tailieunhanh - Modern Analytical Cheymistry - Chapter 4

Evaluating Analytical Data Một vấn đề đưa ra các yêu cầu chúng ta đặt trên các phép đo và kết quả của chúng tôi. Cơ quan quản lý, ví dụ, đặt các yêu cầu nghiêm ngặt về độ tin cậy của các phép đo và kết quả báo cáo cho họ. Đây là lý do cho việc tạo ra một giao thức cho các vấn đề pháp lý. Sàng lọc các sản phẩm của một tổng hợp hữu cơ, mặt khác, những nơi ít nhu cầu về độ tin cậy của các phép đo, cho phép các nhà hóa học. | Chapter 4 Evaluating Analytical Data A . . problem dictates the requirements we place on our measurements and results. Regulatory agencies for example place stringent requirements on the reliability of measurements and results reported to them. This is the rationale for creating a protocol for regulatory problems. Screening the products of an organic synthesis on the other hand places fewer demands on the reliability of measurements allowing chemists to customize their procedures. When designing and evaluating an analytical method we usually make three separate considerations of experimental First before beginning an analysis errors associated with each measurement are evaluated to ensure that their cumulative effect will not limit the utility of the analysis. Errors known or believed to affect the result can then be minimized. Second during the analysis the measurement process is monitored ensuring that it remains under control. Finally at the end of the analysis the quality of the measurements and the result are evaluated and compared with the original design criteria. This chapter is an introduction to the sources and evaluation of errors in analytical measurements the effect of measurement error on the result of an analysis and the statistical analysis of data. 53 54 Modern Analytical Chemistry 4A Characterizing Measurements and Results Let s begin by choosing a simple quantitative problem requiring a single measurement. The question to be answered is What is the mass of a penny If you think about how we might answer this question experimentally you will realize that this problem is too broad. Are we interested in the mass of United State pennies or Canadian pennies or is the difference in country of importance Since the composition of a penny probably differs from country to country let s limit our problem to pennies minted in the United States. There are other considerations. Pennies are minted at several locations in the United States this is the .