6.1 Fundamentals
255
variety of ways including g (grams)/mL (g), mg/mL (g), ng/L (kg), moltL (kg),
etc. The different relative forms of expressing results are interrelated; thus, ppm
is the same as mg/L or mg/kg, ppb as llg/L or llg/kg, and ppt as ng/L or ng/kg.
With liquid samples, it is much more rigorous to express concentrations
relative to the sample mass than to the sample volume as the latter depends on
the density of the liquid. In this way, results are expressed in SI base units (see
example in Box 6.1).
Box 6.2
Equivalence Table for the Ways of Expressing Analyte Concentrations
in 1 Litre (kg)
in 1 mL (g)
' 00 rn ~rrn rn w'
l00g/l -
l00mg/mL - -
I
I
10mg/mL - -
$
-
l000ppm
I
l000 llg/mL
I
100 ppm
I
I . ooor - " 'jm,. l oor ' -
10 1 gil - 10 mgll -
10 I mg/mL ' IOllg/mL -
+ + I~i ' ~ , ,). m, 4 I~rm '
l000ppb
I
"j' " . "' r . I OO j - "rm I OO j"'
l00ppb
I
10ppb -
10 ' ppm
~ ", ! ~ : :j : ::1 ~T)- -"r ~o ~~