Reference materials standard solutions

Standard Reference Material See certified reference material, standard solution A solution whose composition is known by virtue of the way that it was made from a reagent of known purity or by virtue of its reaction with a known quantity of a standard reagent, standard state The standard state of a solute is 1 M and the standard state of a gas is 1 bar. Pure solids and liquids are considered to be in their standard states. In equilibrium constants, dimensionless concentrations are expressed as a ratio of the concentration of each species to its concentration in its standard state. 

The primary element standards especially the primary pure elements are used for the production of other reference materials (Element-solutions for PTB/Merck and EMPA/Fluka as well as isotopic standards for IRMM [Joint European Project for Primary Isotopic Measurements=JEPPIM]). 

An analyst needs to calibrate an atomic absorption spectrophotometer used for the determination of lead in milk samples. The analyst can purchase a certified reference material (CRM) solution of lead in nitric acid. This CRM is used to prepare a set of calibration standard solutions of known concentration of lead. These calibration standards, along with a suitable blank material (see Section 5.4), are used to calibrate the instrument. 

Adapted from Y. C. Wu, W. K. Koch, and R. A. Durst, Standard Reference Materials Standardization of pH Measurements, NIST lecial Publication 260-53. Gaithersburg, MD U.S. Department of Commerce. 1988, http //ts.nist.gov/is/hldocs/230/232/SP PlJBUCAnONS/docuiiients/SP260-53-pdf. Updated values from most recent NIST SRM ceriihcates. m B molality (mol solute/kg HjO). 

It should be noted that the costs of calibration standards, reference materials, chemicals, solutions, and acids are also something you have to plan for, but will not be used in this evaluation as they are not considered instrument-running costs. However, they are also required to carry out a complete assessment of each of the four techniques. For example, in ICP-MS, multielement standards are generally less... 

It should be noted that the costs of calibration standards, reference materials, chemicals, solutions, and acids are also something you have to plan for, but will not be used in this evaluation as they are not considered instrument-running costs. However, they are also required to carry out a complete assessment of each of the four techniques. For example, in ICP-MS, multielement standards are generally less expensive than purchasing the same number of single-element standards. In flame AA, it is fairly common to use iouization buffers to minimize the effects of easily ionizable elements. In ETA, matrix modifiers are widely used to change the volatility of analyte or matrix elements. Whereas in ICP-OES and ICP-MS, internal standards are used in the majority of analyses, especially if the sample matrices are different from the calibration standards. 

Vapor-phase decomposition and collection (Figs 4.16 to 4.18) is a standardized method of silicon wafer surface analysis [4.11]. The native oxide on wafer surfaces readily reacts with isothermally distilled HF vapor and forms small droplets on the hydrophobic wafer surface at room temperature [4.66]. These small droplets can be collected with a scanning droplet. The scanned, accumulated droplets finally contain all dissolved contamination in the scanning droplet. It must be dried on a concentrated spot (diameter approximately 150 pm) and measured against the blank droplet residue of the scanning solution [4.67-4.69]. VPD-TXRF has been carefully evaluated against standardized surface analytical methods. The user is advised to use reliable reference materials [4.70-4.72]. 

The accuracy of the method depends upon the precision with which the two volumes of solution and the corresponding diffusion currents are measured. The material added should be contained in a medium of the same composition as the supporting electrolyte, so that the latter is not altered by the addition. The assumption is made that the wave height is a linear function of the concentration in the range of concentration employed. The best results would appear to be obtained when the wave height is about doubled by the addition of the known amount of standard solution. This procedure is sometimes referred to as spiking. 

Quantification is by reference to an external standard solution of the feedstock appropriate to the sample to be analyzed. The method assumes that the free oil has the same refractive index as the appropriate feedstock material. 

Prepare stock solutions (nominally 0.1 mgmL 100 ppm) of each labeled analyte (to be used as internal standards), by dissolving reference material in methanol. The reference materials should be stored in a refrigerator and protected from light when not in use. 

Accuracy of in vivo and in vitro measurements of americium is determined through the use of standard, certified radioactive sources with known concentrations of americium. The primary source of certified americium standards is the National Institute of Standards and Technology (NIST). Standard solutions are available for241 Am (SRM 4322, 40 Bq/g [1.1 nCi/g]) and 243Am (SRM 4332, 40 Bq/g [1.1 nCi/g]). Standard Reference Materials for human lung (SRM 4351) and human liver (SRM 4352) are also available from NIST. 

In analytical chemistry, we do not have a standard mole. Therefore, solutions made up to a well-defined concentration using very pure chemicals are used as a basis from which we can compare other solutions or an instrument scale. This process is calibration . For some analyses, the chemical used may be a Certified Reference Material which has a well documented specification, e.g. in terms of the concentration of a particular species and the uncertainty of the specified value. However, it is not sufficient just to calibrate the apparatus/equipment used, it is important that the complete method of analysis is validated from extraction of the analyte from the sample to the final measurement. 

The limit of quantitation (LoQ) is the lowest concentration of analyte that can be determined with an acceptable level of uncertainty. This should be established by using an appropriate reference material or sample. It should not be determined by extrapolation. Various conventions take the approximate limit to be 5, 6 or 10 times the standard deviation of a number of measurements made on a blank or a low-level spiked solution. 

A standard reference material with an accepted analyte content of 5.85 ppm was used to compare the performance of two alternative methods of analysis. Solutions were prepared using a range of sample weights. Each solution was analysed by the two methods. Use the results obtained to assess any determinate errors exhibited by the methods. 

Generally speaking, alternative methods (including on-line, off-line or in situ methods) may be used provided it can be demonstrated that equivalent results with those of reference procedures can be obtained. The experiments are generally carried out with standard solutions and reference materials for the determination of the method characteristics. The equivalence between methods must be statistically verified by plotting the results (Fig. 5) and checking the coordinates of the experimental regression fine (comparison of the slope and intercept values, which must be not statistically different from respectively 1 and 0 values of the theoretical fine). 

Ideally both the control materials and those used to create the calibration should be traceable to appropriate certified reference materials or a recognised empirical reference method. When this is not possible, control materials should be traceable at least to a material of guaranteed purity or other well characterised material. However, the two paths of traceability must not become coincident at too late a stage in the analytical process. For instance, if control materials and calibration standards were prepared from a single stock solution of analyte, IQC would not detect any inaccuracy stemming from the incorrect preparation of the stock solution. 

Since certified reference materials for seawater nutrient analysis are currently unavailable, individual laboratories must prepare their own standard solutions for instrument calibration. Standard stock solutions are prepared at high concentrations (mM) so that they can be used for months without significant alterations in concentration. Working low-concentration standard solutions are unstable and need to be prepared daily by diluting stock solutions with distilled water or low-nutrient seawater. In this case, the accuracy of nutrient analysis at a given laboratory is highly dependent upon the accuracy of the daily preparation of the calibration solutions. 

In the 1970s, the Sagami Chemical Research Center in Japan provided nutrient reference material for the Cooperative Study of the Kuroshio Current (the so-called CSK standards). These solutions were not prepared in seawater, which limits their general utility (see below), however they are still distributed and widely used as a common reference. French and British scientists have conducted some studies on nutrient reference material (Aminot and Keroul, 1991, 1996 Zhang et al., 1999) with limited success. 

A QC assessment was done for all samples. De-ionized water field blanks were collected on seven different days to evaluate process contamination. Site duplicates were taken at eight sites to evaluate repeatability and site variation. Instrumental precision was constrained by analysis of laboratory duplicate solutions, and is typically less than 5%. Finally, standard reference material (SRM) water standards were analyzed with sample batches, to assess instrumental accuracy. 

In this book, standard is used only in the sense of written standard and the term measurement standard or etalon (in French etalon )(see slide 36) is used to describe chemical or physical standards used for calibration purposes such as chemicals of established purity and their corresponding solutions of known concentration, UV filter, weights, etc. They are also called reference materials. 

A sample for which the true response is already known or is established is called a standard. A standard can be a primary standard, which is a standard through which other substances or solutions are made to be standards. It can also be a secondary standard, a solution whose concentration is known accurately either because it was prepared using a primary standard or because it was compared to another standard. All standards must ultimately be traced to a standard reference material (SRM). Standard reference materials are available from the National Institute of Standards and Technology (NIST) and should not be used for any other purpose in the laboratory (Section 5.4). Standardization is an experiment in which a solution is compared to a standard in order for itself to be a standard. The solutions used to establish a standard curve are often called reference standards and these must also be traceable to an SRM. 

In the above discussion, standard reference materials (SRMs) were mentioned often. A reference material (RM) is a material or substance suitable for use in calibrating equipment or standardizing solutions. A certified reference material (CRM) that a vendor indicates, via a certificate, is an RM. A standard reference material (SRM) is one that is distributed and certified by a certifying body, such as NIST. The SRM is the material to which all calibration and standardization materials should be traceable. A standard material becomes one when it is compared to or prepared from another. Ultimately, it all rests on the SRM — meaning all standard materials are traceable to an SRM (see Figure 5.10). 

In this reaction purified tetrahydrofuran (THF) is required, as well as a standardized solution of Li[AlH4] in tetrahydrofuran. The THF from freshly opened bottles is distilled from Li [A1H4]. ("Caution. Li[AlHJ is a hazardous material and must be handled in dry conditions and in small quantitites. Serious explosions can occur when impure THF is purified if it contains peroxides (see Reference 7). 

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