Check standard

A Thermo Finnigan Element 2 Inductively Coupled Plasma Sector-Field Mass Spectrometer (ICP-SF-MS) with guard electrode was employed for trace element analyses. RSD values derived from internal check standard never exceeded 10%. Accuracy was better than 15% for all elements as determined by analyzing the certified reference standard NWRI TM-RAIN 95 trace metal fortified rainwater, every 5 to 8 samples. 

The accuracy of an analysis can be determined by several procedures. One common method is to analyze a known sample, such as a standard solution or a quality control check standard solution that may be available commercially, or a laboratory-prepared standard solution made from a neat compound, and to compare the test results with the true values (values expected theoretically). Such samples must be subjected to all analytical steps, including sample extraction, digestion, or concentration, similar to regular samples. Alternatively, accuracy may be estimated from the recovery of a known standard solution spiked or added into the sample in which a known amount of the same substance that is to be tested is added to an aliquot of the sample, usually as a solution, prior to the analysis. The concentration of the analyte in the spiked solution of the sample is then measured. The percent spike recovery is then calculated. A correction for the bias in the analytical procedure can then be made, based on the percent spike recovery. However, in most routine analysis such bias correction is not required. Percent spike recovery may then be calculated as follows ... 

An interference check standard is a standard solution used to verify an accurate analyte response in the presence of possible interferences from other analytes present in the samples. For methods that have known interference problems arising from the matrix or that are inherent in the method, such as ICP-AES (spectral interference lines) and ICP-MS (isotope combinations with similar masses to analyte), these solutions are used in the batch. The interference check standard must be matrix matched to acid content of the samples. Acceptance criteria are set—for example, the magnitude of uncorrected background and spectral interference must not be greater than a stated value. 

Laboratories using these methods for regulatory purposes are required to operate a formal quality control program. The minimum requirements of the program consist of an initial demonstration of laboratory capability and an ongoing analysis of spiked samples to evaluate and document data quality. The laboratory must maintain records to document the quality of data that is generated. Ongoing data quality checks are compared with established performance criteria to determine whether or not the results of analyses meet the demonstrated performance characteristics of the method. When results of spike sample analyses indicate atypical method performance, a quality control check standard must be analyzed to confirm that the measurements were performed in an in-control mode of operation. 

If any individual P falls outside the designated range for recovery, that parameter has failed the acceptance criteria. When this situation occurs, a quality control check standard containing each parameter that failed the criteria must be analyzed independent of the matrix, that is, spiked reagent water, to demonstrate that the laboratory is operating in control. If this second test is failed, the sample results for those parameters are judged to be out of control, and the problem must be immediately identified and corrected. The analytical results for those parameters in the unspiked sample are suspect and may not be reported for regulatory purposes. 

Although the results for check standards were somewhat high, the extremely low results for the three replicates of lead in the effluent waters from the resins clearly indicate that lead is being removed from the water upon passage through the resin. 

Calibrations were carried out for the GC/PID or the GC/MS daily. Calibration standards were prepared based on standard reference materials obtained from Supelco Chromatography products. A check standard was analyzed every ten samples to assure calibration and accuracy. A reagent blank was included in each analytic batch of samples. Blanks were made from reagent or make-up water and matrix similar to the sample. A spiked sample was analyzed every twenty samples. This was done by splitting an appropriate sample into two subsamples and adding a known quantity of TCE to one of the split samples. The purpose of a spiked sample is to determine the extent of matrix bias or interference on TCE recovery and sample to sample precision. Accuracy was assessed by analysis of external reference standards (separate from calibration standards) and by percent recoveries of spiked samples. Precision was assessed by means of replicate sample analysis. It is expressed as relative percent difference (RPD) in the case of duplicates or relative standard deviation (RSD) for triplicate (or more) analyses. Recovery was 96% or more for all spiked samples, and RPD/RSD are less than 7% for all samples. 

The preparation of a standard calibration curve is required for many colorimetric and gas chromatography analyses. A fresh calibration check standard at any selected concentration should be prepared daily and analyzed prior to sample analysis. If the response for the check standard falls outside of 15% standard deviation for the same concentration in the standard calibration curve, then a new calibration curve should be prepared. 

Routine GC analysis for environmental samples involve running one of the calibration check standards before sample analysis to determine if the area or height response is constant (i.e., within 15% standard deviation of the response factor or calibration factor, and to check if there is a shift in the retention times of the analytes peaks. The latter can occur to a significant degree due to any variation in conditions, such as temperature or the flow rate of the carrier gas. Therefore, an internal standard should be used if possible in order to determine the retention time shift or to compensate for any change in the peak response. If an analyte is detected in the sample, its presence must be ascertained and then confirmed as follows ... 

Limits or combination of limits which, when exceeded, trigger analyst intervention. These limits may be defined statistically or based on test method requirements. Control limits may be assigned to method blanks, check standards, spike recoveries, duplicates and reference samples. Most control limits for toxicity tests are based on thrice the standard deviation of the mean (i.e., one in every 100 tests would be expected to exceed the control limits due to chance alone). Volume 1(10). 

The ORP probes do not require calibration, however, we may use reference standards to verify the probe performance. Standards of a known potential are available from manufacturers the ZoBell s solution may also serve a calibration check standard. 

The ICV check standard has the acceptance criteria that must be met before the analysis may start. 

It should be noted that the tests and specifications listed in Table 7 are provided for guidance and should be set for each individual method based on its application and performance. For example, there may be no resolution requirement for an HPLC dissolution assay. For the same method, it may also be impractical to set the injector repeatability requirement at an RSD of < 1% if the peak response for the API is very small. Again, in the same example it is also impractical to require a check standard to be within 1% of the working standard if the RSD requirement for replicate analyses of the working standard is <2 %. Some ion exchange columns may not provide plate counts of > 2000 or tailing factors of < 2. 

Analytical measurements should be made with properly tested and documented procedures. These procedures should utilise controls and calibration steps to minimise random and systematic errors. There are basically two types of controls (a) those used to determine whether or not an analytical procedure is in statistical control, and (b) those used to determine whether or not an analyte of interest is present in a studied population but not in a similar control population. The purpose of calibration is to minimise bias in the measurement process. Calibration or standardisation critically depends upon the quality of the chemicals in the standard solutions and the care exercised in their preparation. Another important factor is the stability of these standards once they are prepared. Calibration check standards should be freshly prepared frequently, depending on their stability (Keith, 1991). No data should be reported beyond the range of calibration of the methodology. Appropriate quality control samples and experiments must be included to verify that interferences are not present with the analytes of interest, or, if they are, that they be removed or accommodated. 

To relate the physical properties of carbon black to rubber properties, we tested these tread blacks in the ASTM natural rubber recipe and in an SBR 1500 test recipe. In both elastomers, we checked standard stress/strain properties of modulus, tensile strength, and hardness. In the natural rubber recipe we also tested Firestone running temperature and rebound, and Goodyear rebound. In the SBR we checked percent swell, extrusion rate, viscosity, and laboratory abrasion. 

The calibration standards should be analysed from the weakest to the strongest, with blanks between samples to demonstrate that there has been no carry-over between injections. The samples can then be analysed, with check standards analysed between every 4th or 5th sample. 

What are check standards and what is their function ... 

Both barbiturates and benzodiazepines can be identified by using GC-MS methodologies, although each drug class requires a different pre-treatment routine prior to analysis. It should also be remembered, as with all chromatographic analyses, that blanks should be run between each sample nnder investigation and check standards analysed as required by the quality assurance (QA) procedures in place in the laboratory. 

These are samples of known identity and concentration which are used to determine that the chromatographic system and detector are functioning correctly. This is achieved through examination of the retention time and, sometimes, a specific chromatographic property, for example, peak asymmetry, area or height. If the system is performing correctly, then the results obtained from such check standards should be the same every time. 

Check standard A standard analysed in a seqnence which allows the performance of an instrument to be monitored. 

A useful study of the efficiency of some of these procedures for the removal of protein from human plasma is presented by Blanchard (1981). However, it is always necessary to check standard methods for your own particular samples. 

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