- Assessment of potential for formation of disinfection by-products (DBP — THM, HAA)
- Fast control of drinking water quality — operational parameter
- Monitoring of surface waters — organic matter load
- Control of sorption effectiveness on activated carbon (GAC/PAC)
- Calculation of SUVA (UV254/DOC) — characterization of organic matter
- On-line monitoring in treatment stations (immersion probes)
- Testing of water in pharmaceutical and electronics industry (purified water)
Key parameters
| Parameter | Value |
|---|---|
| Wavelength | 254 nm (UV) |
| Result | Absorbance [cm⁻¹] or SAC254 [m⁻¹] |
| Cuvette | Quartz, 1 cm (standard) or 5 cm (low absorbance) |
| Sample filtration | 0.45 µm (for dissolved organic matter) |
| Typical values (drinking water) | <0.1 cm⁻¹ (SAC254 <10 m⁻¹) |
| SUVA = UV254/DOC × 100 | >4: hydrophobic (aromatic), <2: hydrophilic |
Standard
- Standard number
- PN-EN ISO 7887:2012
- Title (PL)
- Jakość wody — Badanie i oznaczanie barwy
- Title (EN)
- Water quality — Examination and determination of colour
Step-by-step procedure
-
Spectrophotometer preparation
Turn on UV-VIS spectrophotometer min. 15 min before measurement (deuterium lamp stabilization). Set wavelength 254 nm.
-
Cleaning quartz cuvettes
Rinse quartz cuvettes with ultrapure water. If necessary soak in HCl 0.1 mol/L for 1 h, then rinse multiple times with ultrapure water. Dry.
-
Sample filtration
Filter water sample through 0.45 µm membrane filter. Discard first 50 mL filtrate (filter saturation). Collect filtrate in clean container.
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Spectrophotometer zeroing
Fill reference cuvette with ultrapure water. Place in spectrophotometer and set zero absorbance (autozero / baseline).
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Sample measurement
Fill measurement cuvette with filtered sample. Rinse three times with sample before measurement. Place in spectrophotometer. Read absorbance at 254 nm.
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Duplicate measurement
Repeat measurement with second portion of filtrate. Difference between duplicates should not exceed 5%.
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Result conversion
For 1 cm cuvette: SAC254 [m⁻¹] = absorbance [cm⁻¹] × 100. For 5 cm cuvette: SAC254 = absorbance / 5 × 100.
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SUVA calculation (optional)
If sample DOC is known: SUVA [L/(mg·m)] = UV254 [cm⁻¹] / DOC [mg/L] × 100. SUVA >4 = high aromaticity, SUVA <2 = low aromaticity.
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Quality control
Check zeroing every 10 samples. Measure reference absorbance filter. Repeatability control: duplicate every 10 samples, deviation <5%.
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Cleaning and storage
Rinse quartz cuvettes with ultrapure water, dry. Store in dedicated case. Do not touch optical surfaces with fingers.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| UV-VIS Spectrophotometer | Hach DR6000, Shimadzu UV-1900i, Thermo Scientific GENESYS 150 | 15,000–45,000 PLN |
| Quartz cuvettes 1 cm | Hellma 100-QS, Starna 1-Q-1 — do not use glass or plastic cuvettes! | 200–600 PLN/pair |
| Quartz cuvettes 5 cm (optional) | Hellma 100-QS, path 50 mm — for waters with low absorbance | 400–1,000 PLN/pair |
| Vacuum filtration system | Sartorius, Merck Millipore — with 0.45 µm filters | 1,500–5,000 PLN |
| Membrane filters 0.45 µm | Cellulose MCE filters 47 mm, Whatman, Sartorius | 150–300 PLN/pack (100 pcs) |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Ultrapure water (Type I) | 7732-18-5 | For zeroing spectrophotometer and rinsing cuvettes. Absorbance <0.01 at 254 nm. Millipore Milli-Q, Elga Purelab system |
| UV absorbance standard solution | — | Optical filters or K₂Cr₂O₇ solution for verification of spectrophotometer absorbance scale |
| Diluted hydrochloric acid (HCl) | 7647-01-0 | 0.1 mol/L for cleaning quartz cuvettes from organic deposits |
Health and safety (OHS)
- UV radiation — do not look directly at deuterium lamp source. Close measurement chamber
- Hydrochloric acid (HCl) — corrosive, use gloves and goggles when cleaning cuvettes
- Quartz cuvettes — fragile and expensive, handle carefully
- Water samples — use protective gloves (potential contamination)
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 7887:2012 — “Water quality — Examination and determination of colour”.
How does this method work?
UV radiation with wavelength 254 nm is passed through a quartz cuvette containing filtered water sample (0.45 µm filter).
What is the measuring range and accuracy?
Wavelength: 254 nm (UV); Result: Absorbance [cm⁻¹] or SAC254 [m⁻¹]; Cuvette: Quartz, 1 cm (standard) or 5 cm (low absorbance); Sample filtration: 0.45 µm (for dissolved organic matter).
How long does the test take?
The times given for the individual stages add up to approximately 50 min. The procedure comprises 10 steps.
What equipment is required?
UV-VIS Spectrophotometer, Quartz cuvettes 1 cm, Quartz cuvettes 5 cm (optional), Vacuum filtration system, Membrane filters 0.45 µm. Indicative cost of the core instrument (UV-VIS Spectrophotometer): 15,000–45,000 PLN.
Where is this test used?
Monitoring of water treatment processes — coagulation and filtration effectiveness; Assessment of potential for formation of disinfection by-products (DBP — THM, HAA); Fast control of drinking water quality — operational parameter; Monitoring of surface waters — organic matter load; Control of sorption effectiveness on activated carbon (GAC/PAC); Calculation of SUVA (UV254/DOC) — characterization of organic matter; On-line monitoring in treatment stations (immersion probes); Testing of water in pharmaceutical and electronics industry (purified water).
What safety precautions apply?
UV radiation — do not look directly at deuterium lamp source. Close measurement chamber; Hydrochloric acid (HCl) — corrosive, use gloves and goggles when cleaning cuvettes; Quartz cuvettes — fragile and expensive, handle carefully; Water samples — use protective gloves (potential contamination).
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-EN ISO 7887.