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33 commonly used concepts in physical and chemical analysis and testing!---Nanjing Binglab

Views: 0     Author: Site Editor     Publish Time: 2023-08-09      Origin: Site

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33 commonly used concepts in physical and chemical analysis and testing!---Nanjing Binglab

To suit applications requiring chemical resistance, high purity and the ability to handle a broad operating temperature range.


In the process of sample atomization and transmission, due to changes in properties such as viscosity and surface tension, especially if the sample contains high-soluble solids or high acidity, it is easy to cause obvious analysis errors. Using a peristaltic pump will reduce this type of interference. ; If the type of interference still exists, the sample must be diluted or corrected by the standard addition method.



1. accuracy:

Analyze the degree of agreement between the detected value and the true value or acceptable reference value. It can be expressed as a percentage of analytical reference standard samples or quality control samples.


2. precision:

The degree of coincidence between the detected values is the repeated analysis and detection of samples. It can be expressed by calculating the relative standard deviation (RSD) of repeated test values of the sample or by calculating the relative difference (Relative percent difference, RPD) of the two repeated analysis values.


3.matrix:

The main substances that make up the sample


4.blank:

Each analysis and detection should be analyzed at the same time, and it can be divided into three types according to its purpose:

① method blank, or reagent blank:
Purpose: To confirm whether the sample is contaminated during the analysis and detection process. Usually, the reagent is used as the sample, and it is processed and analyzed with the same detection method as the sample to be tested, and the measured value is the method blank value.

② trip blank:
Detect organic matter samples for contamination during transport. The reagents can be packed into the same container as the sample and sealed to the sampling site, and then shipped back to the laboratory with the sample. As the same sample for detection and analysis. The measured value is the shipping blank value.

In the laboratory, put the reagent, aqueous solution or adsorbent that does not contain the substance to be tested into the same sampling bottle as the sample to be tested, screw the cap tightly and bring it to the sampling site, but do not open it on site. After the sampling is completed, bring it back to the laboratory at the same time as the sample to be tested, and use the same pretreatment and analysis steps as the sample to be tested to test; the analysis results of the blank sample can be used to determine whether the sample has been contaminated during transportation.

③Field blank:
When sampling at the sampling site, open the cap of the reagent bottle and close it tightly after the sampling operation is completed, then the reagent is a blank sample on site. In the laboratory, put the reagent, aqueous solution or adsorbent that does not contain the substance to be tested into the same sampling bottle as the sample to be tested, screw the cap tightly and bring it to the sampling site, unpack it on site and simulate the sampling process, but do not Take actual samples, seal them and bring them back to the testing room at the same time as the samples to be tested. It is tested according to the same pretreatment and analysis steps as the sample to be tested; the analysis result of the blank sample on site can determine whether the sample is contaminated during the sampling process.

For blank sample analysis, the laboratory can perform field blank and transport blank sample analysis according to actual needs. However, the laboratory should at least carry out a sample analysis of a reagent blank when analyzing samples of the same batch, and the measured result is the blank value of the laboratory. Unless otherwise specified, usually at least one reagent blank sample analysis should be performed for every 10 samples, and if the number of samples per batch is less than 10, one reagent blank sample analysis should be performed per batch. The laboratory should record the blank sample number, analysis date, and blank measured value.

The blank sample analysis of the gravimetric method is replaced by the empty weight of the filter paper, and no separate blank sample analysis is required. When samples are analyzed by gravimetric method, each sample shall be analyzed at least twice before a report can be issued.

The meaning of the reagent blank sample analysis is different from that of the zero point of the calibration line. In some detection methods (such as: hexavalent chromium), the zero point of the calibration line cannot be used instead of the reagent blank sample analysis. Sample analytical absorbance shall not be deducted.


5.duplicate:

Repeated sample analysis refers to dividing a sample into two equal parts, and performing more than two analyzes on the same sample in the same batch according to the same pretreatment and analysis steps (including sample pretreatment and analysis steps), so as to determine the operating procedure of precision. Samples for repeated analysis shall be quantifiable samples. Unless otherwise specified in the test method, usually at least one repeated sample analysis shall be performed for every 10 samples. If the number of samples per batch is less than 10, one shall be performed per batch. Repeat sample analysis. If repeated analysis of samples cannot be performed, at least repeated analysis of check samples should be performed. The laboratory should record the number of repeated samples, the date of analysis, and the measured value of repeated analysis.


6.matrix spike:

Add a concentrated standard of known concentration to the sample, and analyze and calculate the recovery rate of the addition through the same procedure as the original sample, which can detect the matrix effect of the sample and the error of the detection method.


7.laboratorycontrol sample:

A sample containing matrix and a known concentration of analyte. Its purpose is to check the efficiency of the whole detection method. Samples with defined concentrations can be used.


8.methoddetection limit(MDL):

Is the smallest concentration value greater than zero that can be detected with 99% confidence. Usually for samples containing matrix, understand the detection limit IDL of the instrument used before execution.


9.instrumentdetection limit(IDL):

The smallest limit that the instrument can detect. Generally, when the signal of the instrument is 2.5~5.0 times of the noise, or the obvious turning point of sensitivity in the range of the calibration line. Obtained by testing samples without the sample preparation process.


10.Batch:

As the basic unit of quality control, it refers to samples that are tested together with the same pretreatment and analysis steps using the same detection method, the same set of reagents, within the same time period or within a continuous period of time. Each batch of samples shall have the same matrix or a similar matrix.


11.QualityCheck Sample:

Refers to the sample prepared by adding a standard product of appropriate concentration (different from the standard product of the prepared calibration line) to a matrix similar to the sample; or directly purchasing a sample with a confirmed concentration as it, by which the accuracy of the analysis results can be determined.


12.SpikedSample:

In order to confirm whether there is matrix interference in the sample or whether the detection method used is appropriate, the sample is divided into two equal parts, one part is directly detected according to the sample pretreatment and analysis steps, and the other part is added with an appropriate amount of standard substance to be tested Then follow the sample pretreatment and analysis steps to detect it, and the latter is called the spiked sample. In this way, the applicability of the detection method and the matrix interference of the sample can be understood. The added concentration should be close to the regulatory standard or equivalent to the sample concentration.


The recovery rate of the added standard product can be calculated from the measured values of the amount of the added standard product, the unspiked sample and the added sample. If the recovery rate falls outside the control range, the cause should be diagnosed immediately, and all the measured values of the same batch should be regarded as different. Reliable, repeat the analysis after taking corrective action. In this way, the matrix interference and applicability of the sample of the detection method can be understood.


Unless otherwise specified in the test method, usually at least one additional sample analysis should be performed for every 10 samples at the same time, if the number of samples per batch is less than 10, then one additional sample should be analyzed per batch. The laboratory shall record the analysis date, added sample number, added standard concentration (amount), unadded sample concentration (amount), added sample concentration (amount), and added recovery rate.


13.CalibrationCurve:

Refers to the correlation curve drawn by a series of standard solutions with known analyte concentrations and the corresponding instrument induction signal values.


14.Verificationof Calibration Curve:

The standard curve confirmation is to check the applicability of the standard curve with the standard solution containing the analyte, and the standard solution should be prepared from a standard different from the standard solution prepared for the standard curve. After the standard curve is prepared, the applicability of the standard curve should be confirmed with a standard solution different from the standard source used for standard curve preparation. The concentration of the standard solution confirmed by the standard curve is recommended to be confirmed by the middle concentration of the standard curve.


If it is a continuous operation on the same working day, the standard curve should also be confirmed every 12 hours. From the sensor signal value on the instrument, use the established standard curve to obtain the concentration, compare the measured value with the standard curve to confirm the concentration of the standard solution, and calculate the relative error value.


15. Check sample analysis:

Refers to the sample prepared by adding the standard substance of appropriate concentration (different from the standard substance for the preparation of the standard curve) to a matrix similar to the sample; or directly purchasing the sample with confirmed concentration to act as it. This allows the accuracy of the analysis results to be determined.

Unless otherwise specified in the testing method, usually at least one check sample should be analyzed at the same time for every 10 samples, if the number of samples per batch is less than 10, one check sample analysis should be performed per batch. The laboratory shall record the number of the check sample, the date of analysis, the concentration value of the check sample, the measured value of the check sample and the recovery rate.


16.Optimumconcentration range:

The concentration range indicated by the upper and lower limits. When the concentration is lower than the lower limit, the scale of the display needs to be enlarged and lowered to extend the range downward; when the concentration is higher than the upper limit, linear correction is required. This concentration range varies with the sensitivity of the instrument and the operating conditions used.


17.Sensitivity:

Atomic absorption spectrometry AA: expressed in milligrams of metals per liter of solution that can produce 1% absorbance. ICP: expressed by the slope of the calibration line established as a function of the intensity of the emitted light and the concentration.


18.Interferencecheck sample,ICS:

Solutions containing known concentrations of interferents and analytes can be used to check background and correction factors for interelemental interferences.


19.Initialcalibration verification (ICV) standard:

A validated or independently prepared solution used to check the accuracy of the initial calibration curve.


20.Continuingcalibration verification,CCV:

Used to confirm the calibration accuracy during analysis. This calibration needs to be done for each analyte in the analytical method. At a minimum, a continuous calibration confirmation standard must be analyzed once before sample analysis and after sample analysis, and its concentration must be at or near the midpoint of the calibration line.


21.Calibrationstandard:

A series of standard solutions of the analyte of known concentration used to calibrate the instrument (ie, to prepare a calibration curve).


22.Lineardynamic range:

The calibration curve presents a linear concentration range.


23.Methodblank:

Reagent water was prepared through the same procedure as the sample.


24.Calibrationblank:

Add the same type and quantity of solution as the standard and sample to the reagent water.


25.Laboratorycontrol standard:

Add the analyte of known concentration to the reagent water, and go through the same preparation and analysis steps as the sample. This system is used to check the sample loss/recovery value.


26.Methodof standard addition,MSA:

The standard addition method is for unknown samples, and several known but different standards are added to the unknown samples for analysis respectively.


27.Sampleholding time:

Under the specified preservation and storage conditions, the validity period after the sample is collected and before the sample is analyzed.

The calibration line must be prepared every day, and there must be at least one blank and four concentration standard solutions. After the calibration line is completed, at least one calibration line blank and one calibration line near the middle concentration must be used to check the standard solution (by reference material or Standard preparation from other independent sources) to determine the calibration curve accuracy. Calibration curves can only be considered valid if the deviation between the measured value of the calibration line reference standard and the true value is within 10%.


28. Dilution test:

For each analysis batch, select a representative sample for serial dilution to determine whether there is interference. The concentration of the analyte must be at least 25 times the estimated limit of detection.


After determining the crude concentration of the undiluted sample first, dilute at least 5 (1+4) times and re-analyze. If all samples from this batch were at concentrations below 10 times the detection limit, then the addition recovery analysis described in the following section was considered correct. If the difference between the undiluted sample concentration and the 5-fold value of the diluted sample concentration is within 10%, it means that there is no interference, and it is not necessary to use the standard addition method for analysis.


29. Recovery rate test:

If the results of the dilution test do not meet the above requirements, it means that interference may exist, and at this time the added sample must be analyzed to help determine the results of the dilution test. Take another part of the test sample, add a known amount of the analyte to make the concentration of the analyte 2 to 5 times the original concentration; if the concentration of the analyte in this batch is lower than the detection limit, the selected samples were spiked 20 times the limit of detection.

The spiked samples were analyzed and spiked recoveries were calculated. If the recovery is lower than 85% or higher than 115%, all samples from the batch must be analyzed by the standard addition method.


30. Standard addition method:

The standard addition technique means adding a known amount of a standard to one or more processed sample solutions. This technique can compensate for the slope deviation (the slope of the sample is different from that of the calibration line) caused by the enhancement or reduction of the analysis signal due to the composition of the sample, but it cannot correct the baseline shift caused by additive interference. The standard addition method is applied to the analysis of extracts from all extraction procedures, commissioned analysis for delisting petitions, and analysis of each new sample matrix.


31. Spectral interference can be divided into:

① Overlapping of spectra of different elements;
② Overlapping of molecular spectra that cannot be resolved;
③The background caused by the spectral continuum phenomenon;
④ Disturbance caused by high-concentration elements.

Interfering elements can be determined separately for overlapping spectra, and then the overlapping spectra can be corrected. The overlapping of sub-spectrum requires selection of different wavelength sources. As for the background value and high concentration spectrum, it can be corrected by adjusting the baseline. When multiple elements are measured simultaneously, there is no spectral interference between elements in the detection channel of the sampling instrument, because each instrument system is different.


32. Physical interference:

In the process of sample atomization and transmission, due to changes in properties such as viscosity and surface tension, especially if the sample contains high-soluble solids or high acidity, it is easy to cause obvious analysis errors. Using a peristaltic pump will reduce this type of interference. ; If the type of interference still exists, the sample must be diluted or corrected by the standard addition method.


In addition, the deposition of high-concentration salts on the sprayer will affect the analysis results, which can be reduced by diluting the sample or using a nozzle washer. The flow rate of argon will also affect the best flow controller for the instrument.


33. Chemical interference:

Refers to disturbances such as the formation of molecular states, ion effects, and solute volatilization effects. Usually these effects are not significant on the technique of ICP, but if they still exist, the interference can be reduced to lowest.



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