Method Characteristic Parameters of a Linear Calibration Function

1 Method Characteristic Parameters of a Linear Calibration Function 

The quantities x and y represent the mean values of the values x , and y,. The slope b is measure for the sensitivity of a method. The larger the slope, the more sensitive the method is and thus, the more easily small concentration differences can be measured. This means that a small concentration change in the samples will lead to an utmost change of the measured value. This demand is especially important for trace analysis. 

An intercept different from zero means that a signal is measured even when the concentration is zero. The blank value represents a constant, systematic error. Although this blank value can be subtracted from all measured values, it is much safer to work with the calculated caUbration function including the intercept. 

The measure for the relation between Xi and y,- is given by the correlation coefficient r y. 

The method characteristic parameters [21,24-27] can be determined with the aid of regression coefficients. This includes the residual standard deviation Sy 

This coefficient is independent of the unit of the characteristics and may have any value between -1 and +1. If = 1, the relation is directly linear. The correlation coefficient is an important criteria for linearity. However, its information value should be regarded in a more distinguished way, because a high absolute value represents a necessary, but not sufficient, measure for linearity. The statement method A has a larger correlation coefficient than method B, therefore, method A is better is per se not correct. Even if r is equally high, we do not know much about the quality of two different methods. It has to be 

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