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eFOOD-Lab_International_01_2016

Quality Management 1/2016 eFOOD-Lab international 21 less analysis gas measurement and less chemical consumption of Copper sticks and Lecosorb. The speed is not affected at all by changing this parameter. The standard 10 cc aliquot loop has been changed by a 3 cc aliquot loop. So the chemical lifetime and maintenance will be ~ 3 times higher than before (e.g. the copper sticks will last 2000 analyses instead of ~ 600). 2) Carrier gas type Generally Helium or Argon can be used as carrier gas. The sensitivity of a TC cell is depending on the difference of thermal conductivity between the carrier gas and the gas that should be measured, in this case between Nitrogen and Helium or Argon. This difference exceeds more than 5 times in case of Helium as a carrier gas instead of Argon. The big advantage of Argon as a carrier gas is the lower price and the more or less unlimited availability. The analysis time is slightly longer and the system will be less sensitive. The question is, if the difference in sensitivity and precision are perceptible and can be tolerated for “real” samples. 3) Instrument setup There are several equilibration and purging times that can be modified to speed up the system. In a special optimization process a high speed mode has been created that is accelerating the analysis speed to increase the sample throughput. The one mode is called “high throughput” the other one “high precision”. So of all possible permutations 3 setups were checked: (a) Helium carrier gas with 10 cc and (b) 3 cc loop and (c) Argon carrier gas with a 10 cc loop. All three configurations were run in the high throughput and high precision mode. Different flour samples together with fodder and pet food samples were used in this comparison test. See table 2 and 3. The four human food samples are samples representing a wheat, rye, rice and corn matrix source. The four samples were all LECO reference materials with certified values for nitrogen/ protein. Generally it can be seen that the difference between the various setups is in the limit of what can be expected in an analytical laboratory. The accuracy is 100% fulfilled for feed and flour (food) samples. It can be seen that the precision for the samples are more or less at the same level, comparing high precision and high throughput methods. Without further data a significant difference cannot be marked. Comparing the 10 cc Helium with the 3 cc Helium and the 10 cc Argon precision slightly drops but is generally still within 1% RSD with a few exceptions. The analytical speed and throughput has increased about 13% by changing the analytical setup to the “high throughput method”. This is roughly the same level the throughput decreases by changing from Helium to the cheaper Argon. Looking to the analysis costs, a change in the setup causes a reduction of analysis costs when changing from 10cc Helium loop to 3 cc Helium loop of roughly 15%. When changing from 10cc Helium loop to 10 cc Argon loop the cost decrease for 7% only. Conclusion: It was shown that sample throughput and operation costs for LECO FP628 total protein analyzer are optimized without sacrificing analytical performance. Even when operating with small aliquot size or cheap argon carrier gas, the instrument demonstrates sufficient analytical performance for all types of food and feed samples. The nitrogen/protein mean value does not show any bias. While changing test conditions or carrier gas. The precision (RSD) is slightly decreasing, while being very acceptable for all applications in the range of 1% or less (beside some exceptions). Examples taken from: “Optimizing a Total Protein Combustion Instrument” – Poster Presentation Dennis Lawrenz, Mason Marsh, Jeffery Gast, Fred Schultz | LECO Corporation, St. Joseph, MI Table 2: Feed samples Table 3: Food samples


eFOOD-Lab_International_01_2016
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