Adulteration/unintentional contamination of milk with melamine could have negative health and economic implications especially in the developing countries due to insufficient laboratory support and surveillance. This paper presents an Isotope Dilution Liquid Chromatography-Mass Spectrometry (ID LC-MS) method developed for detection of melamine in powdered milk. The rapid sample preparation involved dissolution of 1g of milk powder in 2.5% formic acid, precipitation of protein with acetonitrile, spiking of samples with melamine (triamine-¹⁵N₃) at 200 µg L^–1 and detection of intrinsic ¹⁴N-melamine molecular ratio to the spike. The isotope dilution calibration procedure was free from matrix effects, unlike other methods where the detector sensitivity can fluctuate up to several orders of magnitude. Limit of detection of the method was 13 µg kg^–1, and the recovery of melamine at 50, 100, and 250 µg kg^–1 was 78.7–126.3%. The method was used to determine melamine levels in 22 milk powder products (local and imported) available in Sri Lanka. Melamine was detected in all the samples (range = 0.33–0.96 mg kg^–1). Full cream milk powders (both local and imported) contained melamine in the range of 0.39–0.84 mg kg^–1, and various health and pregnancy formulas contained <0.5 mg kg^–1 of melamine. Two imported infant formula samples contained the highest levels of melamine (0.96 and 0.94 mg kg^–1). Although these melamine levels are below the regulatory limit in Sri Lanka (1 mg kg^–1), a monitoring programme would ensure consumer safety.

Information on the geographic origin of milk is important in determining quality attributes and for economic gain through building brand value associated with origin. Stable isotope signatures and trace element concentrations have been increasingly used in authentication of milk, though information on the power of such technology in verifying agroclimatic origin in small continents with diverse climatic, environmental conditions, and animal management practice is scarce. Therefore, the main objective of this study was to investigate the possibility of using a stable isotope composition of C, N, O, and H and element fingerprints to determine the agroclimatic origin of milk produced in different agroclimatic zones of Sri Lanka. Stable isotopes ratios of C, N, H, and O, and elemental fingerprints of milk samples were determined by IRMS and ICP-MS, respectively. Significant variations were observed in stable isotope ratios, especially δ¹⁸O and the mean content of Li, Al, Cr, Mn, and Sr in the bulk milk samples obtained from different agroclimatic zones. A linear discriminant analysis differentiated cow milk produced from four agroclimatic zones based on stable isotope ratios, and the inclusion of elemental ratios enhanced the discriminating ability.

Aflatoxins (AFs) are a group of mycotoxins produced by certain fungi of Aspergillus spp. AFs of major concern are B1 (AFB1), B2 (AFB2), G1 (AFG1), G2 (AFG2), and M1 (AFM1). AFM1 is a hydroxylated metabolite of AFB1 formed inside the animal's body which is excreted into milk of cows that consumed AFB1 contaminated feed. Consumption of AFM1-contaminated milk and subsequent dairy products causes negative health effects in consumers. This study was conducted to determine the occurrence and levels of AFM1 in cheese products available in the Sri Lankan market where AFM1 is not regularly monitored in milk while having an outdated regulatory limit of 1 ppb established for dairy products. Processed cheese (n = 28), hard cheese (n = 14), semi-hard cheese (n = 5), and soft cheese (n = 3) representing seven popular brands were collected. The samples were analyzed by Ultra High-Performance Liquid Chromatography Fluorescence Detection. AFM1 was detected in 40 samples (80 %), while 17 (34 %) and 37 (74 %) of the samples had AFM1 levels exceeding the maximum permitted limit set by Codex Alimentarius Commission (0.5 ppb) and the Netherlands (0.2 ppb). Further, 10 samples violated the Sri Lankan maximum limit of 1 ppb. Thirteen out of the 14 hard cheese (92.9 %, 0.11–14.43 ppb) and all semi-hard cheese samples (100 %, 0.29–0.65 ppb) contained AFM1. Most of the soft (66.7 %, 0.35–0.45 ppb) and processed (71.4 %, 0.11–1.35 ppb) cheese samples had AFM1. Most of the locally manufactured cheese products in Sri Lankan market may pose health risks to consumers. The results highlight the significance of regular monitoring of AFM1 in dairy products and the importance of updating regulations on par with international standards concurrently to ensure consumer safety.

A commercial MALDI-TOF mass spectrometer has been combined with a tunable ns-pulse laser ionisation system consisting of two dye lasers pumped by the second (532 nm) and the third (355 nm) harmonics of a Nd:YAG laser. Uranium samples in the form of solutions, suspensions or small solid grains can be placed onto an aluminium substrate without the MALDI matrix from which they are desorbed by a 337 nm nitrogen laser with a spatial resolution of ∼20 μm. A rapid and simple sample preparation process not involving any chemical separation, pre-concentration or need for chemical derivatisation reactions is employed. The neutral uranium atoms and molecules are resonantly ionised by the photoionisation system. Highly selective and efficient uranium photoionisation schemes have been developed. They are three-colour, two-step photoionisation schemes involving resonance excitation from the ground state by a 424.23 nm laser (∼1 μJ per pulse) and subsequently by either 578.48 nm, 575.42 nm or 574.10 nm lasers (∼20 μJ per pulse) with 1064 nm (>1 mJ) ionisation into the continuum. Three-colour excitation, targeting specific uranium atomic levels, allows for selective ionisation of uranium atoms. The photo-ions have the yields of up to two orders of magnitude higher than those formed in laser desorption making them extremely suitable for the detection of isotope ratios of samples with trace concentrations. A series of measurements of reference materials with concentrations between 10¹⁰ and 10¹⁶ atoms per sample (10⁻¹⁵ to 10⁻⁷ g) and various isotope compositions ranging from depleted and natural to enriched uranium positively confirm the method applicability. For instance, for the samples of depleted uranium the ²³⁵U/²³⁸U < 0.003 ratio was determined with <7% precision (2σ errors) for the total uranium concentrations not exceeding ∼80 fg per sample.