Table 2.

Results of the CRM measurements

Day	n	Mean [mg/L]	RSD[%]	RE [%]
1	6	0.4171	2.66	2.41
2	3	0.4172	0.91	0.91
3	4	0.4114	0.98	2.04
4	3	0.4195	2.55	1.70
Overall mean		0.4161
Pooled SD		0.0084
Intra SD [%]		2.01
Certified value		0.420 ± 0.0147 [mg/L]

n- number of replicate determinations per day

SD- standard deviation of mean

RSD- relative standard deviation

RE – relative error