Sensitivity improvement of the LC–MS/MS quantification of carbidopa in human plasma and urine by derivatization with 2,4-pentanedione

Quantitative Colorimetric Sensing of Carbidopa in Anti-Parkinson Drugs Based on Selective Reaction with Indole-3-Carbaldehyde

The quality of life of patients affected by Parkinson's disease is improved by medications containing levodopa and carbidopa, restoring the dopamine concentration in the brain. Accordingly, the affordable quality control of such pharmaceuticals is very important. Here is reported the simple and inexpensive colorimetric quantification of carbidopa in anti-Parkinson drugs by the selective condensation reaction between the hydrazine group from carbidopa and the formyl functional group of selected aldehydes in acidified hydroalcoholic solution. An optical assay was developed by using indole-3-carbaldehyde (I3A) giving a yellow aldazine in EtOH:H2O 1:1 (λmax~415 nm) at 70 °C for 4 h, as confirmed by LC-MS analysis. A filter-based plate reader was used for colorimetric data acquisition, providing superior results in terms of analytical performances for I3A, with a sensitivity ~50 L g-1 and LOD ~0.1 mg L-1 in comparison to a previous study based on vanillin, giving, for the same figures of merit values, about 13 L g-1 and 0.2-0.3 mg L-1, respectively. The calibration curves for the standard solution and drugs were almost superimposable, therefore excluding interference from the excipients and additives, with very good reproducibility (avRSD% 2-4%) within the linear dynamic range (10 mg L-1-50 mg L-1).

Determination of levodopa by chromatography-based methods in biological samples: a review

Levodopa (L-DOPA) is the most effective drug for Parkinson's disease; however, various side effects occur during therapy. L-DOPA metabolites and the high cumulative dose of L-DOPA were responsible for its side effects. It is necessary to monitor the concentration of L-DOPA and its metabolites for individualized therapy. This review focuses on L-DOPA analysis by chromatography-based methods in biological matrices. Literature published up to September 2021 was collected in the PubMed, Web of Science, and Embase by using search strategy ("levodopa" OR "L-DOPA") AND ("chromatography"). A total of 1249 articles were identified and 32 articles were included. The contents for method development and validation were summarized and analyzed. Due to the instability of catecholamines (L-DOPA, dopamine, and 3-O-methyldopa) and carbidopa, antioxidation (0.5 mg sodium metabisulfite for 100 μL sample) and environment temperature control were used alone or in combination to enhance stability. Sample was mainly pretreated by protein precipitation (0.4-0.7 M perchloric acid). Separation was usually achieved using methanol or acetonitrile:water (with formic acid) on C18 columns. Mass spectrometry, electrochemical detector, ultraviolet-visible detector and fluorescence detector were used for detection. For L-DOPA, the calibration range was 2.5-10,000 ng/mL, the matrix effect and its coefficient of variation was 85-115 and -9.0-8.5%, and the recovery was 66.8-127.0%. Without stabilization strategy, L-DOPA was stable in plasma at room temperature for 1-7 h (4-6 h for most studies), at - 70 °C to - 80 °C for 10-20 days and after 3-5 freeze-thaw cycles. With stabilization strategies, the stability of L-DOPA in plasma was significantly improved. Metabolites of L-DOPA and enzyme inhibitors (carbidopa, entacapone, tolcapone and benserazide) were all stable in biological matrix. This study might be useful for researchers to develop their methods for individualized therapy of patients with Parkinson.

Technologies to improve the sensitivity of existing chromatographic methods used for bioanalytical studies

Chromatographic method has long been recognized as the most widely used separation method in bioanalytical research. However, the relatively low sensitivity of existing chromatographic methods remains a significant challenge, as the requirements for experimental procedures become more demanding. This review discusses the main causes for the low sensitivity of chromatographic methods and aims to introduce different technologies for enhancing their sensitivity in the following aspects: (i) different pretreatment methods for improving clean-up efficiency and recovery; (ii) derivatization step for altering the chromatographic behavior of analytes and enhancing MS ionization efficiency; (iii) optimal LC-MS conditions and appropriate separation mechanism; and (iv) applications of other chromatographic methods, including miniaturized LC, 2D-LC, 2D-GC, and supercritical fluid chromatography. Altogether, this review is devoted to summarizing the recent technologies reported in the literature and providing new strategies for the detection of bioanalytes.

The effect of ultrasonic irradiation on the morphology of NiO/Co3O4 nanocomposite and its application to the simultaneous electrochemical determination of droxidopa and carbidopa

The present work deals with the preparation of NiO/Co₃O₄ nanocomposites in presence of ultrasonic irradiation, and its use in electrochemical determination of Parkinson's drugs. NiO/Co₃O₄ nanocomposites are prepared using ultrasound assisted method. The impact of ultrasonic irradiation power (0, 75, 150, 300 and 600 W) on the structure and morphology of NiO/Co₃O₄ nanocomposites was investigated. Various particle morphologies were attained because of the existence of ultrasonic irradiation. The nanoparticles' structure exhibited more uniformity whilst the particles sizes and nanoparticle accumulation was reduced when ultrasonic irradiation power was increased. The NiO/Co₃O₄ nanocomposite was determined via X-ray diffraction, scanning electron microscopy i.e. SEM as well as energy dispersion X-ray spectroscopy (EDX). Drop casting NiO/Co₃O₄ nanocomposites suspension on glassy carbon electrode was employed to fabricate the modified glassy carbon electrode (NiO/Co₃O₄/GCE). The electrochemical studies on the NiO/Co₃O₄ nanocomposite towards droxidopa and carbidopa were experimented via cyclic voltammetry (CV), chronoamperometry (CHA) and differential pulse voltammetry (DPV). The CV examinations displayed increased catalytic behavior of droxidopa because of synergistic impact of the nanocomposite that was bolstered through enhanced material surface roughness. By using differential pulse voltammetry, the droxidopa detection limit and linear range was determined as 0.01 μM and 0.1-500.0 μM, respectively. Also, the adjusted electrode was implemented to ascertain droxidopa in the presence of carbidopa by differential pulse voltammetry. This sensor exhibited long term reproducibility and stability. Droxidopa and carbidopa quantification within biological specimens of fluids i.e. human urine and serum were conducted to validate the suitability in the application of this sensor.

Monitoring of the deuterated and nondeuterated forms of levodopa and five metabolites in plasma and urine by LC-MS/MS

To compare pharmacokinetics, metabolism and excretion of levodopa and a triply deuterated form, which is being developed as an improved treatment for Parkinson's disease, methods were needed for quantification of the deuterated and nondeuterated forms of levodopa and five metabolites in human plasma and urine. Results: The natural heavy isotopes in the nondeuterated compounds caused an absolute contribution of up to 100% in the response of the deuterated compounds. Similarly, heavy isotopes in the deuterated analytes contributed to the response of the internal standards, but this did not affect the reliability of the results. Conclusion: Deuterated and nondeuterated analytes can be quantified together by LC-MS/MS, but overestimation of the concentrations of the deuterated molecules may be unavoidable and a careful interpretation of the concentration data is essential.