What is a standard solution?
What is a standard solution?standard solutionRefers to a solution containing a specific concentration of parameters, such as a standard solution of Cl or Fe. When a standard solution is used instead of a sample for testing, the results obtained should match the concentration of the known standard solution. If a consistent result is obtained, the test operation is correct. If there is any obvious error (greater than 10%) between the result and the standard value, it indicates that there is an error and needs to be analyzed. The National Standards Network has a variety of standard solutions with concentrations in most test ranges, all of which are nationally recognized products.
Some standard solutions cannot be used because they are so unstable that they are difficult to formulate and use. Such standard solutions include hydrogen sulfide (H2S), chlorine dioxide (ClO2), dissolved oxygen (DO), and ozone (O3). Liquid chlorine standard solutions can only be formulated as high-concentration solutions, so they must be diluted with high-purity water, and glassware that does not consume liquid chlorine must be used.
Standard solutions can also be used to calibrate instruments such as colorimeters and spectrophotometers, as well as electrochemical instruments such as pH meters and pH/ISE meters. Standard solutions of different concentrations can be used to draw calibration curves, so that the resulting calibration curves can be used to check the concentration of the test sample.
Precautions for preparing standard solutions
(1) The water used in the preparation of the solution shall comply with the third-class water specification in GB6683 unless other requirements are indicated. The ethanol used refers to 95% ethanol.
(2) The reagents used in the calibration solution and the preparation of the reference solution are the reference reagents for volumetric analysis. The purity of the reagents used in the preparation of general solutions is not lower than the analytical purity.
(3) The weights, burettes, volumetric bottles and pipettes of the analytical balance used in the preparation of the solution shall be regularly verified according to the requirements of the metrological verification procedures.
(4) The quality of the reagents weighed in the prepared solution should be within ± 10% of the specified quality.
(5) When calibrating the concentration of the standard titration solution, the difference between the concentration value of a single calibration and the arithmetic mean should not be greater than 0.2% of the arithmetic mean. Take the arithmetic mean of at least three calibration results as the actual concentration of the standard titration solution.
(6) Take four significant digits for the concentration of the standard titration solution and the reference solution.
(7) The difference between the concentration value of the prepared standard titration solution and the specified concentration value should not exceed ± 5% of the specified concentration value.
(8) When calibrating the concentration of a solution by calibration and comparison, if there is any dispute, the calibration method shall prevail.
