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Detecting the total melamine method in food
At present, numerous methods exist for detecting melamine, with high-performance liquid chromatography (HPLC), gas chromatography (GC), and liquid chromatography being among the most widely used techniques. This article compiles some domestic research studies and organizes them to provide a comprehensive overview of current detection approaches. These include GC-MS, Spectra-Quad online analysis, ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS), reversed-phase HPLC, HPLC-diode array detection (DAD), HPLC-quadrupole mass spectrometry, solid-phase extraction coupled with HPLC, and liquid chromatography-tandem mass spectrometry (LC-MS/MS).
One of the most effective methods involves using ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) for determining residual melamine in feed. The sample was extracted using 1% trichloroacetic acid and dimethyl sulfoxide, purified with a Waters Oasis MCX column, separated by UPLC, and detected via ESI-MS/MS. The method showed good linearity between 10 and 5,000 μg/kg (r > 0.99), with recovery rates ranging from 83% to 94%. The detection limit was 10 μg/kg.
Another technique uses HPLC coupled with quadrupole mass spectrometry to detect melamine in feed. An automatic solid-phase extraction system was employed, and the Agilent HP1100 HPLC-MS system was optimized for accurate quantification. The linear range was 0.010–0.500 μg/mL, with relative standard deviation (RSD) between 3.2% and 7.7%, and recovery rates from 72.4% to 91.2%.
For pet food, LC-MS/MS has proven to be a highly sensitive and selective method. Compared to traditional GC-MS and LC methods, it offers simpler sample preparation and greater accuracy. Similarly, LC-MS/MS was used to analyze melamine in feed, where samples were extracted with acetonitrile-water (1:1), and analyzed after centrifugation. The mobile phase was acetonitrile-water (80:20), with a detection limit of 0.2 mg/kg.
A solid-phase extraction-LC-MS/MS method was also developed for melamine detection in food. After homogenization and extraction with 1% trichloroacetic acid, samples were purified using an OASIS MCX cartridge and analyzed by LC-MS/MS. The linear range was 0.1–10.0 mg/kg, with a correlation coefficient of 0.9999 and recovery rates between 71% and 95%.
The Spectra-Quad online analyzer from Thermo Fisher Scientific provides real-time, non-contact detection of melamine using near-infrared absorption technology. Unlike traditional methods that are affected by protein nitrogen content, this system offers continuous monitoring without sample damage. It can be integrated into production lines and used with powder samplers for automated melamine testing, ensuring product safety.
In terms of HPLC-based methods, reversed-phase HPLC is commonly used for feed analysis, while the diode array method is suitable for high-protein foods. The latter method involved different pretreatment steps, with a Symmetry C18 column and a diode array detector at 235 nm. The method demonstrated excellent precision, with RSD < 1.2% and a detection limit of 0.01 μg/mL.
Additionally, HPLC was applied to determine melamine in feed using a C18 column and a UV detector at 236 nm. The method was simple, fast, and reproducible, with average recoveries exceeding 90% and RSD below 3%. Another study used solid-phase extraction combined with HPLC to analyze melamine in pet food, achieving satisfactory results.
These advanced analytical techniques offer reliable, accurate, and efficient ways to monitor melamine contamination in various food products, ensuring consumer safety and regulatory compliance.