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HPLC Method for Simultaneous Determination of Melamine Cyanuric Acid and Uric Acid

Melamine and its by-product, cyanuric acid, are common chemical raw materials, and their illegal presence in food will cause serious harm to the human body. Melamine can combine with cyanuric acid and uric acid in the body to form insoluble complexes or salts, leading to kidney damage, including the formation of calculi. The 2008 melamine-contaminated milk powder incident has made the detection of melamine and its associated harmful substances a key focus of food safety and biomedical research. At present, detection methods for a single substance, such as melamine, are relatively mature, but the simultaneous determination of melamine, cyanuric acid, and uric acid in biological samples, such as plasma and calculus, remains a technical challenge.

This article details a HPLC Method for Simultaneous Determination of Melamine Cyanuric Acid and Uric Acid, including its experimental design, optimization process, performance indicators, and practical application value, providing a reliable technical solution for relevant research and detection.

Research Background

Melamine produces cyanuric acid as a by-product during industrial production, and the two can form a water-insoluble network crystal through hydrogen bonds. In the human body, melamine not only binds to cyanuric acid to form the melamine cyanurate complex, but also forms insoluble salts with uric acid, which accumulate in the urinary system and can cause calculus, even acute renal failure in severe cases.

For the study of the metabolic transformation of melamine in the animal body and the diagnosis of melamine-induced pathological damage, it is not enough to detect only melamine content—the simultaneous determination of melamine, cyanuric acid, and uric acid in biological samples such as plasma and calculus is needed to comprehensively analyze the interaction and content changes of the three substances.

In the existing detection technology:

Melamine powder detection has mature methods such as HPLC, LC-MS, and GC-MS;
Uric acid detection also has multiple chromatographic and mass spectrometric methods.
Cyanuric acid research is scarce, and the existing HPLC methods all use expensive, specialized chromatographic columns (such as Acclaim Mixed-Mode WAX-1, ZICHILIC, and Atlantis HILIC), which are not suitable for widespread use in conventional laboratories.

Based on this, establishing a method for the simultaneous determination of the three substances using a common C18 chromatographic column has important practical significance for reducing detection costs and improving detection efficiency.

Experimental Design of HPLC Simultaneous Detection Method

This method is designed for plasma and calculus samples, with core steps including sample pretreatment, chromatographic condition optimization, standard curve preparation, and performance verification. The entire experimental process follows the principles of simplicity, accuracy, and high efficiency, and the key instruments and reagents are conventional laboratory supplies that are easy to replicate.

Main Instruments and Reagents

Core Instruments

Agilent1100 Series HPLC (equipped with binary pump, automatic sampler, variable wavelength UV detector);
Sartorius BP121S electronic analytical balance;
KH-300DB numerical control ultrasonic cleaner;
Sigma 3-15 centrifuge;
Phemomenex Gemini C18 chromatographic column (4.6×250mm i.d., 5μm) + C18 guard column (the core of the method, common type with low cost).

Key Reagents

Chromatographically pure acetonitrile, ultrapure water (Milli-Q system);
Analytical grade melamine (≥99.5%), cyanuric acid (≥98.0%), uric acid (≥99%);
Potassium hydrogen phosphate, potassium dihydrogen phosphate, and sodium hydroxide (analytical grade) for preparing the mobile phase and solvent.

Sample Pretreatment: Targeted Optimization for Plasma and Calculus

The matrices of plasma and calculus are quite different, so the pretreatment methods are optimized separately to ensure full extraction of the three target substances and the removal of matrix interference.

Plasma Sample Treatment

Weigh 0.1000g plasma into a 10mL centrifuge tube, add 6mL acetonitrile-water (V:V=2:1) as extraction solvent;
Ultrasonic extraction for 30min, centrifugation at 9000r/min for 15min;
Transfer the supernatant to a glass vial, blow-dry with nitrogen, redissolve in 2mL ultrapure water, and filter through a 0.22 μm membrane for HPLC determination.
Key point: Acetonitrile-water (2:1) can effectively precipitate plasma protein and avoid hemoglobin interference on chromatographic analysis.

Calculus Sample Treatment

Grind the calculus into fine powder with an agate mortar, accurately weigh 0.0100g into a 10mL centrifuge tube, add 6mL ultrapure water;
Ultrasonic extraction for 30min, centrifugation at 9000r/min for 15min;
Filter the supernatant through a 0.22 μm membrane, dilute 20-fold, and perform HPLC analysis.
Key point: Calculus has a solid matrix, and grinding into fine powder combined with ultrasonic extraction can improve the extraction rate of the target substances.

Chromatographic Condition Optimization

The biggest challenge in the simultaneous detection of three substances is achieving complete separation under a single set of chromatographic conditions. The experiment optimizes the detection wavelength, mobile phase, and solvent through a large number of comparative tests and finally determines the optimal conditions with a good separation effect and high response.

Optimal Chromatographic Conditions

Mobile phase: 100% phosphate buffer (K₂HPO₄+KH₂PO₄, 10mmol/L, pH=7.50);
Flow rate: 1mL/min;
Column temperature: Room temperature;
Detection wavelength: 200nm;
Injection volume: 20μL.

Key Optimization Details

Detection wavelength selection: Cyanuric acid has a maximum absorption at 200nm (melamine at 240nm, uric acid at 280nm). To ensure the effective detection of cyanuric acid (the substance with the scarcest research), 200nm is selected as the unified detection wavelength.
Mobile phase optimization: 5% acetonitrile + 95% phosphate buffer cannot separate the three peaks; 100% phosphate buffer (pH=7.50) can realize complete separation after the sample is redissolved with ultrapure water.
Solvent selection: Sodium hydroxide solution can cause melamine hydrolysis and deterioration, so ultrapure water is used as the solvent for melamine and cyanuric acid, and a 1 mmol/L NaOH solution is used as the solvent for poorly water-soluble uric acid.

Standard Curve Preparation

Dilute the standard stock solutions of the three substances with ultrapure water to prepare a series of standard solutions with gradient concentrations:

Cyanuric acid and uric acid: 0.1~50μg/mL;
Melamine: 0.05~50μg/mL (additional low concentration due to high response).

Under optimal chromatographic conditions, inject 20 μL of each standard solution, plot the standard curve with concentration on the abscissa and peak area on the ordinate, and obtain the linear regression equation.

Performance Indicators of HPLC Simultaneous Detection Method

The method is verified with respect to linear relationship, precision, minimum detection limit (LOD), minimum quantitative limit (LOQ), and recovery rate, and all performance indicators meet the requirements for trace detection in biological samples, thereby meeting the requirements for practical application.

Excellent Linear Relationship

The three substances show a good linear relationship in the designed concentration range, and the correlation coefficient (r) is close to 1, which ensures the accuracy of quantitative calculation:

Cyanuric acid: , ;
Uric acid: , ;
Melamine: , .

High Precision

Taking 5μg/mL melamine standard solution as an example, continuous injection for 6 times:

RSD of retention time: 0.1281%;
RSD of peak area: 0.0621%.

The extremely low RSD value indicates that the method has good repeatability and stable detection results.

Ultra-low Detection and Quantitative Limit

Determine LOD by S/N=3 and LOQ by S/N=10, the method has high sensitivity and can detect trace amounts of the three substances in biological samples:

Cyanuric acid: LOD=0.0248μg/mL, LOQ=0.0830μg/mL;
Uric acid: LOD=0.0231μg/mL, LOQ=0.0780μg/mL;
Melamine: LOD=0.0045μg/mL, LOQ=0.0150μg/mL (the lowest sensitivity, suitable for trace detection).

Ideal Recovery Rate

Add standard substances of different concentrations to blank plasma for the recovery experiment, and the recovery rate of the three substances is in the range of 92.6%~101.3%:

Cyanuric acid: 99.1%~100.5%;
Uric acid: 92.6%~95.8%;
Melamine: 97.3%~101.3%.

The high recovery rate indicates that the sample pretreatment process results in no significant loss of target substances and effectively eliminates matrix interference in the plasma.

Advantages and Application Value of the Method

Compared with the existing detection technologies, this HPLC simultaneous determination method has three core advantages, which make it have great promotional value in conventional laboratories and relevant research fields:

Low Detection Cost, Easy to Promote

A common chromatographic column is used instead of expensive specialized columns (such as HILIC or WAX-1) for cyanuric acid detection, thereby greatly reducing instrument cost and making it suitable for popularization and application in ordinary laboratories.

Simple Operation, High Efficiency

The sample pretreatment process is optimized, and conventional instruments such as ultrasound and a centrifuge are used; the chromatographic conditions are stable and easy to control, and the simultaneous detection of the three substances is achieved in a single analysis, thereby shortening the detection time compared with the separate detection of a single substance.

Comprehensive Performance, Wide Application Range

The method has high sensitivity, good precision, an ideal recovery rate, and strong anti-interference ability, and can be applied to the detection of plasma and calculus samples. It provides a reliable technical means for:

The study of melamine metabolic transformation in animal bodies.
The clinical diagnosis of melamine-induced kidney damage.
The safety evaluation of food contaminated by melamine and cyanuric acid.

conclusion

This study successfully established an HPLC method for the simultaneous determination of melamine, cyanuric acid, and uric acid in plasma and calculus using a common chromatographic column. The method has the advantages of simple operation, low cost, accurate quantification, high precision, and an ideal recovery rate, and solves the technical problems of high cost and a single detection object in existing cyanuric acid detection. It is not only suitable for biomedical research on melamine-induced pathological damage but also provides a new approach for the simultaneous detection of multiple melamine-related harmful substances in food and biological samples.

With the continuous improvement in food safety detection requirements and biomedical research, the simultaneous detection of multiple harmful substances will become a development trend. On the basis of this method, the follow-up can further optimize the chromatographic conditions to shorten the analysis time, and expand the detection matrix to milk, dairy products, feed and other food samples, so as to realize the multi-matrix and multi-substance simultaneous detection of melamine, cyanuric acid and uric acid, and provide a more comprehensive technical guarantee for food safety and public health.

Tech Blog

HPLC Method for Simultaneous Determination of Melamine Cyanuric Acid and Uric Acid

This article details a HPLC Method for Simultaneous Determination of Melamine Cyanuric Acid and Uric Acid, including its experimental design, optimization process, performance indicators, and practical application value, providing a reliable technical solution for relevant research and detection.

Research Background