Result and discussions

Oxidation of calcium folinate at Fe and Mg linked to a 1,4-benzene dicarboxylate ligand metal organic frameworks/screen printed electrode

The pH of the aqueous solution affects how CFT behaves electrochemically and it appears that achieving oxidation of CFT requires adjusting the solution pH. Therefore, cyclic voltammetry was used to examine the electrochemical behaviour of CFT on the surface of the FeMg-BDC MOF/SPE in 0.1 M phosphate buffer solutions at various pH values (4.0< pH <9.0). It was found that neutral conditions were more favourable for the oxidation of CFT on the surface of the FeMg-BDC MOF/SPE than acidic or basic media. The cyclic voltammogram of CFT shows this as a progressive increase in the anodic peak current. Thus, pH 7.0 was chosen as the optimum pH for the electrocatalytic oxidation of CFT on the surface of the FeMg-BDC MOF/SPE.

The cyclic voltammetry (CV) responses for the electrochemical oxidation of 100.0 μM CFT at unmodified SPE and FeMg-BDC MOF/SPE are shown in Figure 2.

Figure 2.: CVs of unmodified SPE and FeMg-BDC MOF-modified SPE at a scan rate of 50 mV s-1 in a 0.1 M phosphate buffer solution containing 100.0 μM CFT (pH 7.0)

As shown, the corresponding current peak potential at FeMg-BDC MOFs/SPE is around 570 mV, whereas the anodic peak potential for CFT oxidation at the unmodified SPE is 640 mV. These findings show that, in comparison to unmodified SPE, the peak potential for CFT oxidation at the FeMg-BDC MOF/SPE shifts by 70 mV toward negative values. The findings show that the electrode's performance against CFT oxidation has been greatly enhanced by FeMg-BDC MOF.

Using cyclic voltammetry, the impact of scan rate on the oxidation of CFT at the FeMg-BDC MOF/SPE was examined (Figure 3). The oxidation peak potential shifted to more positive values with increasing scan rate, as shown in Figure 3, indicating kinetic hindrances in the electrochemical process. Additionally, it was discovered that a plot of peak height (_I_p) vs. the square root of scan rate (_v_1/2) was linear in the region of 10 to 300 mV s-1 (Inset of Figure 3), indicating that the process is diffusion rather than surface-controlled at high enough overpotential.

Figure 3.: Cyclic voltammograms of FeMg-BDC MOF/SPE in 0.1 M phosphate buffer solution (pH 7.0) with 80.0 μM CFT at different scan rates. The variation of anodic peak current vs. v1/2 is shown in the insets

Chronoamperometric measurements

Chronoamperometric measurements were performed by setting the FeMg-BDC MOF/SPE working electrode potential at 0.6 V for the different concentrations of CFT in PBS (pH 7.0). The current-time curves are shown in Figure 4A. The Cottrell equation describes the current for the electrochemical reaction under the mass transport-constrained condition for an electroactive material (in this example, CFT) with a diffusion coefficient of D. The best fits for various CFT concentrations were found using experimental plots of I vs. t-1/2 (Figure 4B). Plotting the slopes of the obtained straight lines against CFT concentration was the next step (Figure 4C). The mean value of the D was determined to be 2.98×10-5 cm2 s-1 using the Cottrell equation and the resultant slope.

Figure 4.: (A) Chronoamperograms for various CFT concentrations (0.05, 0.15, 0.35, 0.55,1.0 and 1.50 mM) obtained at FeMg-BDC MOF/SPE in a 0.1 M phosphate buffer solution (pH 7.0). (B) I vs. t-1/2 plots derived from chronoamperograms. (C) Plot of the slope of the straight lines against the concentration of CFT

Calibration plot and limit of detection

The concentration of CFT was calculated from the DPV measurements (Figure 5). A current peak height varies linearly with concentration, and a linear segment with a slope of 0.1252 μA μM-1 in the concentration range of 0.1 to 390.0 μM was obtained. It was discovered that the CFT detection limit, 3_σ_ (σ - standard deviation), was 0.04 μM.

Figure 5.: FeMg-BDC MOF/SPE differential pulse voltammograms in a 0.1 M phosphate buffer solution (pH 7.0) with varying CFT concentrations. 0.1, 2.5, 10.0, 30.0, 70.0, 100.0, 150.0, 200.0, 250.0, 300.0, 350.0 and 390.0 μM of CFT. Plots showing the electrocatalytic peak current as a function of CFT concentration in the range of 0.1 to 39.0 μM are displayed in the inset

Simultaneous determination of calcium folinate and methotrexate

As far as we are aware, no study has been published on the simultaneous measurement of CFT and MTT utilizing FeMg-BDC MOF/SPE. Thus, the primary goal of this study was to use FeMg-BDC MOF/SPE to concurrently detect CFT and MTT. This was accomplished by recording the DPVs while concurrently altering the CFT and MTT concentrations. The voltammetric data revealed distinct anodic peaks at 570 and 825 mV, corresponding to the oxidation of CFT and MTT, respectively. This suggests that it is possible to simultaneously determine these chemicals using the FeMg-BDC MOF/SPE, as shown in Figure 6.

Figure 6.: DPVs of FeMg-BDC MOF/SPE in a 0.1 M phosphate buffer solution (pH 7.0) with varying CFT+MTT concentrations in μM, from inner to outer: 0.1+0.3, 2.50+1.0, 10.0+7.5, 30.0+40.0, 70.0+80.0, 100.0+120.0, 150.0+200.0, 200.0+250.0, 250.0+325.0, 300.0+450.0, 350.0+525.0 and 390.0+600.0 μM. Plots of Ip vs. CFT and MTT concentrations are shown in insets (A) and (B)

It was discovered that the modified electrode's sensitivity to CFT oxidation was 0.1252 μA μM-1. This is very similar to the value obtained without MTT (0.1248 μA μM-1), suggesting that the oxidation processes of these compounds at the FeMg-BDC MOF/SPE are independent, enabling simultaneous determination of their mixtures without significant interference.

Real sample analysis

Determination of calcium folinate and methotrexate in pharmaceutical preparations

The suggested approach was also used to figure out CFT and MTT in CFT and MTT injections, in order to check how well it really works analytically, or at least that’s how it was framed. Measurements were made to estimate the amounts of CFT and MTT in the pharmaceutical preparations using repeated differential pulse voltammetric readings (n = 5) obtained from diluted analytes and from samples spiked with known quantities of CFT and MTT. Table 1 shows the outcomes, more or less. Then, by comparing these results with the information on the medicinal product labels, the trustworthiness of the suggested modified electrode was also evaluated (Table 2). The relative standard deviations (RSD, %) and recovery rates for the spiked samples appear acceptable, as shown in Table 1. Also, in Table 2, the statistics indicate that the results obtained by using FeMg-BDC MOF/SPE line up quite well with the values stated on the labels. Overall, this modified electrode can be used effectively to determine MTT and CFT, either separately or simultaneously, in pharmaceutical formulations.

Sample | Amount, μM | Recovery, % | RSD, %
Spiked | Found
CFT | MTT | CFT | MTT | CFT | MTT | CFT | MTT
CFT injection | 0 | 0 | 2.9 | - | - | - | 3.3 | -
2.0 | 5.0 | 4.8 | 5.1 | 97.9 | 102.0 | 2.3 | 3.2
3.0 | 6.0 | 6.1 | 5.8 | 103.4 | 96.7 | 3.0 | 1.8
4.0 | 7.0 | 6.8 | 7.2 | 98.5 | 102.9 | 1.9 | 2.4
5.0 | 8.0 | 8.0 | 7.9 | 101.3 | 98.7 | 2.5 | 2.6
MTT injection | 0 | 0 | - | 4.1 | - | - | - | 2.8
5.5 | 1.0 | 5.4 | 5.2 | 98.2 | 102.0 | 3.6 | 2.7
6.5 | 2.0 | 6.7 | 5.9 | 103.1 | 96.7 | 2.5 | 1.9
7.5 | 3.0 | 7.4 | 7.2 | 98.7 | 101.4 | 2.0 | 2.6
8.5 | 4.0 | 8.6 | 8.0 | 101.2 | 98.7 | 2.3 | 2.4

Samples | Declared concentration, mg mL-1 | Found concentration, mg mL-1 | RSD, %
CFT injection | 10.00 | 10.03 | 2.6
MTT injection | 25.00 | 24.92 | 2.5

Determination of calcium folinate and methotrexate in urine sample

The suggested approach was also used to determine CFT and MTT in a urine sample to assess the analytical utility of the method. Table 3 shows the results obtained when identifying the two species in the urine sample. For both CFT and MTT, a reasonable recovery of the experimental results was seen. The mean relative standard deviation R.S.D. suggested the method was repeatable.

Amount, μM | Recovery, % | RSD, %
Spiked | Found
CFT | MTT | CFT | MTT | CFT | MTT | CFT | MTT
0 | 0 | - | - | - | - | - | -
4.0 | 4.5 | 4.1 | 4.4 | 102.5 | 97.8 | 2.5 | 3.6
6.0 | 6.5 | 5.9 | 6.6 | 98.3 | 101.5 | 3.5 | 2.7
8.0 | 8.5 | 8.1 | 8.4 | 98.9 | 98.9 | 1.9 | 2.8
10.0 | 10.5 | 9.9 | 10.9 | 103.8 | 103.8 | 2.0 | 2.2