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In this work, an automated dissolution system (dissoBOT) was used for dissolution testing for the first time. Carry-over (CO) of the dissoBOT was determined for paracetamol (PA) and diclofenac sodium (DS), which are active pharmaceutical ingredients (APIs). Initially, partial method validation of the UV-VIS spectrophotometry method for PA and DS determination was performed by defining the limit of detection (LOD), the limit of quantification (LOQ), linear concentration range, accuracy, and precision. The LODs and LOQs were less than 0.01 mg/L for both APIs. The determined linear concentration ranges were from 1.00 mg/L to 30.00 mg/L for PA and from 0.50 mg/L to 3.50 mg/L for DS (the square of the correlation coefficient was greater than 0.9990, and the quality coefficient was less than 1.00 % for both APIs). The accuracy of the method was evaluated by calculating the recovery (Re) of the solutions of standards with known concentrations. The method for both APIs was deemed to be accurate (the average Re for PA and DS were 99.81 % and 101.43 %, respectively). Precision was evaluated by calculating the relative standard deviation (RSD). The method for PA and DS was deemed to be precise, as the RSD value for PA was 0.13 %, and for DS was 0.38 %. The volume (V) of the washing medium in both cleaning cycles performed by the dissoBOT system, as well as the medium dispensing V, were established, where the medium dispensing V was in accordance with the United States Pharmacopeia requirements. The CO of the dissoBOT system, using tap water as the washing medium, was determined to be less than 1.00 % for both APIs. The CO values for one cleaning cycle of the sampling station with a V of 2 mL was in the range of 1.24-1.54 %, for V of 5 mL was in the range of 0.78-0.93 %, and for V of 10 mL was in the range of 0.27-0.36 %. In addition, the CO of the dissoBOT, when employing two cleaning cycles of the sampling station (each V of 10 mL) was reduced (CO <0.20 %). Finally, the dissoBOT was successfully employed for the dissolution PA and DS tables.
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An electrochemical sensor for the detection of insulin in a single drop (50 µL) was developed based on the concept of molecularly imprinted polymers (MIP). The synthetic MIP receptors were assembled on a screen-printed carbon electrode (SPCE) by the electropolymerization of pyrrole (Py) in the presence of insulin (the protein template) using cyclic voltammetry. After electropolymerization, insulin was removed from the formed polypyrrole (Ppy) matrix to create imprinting cavities for the subsequent analysis of the insulin analyte in test samples. The surface characterization, before and after each electrosynthesis step of the MIP sensors, was performed using atomic force microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The performance of the developed MIP-SPCE sensor was evaluated using a single drop of solution containing K3Fe(CN)6 and the square-wave voltammetry technique. The MIP-SPCE showed a linear concentration range of 20.0-70.0 pM (R2 = 0.9991), a limit of detection of 1.9 pM, and a limit of quantification of 6.2 pM. The rapid response time to the protein target and the portability of the developed sensor, which is considered a disposable MIP-based system, make this MIP-SPCE sensor a promising candidate for point-of-care applications. In addition, the MIP-SPCE sensor was successfully used to detect insulin in a pharmaceutical sample. The sensor was deemed to be accurate (the average recovery was 108.46%) and precise (the relative standard deviation was 7.23%).
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Impresión Molecular , Polímeros , Polímeros/química , Polímeros Impresos Molecularmente , Insulina , Impresión Molecular/métodos , Pirroles/química , Carbono/química , Electrodos , Técnicas Electroquímicas/métodos , Límite de DetecciónRESUMEN
Sample preparation is crucial for elemental determination, and various techniques are available, one of which involves homogenization followed by acid digestion. Special care is required during sample handling in the preparation stage to eliminate or minimize potential contamination and analyte loss. Homogenization is a process that simultaneously reduces particle size and uniformly distributes sample components. Following homogenization, the sample undergoes acid digestion, wherein it is digested with acids and auxiliary chemicals at elevated temperatures, transforming solid samples into a liquid state. In this process, metals in the original sample react with acids to form water-soluble salts. Samples prepared through acid digestion are suitable for elemental analysis using techniques such as inductively coupled plasma mass spectrometry, inductively coupled plasma optical emission spectroscopy, atomic absorption spectroscopy, electrochemical methods, and other analytical techniques. This work details the preparation of food samples for multi-element determination using inductively coupled plasma mass spectrometry. The step-by-step procedure involves the homogenization process using a laboratory-sized mixer with ceramic blades, followed by acid digestion in closed vessels using microwave-assisted wet acid digestion. A mixture of 5.0 mL of 68 wt% HNO3 and 1.0 mL of 30 wt% H2O2 serves as an auxiliary reagent. This guide provides an explanation of the processes involved in both stages.
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Peróxido de Hidrógeno , Microondas , Cerámica , Espectrofotometría Atómica , DigestiónRESUMEN
The preconditioning and modification of the supporting electrode surface is an essential step in every biosensor architecture. In particular, when using screen-printed carbon electrodes (SPEs) as inexpensive and convenient disposable sensor substrates, their somewhat lower electrochemical (surface) reproducibility might represent a complex hurdle. Herein, we investigated the effect of selected preconditioning strategies, such as cyclic voltammetric pretreatment, in H2SO4 and H2O2 and plasma pretreatment with a positive and negative glow discharge, which all improved the electrochemical stability of the unmodified SPEs. Furthermore, we studied the influence of preconditioning strategies on the adsorption kinetics of the two most commonly used building blocks for biosensor preparation, i.e., bovine serum albumin (BSA) and protein A. We observed an advantageous effect of all the examined preconditioning strategies for the modification of SPEs with protein A, being the most effective the negative glow discharge. On the other hand, BSA exhibited a more complex adsorption behavior, with the negative glow discharge as the only generally beneficial preconditioning strategy providing the highest electrochemical stability. Protein A revealed a more substantial impact on the electrochemical signal attenuation than BSA considering their same concentrations in the modification solutions. For both BSA and protein A, we showed that the concentrations of 5 and 10 µg mL-1 already suffice for an electrochemically satisfactorily stable electrode surface after 60 min of incubation time, except for BSA at the positive-plasma-treated electrode.
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Carbono , Técnicas Electroquímicas , Adsorción , Electrodos , Peróxido de Hidrógeno , Reproducibilidad de los Resultados , Albúmina Sérica BovinaRESUMEN
This work demonstrates the analysis of epinephrine (EP) and uric acid (UA) in a single drop (the volume of the test solution was only 50 µL) using a screen-printed carbon electrode (SPCE) sensor and square-wave voltammetry (SWV). The limit of detection, limit of quantification, linearity, accuracy, precision, and robustness were validated. The normality of the experimental data was tested and confirmed for both methods. Heteroscedasticity was checked by residual analysis followed by a statistical F-test. The latter was confirmed for both analytes. The low relative standard deviations (RSD) at all calibration points and repetitive slopes justified the use of a calibration curve; therefore, the standard addition methodology was avoided (the latter is common in electroanalysis, but time-consuming). Since the conditions for using an ordinary least squares (OLS) regression were not met, weighted linear regression (WLR) was used to improve the accuracy of the analytical results at low concentrations of the analytes. In this manner, the best weighted model was determined and used for the quantification. A comparison was made between the OLS and WLR methods to show the necessity of using the WLR method for EP and UA analysis. The newly developed and validated methods were also shown to be effective in the analysis of real samples. The content of EP in an EP auto-injector and UA in human urine was tested by employing the best weighted model. For EP and UA, the accuracy in terms of the average recovery value was 101.01% and 94.35%, and precision in terms of RSD was 5.65% and 2.75%, respectively. A new analytical methodology is presented that uses a low volume (a single drop), and it offers the advantage of electroanalysis for on-site analysis, where conventional chromatographic techniques cannot be easily employed. Furthermore, the developed technique has additional advantages in terms of speed, cost, and miniaturization.
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Electrodos , Epinefrina/análisis , Ácido Úrico/análisis , Ácido Ascórbico , Técnicas Biosensibles , Catálisis , Técnicas Electroquímicas , Electroquímica , Humanos , Nanotubos de CarbonoRESUMEN
In this study, the use of weighted linear regression in the development of electrochemical methods for the determination of epinephrine (EP), ascorbic acid (AA), and uric acid (UA) is presented. The measurements were performed using a glassy carbon electrode and square-wave voltammetry (SWV). All electroanalytical methods were validated by determination of the limit of detection, limit of quantification, linear concentration range, accuracy, and precision. The normal distribution of all data sets was checked using the quantile-quantile plot and Kolmogorov-Smirnov statistical tests. The heteroscedasticity of the data was tested using Hartley's test, Bartlett's test, Cochran's C test, and the analysis of residuals. The heteroscedastic behavior was observed with all analytes, justifying the use of weighted linear regression. Six different weighting factors were tested, and the best weighted model was determined using relative percentage error. Such statistical approach improved the regression models by giving greater weight on the values with the smallest error and vice versa. Consequently, accuracy of the analytical results (especially in the lower concentration range) was improved. All methods were successfully used for the determination of these analytes in real samples: EP in an epinephrine auto-injector, AA in a dietary supplement, and UA in human urine. The accuracy and precision of real sample analysis using best weighted model gave satisfactory results with recoveries between 95.21-113.23% and relative standard deviations between 0.85-7.98%. The SWV measurement takes about 40 s, which makes the presented methods for the determination of EP, AA, and UA a promising alternative to chromatographic techniques in terms of speed, analysis, and equipment costs, as the analysis is performed without organic solvents.
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In this work, unmodified screen-printed electrode (bare SPE) and Sb-film modified SPE (SbFSPE) sensors were employed for the analysis of trace amounts of Pb(II) in non-deaerated water solutions. The modified electrode was performed in situ in 0.5 mg/L Sb(III) and 0.01 M HCl. The methodology was validated for an accumulation potential of â»1.1 V vs. Ag/AgCl and an accumulation time of 60 s. A comparative analysis of bare SPE and SbFSPE showed that the detection and quantification limits decrease for the bare SPE. The method with the bare SPE showed a linear response in the 69.8â»368.4 µg/L concentration range, whereas linearity for the SbFSPE was in the 24.0â»319.1 µg/L concentration range. This work also reports the reason why the multiple standard addition method instead of a linear calibration curve for Pb(II) analysis should be employed. Furthermore, the analytical method employing SbFSPE was found to be more accurate and precise compared to the use of bare SPE when sensors were employed for the first time, however this performance changed significantly when these sensors were reused in the same manner. Furthermore, electrochemical impedance spectroscopy was used for the first time to analyse the electrochemical response of sensors after being used for multiple successive analyses. Surface characterisation before and after multiple successive uses of bare SPE and SbFSPE sensors, with atomic force microscopy and field emission scanning electron microscopy, showed sensor degradation. The interference effect of Cd(II), Zn(II), As(III), Fe(II), Na(I), K(I), Ca(II), Mg(II), NO3â», Bi(III), Cu(II), Sn(II), and Hg(II) on the Pb(II) stripping signal was also studied. Finally, the application of SbFSPE was tested on a real water sample (from a local river), which showed high precision (RSD = 8.1%, n = 5) and accurate results.