Determination of melamine in milk-based products and other food and beverage products by ion-pair liquid chromatography-tandem mass spectrometry.
This paper describes a fast method for the sensitive and selective determination of melamine in a wide range of food matrices, including several milk-based products. The method involves an extraction with aqueous 1% trichloroacetic acid before the injection of the 10-fold diluted extract into the liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS) system, using labelled melamine as the internal standard. As melamine is present in aqueous media in the cationic form, the chromatographic separation in reversed-phase LC requires the use of anionic ion-pair reagents, such as tridecafluoroheptanoic acid (THFA). This allows a satisfactory chromatographic retention and peak shape in all the types of food samples investigated. The method has been validated in six food matrices (biscuit, dry pasta and four milk-based products) by means of recovery experiments in samples spiked at 1 and 5 mg kg(-1). Average recoveries (n=5) ranged from 77% to 100%, with excellent precision (RSDs lower than 5%) and limits of detection between 0.01 and 0.1 mg kg(-1). In addition, accuracy and robustness of the method was proven in different soya-based matrices by means of quality control (QC) sample analysis. QC recoveries, at 1 and 2.5 mg kg(-1), were satisfactory, ranging from 79% to 110%. The method developed in this work has been applied to the determination of melamine in different types of food samples. All detections were confirmed by acquiring two MS/MS transitions (127>85 for quantification; 127>68 for confirmation) and comparing their ion intensity ratio with that of reference standards. Accuracy of the method was also assessed by applying it to a milk-based product and a baking mix material as part of an EU proficiency test, in which highly satisfactory results were obtained.
Ibáñez
María
M
Research Institute for Pesticides and Water, University Jaume I, E-12071, Castellón, Spain.
Sancho
Juan V
JV
Hernández
Félix
F
D000818:Animals; D001628:Beverages / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005466:Fluorocarbons / Q000737:chemistry; D005504:Food Analysis; D005506:Food Contamination / Q000032:analysis*; D006538:Heptanoic Acids / Q000737:chemistry; D008892:Milk / Q000737:chemistry*; D052616:Solid Phase Extraction; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014227:Triazines / Q000032:analysis* / Q000302:isolation & purification
D005466:Fluorocarbons; D006538:Heptanoic Acids; D014227:Triazines; C101815:perfluoro-n-heptanoic acid; C011907:melamine