Standard reference material section preparation

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. 

Certified (Standard) Reference Materials (CRM/ SRM) Real-world samples, as similar as possible to the unknown samples to be analyzed, for which the concentra-tion(s) of analyte(s) have been certified by expert laboratories using several independent analytical methods under strict international conditions (Section 2.2.1). Such materials are rare and expensive, and if available are used only occasionally to check on the performance of the method and/or to validate reference materials prepared in-house. 

In many instances, the analytical reference standard will be readily available from one or more commercial sources but this is not always the case. Certified reference materials (Section 2.2.2, not natural matrix CRMs but calibration solutions that are solutions of a reference standard at a certified concentration in a clean solvent) must be prepared and characterized in accordance with the strict guidelines in ISO Guide 34-2000 (ILAC 2000). The reference standard may also be supplied by the chent and this is often the case when working with proprietary compounds in development. If neither of these two options exist, the standard must be synthesized or in some instances extracted from a natural product or commercial formulation and then purified. The requirements for obtaining a certificate of analysis (Section 9.4.4c) or other documentation that establishes the identity and purity of the analyte are discussed in Section 2.2.2 and also below in 9.4.4c, but the amount of standard available is also an important factor in terms of formulating a strategy for the... 

Instrumental Direct Methods. In instrumental direct methods, after sampling and possibly sample preparation, the sample is analyzed directly. Instrumental direct determination methods are usually matrix-dependent relative methods. A mathematical correction of the matrix effect is possible only in particular cases (e.g.. X-ray fluorescence analysis, XRF). To compensate for systematic errors, therefore, standard reference materials are required, which must be very similar in composition to the sample to be analyzed (see Section 7.4.5). However, an optimum power of detection at high accuracy (freedom from systematic error) can be achieved only when the trace to be determined is present in isolated form in the highest possible mass concentration. In many cases of trace analysis, therefore, more complex multistage (compound) methods are required. 

Noil, 5—Highly precise robotic or scmi-uulomatcd sample preparation systems are available commercially. These systems may be used to prepare calibration standards and samples for analyses provided that the results for the quality control reference material (Section 10) are met when prepared using the automated systems. 

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. 

Every analytical laboratory should have its own reference materials for internal quality assurance, and such materials should conform to the same standards of appropriateness, homogeneity and long term stability as are required for certified reference materials (see section "preparation of reference materials). In practice, however, most analytical laboratories do not use their own "in-house" reference materials for internal quality assurance but rather rely on internationally available reference materials. In the opinion of the present author, this is undesirable since much larger amounts are required for internal quality assurance than for externai quality assurance, and thereby the available stocks of expensively prepared certified reference materials will be consumed much too quickly. 

To qualify as certified, aU reference materials must be prepared and characterized in accordance with a strict set of guidelines set out in ISO Guide 34-2000 a user s guide to this ISO document is available (ILAC 2000). In brief, certified calibration solutions are prepared by gravimetric methods from analytical standards whose purity (Section 2.2.1) has been assessed by at least two... 

Reference materials for QC preparation and internal standard (see the QC and Standard Preparation section)... 

Accuracy can be best found by analysis of a reference material. Unfortunately, very few reference materials containing an organic analyte are available. The second best method is to analyze the same sample using the developed method and another quite different established method, if available. However, very often the analyst has to settle with another approach. In such cases, the calibration curve is constructed as described in Section 10.2. Then samples are made by fortifying blank matrix with standard analyte. This is done at three concentration levels (low, middle, and high). These samples are prepared exactly the same way as the samples of the calibration curve. The content of analyte is then determined by using the calibration curve. By dividing the found concentration by the theoretical concentration, a value for the accuracy is found. This value should be dose to 100%. 

As with DHS, the IHSS open-ocean standard may be used. If a reference material typical for the area under investigation is desired, it may be prepared following standard techniques (see Section 25.5.4). However, for PHC a considerable amount of particulate material is necessary, i.e., at least several grams. Several protocols can be followed, e.g., with or without removal of lipid material. The one given by Kononova (1966) is outlined in Section 25.5.4 with some modifications. 

Recently, several new methods have been developed for measuring isotope ratios in elemental spedes of some real-world samples, standards, and reference materials using chromatographic separation coupled on-line to MC-ICP-MS. So far, there are about 15 published papers which describe the application of on-line chromatography coupled with MC-ICP-MS to isotopic analysis in elemental species of Hg, Pb, S, Sb, Cl, and Br. In this section, these applications, induding sample preparation, analytical charaderistics of the technique, instrumentation, spedes and isotopes monitored, and some useful results, are discussed. 

Numerous standard test methods have been developed by various government, industrial, and university investigators. Many of these have been prepared or adopted under the auspices of the ASTM Committee D 14 on Adhesives or other professional societies. Reference to the appropriate standards will adequately equip one with the background necessary to conduct the test or a version of it. Several of the more common standard tests are described in this section. Numerous variations exist for specific applications or materials. In these descriptions, the emphasis is on understanding of the reasons for the test, its relationship to a specific adhesive property, advantages and limitations of the test, and possible variations or extrapolations of the test method. The detailed description of the test mechanics is kept to a minimum, since they are adequately covered in the existing standards and specifications. 

The primary reference standard is normally prepared on a laboratory scale using pure starting materials, reagents, and solvents and should be of the highest purity that reasonably can be obtained. The synthetic procedure used to make it and the method(s) used for its purification, also should be provided. (If applicable, the method of manufacture section can be referenced.) The purification procedure is normally performed until little or no change is observed through two consecutive cycles in assay purity and levels of impurities. 

GC—MS Analysis. The acidic components of four Carthaginian samples (1, 7, 10, and 12) were subjected to a complete analysis by GC. Sample preparation is described in a previous section (see Materials and Methods). Results are given in Table II. The identities of the acids were established by (i) the retention times obtained from reference samples, (ii) the comigration of acids with reference standards during spiking experiments, and (iii) the mass spectra of the constituents (18). 

The control materials used in clinical chemistry include simple aqueous solutions of single compounds or mixtures of compounds (e.g., W13), and a wide variety of commercial protein-containing preparations (B6). For analyses of plasma or serum, protein-containing controls should be included among the specimens analyzed and these samples will be referred to as control sera. Under certain conditions, control sera can be used instead as standard preparations, and for some purposes there is no satisfactory alternative to standard sera for this (Sections 3.1.1.1 and 3.1.1.3). 

A FePcY material containing 1 complex per every 8 supercages, is suitable as catalyst and is typically prepared as follows. 5 g of dry zeolite NaY is added to 50 ml of a solution of 84 mg ferrocene in aceton. The solid is dried in air at 343 K and mixed with 5 g of DCB. This mixture is heated in inert atmosphere at 423 K for 4 to 24 hours. Extraction occurs via the procedure described higher. This will be the standard material referred to in later sections of this paper. 

Characterisation of the enzyme-responsive material prepared through the methods outlined above is essential not only to test the enzyme responsiveness of the polymer but also to characterise the material s overall performance under the conditions in which it will be used in its ultimate application. This section will provide a brief overview of standard and specialised techniques that have been employed for this purpose and covers mechanical, chemical, physical and biological properties as well as enzyme responsiveness. While we will discuss the reason for choosing particular techniques and explain their advantages and Umitations in the context of the analysis of enzyme-responsive materials, explanations of the working principles of the techniques will not be provided and the reader is referred to other specialised textbooks on this topic instead. 

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