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eFOOD-Lab_International_01_2016

20 1/2016 eFOOD-Lab international Quality Management or formed during the combustion process are running through the whole system. So the consumption of chemicals and maintenance intervals are tending to be quite high. The second issue is concerning the combustion. Due to the fact that all gases have to pass the TC cell the Oxygen has to be dosed very carefully to avoid the chemicals being used too quickly. Combustion in pure Oxygen is therefore not possible which can cause some issues with incomplete combustion and matrix dependencies. The third commonly used method is working different and is described more in detail: Sample sizes in the macro range are required to overcome the inhomogeneity issues. Typical sample sizes are between 100 mg up to 1 g. Solid samples can be wrapped into tin foils, tin or gel capsules or even get measured directly. Liquid samples can be inserted easily with an eyedropper into a large tin capsule. With the LECO FP 628 system the combustion is done in a vertical furnace at temperatures up to 1050°C in pure Oxygen. For nearly all food and feed matrixes, one analytical method and one calibration is sufficient to cover the whole range of samples being present in a lab. Under these conditions -high temperature and pure Oxygen- any issues with incomplete combustion or formation of methane are avoided principally. Food and feed samples generally contain a higher quantity of water or moisture, which is introduced into the analytical system. A high effective thermoelectric cooler is used to remove moisture/water from the gases. All gases (mainly Oxygen, Nitrogen/NOx, CO2 and some others) are collected in a ballast volume. After combustion is finished the instrument is using an aliquot volume, taken from the collected gases, pushed by an inert carrier gas through the rest of the system. A so called catalyst furnace with hot copper sticks is used to remove excessive Oxygen Picture 2: Gas Flow Schematics FP 628 Table 1: Analysis time High Throughput/High precision and to reduce Nitrogen Oxides. Subsequently CO2 (SO2 and others) are removed by Lecosorb (Sodium Hydroxide on a carrier) and finally Nitrogen is detected by a TC cell in reference flow with the pure carrier gas. See Picture (2) for an overview. This whole process from sample introduction to transmit of result is lasting in the standard setup 4 minutes = 240 seconds. In this setup, Helium is taken as carrier gas and 10 cc aliquot is taken from the ballast volume. So the question is pending how this method can be improved and optimized for higher throughput and lower analysis costs without sacrificing the analytical performance, especially accuracy and precision. Generally 3 parameters were checked here. 1) Aliquot size It is obvious that using a smaller aliquot will lead to two effects: Less sensitivity because of


eFOOD-Lab_International_01_2016
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