Arsenic has no taste, no colour and no smell, yet drinking water with too much of it can harm health over many years. It enters water naturally from rocks and soils, and through mining, industry and some treatment processes. Seawater holds a small natural background level, so measuring it takes a method that copes with a salty matrix. Therefore, laboratories use spectrophotometry, a technique that links the colour or light absorption of a solution to the amount of arsenic present. At METS Laboratories, we help water suppliers, private well owners, industrial sites and marine operators check arsenic levels with clear, documented results.
Why Does Arsenic in Water Matter?
Long-term exposure to arsenic in drinking water is a recognised health concern, so regulators set strict limits.
- Health risk: Chronic exposure is linked to skin changes and a higher risk of several cancers.
- Drinking water limits: The World Health Organization guideline and the UK drinking water standard are both 10 µg/l.
- Private supplies: Moreover, private wells and boreholes sit outside the mains network, and owners must check them. In some areas, such as former mining regions, natural arsenic levels run higher.
- Seawater and marine use: In addition, desalination plants, aquaculture and marine monitoring need reliable arsenic data.
Potable Water Arsenic Detection
Arsenic testing measures the total arsenic, and sometimes its forms, in drinking water and other waters.
- Total arsenic: It shows the full amount, whatever its form.
- Arsenic species: Arsenic(III) and arsenic(V) differ in toxicity and behaviour, so some projects measure them separately.
- Units: Results appear in micrograms per litre (µg/l), which is the same as parts per billion.
Arsenic Analysis Using Spectrophotometry
Spectrophotometry shines light through a prepared solution and measures how much the solution absorbs. The more arsenic, the stronger the signal.
- Silver diethyldithiocarbamate method: Arsenic converts to arsine gas, which then reacts to form a red-coloured complex. We measure the colour intensity.
- Molybdenum blue method: Arsenic reacts with molybdate to form a blue complex. This approach suits seawater and can help separate arsenic forms.
- Hydride generation atomic absorption: Arsine gas passes into a heated cell, where an atomic absorption spectrophotometer measures it at very low levels.
- Calibration: In every case, we compare the sample against standards of known concentration.
Why is Seawater Harder to Analyse?
Seawater contains about 3.5 percent dissolved salts, and that matrix complicates the spectrophotometric determination of arsenic.
- Salt interference: High chloride and other salts can affect colour development.
- Very low natural levels: Seawater normally holds only a few µg/l of arsenic, so sensitivity matters.
- Matrix matching: For this reason, labs match standards to the sample matrix or dilute carefully.
- Contamination control: Finally, clean reagents and equipment prevent false readings.
How Do We Handle Interferences?
Other substances can mimic or hide arsenic, so the method includes controls.
- Sulphide and antimony: They can interfere with arsine methods, and traps or pre-treatment remove them.
- Blanks: Reagent blanks show whether any contamination comes from the process.
- Spikes and duplicates: They confirm that the method recovers arsenic and repeats well.
- Reference materials: Certified materials check accuracy.
Samples Tested
Arsenic analysis applies to many types of water.
- Mains drinking water: Treated supply and distribution samples.
- Private water supplies: Wells, boreholes and springs.
- Bottled and mineral water: Packaged products that need compliance data.
- Seawater and estuary water: Marine, coastal and desalination samples.
- Process and wastewater: Industrial discharges and treatment plant samples.
How Does the Testing Process Work?
- Sample receipt: First, we log your sample and check its container and condition.
- Preparation: Next, we preserve or digest the sample as the method requires.
- Colour development or generation: Then we form the coloured complex or release arsine gas.
- Measurement: After that, the spectrophotometer reads the signal against the calibration.
- Report: Finally, we compare results with the limit and issue a report.
Arsenic Testing at METS Laboratories
Reliable arsenic results rely on sensitive measurement, careful matrix handling and clear reporting, and we aim for all three.
- Matrix-aware methods: We choose the approach that suits drinking water or seawater.
- Quality controls on each batch: Blanks, spikes and reference materials support trustworthy results.
- Total and species options: We can report total arsenic or its forms.
- Clear reporting: Results appear beside the limit, so pass or fail is plain.
METS Laboratories delivers environmental monitoring services built on ISO/IEC 17025 methodologies, and its water testing supports compliance with national and international standards, including ISO, EN and BS requirements.
Conclusion
Spectrophotometry turns an invisible contaminant into a number you can act on. As a result, it protects drinking water, supports marine and industrial work and keeps supplies within legal limits. Test private supplies regularly, and use a method that suits the sample matrix. Share your water details with METS Laboratories, and we will recommend the right arsenic testing plan.
Frequently Asked Questions
1. What is the arsenic limit in UK drinking water?
Ans: The UK standard is 10 µg/l, in line with the WHO guideline. Check the current regulation for your type of supply.
2. Can spectrophotometry measure arsenic in seawater?
Ans: Yes, with the right method. Seawater needs matrix-matched standards and careful handling because of its salt content.
3. Why test private wells for arsenic?
Ans: Private supplies are not treated or monitored by a water company, and local geology can raise natural arsenic levels.
