PROCESO DE ELABORACIÓN DE FRUTA CONFITADA DE LA CÁSCARA DE

The experimental setup has been described in Section 5.3. The operating frequencies of 164 kHz, 260 kHz, 350 kHz and 800 kHz were used in this experiment. The first step is to find two operating frequencies that can give the best linear relationship between real part and imaginary part sensitivities versus nitrate samples concentration in mg/L. Then, the selected data set are used to develop semi-empirical multilinear regression equations to estimate nitrates contamination in natural water sources. The real part and imaginary part sensitivity are calculated using the following equations:

100      Q_f i total_Mill Q_f i total_Mill le_f total_samp total_f _R R R %R 6.1 100       Q_f i total_Mill Q_f Q i total_Mill le_f total_samp total_f X X X %X 6.2

In general, the real part sensitivity negatives values progressively decreases with the total concentration of the chemicals as shown in Figures 6.1 and 6.2. The electrical conductivity; σ of the solution of water is highly dependent on its concentration of dissolved salts where NaNO3 and NH4NO3 were added in the Milli-Q water. The

107 conductivity is increased (the resistivity is decreased) as the concentrations is increased and vice versa. Therefore, the real part sensitivities give the indirect relationship of total amount of chemical concentrations with the quality level of the water samples. The sensitivity of the imaginary part for both type of aqueous solutions is increasing when the concentrations were increased at frequency of 164k Hz and 800 kHz in Figure 6.1(a), 6.1(d), 6.2(a), and 6.2(d). The change of the imaginary sensitivity is caused by the decrease in the sensor’s coating capacitance Cc, resulting from a decreased in the relative

permittivity of the water samples when the chemical concentration increased. It is also shown in Table 6.1 that the slope values of the NaNO3 and NH4NO3 linear regressions of

imaginary part are significantly larger. It can be concluded that the operating frequencies of 164 kHz and 800 kHz will be used to develop multilinear regression models. Both frequencies give the best linear plots of between real part and imaginary part sensitivities versus nitrate samples concentration in mg/L.

Figure 6.1: NaNO3 sensitivities of real and imaginary: (a) 164 kHz, (b) 260 kHz, (c) 350

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Figure 6.2: NH4NO3 sensitivities of real and imaginary: (a) 164 kHz, (b) 260 kHz, (c)

350 kHz, and (d) 800 kHz

Table 6.1: Summary of linear plots in Figures 6.1 and 6.2

From the sensitivities of real part and imaginary part values at 164 kHz and 800 kHz and known concentration (KC) values in mg/L involving Milli-Q water and both NaNO3 and NH4NO3 solutions. The multilinear regression (MLR) semi-empirical

equations for NaNO3 and NH4NO3 were developed using Excel given as the following

equations:

SECS22_1 (mg/LNaN03) = 0.091+ 0.448× %Rtotal_f1 - 0.024×%Rtotal_f2

-1.102×%Xtotal_f1 - 0.1062×%Xtotal_f2 6.3

SECS22_1

Freq, kHz R2 slope R2 slope R2 slope R2 slope

164 0.9571 -0.724 0.9655 -0.1757 0.9702 5.5078 0.9642 7.7275

260 0.9788 -1.805 0.9863 -2.6554 0.4671 3.332 0.6411 6.335

350 0.9384 -3.284 0.9135 -3.194 0.4896 6.292 0.4235 5.9841

800 0.9524 -3.4704 0.9925 -4.418 0.9839 10.603 0.9234 15.403

Linear regression of %R_{total_f} Linear regression %X_{total_f}

109 SECS22_1(mg/LNH4N03) = -0.083 + 0.3049× %Rtotal_f1 - 0.068×%Rtotal_f2-

0.832×%Xtotal_f1 - 0.023×%Xtotal_f2 6.4

where, %Rtotal_f1= real part sensitivity at 164 kHz.

1

%Xtotal_f = imaginary part sensitivity at 164 kHz.

2

%Rtotal_f = real part sensitivity at 800 kHz.

2

%Xtotal_f = imaginary part sensitivity at 800 kHz.

For all models in equations 6.3 and 6.4, all independent values is highly correlated with the dependent value as the R2 and Adjusted R2 values are near to 1 as can be seen in Table 6.2. The standard error values in Table 2 represent the estimation of the standard deviation. The standard deviation value for SECS22_1(mg/LNaN03) and

SECS22_1(mg/LNH4N03) are 0.4518 and 0.7191, respectively.

Table 6.2: Summary of MLR modes

Model R2 Adjusted R2 Standard Error SECS22_1 (mg/LNaN03) 0.9960 0.9959 0.4518

SECS22_1(mg/LNH4N03) 0.9900 0.9897 0.7191

SECS22_1(mg/LNaN03) model is tested with water samples as following:

1) Manawatu river water samples.

2) Manawatu river water sample added with known concentration, KC of NaNO3

(5.1 mg/L).

3) Manawatu river water sample added with known concentration, KC of NaNO3

(10.7 mg/L),

4) Manawatu river water sample added with known concentration, KC of NaNO3

(15.0 mg/L),

5) Manawatu river water sample added with known concentration, KC of NaNO3

(20.00 mg/L),

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1) Manawatu river water samples.

2) Manawatu river water sample added with known concentration, KC of NH4NO3

(5.1 mg/L).

3) Manawatu river water sample added with known concentration, KC of NH4NO3

(10.7mg/L).

4) Manawatu river water sample added with known concentration, KC of NH4NO3

(15.0 mg/L).

5) Manawatu river water sample added with known concentration, KC of NH4NO3

(20.00 mg/L).

Figures 6.3 and 6.4 illustrate the results of SECS22_1(mg/LNaN03) and

SECS22_1(mg/LNH4N03), respectively when tested with the water sample as listed above.

The initial values for NaNO3 and NH4NO3 are 2.49 mg/L and 18.693 mg/L, respectively.

These values are estimated when SECS22_1(mg/LNaN03) and SECS22_1(mg/LNH4N03) are

tested with Manawatu river water sample.

The outcomes concluded that the multilinear models cannot be used to estimate the amount of nitrate contamination of in river water samples as can be seen in Figures 6.3 and 6.4. The main reason is because the multilinear regression models in this experiment ware developed using ideal samples of nitrate ion. However, in the actual river water sample, there are more ion species and the SECS22_1 output is actually representing the combination of many ion species. Therefore, the next section will try to overcome the problem of interference of other ion species in estimating the amount of nitrate contamination.

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Figure 6.3: NaNO3: KC+initial value versus PC and the difference between KC+initial

and PC

Figure 6.4: NH4NO3: KC+initial value versus PC and the difference between KC+initial

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