# There are several points to be done on the water quality testing standard curve (what is the basis for the standard curve)

by：BOQU     2022-08-09

The purpose of drawing a standard curve in water quality testing is to find out the content of the substance to be tested according to the standard curve, so the formulation of the standard curve is essential to work in laboratory work. However, in the real experiment process, various problems will be encountered in making the standard curve, such as how many points should the standard curve need? Let's analyze it below.

The standard curve requires several data points, which are related to the concentration range of the detected component, the response characteristics of the analyzer, the interference factors, the concentration, and the response type of the detected signal.

3 points: For some low concentrations, especially microanalysis, and the concentration range is not very large, the detector response is reliable, and the background interference is very small, you can choose fewer working points, generally there are 3 concentration points. Enough is enough, some can even use only one concentration point, and the other point directly uses the coordinate origin.

4 to 6 points: For the sample concentration range measured at ordinary times is wide, and the detector response is not completely a linear curve (straight line), a quadratic curve or piecewise correction method can be used to reduce the data deviation. Need to use a few more data points, if not segmented, 4~6 data points are enough.

At least two points: But in the case of segmented corrections, at least two data points are required per segment. For some samples with no regularity in the concentration range, especially some testing institutions, if the detection response of the analyzer is reliable and the influence of environmental factors is small, a calibration curve can be made. If the influence of environmental factors is large, it is not necessary to make a calibration curve, and it is simpler to use the standard addition method or the standard addition-one-dilution method.

In fact, we generally make five points for the standard curve (excluding zero concentration); generally, the first point is 5~10 times of the detection limit, and then increases by 1 time, and the highest concentration is 10~20 times the lowest concentration. times is appropriate (for example, physical and chemical analysis experiments). Of course, it should be adjusted according to the sensitivity of the instrument.

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