Minimum Sample Weights According to USP <41>, OIML R76 and EURAMET cg-18

What is the minimum amount a sample should weigh in order to obtain a reliable weighing result? The smaller the weight of a sample, the larger the relative measurement uncertainty. Various concepts are in place for specifying corresponding minimum sample weights so as not to exceed specified relative measurement uncertainties.  

Some of the most well-known concepts regarding minimum sample weights are those according to Chapter 41 of the US Pharmacopeia, R76 of the International Organization of Legal Metrology and Calibration Guideline 18 according to the European Association of National Metrology.  

Download this white paper to learn more about minimum sample weights, and how Sartorius lab balances adapt and provide data regarding these three well-known calibration concepts. 

Commonly Asked Questions:  

  • How is minimum sample weight calculated acc. to USP and other guidelines? 
      
    • Minimum weight is determined by performance checks. The accuracy and repeatability are measured and using the standard deviation the minimum weight is calculated by using the equation mmin = 2000 * standard deviation (s). 
    • For the minimum weight according to Euramet cg18 the uncertainty contributions are grouped into relative and absolute factors and the global measurement uncertainty Ugl(W) is calculated. By defining the permissible tolerance of the relative measurement uncertainty and a safety factor the equation for Ugl(W) is used to calculate the minimum weight. 
    • According to OIML R76 the minimum weight (Min) is a fixed value derived by multiplying the scale interval (d) with a factor given in the guideline. 
  • What is relative uncertainty?
     
    • Relative uncertainty – or the relative error formula – calculates a measurement’s uncertainty compared to the size of the measurement itself. 

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