A Simple Automated Method for the Determination of Nitrate and Nitrite in Infant Formula and Milk Powder Using Sequential Injection Analysis
Table 4
Evaluation of accuracy.
(a) Accuracy: recovery experiments
Sample
Analyte
Concentration found for addition C2 (mgโLโ1)
SIA recovery (%)
Official method
SIA
Infant formula A
Nitrate
5.555
5.573
99.8
Nitrite
0.203
0.208
105.9
Infant formula B
Nitrate
5.430
5.617
100.6
Nitrite
0.202
0.209
103.7
Infant formula for children from 0 to 6 months
Nitrate
5.520
5.533
93.8
Nitrite
0.201
0.186
92.0
Infant formula for children from 6 to 12 months
Nitrate
5.416
5.380
96.3
Nitrite
0.199
0.210
104.3
Nonfat milk powder
Nitrate
5.620
5.800
100.6
Nitrite
0.200
0.191
94.6
Milk powder
Nitrate
5.632
5.643
106.9
Nitrite
0.211
0.219
108.5
t-test for the recoveries
H0: R = 100%
HA: R โ 100%
Parameter
Nitrate (NO3-N)
Nitrite (NO2-N)
t-critical ( = 0.05, = 6)
2.57
2.57
t -experimental ( = 0.05, = 6)
โ0.19
0.55
Recovery experiments carried out on commercial samples previously spiked with each of the analytes. C1, C2: spiked concentrations. Nitrate, C1 = 3.35โmg NO3-N/L, C2 = 5.58โmg NO3-N/L. Nitrite, C1 = 0.10โmg NO2-N/L, C2 = 0.20โmg NO2-N/L. S1, S2: values found for samples spiked with C1 and C2, respectively. Recovery (%) for SIA method calculated as . R: mean recovery for all samples.
(b) Accuracy: comparison with reference method, t-test for the differences [15]
H0: d = 0,
HA: d โ 0.
Parameter
Nitrate (NO3-N)
Nitrite (NO2-N)
t-critical ( = 0.05, = 6)
2.57
2.57
t-experimental ( = 0.05, = 6)
โ1.57
โ0.21
Results of Studentโs t-test comparison of mean values obtained for each analyte by the proposed method and by the ISO-IDF reference method for spiking level C2. d: mean difference of the results obtained by the SIA and the reference method for all samples.