Quality assurance of analysis is often demanded by a wide range of users interested in the analysis of raw steel or finished steel products. These users include international public and private organizations, such as the ISO, JIS, ASTM, ASME, LA, and Defense Agencies, manufacturers, such as automobile makers, and individual users. The most important factor required by any quality assurance is the accuracy of analysis making it possible for all values analyzed to meet authorized standards. The second most important factor is the ease of tracking back to find when, how, by who, and under what conditions or environments the analysis was made. In order to satisfy these factors, the above tasks must be standardized and prepared in writing as guidelines or references. Their contents must provide steps to make it possible to ensure that the results of analysis will be obtained by taking the provided steps. As an example, quality assurances of analysis are explained below with the carbon detection method (EMIA) and nitrogen detection method (EMGA) provided in Steel Analysis (Analysis of Control of Processes in 24-hour Operation). The example introduced here is typical. Other quality assurance systems may be applied if they are proper and suitable. 紅外碳硫分析儀（EMIA-920V2系列） 紅外碳硫分析儀（EMIA-320V2）