Determination of trace amounts of estriol and estradiol by adsorptive cathodic stripping voltammetry

Electrochemical biosensors for monitoring of selected pregnancy hormones during the first trimester: A systematic review

The hormones human chorionic gonadotropin, progesterone, estrogen and four of its metabolites (estradiol, estrone, estriol, estetrol), as well as relaxin play an essential role in the development of the fetus during the first trimester. Imbalances in these hormones during the first trimester have been directly linked to miscarriages. However, frequent monitoring of the hormones is limited by the current conventional centralized analytical tools that do not allow a rapid response time. Electrochemical sensing is considered an ideal tool to detect hormones owing to its advantages such as quick response, user-friendliness, low economic costs, and possibility of use in point-of-care settings. Electrochemical detection of pregnancy hormones is an emerging field that has been demonstrated primarily at research level. Thus, it is timely with a comprehensive overview of the characteristics of the reported detection techniques. This is the first extensive review focusing on the advances related to electrochemical detection of hormones linked to the first trimester of pregnancy. Additionally, this review offers insights into the main challenges that must be addressed imminently to ensure progress from research to clinical applications.

Glassy carbon electrode modified with carbon black for sensitive estradiol determination by means of voltammetry and flow injection analysis with amperometric detection

A voltammetric method for fast and sensitive estradiol determination using carbon black modified glassy carbon electrode (CBGC) is proposed. The use of carbon black as a modifying layer led to obtain low detection limit (9.2·10^-8 mol L^-1 for a preconcentration time of 60 s) and stability of registered signals (measured as RSD is 1.3%, n = 7, estradiol concentration 0.5·10^-6 mol L^-1). Cyclic voltammetry study revealed that in phosphate media estradiol suffers irreversible one-proton and one-electron oxidation process. Under the optimum conditions, estradiol calibration curve was linear in the concentration range from 0.15·10^-6 to 3.5·10^-6 mol L^-1. The proposed method enable to determine estradiol content in different pharmaceutical formulation with good recovery. Amperometric measurements of estradiol were performed as well to indicate the possibility of its fast and accurate determination under the flow conditions.

A sensitive determination of estrogens with a Pt nano-clusters/multi-walled carbon nanotubes modified glassy carbon electrode

On the top of a multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (MWNTs/GCE), Pt nanoclusters were electrochemically deposited, fabricating a Pt/MWNTs composite modified electrode, Pt/MWNTs/GCE. X-ray photoelectron spectroscopy, powder X-ray diffraction and field emission scanning electron microscope were used for the surface characterization of the electrode, and demonstrated the formation and distribution of Pt clusters of Pt nanoparticles of 8.4 nm in averaged size in the MWNTs matrix. The preliminary study found that this composite modified electrode has strong electrocatalytic activity toward the oxidation of estrogens involving estradiol, estrone and estriol. The voltammetric behavior of estrogens on this electrode was investigated by cyclic voltammetry, linear sweep voltammetry and square-wave voltammetry. In comparison with the MWNTs/GCE or a Pt nanoparticles modified GCE prepared in the similar way, this composite modified electrode exhibited much higher current sensitivity and catalytic activity. This electrode is also stable. The linear range of square-wave voltammetric determination was 5.0 x 10(-7)-1.5 x 10(-5)mol/L for estradiol, 2.0 x 10(-6)-5.0 x 10(-5)mol/L for estrone, and 1.0 x 10(-6)-7.5 x 10(-5)mol/L for estriol. Under an assumption that the concentration ratio of estradiol:estrone:estriol is 2:2:1, the real sample of blood serums was tested for the determination using this electrode. Satisfactory result was obtained with averaged recovery of 105%.

Simultaneous determination of endocrine disrupting phenolic compounds and steroids in water by solid-phase extraction–gas chromatography–mass spectrometry

A solid-phase extraction (SPE)-gas chromatography (GC)-mass spectrometry (MS) analytical method for the simultaneous separation and determination of endocrine disrupting chemicals (EDCs) from water samples is described in detail. Important and contrasting EDCs including estrone, 17beta-estradiol, 17beta-ethynylestradiol, 16beta-hydroxyestrone, 4-nonylphenol, bisphenol A and 4-tert-octylphenol were selected as the target compounds. The SPE technique, followed by the derivatisation with bis (trimethylsilyl) trifluoroacetamide was used for the extraction recoveries of target compounds from water samples. A number of parameters that may affect the recovery of EDCs, such as the type of SPE cartridges, eluents, as well as water properties including pH value, and concentration of salts and humic substances were investigated. It is shown that the Oasis cartridges produced the best recoveries of target EDCs while ethyl acetate was efficient in eluting EDCs from SPE cartridges. The recovery of some EDCs was enhanced by the addition of salt, but reduced by the increase in pH value and humic acid concentration. The optimised method was further verified by performing spiking experiments in natural river water and seawater matrices, with good recovery and reproducibility for all the selected compounds. The established method was successfully applied to environmental water samples from East and West Sussex, UK, for the determination of the target EDCs.

Voltammetric investigation of beta-estradiol

Electrooxidation of beta-estradiol was investigated using a glassy carbon electrode (GCE) by cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The statistical analysis of the linear relationships between concentration and peak current permits the quantitation of beta-estradiol by both CV and DPV in the concentration range of 4 x 10(-5)-10(-3) M with enough precision and accuracy. A mechanism was proposed about the electrooxidation of this substance. The methods were applied to a tablet form and a transdermal therapeutic system (TTS) of this drug. The results were statistically compared with those of official high performance liquid chromatography (HPLC) method and the differences were found as insignificant.

HPLC-fluorescence determination of unconjugated estrogens in pharmaceuticals

A fluorimetric liquid chromatographic method (lambda(ex) = 280 nm; lambda(em) = 312 nm) was developed for measurements of unconjugated estrogens (estradiol and estriol) in pharmaceutical dosage forms using a reversed-phase column with water acetonitrile at different composition as mobile phase. The in vitro release profiles of three different estradiol transdermal therapeutic systems were determined through a medical-grade silicone rubber subdermal implant material membrane, using a modified Franz diffusion apparatus at 37 degrees C in presence of PEG 400. The HPLC method possesses advantages of rapidity, simplicity and accuracy.

Separation of urinary estrogens by micellar electrokinetic chromatography

Urinary estrogen levels are important for monitoring the normal pregnancy process as well as for the diagnosis of reproductive diseases. 17 beta-Estradiol and estrone are maintained at very low concentrations in urine and, therefore, are difficult to determine using standard chromatography with UV detection. In the present study, we describe a potential method for the determination of urinary estrogens (estrone, estradiol and estriol) using a solid-phase extraction and rapid capillary electrophoretic (CE) separations. Micellar electrokinetic chromatographic (MEKC) analysis was optimized by evaluating the number of surfactants in a 5 mM borate-5 mM phosphate separation buffer, of which sodium cholate (75-90 mM) was found to be optimal. Changing the hydrophobic character of the separation buffer with organic additives had a significant effect on the resolution of the three estrogens and an internal standard (d-equilenin). The addition of an organic additive (20% acetonitrile) was found to be necessary for the resolution of all components of the mixture. Substitution with 20% methanol provided a similar separation with better resolution but at the cost of increased analysis time. Analysis of two extracted urine samples from 18-weeks and 21-weeks pregnant women showed that, with the present technology, CE can provide adequate resolution and superior speed, but the sensitivity limits attainable with the existing technology may limit its utility to the measurement of estriol and estrone.