Abstract
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.
Highlights
Epinephrine (EP) is an important and well-known member of the catecholamine family produced by the adrenal glands; it is present in low concentrations in extra-adrenal tissues, primarily in sympathetic nerves
We can confirm that the use of the weighted linear regression (WLR) method improved the accuracy at lower concentrations for both analytes as expected, and is usually the main reason for employing the WLR method
No significant difference was observed between the results evaluated using the ordinary least squares (OLS) and WLR methods for the determination of uric acid (UA) at all three tested levels
Summary
Epinephrine (EP) ( named adrenaline) is an important and well-known member of the catecholamine family produced by the adrenal glands; it is present in low concentrations in extra-adrenal tissues, primarily in sympathetic nerves. It is classified as a hormone and neurotransmitter in the mammalian central nervous system [1,2,3]. EP can be used as a drug and is used in the treatment of cardiac surgery, bronchial asthma, hypertension, cardiac arrest, asthma, heart blockages, anaphylaxis, etc. For the treatment of anaphylactic shock, EP is used in the form of an easy-to-use auto-injector due to its cardiovascular and bronchial effects [11,12,13]
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