978-1-4244-2120-6/08/$25.00 ©IEEE. AbstractｲRecently, there have been numerous food scares particularly with the production of milk powders for infants. This has been caused by the addition of excess melamine to increase the tested protein count of a powder. In this paper we investigate the potential of THz-TDS for use in food quality control and compare this technique to other established techniques. I. INTRODUCTION AND BACKGROUND ELAMINE is a nitrogen rich molecule, with six out of the fifteen atoms being nitrogen (C 3 H 6 N 6 ). This high nitrogen content has led to its use as a protein supplement in food powders. This has been the case, with pet foods supplied in the United States 1 , milk powders supplied in mainland China 2 and poultry feed in France 3 . Melamine has typically been thought of as a harmless chemical, as it is used in its plastic form for food packaging. In some recent incidents however, contamination levels of melamine exceeded the European Union tolerable daily intake of 0.5 mg/kg of body weight 4 . This has caused deaths in pets from tainted pet foods, infant deaths and kidney failures from contaminated milk powders and caused a poultry scare with laced chicken feed. In the interests of public safety and to ensure adequate quality of foods, quick and effective methods need to be developed to detect whether foods are within safe standards (no more than 2.5 mg/kg of melamine in food products, set by the European Union 4 ). Mass spectroscopy 5 and liquid chromatography 6 have typically been used for the detection of melamine in food products. These methods have proven to be effective in determining if melamine is present in a sample and also the quantity to within parts per million. However, fairly complex sample preparation is required, and thus blanket sample testing is not possible. Melamine by itself is not the only cause for kidney failures in humans and animals. When melamine is combined with cyanuric acid ((CNOH) 3 ) within an aqueous solution, melamine - cyanurate crystals are formed, causing kidney stone formation and the possibility of acute renal failure 6 . THz-TDS provides an alternative to these established methods. Recently, Harsha et. al. 7 have shown that melamine has characteristic signatures in the THz region with two distinct spectral features at 1.98 and 2.25 THz. THz-TDS provides advantages over these techniques, as it is able to penetrate plastic packaging, sample preparation is simple and cost effective and detection is fast (within minutes). However, the limit of detection of THz-TDS may prove to be a disadvantage when determining the exact quantity of melamine and cyanuric acid present in a given sample. We thus attempt to determine an estimate for the detection limit and compare this with other detection techniques, putting into perspective the advantages and disadvantages of THz-TDS with respect to other techniques. In particular, we compare THz-TDS with an FTIR approach to detection. II. RESULTS Samples of melamine, cyanuric acid, and mixtures are prepared by mixing with polyethylene, which are then compressed forming pellets. These sample pellets are optimized in thickness for maximum bandwidth for both transmission and reflection mode THz-TDS, by varying the amount of sample used. Sample pellets are measured at room temperature to match possible real world usage. Concentrations of melamine were varied, with a dilution table formed to determine the minimal detectable limit of melamine within a sample. The absorption peaks previously reported in literature for both THz-TDS 7 and FTIR 8 were reproduced in experiments, and subsequently we proceeded directly into a dilution series of melamine, cyanuric acid and infant formula. Figure 1: Melamine FTIR spectra from wave numbers 400 to 4000 cm -1 . III. EXPERIMENTAL PARAMETERS Melamine and cyanuric acid were purchased from Sigma Aldrich (M2659 and 185809), while Indocus 13/3 polyethylene was used as a buffering compound and Nestle S-26 infant formula was used as the basis for the dilution series. The mixture was weighed and then mixed crushed into a homogeneous mixture in a mortar and pestle. Pellets of 12 mm diameter were then produced by compressing the mixture in a 10 ton press. Concentrations of melamine and cyanuric acid Benjamin S.Y. Ung, Bernd M. Fischer, Brian H.-W. Ng, and Derek Abbott Centre of Biomedical Engineering, School of Electrical & Electronic Engineering, The University of Adelaide, North Terrace, Adelaide, South Australia, Australia, 5005 Comparative Investigation of Detection of Melamine in Food Powders M         