Physical and chemical testing is one of the main testing parts of laboratory testing, and its testing results are the main scientific basis for determining product quality. There are three main sources of error in physical and chemical laboratories: systematic error, random error and human error. Then, what are the specific causes of each error?
Instruments, equipment, laboratory environment, operating procedures, reagents, samples and other factors have seriously affected the quality of physical and chemical testing, resulting in many errors in physical and chemical testing.
system
General Error (also known as regular error)
Systematic error refers to the repeated measurement of the same object under repeated measurement conditions. The magnitude of the error value is either positive or negative, which is called the fixed system error, or When the measurement conditions change, the error changes exhibit a certain law, which is also called the variable system error.
Systematic error is mainly caused by the incorrect measurement method, the wrong method of using the instrument, the failure of the measuring instrument, the performance of the testing device itself, the improper use of the standard substance and the change of environmental conditions. Such errors can be reduced and corrected by certain measures.
The main sources of system errors are the following:
1. Method error:
The method error refers to the error caused by the physical and chemical test analysis method itself. This error is unavoidable, so the test result is often low or high. For example, when performing gravimetric analysis in physical and chemical tests, the dissolution of the precipitate is likely to cause errors; there is no complete reaction during the titration, or a side reaction occurs due to the inconsistency of the end point of the titration with the metering point; the high temperature test leads to some volatile substances. Volatilization has occurred.
2. Instrument error:
The instrument error is mainly caused by the inaccuracy of the instrument. For example, if the meter dial is inaccurate or the zero point is inaccurate, the test result will be too small or too large. This error is a constant value; the electronic balance is used. If the calibration is not carried out after too long, the weighing error will inevitably occur; the glass gauge has not passed the inspection of the quality and the scale, and it is used after being purchased from the supplier, which will cause the instrument error to appear.
3. Reagent error:
The error of the reagent is mainly caused by the impure reagent or the failure to meet the experimental requirements, such as the presence of impurities in the reagent used in the physical and chemical testing process, or the presence of interference in the distilled water or reagent, which may affect the inspection result, or due to storage or operating environment. Reagent changes and the like can cause reagent errors.
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Machine error
Repeated measurement of the same object under the same operating conditions, although the occurrence of systematic errors can be avoided to some extent, the obtained test results are not necessarily consistent, and the error caused by various uncertain factors is called random error. This error presents irregular random changes, mainly due to a variety of small, independent, and accidental factors.
From the surface, the random error is irregular, because it is accidental, so the random error is also called unmeasurable error or accidental error.
The randomness characteristic means that the same measurement object is repeatedly measured repeatedly, and the error of the test result exhibits irregular fluctuation, and the test result may be too large (positive) or small (negative), and There is no certain law, but the chances of positive and negative errors appear the same in the case of repeated measurements. It is precisely because of this irregular characteristic that there may be a positive or negative offset of the sum of many random errors. In the case, this is the nature of random error compensability.
Therefore, in the case of eliminating system errors, random errors can generally be eliminated by increasing the number of measurements.
However, it should be noted that both systematic error and random error exist in the normal physical and chemical testing process, which has certain inevitability. The difference in results caused by the normal physical and chemical inspection staff’s inspection process error, incorrect reagent addition, inaccurate operation or reading, calculation error, etc., should be called an “error”, not an error.
Therefore, if there is a large difference between repeated measurements of the same measurement object, it should be considered whether it is caused by “error”. The cause of this result should be carefully analyzed and its properties determined.
people Error
The human error mentioned here mainly refers to the error caused by the inspector’s factors in the physical and chemical inspection process, mainly in the following three aspects:
1. Operational error:
Operational error refers to the subjective factors of physical and chemical inspectors in the case of normal operation.
For example, the inspector’s sensitivity to color observation will lead to errors;
Or when the sample is weighed, there is no effective protection, so that the sample is hygroscopic;
There is an error in the absence of sufficient washing or excessive washing when washing the precipitate;
Did not master the temperature during the burning precipitation;
If the burette is not rinsed before the liquid leakage in the physical and chemical inspection process, the liquid hanging phenomenon will occur, which will cause the air bubbles to remain at the lower end of the burette after the liquid is injected;
Inspectors looking up (or looking down) the scale at the time of the degree will cause errors.
2. Subjective error:
Subjective errors are mainly due to subjective factors of physical and chemical testing analysts.
For example, due to the difference in the degree of sharpness of color observation, some analysts feel that the color is dark when the color of the endpoint of the titration is discriminated, but some analysts think that the color is lighter;
Since the angles at which the scale values are read are different, there are situations in which some analysts feel high, but some analysts feel low.
In addition, for many analysts in the actual physical and chemical inspection work, there will be a “pre-entry” habit, that is, subjectively unconsciously biased towards the first measurement value when reading the second measurement value, above The situation will lead to subjective errors.
3. Negligible error:
Negligible error refers to the error caused by the inspector’s reading error, operation error, calculation error, etc. during the physical and chemical inspection.
Errors can lead to inaccurate results, so understanding the causes of errors can help us minimize the occurrence of errors and improve the quality of the test results.
If you’re in need of information or have any questions, please contact WUBOLAB, the laboratory glassware manufacturer.
