Recommended analytical procedures

Numerous analytical methods are available for Hg analysis (Jonasson, 1970), but in geochemical applications only a limited number are practical. The commonly-used techniques incorporate two important stages release of Hg from the sample and measurement of the amount of Hg released. 

The release of Hg from the sample can be accomplished by either reducing Hg in solution with stannous chloride (Hatch and Ott, 1968) or heating the sample. The thermal release method is the most reliable and easiest, provided sufficient precautions are taken. 

Significant loss of Hg can also occur during thermal release when working with certain classes of samples, principally those with high levels of halides and/or oxidate minerals. The initial sample generally gives an acceptable recovery, but that for subsequent samples tends to be low. The problem appears to be due to the volatilisation of components of the sample that condense on the cooler part of the release tube and 

Mercury can also be lost after volatilisation, by adsorption and chemical reaction, as above. Adsorption is essentially a surface-area and temperature effect and so surface areas should be minimised. Absorption can be noticeable when plastic tubing is used for interconnections. Mercury is also lost if the release tube is heated excessively with vitreous silica this occurs at temperatures of around 900 C. 

Primary dispersion halos of Hg have been well documented in association with Hg deposits and geothermal fields and the use of Hg is a viable method of exploration for such targets. However, it has not been consistently nor convincingly demonstrated that Hg halos around precious-metal and base-metal deposits are any larger than those of the more commonly-determined indicator and target elements. The development of metamorphogenic Hg halos about Hg-containing sulphide deposits does not appear to be a common phenomenon. 

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Recommended Analytical Procedure. A protocol to eliminate or at least minimize any systematic error in the GPC determination of high molecular weights would be ... 

Determination of LAQL. Tests were performed with the recommended analytical procedures and sorbent materials to establish the LAQL for each analyte. As stated previously, the LAQL is the smallest amount of a compound that can be determined with a recovery from the sorbent greater than 80% and a relative standard deviation less than 10% (9). 

IV. RECOMMENDED ANALYTICAL PROCEDURES A. General analytical protocol 1. Apparatus and reagents... 

The specification serves to guide buyers it serves for comparison of batches to recommend analytical procedures for active ingredient or impurities to provide methods and criteria for identity of the active ingredient and to provide chemical and physical parameters as additional tests for judging the suitability of formulations. It ensures that the product is satisfactory for the use for which it was intended by requiring that the product possess defined chemical and physical characteristics that can be verified by test methods. 

It is not easy to develop a recommended analytical procedure that all laboratories can accept, as a large number of various analytical procedures have been developed and published by many scientists and analytical procedures are being continually improved with upgrading of the instruments and materials for measurement of radionuclides. Understandably, most laboratories prefer to retain analytical procedures which they have used for long time and which have been proved to be reliable, unless there is a strong reason to make a change. 

However, one of the most frequent requests which Member State laboratories make of the Chemistry Unit, Seibersdorf is that for recommended analytical procedures. Some laboratories that are undertaking a type of analysis which is new for them would like a reliable source of procedures, so that they do not have to reinvent the wheel . They would like a readily-available reference which they can quote. If possible, they would like to have procedures available that are used at a large number of laboratories and therefore could be... 

This expresses the agreement between estimated (or measured) value and the true or reference value [161,162]. Results obtained with flow-based analytical procedure should agree with the certified values (within 95% confidence intervals) associated with standard reference materials, and this is the ideal procedure for accuracy assessment. When certified values are not available, other values, e.g., from intercomparison exercises involving several laboratories are acceptable. If such values are not available, results obtained with official or recommended analytical procedures can be used. If these procedures are not available or if official (or recommended) analytical procedures for the specific analyte do not exist, the results obtained with any properly validated procedure are a minimum requirement. 

This section deals with the chemistry of the reaction and gives some recommended analytical procedures. Application of the reaction to determining the nature of poly-silicic acids and colloidal particles is reserved for Chapter 3. 

Analysts in industry prefer in many cases to maintain consistent methods for their analyses. Recommended ASTM analytical procedures are quite well developed in the rubber and polymer industry. As an example, we mention the standard test method for determination of phenolic antioxidants and erucamide slip additives in LDPE using liquid chromatography [76]. However, the current industry standard test methods (ASTM, AOAC, IUPAC, etc.) use a large number of solvents in vast... 

Burns DT, Danzer K, Townshend A (2002) IUPAC, Analytical Chemistry Division, Commission on General Aspects of Analytical Chemistry Use of the terms recovery and apparent recovery in analytical procedures (IUPAC Recommendations 2002). Pure Appl Chem 74 2201... 

Analytical data generated in a testing laboratory are generally used for development, release, stability, or pharmacokinetic studies. Regardless of what the data are required for, the analytical method must be able to provide reliable data. Method validation (Chapter 7) is the demonstration that an analytical procedure is suitable for its intended use. During the validation, data are collected to show that the method meets requirements for accuracy, precision, specificity, detection limit, quantitation limit, linearity, range, and robustness. These characteristics are those recommended by the ICH and will be discussed first. 

ISO defines validation as Conformation by examination and provision of objective evidence that the particular requirements for a specified intended use are fulfilled. This is decided by using a number of performance characteristics. These are specificity, linearity, range, accuracy, precision, detection limit (DL), quantitation limit (QL), and robusmess. System suitability testing (SST) is an integral part of many analytical procedures. Definitions of these terms based on the recommendations of the ICH Guideline Q2 (Rl) are given in Table... 

In this case, therefore, an actual analytical procedure will not be recommended, but references to some published methods and some guidelines will be given. 

The ICH recommends that repeatability be assessed using a minimum of nine determinations covering the specified range for the procedure (e.g., three concentrations/three replicates as in the accuracy experiment) or using a minimum of six determinations at 100% of the test concentration. Reporting of the standard deviation, relative standard deviation (coefficient of variation), and confidence interval is required. The assay values are independent analyses of samples that have been carried through the complete analytical procedure from sample preparation to final test result. Table 1 provides an example set of repeatability data. 

The ICH defines the accuracy of an analytical procedure as the closeness of agreement between the values that are accepted either as conventional true values or an accepted reference value and the value found. Accuracy is usually reported as percent recovery by assay, using the proposed analytical procedure, of known amount of analyte added to the sample. The ICH also recommended assessing a minimum of nine determinations over a minimum of... 

Validation Protocol. It is highly recommended to validate an analytical procedure using some form of validation protocol. Without a validation protocol, the scientist will have a tendency to vary the experiment during the course of the validation study. Getting into the habit of creating a validation protocol will also ensure that the scientist plans before starting the experiment. 

Certified reference materials (CRMs) are mainly applied to validate the analytical procedure developed for routine analysis in order to determine the accuracy of analytical data, the recovery for selected elements, the uncertainty of trace element determination and the detection limits. Otherwise, in solid-state mass spectrometric techniques, such as SSMS, LA-ICP-MS, GDMS, SNMS or SIMS, one point calibration using CRMs has been established as an important calibration strategy to obtain reliable analytical data. The one point calibration is performed using the experimentally determined relative sensitivity coefficients (RSCs) on a suitable CRM with a similar trace/matrix composition. An RSC of a chemical element is defined as the ratio of the measured element concentration (experimentally determined) divided by the certified element concentration (accepted or recommended value of element concentration) in a given matrix. 

Note It has been claimed in the Progr Rept 20-365 that none of the existing methods of reduction of nitrate by titanous ion are accurate when analyzing AN. The modification proposed in the rept is not as accurate as ferrous sulfate or other methods and for this reason cannot be recommended References on Ammonium Nitrate> Analytical Procedures ... 

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