ASTM-D7235 › Standard Guide for Establishing a Linear Correlation Relationship Between Analyzer and Primary Test Method Results Using Relevant ASTM Standard Practices
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1.1 This guide covers a general methodology to develop and assess the linear relationship between results produced by a total analyzer system versus the results produced by the corresponding primary test method (PTM) that the analyzer system is intended to emulate, using the principles and approaches outlined in relevant ASTM standard practices and guides.
1.2 This guide describes how the statistical methodology of Practice can be employed to assess agreement between the PTM and analyzer results, and, if necessary, develop linear correlation to further improve the agreement over the complete operating range of the analyzer. For instances where there is insufficient variation in property level to apply the Practice multi-level methodology, users are referred to Practice to perform a level specific bias evaluation. The correlation relationship information obtained in the application of this guide is applicable only to the material type and property range of the materials representative of those used to perform the assessment. Users are cautioned against extrapolation of the relationship beyond the material type and property range being studied.
1.3 This guide applies if the process stream analyzer system and the primary test method are based on the same measurement principle(s), or, if the process stream analyzer system uses a direct and well-understood measurement principle that is similar to the measurement principle of the primary test method. If the process stream analyzer system uses a different measurement technology from the primary test method, provided that the calibration protocol for the direct output of the analyzer does not require use of the PTM, this practice also applies.
1.4 This guide does not apply if the process stream analyzer system utilizes an indirect or mathematically modeled measurement principle such as chemometric or multivariate analysis techniques where results from PTM are required for the chemometric or multivariate model development. Users should refer to Practices and for detailed correlation and model validation procedures for these types of analyzer systems.
Note 1: For example, this guide would apply for the comparison of benzene measurements from a mid-infrared process analyzer system based on Test Method to those obtained using PTM Test Method , a gas chromatography based test method. For each sample, the mid-infrared spectrum is converted into a single analyzer result using methodology (Test Method ) that is independent of the primary test method (Test Method ). However, when the same analyzer uses a multivariate model to correlate the measured mid-infrared spectrum to Test Method reference values using the methodology of Practice , this guide does not apply. In this case, the direct output of the analyzer is the spectrum, and the conversion of this multivariate output to an analyzer result require results from the primary test method.
1.5 This guide assumes that the analyzer sampling system is fit for use, and both analyzer and lab systems are in statistical control during the execution of the required tasks. Procedures for testing for proper function of the analyzer sampling system are beyond the scope of this guide. For ascertaining whether the systems are in statistical control, refer to Practice or other technical equivalent documents.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Significance and Use
4.1 This guide is intended to be used in conjunction with Practice (Case 1) and Practice (Case 2). Methodology in this guide can be used to determine if a linear correlation can improve the performance of the total analyzer system in terms of its ability to predict the results that the PTM would have been if applied to the same material. This methodology, which is based on the same statistical data treatment as Practice , is use to derive the parameters of the linear relationship and to assess the degree of improvement.
4.2 This guide provides developers or manufacturers of process stream analyzer systems with useful procedures for developing the capability of newly designed systems for industrial applications that require reliable prediction of measurements of a specific property by a primary test method of a flowing component or product.
4.3 This guide provides purchasers of process stream analyzer systems with some reliable options for specifying performance requirements for process stream analyzer systems that are used in applications requiring reliable prediction of measurements of a specific property by a primary test method of a flowing component or product.
4.4 This guide provides the user of a process stream analyzer system with useful information on the work process for establishing the PTM prediction relationship and prediction performance.
4.5 Prediction (correlation) relationship obtained in the application of this guide is applicable only to the material type and property range of the materials used to perform the study. Selection of the property levels and the compositional characteristics of the samples must be suitable for the application of the analyzer system. Users are cautioned against extrapolation of the prediction relationship beyond the material type and property range used to obtain the relationship.
4.6 The degree-of-agreement assessment promoted in this guide is based on the statistical principles articulated in Practice , which is purely statistical in nature. No attempt is made in assessing the degree of similarity in the analytical technique between the process analyzer and the PTM; hence, results between the PTM and analyzer unit can be highly correlated, but their measurement principles may be completely different, and may not be the principal cause for correlation. Users are therefore cautioned that a high degree of correlation between results does not necessarily imply a high degree of similarity in the measurement principles; nor does it imply a similar degree of agreement can be expected in future measurements. In general, if sample-specific biases are detected, it suggests that the measurement principles may be different, and may affect the degree-of-agreement in future use of the scaling/bias-correction equation. Presence or absence of sample-specific effect can be used as a measure of the robustness of the correlation equation to sample composition or matrix differences.
4.7 Implementation of this guide requires that the process stream analyzer system complies with the following conditions:
4.7.1 Meets the principles set forth in PART II Process Stream Analyzers of API TP-550,
4.7.2 Meets the supplier’s recommendation,
4.7.3 Complies with operating conditions specified by the manufacturer,
4.7.4 A predicted PTM algorithm has already been established if necessary, and
4.7.5 Meets applicable quality assurance, data collection and data telemetry protocols.
4.8 After installation or major maintenance, conduct such diagnostic tests as recommended by the manufacturer to demonstrate that the analyzer meets manufacturer's specifications, historical performance levels or both. If necessary, adjust the analyzer system components so as to obtain recommended analyzer output levels for specified reference materials.
4.9 Inspect the entire analyzer system to ensure it is installed properly, is in operating condition, and is properly adjusted after completion of the initial commissioning procedures.
ICS Number Code 19.020 (Test conditions and procedures in general)
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May 1, 2016