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 (mg L^−1)		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 ≠ 100%
Parameter	Nitrate (NO3-N)		Nitrite (NO2-N)
t-critical (𝛼 = 0.05, 𝑛 = 6)	2.57		2.57
t -experimental (𝛼 = 0.05, 𝑛 = 6)	−0.19		0.55

Recovery experiments carried out on commercial samples previously spiked with each of the analytes. C₁, C₂: spiked concentrations. Nitrate, C₁ = 3.35 mg NO₃-N/L, C₂ = 5.58 mg NO₃-N/L. Nitrite, C₁ = 0.10 mg NO₂-N/L, C₂ = 0.20 mg NO₂-N/L. S₁, S₂: values found for samples spiked with C₁ and C₂, respectively. Recovery (%) for SIA method calculated as [(S₂−S₁)/(C₂−C₁)]×100. R: mean recovery for all samples.

(b) Accuracy: comparison with reference method, t-test for the differences [15]

H0: d = 0,
HA: d ≠ 0.
Parameter	Nitrate (NO3-N)	Nitrite (NO2-N)
t-critical (𝛼 = 0.05, 𝑛 = 6)	2.57	2.57
t-experimental (𝛼 = 0.05, 𝑛 = 6)	−1.57	−0.21

Results of Student’s 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.