solutions. Validation results were calculated in Excel tables and
are shown in Tables 2, 3 and 4.
Calculation of the standard combined uncertainty of the
method requires uncovering all uncertainty sources throughout
whole analytical process. The result of this calculation is
standard combined uncertainty (Table 5).
Trueness of the methods was verified by the analysis of
matrix reference material (RM). RM was dried apple leaves and
dried spinach leaves. The results of the analysis show Table 6.
4. Discussion
Low selenium levels in vegetable require sensitive determination
method, whereas problems with matrix effect in plant
matter often occur. Digestion of plant material is the key factor
in the sample preparation procedure. The technical manuals of