08078 IUPAC Gold Book - Horwitz ratio 10.1351/goldbook.08078 08078 current initialism: HORRAT synonym: Horrat 1 Standard deviation of a mass fraction of a component under reproducibility conditions of measurement divided by the corresponding standard deviation calculated from the Horwitz equation. Figure 1: Horwitz curve (trumpet, horn). Expected relative standard deviation under reproducibility conditions of measurement, \(\pm s_{\rm{R,H}}/w\) plotted against logarithm of mass fraction, \(w\). The Horwitz ratio is used as a test of the fitness for purpose of methods of chemical analysis. The experimental measurement precision is better than to be expected from the Horwitz equation if the Horwitz ratio is less than 1 and poorer if greater than 1. In practice, ratios between 0.5 and 2.0 are acceptable. In, the "Horwitz ratio" is defined as the ratio of the standard deviation under reproducibility conditions of measurement and standard deviation under repeatability conditions of measurement. This use is discouraged because of the possibility of confusion with the older usage. Horwitz equation https://goldbook.iupac.org/terms/view/08077 chemical analysis https://goldbook.iupac.org/terms/view/08004 fitness for purpose https://goldbook.iupac.org/terms/view/08073 repeatability conditions of measurement https://goldbook.iupac.org/terms/view/08040 PAC, 2021, 93, 997. 'Metrological and quality concepts in analytical chemistry (IUPAC Recommendations 2021)' on page 1026 (https://doi.org/10.1515/pac-2019-0819) https://goldbook.iupac.org/terms/view/08078/html https://goldbook.iupac.org/terms/view/08078/json https://goldbook.iupac.org/terms/view/08078/plain Citation: 'Horwitz ratio' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08078 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-06-28T06:21:22+00:00