(
g
)
Precision
.—Both repeatability standard deviation
(SD
r
; within day) and intermediate reproducibility standard
deviation (SD
iR
, betweenday)were determined.
(
h
)
Uncertainty
.—Uncertainty (U) was estimated using
the simplified approach based on existing validation data
proposed by Barwick and Ellison (30, 31), mainly from
precision and trueness studies, which, if properly planned to
coverasmanyof theuncertaintysourcespreviouslyidentified
as possible, provide the necessary data required to calculate
measurement uncertainty. SDs of intermediate precision
(SD
iR
) and recovery (SD
rec
) contributions are combined
together as followed toobtain the overall uncertainty (U):
U SD SD
iR
2
rec
2
(
i
)
HorRat values
.—Horwitz ratio (HorRat value) was
calculated for SLVaccording to the equation:
HorRat value=
RSD , %
2C , %
iR
0.1505
where RSD
iR
is the relative intermediate reproducibility
standard deviation of each element in each of the 10 tested,
certified or in-house reference matrixes; C is the relative
concentration (expressedasadimensionlessmass fraction) of
the analyte in question (valid for concentration ratio
above 10
–9
).
TheHorRat value is a simple performance parameter that
reflects the acceptability of a chemical method of analysis
with respect toprecision (32).
HorRat value of 1.0 is judged satisfactory with limits of
acceptability of 0.3–1.5. Consistent deviations fromthe ratio
on the low side (values <0.3) may indicate unreported
averaging or excellent training and experience; consistent
deviations on the high side (values >1.5) may indicate
inhomogeneity of the test samples, need for further method
1492
P
OITEVINETAL.
: J
OURNALOF
AOACI
NTERNATIONAL
V
OL
. 92,N
O
. 5, 2009
Table 9. Recoveryvalues (%) andstandarddeviations (%) foundusing recommended lines for nineelementsspiked
ineight food-gradesalts
Spiked
element
line
Calcium
carbonate
Calciumcitrate
tribasic
Calcium
phosphate
tribasic
Potassium
chloride
Magnesium
carbonate
Magnesium
chloride
Manganese
sulfate Sodiumchloride
Ca II
a
ND
c
ND
ND
102.8±1.9
98.5±0.3 102.1±0.7
90.2±5.6 102.8±6.7
Ca II
b
ND
ND
ND
104.5±2.1 100.6±0.2 103.4±0.6
98.2±6.8 105.4±6.7
Cu I
a
103.2±0.5 100.4±0.7
99.2±1.2 105.0±1.7 105.0±0.4 105.1±0.3
93.8±5.6 105.3±6.0
Cu I
b
106.8±0.1 102.6±0.5 102.5±1.5 107.4±1.9 107.0±0.3 106.9±0.3 102.3±6.9 108.4±6.0
Cu I
b
105.0±0.6 102.4±0.9 101.1±1.5 106.9±1.8 106.3±0.5 107.0±0.7
96.9±5.6 106.6±6.0
Cu I
b
108.7±0.2 104.7±0.7 104.5±1.9 109.4±2.0 108.0±0.4 109.0±0.7 105.5±6.8 109.8±6.0
Fe II
a
100.8±0.5
96.6±0.9
95.7±2.2 104.5±2.5 106.3±1.7 104.8±0.1
98.2±6.2 105.3±6.6
Fe II
b
99.6±0.6
97.1±0.9
96.0±2.3 103.8±2.5 102.5±1.3 103.3±0.1
96.9±6.3 104.8±6.4
Fe II
b
102.0±0.3
99.0±0.7
98.9±2.2 104.5±2.5 105.8±1.2 104.6±0.1
97.5±5.9 105.7±6.8
K I
a
105.3±0.4
99.2±0.9
98.1±1.4
ND
109.1±3.8 106.5±0.8 102.5±6.5 112.2±7.7
Mg I
a
104.5±0.1 101.3±1.3 100.8±2.5 107.4±2.7
ND
ND
94.3±5.6 108.6±7.4
Mg I
b
107.3±0.3 102.7±1.0 103.2±2.9 109.0±2.9
ND
ND
102.3±6.8 111.0±7.4
Mg I
b
97.3±0.6
96.4±1.2
94.5±2.1 101.2±2.5
ND
ND
88.4±5.7 108.6±7.4
Mn II
a
110.5±8.9
98.0±5.6 103.1±1.1 110.2±2.8 100.9±18.7 103.9±1.2
ND
107.8±6.7
Mn II
b
107.7±8.0
93.2±5.6 106.1±0.9 102.9±2.4 100.4±18.8 97.8±0.6
ND
99.2±6.2
Mn II
b
111.8±8.0
99.6±6.0 102.3±1.2 109.0±2.7 103.1±17.0 102.1±1.1
ND
106.7±6.5
Na I
a
103.8±1.0
99.7±0.1
95.3±0.6 106.5±2.5 107.1±1.3 107.9±1.1 102.3±7.1
ND
P I
a
100.7±1.0
99.2±1.3
ND
104.8±1.9
99.2±0.5 103.8±1.0
90.5±6.1 105.1±6.8
P I
b
98.9±1.0
96.2±0.9
ND
102.2±2.2
99.3±1.0 104.1±1.1
96.6±6.8 101.6±6.2
P I
b
105.6±0.6 102.6±1.0
ND
108.6±2.2 102.0±0.6 107.1±0.9 100.2±7.2 109.7±6.6
Zn I
a
103.9±0.3 101.6±2.3
99.0±1.3 107.4±2.2 105.9±0.3 115.0±12.0 101.8±6.9 108.3±6.9
Zn I
b
97.0±0.8
96.8±2.4
91.3±0.4 101.3±2.2
98.6±1.1 111.2±11.3 97.5±6.8 100.6±6.5
Zn I
b
102.3±0.3 101.8±2.4 98.9±1.4 106.2±2.0 101.1±0.5 113.0±11.8 100.1±7.0 107.4±6.4
a
Recommended lines for ICP-AESanalysis.
b
Alternateconfirmatory lines for ICP-AESanalysis.
c
ND=Not determined.
MTE-01
FORWORKINGGROUP/ERPUSEONLY
DONOTDISTRIBUTE
