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Determination of melamine content by UV spectrophotometry

Industrial melamine powder is a key raw material in industries such as wood processing, adhesives, and coatings, and its purity directly affects product performance and safety. Accurate determination of melamine content in various industries, from polymer manufacturing to agriculture, is not only related to quality control but also often the key to ensuring safety and compliance.

Given the wide range of melamine uses and the limitations of current detection methods, it is necessary to develop simple, rapid methods for raw material procurement inspection (especially for small and medium-sized enterprises), as well as for melamine production control and end-of-line inspection.

Although methods such as high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) are common, there is still an urgent need for a fast, economical, and reliable conventional analytical technique. UV spectrophotometry emerged in this context and has become a powerful tool. This article provides a detailed introduction to ultraviolet spectrophotometry for determining the content of industrial melamine, including its scientific principles, steps, and advantages.

Why is it necessary to test the content of industrial melamine?

Before delving into the methodology, it is necessary to first understand why we need to detect melamine. There are two reasons, and they are completely different in different contexts:

Industrial quality control

In legal applications, melamine powder is a key component in the synthesis of melamine formaldehyde (MF) resin. These resins are used to produce durable laminates, coatings, adhesives, and tableware. The precise concentration of melamine monomer is crucial to ensure that the final product possesses the required properties, such as hardness, heat resistance, and stability. Improper concentration can lead to product failure.

Food and feed safety

The notorious food safety scandal in 2008 exposed the illegal use of melamine to artificially increase the protein content in products such as milk powder and pet food. Because standard protein detection methods (such as Kjeldahl nitrogen determination) measure total nitrogen content, nitrogen-rich melamine (with a nitrogen mass fraction of 66%) can mimic proteins. However, consuming melamine can lead to severe kidney stones and kidney failure.

Principle of determination of melamine content by UV spectrophotometry

This method utilizes the unique UV absorption characteristics of melamine powder and efficient ultrasonic dissolution technology to achieve rapid and accurate quantification:

Key mechanism

After dissolving in water, melamine exhibits a characteristic strong absorption peak at 250 nm. At this wavelength, water as a reference medium has extremely low UV absorption and can accurately capture the absorbance signal of melamine. The absorbance value is linearly correlated with melamine concentration and can be quantified using a standard curve.

Core technical parameters

Linear range: The mass concentration of melamine is in the range of 0.05-1.50 mg/mL and shows a good linear relationship with absorbance (when using a 1 cm quartz cuvette, the correlation coefficient R² is 0.9977);

Precision: The relative standard deviation (RSD) of sample determination is ≤ 0.47% (n=6), and the actual RSD of sample detection is as low as 0.26%, fully meeting the requirements of industrial quality control;

Accuracy: The test results are highly consistent with the GB/T 9567-2016 picric acid method, with an absolute deviation of only 0.40%.

Detection process of melamine content by UV spectrophotometry

Following the standardized process can achieve efficient determination of melamine content for industrial use (based on optimized validation methods):

1.Preparation of reagents and instruments

Reagent: Deionized water of grade III or higher purity; Melamine standard with purity greater than 99.5%;
Instruments: UV spectrophotometer (such as UV2310II), ultrasonic cleaner (such as VGT-1730QTD), analytical balance with an accuracy of 0.0001g, 200 mL volumetric flask, 1 cm quartz colorimetric dish.

2.Sample preparation

Accurately weigh 0.2 g of industrial melamine sample (accuracy ± 0.0001 g) and transfer it to a 200 mL volumetric flask;

Dissolve the sample in deionized water and make up to the 200 mL mark.

Place the volumetric flask in an ultrasonic cleaner and sonicate at room temperature for 5 minutes to ensure complete dissolution of the sample.

3.Calibration and Measurement

Using the same ultrasonic dissolution method, prepare a series of melamine standard solutions with concentrations of 0.05, 0.10, 0.25, 0.50, 1.00, and 1.50 mg/mL;
Set the UV spectrophotometer to 250 nm and use deionized water as the reference blank.
Use a 1 cm quartz cuvette to measure the absorbance of the standard solution and sample solution in sequence.

4.Result calculation

The linear regression equation (y=1.0125x+0.0334) derived from the standard curve is used to calculate the concentration of melamine (ρ) based on the absorbance of the sample, and then substituted into the formula.

Advantages of UV spectrophotometry

Extremely fast analysis speed

Ultrasonic dissolution only takes 1-5 minutes (manual or magnetic stirring takes more than 30 minutes);

The entire testing time for a single sample has been shortened to about 30 minutes, -12 times faster than the picric acid method and 6 times faster than the sublimation method.

Environmental protection and safety

Only use deionized water as a solvent, without the need for hazardous reagents such as explosives and drugs;

No chemical waste generated, avoiding environmental pollution risks, simplifying environmental protection and workplace safety compliance processes.

Accurate and reliable

A narrow linear range of 0.05-1.50 mg/mL, suitable for the common purity range of industrial melamine (70% -99.8%+);

An RSD value as low as 0.26% ensures consistency of results in scenarios such as incoming acceptance, process control, and finished product inspection.

Cost is controllable and easy to popularize

The required equipment is a standard laboratory setup: a UV spectrophotometer, an ultrasonic cleaner, an analytical balance, and a volumetric flask, without the need for expensive specialized instruments.

Only deionized water is consumed, and the subsequent testing cost is extremely low.

Core application scenarios for determining melamine content using UV spectrophotometry

Raw material procurement acceptance: Quickly verify the purity of melamine stored in the warehouse, and prevent unqualified raw materials from entering the production process.

Process control: Real-time monitoring of changes in the content of melamine synthesis or formulation processes (such as adhesive and coating production);

Finished product inspection: Ensure that melamine-based products meet industrial quality standards.

High throughput detection: parallel detection of multiple samples in mass production scenarios (such as wood processing plants, adhesive factories).

conclusion

This method can provide fast, efficient, and accurate detection results for industrial melamine, especially for the paint industry that uses melamine as a raw material for rapid procurement acceptance, rapid central control testing for melamine production enterprises, and finished product inspection on production lines. It has unique advantages. This method can also be used to detect melamine at corresponding concentration levels in other industries.

For manufacturers in industries such as wood processing, adhesives, coatings, etc., this method can optimize quality control processes, reduce operational risks, and improve production efficiency. It achieves the best balance between speed, cost, and simplicity, providing reliable process control data when the sample matrix composition is clear and interference is minimal.