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Determination of Melamine Residue in Wastewater With Resonance Scattering Spectral Method

Melamine contamination in industrial wastewater and environmental water poses potential risks to aquatic ecosystems and human health. Traditional detection methods such as HPLC, GC-MS, and titration are often time-consuming, costly, or require complex pretreatment. In this study, a novel resonance scattering spectral method is established for rapid and sensitive determination of melamine in wastewater.

This article introduces the determination of melamine residue in wastewater with resonance scattering spectral method principle, experimental conditions, performance indicators, and application of this method.

Why Resonance Scattering Spectroscopy for Melamine Detection

Melamine powder is a widely used industrial chemical, but excessive discharge into water can cause environmental pollution and potential biotoxicity. Common melamine detection methods have obvious limitations:

Titration, sublimation, and picric acid methods: heavy workload, poor sensitivity, low accuracy.
Chromatographic and mass spectrometry methods: high instrument costs, complex operation, and long analysis times.
Fluorescence and UV methods: relatively poor selectivity, susceptible to matrix interference.

The resonance scattering spectral method has obvious advantages:

Fast analysis: the entire process can be completed within 15 minutes.
High sensitivity: detection limit down to 33 μg/L, suitable for trace analysis.
Simple operation: no expensive instruments, mild reaction conditions.
Good selectivity: less interference from common metal ions and organic matter.
Suitable for wastewater: can resist interference from urea, glucose, starch, and metal ions.

Principle of the Resonance Scattering Method

In a NaAc-HAc buffer solution at pH 3.6, melamine exists in a cationic form. It combines with anionic surfactant sodium laurylsulfonate (SLS) through electrostatic attraction to form hydrophobic MA–SLS association particles with an average particle size of about 192 nm.

These particles exhibit a strong, stable resonance-scattering effect at 472 nm. Within a certain concentration range, the scattering intensity is linearly proportional to melamine concentration, enabling quantitative detection.

Experimental Conditions & Procedures

1. Instruments & Reagents

Fluorescence spectrophotometer (for resonance scattering scanning)
Nano particle size analyser
pH meter
Melamine standard solution: 1 mg/mL
Sodium laurylsulfonate (SLS): 2.8 mol/L
NaAc-HAc buffer solution: pH 3.6

2. Optimized Experimental Parameters

Buffer system: NaAc-HAc (pH 3.6)
SLS concentration: 5.6×10⁻⁴ mol/L
Reaction time: 15 minutes at room temperature
Detection wavelength: 472 nm
Stability: stable for at least 2 hours

3. Analytical Steps

Add buffer solution, melamine sample, and SLS solution in sequence.
Dilute with distilled water and mix well.
Let it stand for 15 minutes to complete the reaction.
Scan synchronously on a fluorescence spectrophotometer.
Measure scattering intensity at 472 nm and calculate ΔI.

Method Performance & Validation

Linear Range

The method has two linear segments:

Low concentration range: 1.1–23.3 mg/L
Regression equation: ΔI₄₇₂nm = 101.97c − 5.27
Correlation coefficient: r = 0.9921
High concentration range: also shows good linearity
Regression equation: ΔI₄₇₂nm = 25.08c − 254.71
Correlation coefficient: r = 0.9952

Detection Limit

DL = 33 μg/L (3 times the standard deviation of blank signals), meeting trace melamine detection requirements in wastewater.

Precision

RSD of 5 parallel tests: 2.5%, showing good repeatability.

Selectivity & Anti-Interference Ability

The method has strong anti-interference. Common coexisting substances show little interference within the allowable multiple range:

Metal ions: Ca²⁺, Mg²⁺, K⁺, NH₄⁺, etc.
Organics: urea, glucose, sucrose, starch
Proteins: HSA, BSA

Metal ions can be masked by EDTA to further eliminate interference.

Recovery Rate

In synthetic wastewater samples:

Recovery rate: 96.5%–103.6%
Consistent with HPLC results, proving high accuracy.

Application in Wastewater Detection

This resonance scattering method was applied to the determination of melamine in synthetic wastewater. The results are highly consistent with those obtained by HPLC, with good repeatability and recovery. It can be directly used for:

Industrial wastewater from melamine production
Surface water and environmental water monitoring
Wastewater from resin, coating, and plastic industries
Pretreated industrial effluent

Advantages Summary

Ultra-sensitive: detection limit as low as 33 μg/L
Fast: 15 minutes per sample
Low cost: no expensive instruments or reagents
Strong anti-interference: suitable for complex wastewater matrix
Stable and reliable: good linearity, precision, and recovery

conclusion

The resonance-scattering spectral method based on melamine–SLS association particles provides a rapid, sensitive, low-cost, and reliable method for determining melamine in wastewater. Under optimized conditions at pH 3.6 and 472 nm, it achieves a low detection limit of 33 μg/L and a wide linear range. With strong anti-interference and high recovery, it is suitable for routine environmental monitoring and industrial wastewater quality control. This method can be used as a preferred screening and quantitative tool for detecting melamine pollution.

Tech Blog

Determination of Melamine Residue in Wastewater With Resonance Scattering Spectral Method

This article introduces the determination of melamine residue in wastewater with resonance scattering spectral method principle, experimental conditions, performance indicators, and application of this method.

Why Resonance Scattering Spectroscopy for Melamine Detection

Principle of the Resonance Scattering Method