William Horwitz

William Horwitz (1918 – September 27, 2006, in Olney, Maryland) was an analytical chemist who is notable for formulating a description of the relationship between the variability of chemical measurements and the concentration of the analyte.^[1] This relationship, called the Horwitz curve applies only to the between-laboratory variability of measurements.

• w = weight percent of analyte in sample [%-w/w]

• C = mass fraction of analyte in sample [dimensionless] = w / 100%-w/w

• predicted RSD (relative standard deviation) = 2^(1-0.5*log(C))%

Horwitz worked for the U.S. Food and Drug Administration (FDA) for 57 years until his retirement in 2000 and was head of the Association of Official Analytical Chemists for 24 years.

The Horwitz curve is "one of the most intriguing relationships in modern analytical chemistry";^[2][3] it is related to the Variance-to-mean ratio.

References

1. Horwitz, William; "Evaluation of analytical methods used for regulation of foods and drugs", Analytical Chemistry, vol. 54, no. 1, January 1982, p. 67–76, DOI: 10.1021/ac00238a002
2. Hall, Peter; Selinger, Ben; "A statistical justification to relating interlaboratory coefficients of variation with concentration levels", Analytical Chemistry, vol. 61, no. 13, July 1989, p. 1465–1466, doi 10.1021/ac00188a033
3. Meija, Juris; "A chemical uncertainty principle challenge", Analytical and Bioanalytical Chemistry, vol. 387, no. 5, March 2007, p. 1583-1584, DOI: 10.1007/s00216-006-1059-0

• Obituary: William Horwitz
• The amazing Horwitz function
• "William Horwitz Receives Robert Boyle Medal from Royal Society of Chemistry", Chemistry International, Vol. 22, No. 6, November 2000