Reference standard check

For example, if a carbonaceous sample (S) is examined mass spectrometrically, the ratio of abundances for the carbon isotopes C, in the sample is Rg. This ratio by itself is of little significance and needs to be related to a reference standard of some sort. The same isotope ratio measured for a reference sample is then R. The reference ratio also serves to check the performance of the mass spectrometer. If two ratios are measured, it is natural to assess them against each other as, for example, the sample versus the reference material. This assessment is defined by another ratio, a (the fractionation factor Figure 48.2). 

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. 

SACHEM Inc. of Cleburne, Texas, manufactures various concentrations of tetramethylammo-nium hydroxide (TMAH) solutions to meet customer specifications. To ensure consistent performance, electronic industry requires very narrow concentration specifications for the solutions. In SACHEM s quality control laboratory, standardized acids such as HC1 or H2S04 are used as titrants for the TMAH solutions to check their concentrations. The performance of the assay titration is controlled by daily analysis of internal reference standards (IRSs). If the IRS results are within controlled limits, then the assay results of a product can be reported. If not, the results cannot be reported until the root cause is uncovered and eliminated. Safety glasses and gloves are worn while performing this work in the laboratory. 

Atomic Absorption Spectrophotometers This is a particular kind of spectrophotometer (see, for example, Figure 5.8) that utilizes a flame for the cuvette (requiring some maintenance for stability) and analyzes samples mostly for metals. The reference standards are thus solutions of metals. Such solutions are readily available and certified as being checked against NIST standards. 

The reference standards used for calibration of instruments should be checked for accuracy annually by an authorized measuring institution (e.g.. Office of Weights and Measures or Bureau of Standards). The reference standard employed should have an uncertainty of measurement which is 1/10 to 1/5 the uncertainty required in the measurement equipment. 

Satisfactory results for a method can only be obtained with well-performing equipment. Therefore, before an instrument is used to validate a method, its performance should be verified using universal standards (47). Special attention should be paid to the equipment specifications that are critical for the performance of the method. For example, if detection limit is critical for a specific method, the detector specifications for baseline noise and the response to the specified compounds should be checked. Furthermore, any reagent or reference standard used to determine critical validation parameters should be double-checked for accurate composition and purity. 

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 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. 

However the chemical community has not been dormant in the period since the Convention of the Meter came into being. A vast range of analytical methods has been developed with ever increasing sensitivity and selectivity. Comparability of measurement results has been achieved in many sectors by the use of collabora-tively studied methods, reference materials, check samples and proficiency testing schemes. It is only recently that steps have been taken to develop traceability to international standards. In developing this traceability much can be learnt from the way traceability has developed for physical measurements. 

The material from an appropriate bulk supply of the matrix material is weighed into a suitable container and homogenised. Where appropriate, portions of the matrix material are tested for the analytes of interest and for possible interferences. Pesticide and environmental test samples are usually prepared by spiking known amounts of substances of specified chemical purity into the bulk sample matrix. The spiking process is witnessed and cross-checked by a second scientist and full records of the process and of reference standard solutions used are maintained so that they can be verified if required. 

The calibration step is critical. In general, the basic principle is always to use two independent calibration solutions. One of these can be made from pure chemicals, for example, Hg° dissolved in concentrated HN03 and diluted to the appropriate volume. For mercury, commercially available standard solutions can be used, but regular checks against a reference standard must be made. Certified reference materials (CRFs) should be used if available, but reference standards can also be prepared from pure mercury compounds. In the absence of aqueous-phase reference standards, solid materials may be used. 

Regarding laboratory controls, a review of laboratory notebooks and chromatograms should be done to check the reliability and authenticity of the supporting data in the methods development and testing of the clinical, bio, and stability batches. Reference standards used should be certified as standards. The FDA expects that, for bulk substances, the suitability of reference standards should be more extensive than that of bulk drug substance specifications. A comparison of analytical methods and specifications for lots of drug substance used in clinical batches and biobatches should be performed to see if any deletions or revisions to any specifications occurred. 

For purposes of the FCC, the melting range or temperature of a solid is defined as those points of temperature within which or the point at which the solid coalesces and is completely melted when determined as directed below. Any apparatus or method capable of equal accuracy may be used. The accuracy should be checked frequently by the use of one or more of the six USP Melting Point Reference Standards, preferably the one that melts nearest the melting temperature of the compound to be tested. 

Note Determine the suitability of the substrate and check the adjustment of the spectrophotometer by performing the assay using USP Trypsin Reference Standard. 

The validity of the method of standard additions depends on the forms of the analyte element in the sample and in the added standard responding in the same way during the atomisation step. This may not always be so in practice. For example, in determining lead in whole blood by this method it would have to be proved (or assumed) that lead added as a lead nitrate solution is atomised to the same extent as lead bound organically in the sample. This is most easily checked by running a certified standard material through the procedure. If no such reference standard exists, as with the above blood example, the sample should also be run after pre-treatment for removal of the matrix, e.g. wet or dry ashing, and the results compared. 

The development and standardization of reliable test procedures requires an ample supply of well-characterized reference materials. These samples are used for round-robin tests by participating laboratories in the method development. A reliable set of reference materials are available from the National Bureau of Standards. These special reference materials are described by Haines in this symposium series. The Bureau has packaged the materials in an appropriate size and secure container. Producer and user laboratories have these reference materials available to cross-check results and resolve differences in specification analyses. These reference standards are available at a reasonable cost. 

The performances of the machine as well as the environmental aspects are checked according to the methodology. All aspects included in the methodology are taken into account and presented on resume graphics. The safety check includes the reference standards used for the inspections made with the date as validity for the test report. An additional section can give information on the national road regtilations and on how to act on... 

Some degradation products are either very polar or very nonpolar in nature this may present an issue in chromatography, where they may not be retained or strongly adsorbed on the column, respectively. One may also want to double check the reference standard for its purity, moisture content, and/or salt/ acid-base ratio for calculation. An analytical chemist must remember to explore all possibilities if mass balance issue is observed (either during method development, validation and/or stability testing). 

As already mentioned, the main advantage of CRMs lies in the availability of the true value . In other words, it is a reference value that is considered as the best estimate analytical sciences can give for the real content of the substance in the particular material. As such CRMs represent the only way to check trueness easily. The verification of trueness will consist in a statistical comparison of the value determined by the operator on the CRM and the certified value. Again it must be stressed that this has no sense if the method s precision is too large. The trueness of a method can be verified within the laboratory or through an interlaboratory study, in particular when a reference standard or an official method is concerned. 

N.S. with another project. Since their main business is to prepare certified reference standard solutions for their customers, their laboratory workers spend much time running tests on these solutions to assure their quality. For example, the atomic absorption standard solutions that were earlier suspected by their lab as being contaminated must have a concentration of the indicated metal of 1000 ppm. Their quality assurance laboratory runs quality checks daily on these solutions and the solutions cannot be sold until the laboratory issues the certificate that states that they indeed have the required concentration. In addition, an expiration date must be stamped on the labels of these solutions and so, occasionally, they run tests on solutions that have been manufactured previously but not shipped. 

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