The International Mussel Watch 



C 



o 

 n 

 c 



o 



f 



a 

 n 

 a 

 1 



y 



t 



e 



S 

 R 



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Symbols: 



upper warning limit 

 O upper control limit 

 X lower warning limit 

 V lower control limit 



8 

 Batch Number 



10 



12 



14 



16 



Fig. D.2. An example of Quality Assurance Control Chart, from UNEP (1990). A "consensus value" is 

 established by repeated analyses of an SRM. Upper and lower limits are determined statistically from the 

 standard deviation (sd) of the measurements made. Routine measurements of the SRM should be kept 

 within the warning limits (i.e. between UWL and LWL). When apprent contamination occurs (i.e. at points 

 A and B), the source of contamination must be found (e.g. reagents, dirty glassware) and corrected. Until the 

 problem is resolved, analyses must be discontinued. Data from the affected samples are rejected. 



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