Liquid-phase microextraction combined with graphite furnace atomic absorption spectrometry: A review

Evaluation of blood lead measurements by the 6-year external quality assessment program in China

BACKGROUND

Blood lead is an important clinical indicator. A typical tool for promoting standardisation or harmonisation is external quality assessment (EQA). Therefore, the National Centre for Clinical Laboratories (NCCL) in China launched the EQA Program for blood lead measurement in 2006 to assess its standardisation process.

METHODS

Blood lead EQA samples tested for homogeneity and stability were sent to participating laboratories. The return data were grouped according to the detection method. The robust mean value, robust coefficient of variation (CV) and standard uncertainty were calculated according to ISO 13528. The evaluation criteria were determined based on a thorough analysis of the previous pass rate and the current detection level. Overall trends in the blood lead EQA program over 6 years were investigated by calculating the pass rates of participating laboratories. We compared the pass rates and current issues of different detection methods and analysed the target values, bias and CV results of mainstream detection methods.

RESULTS

A total of 4,283 laboratories participated in EQA programs from 2017 to 2022. The pass rates were generally increasing while the inter-laboratory mean CVs were decreasing. For samples with varying concentrations, the higher the concentration, the smaller the CV. According to the evaluation criteria, the most used measurement methods, Graphite Furnace Atomic Absorption Spectrometry (GFAAS) and Tungsten Ship Atomic Absorption Spectrometry (TSAAS) demonstrated better performances than Differential Potentiometric Stripping (DPS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Flame Atomic Absorption Spectrometry (FAAS). Furthermore, DPS, ICP-MS and FAAS outperformed Anodic Stripping Voltammetry (ASV).

CONCLUSION

Our study provides reliable information on the standardisation of blood lead measurement procedures for manufacturers and clinical laboratories. Further improvements for standardisation are still required to make laboratories more patient-centred.

A Green Method for the Determination of Cadmium in Natural Waters Based on Multi-Fibre Supported Liquid Membranes

Supported liquid membranes have been used to implement a hollow fibre liquid-phase microextraction (HF-LPME) method for the preconcentration of Cd(II) in natural waters as a sample preparation step for its determination by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS). This system was designed to use four hollow fibres simultaneously with the same sample, thus improving the simplicity, speed and reproducibility of the results. The organic liquid membrane bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex^® 272) dissolved in dihexylether (DHE) was immobilised into the pores of the walls of polypropylene hollow fibres. After extraction, the cadmium-enriched acidic phases were recovered and analysed by triplicate. To optimise the extraction process, the effect of both physical and chemical variables was studied, and optimum results with an enrichment factor (EF) of 292 were obtained for a fibre length of 6 cm, 1.06 M Cyanex 272, 0.04 M HNO₃, stirring rate of 600 rpm and an extraction time of 4.26 h. For practical applications, extraction time was reduced to 2 h, keeping the EF as high as 130. Under these conditions, a detection limit of 0.13 ng L^-1 Cd(II) was obtained, with a reproducibility of 3.3 % and a linear range up to 3 µg L^-1 being achieved. The proposed method was successfully applied to the determination of cadmium in mineral, tap and seawater samples.

Heavy Metal Ions Detection Using Nanomaterials-Based Aptasensors

Heavy metals ions as metallic pollutants are a growing global issue due to their adverse effects on the aquatic ecosystem, and human health. Unfortunately, conventional detection methods such as atomic absorption spectrometry exhibit a relatively low limit of detection and hold numerous disadvantages, and therefore, the development of an efficient method for in-situ and real-time detection of heavy metal residues is of great importance. The aptamer-based sensors offer distinct advantages over antibodies and emerged as a robust sensing platform against various heavy metals due to their high sensitivity, ease of production, simple operations, excellent specificity, better stability, low immunogenicity, and cost-effectiveness. The nucleic acid aptamers in conjugation with nanomaterials can bind to the metal ions with good specificity/selectivity and can be used for on-site monitoring of metal ion residues. This review aimed to provide background information about nanomaterials-based aptasensor, recent advancements in aptamer conjunction on nanomaterials surface, the role of nanomaterials in improving signal transduction, recent progress of nanomaterials-based aptasening procedures (from 2010 to 2022), and future perspectives toward the practical applications of nanomaterials-based aptasensors against hazardous metal ions for food safety and environmental monitoring.

Overview of Different Modes and Applications of Liquid Phase-Based Microextraction Techniques

Liquid phase-based microextraction techniques (LPµETs) have attracted great attention from the scientific community since their invention and implementation mainly due to their high efficiency, low solvent and sample amount, enhanced selectivity and precision, and good reproducibility for a wide range of analytes. This review explores the different possibilities and applications of LPμETs including dispersive liquid–liquid microextraction (DLLME) and single-drop microextraction (SDME), highlighting its two main approaches, direct immersion-SDME and headspace-SDME, hollow-fiber liquid-phase microextraction (HF-LPME) in its two- and three-phase device modes using the donor–acceptor interactions, and electro membrane extraction (EME). Currently, these LPμETs are used in very different areas of interest, from the environment to food and beverages, pharmaceutical, clinical, and forensic analysis. Several important potential applications of each technique will be reported, highlighting its advantages and drawbacks. Moreover, the use of alternative and efficient “green” extraction solvents including nanostructured supramolecular solvents (SUPRASs, deep eutectic solvents (DES), and ionic liquids (ILs)) will be discussed.

A review of new adsorbents for separation of BTEX biomarkers

The biomarker analysis of benzene, toluene, ethylbenzene and xylene (BTEXs) in biological samples is the primary technique for evaluating these compounds in occupational and environmental exposures. The BTEX biomarkers are widely used to study the BTEX distribution in the environment and workplaces. Liquid-liquid extraction and solid-phase liquid extraction are among the most commonly used conventional methods to analyze biological indices of BTEXs. New methods have been proposed to analyze BTEX biomarkers using novel adsorbents such as sol-gel composite nanotubes, molecularly imprinted polymers and metal-organic frameworks, which are based on the application of needle trap devices, microextraction by packed sorbent, and solid-phase microextraction techniques. This paper provides an overview of new methods since 2015 regarding applying microextraction methods based on new adsorbents and analyzing BTEX biomarker compounds for occupational and environmental exposures. The results were compared with the liquid-phase microextraction methods recommended for urinary BTEX biomarkers.

Unravelling neurological disorders through metallomics-based approaches

Understanding the biological process involving metals and biomolecules in the brain is essential for establishing the origin of neurological disorders, such as neurodegenerative and psychiatric diseases. From this perspective, this critical review presents recent advances in this topic, showing possible mechanisms involving the disruption of metal homeostasis and the pathogenesis of neurological disorders. We also discuss the main challenges observed in metallomics studies associated with neurological disorders, including those related to sample preparation and analyte quantification.

Understanding the relationship between viral infections and trace elements from a metallomics perspective: implications for COVID-19

Recently, the World Health Organization (WHO) declared a pandemic situation due to a new viral infection (COVID-19) caused by a novel virus (Sars-CoV-2). COVID-19 is today the leading cause of death from viral infections in the world. It is known that many elements play important roles in viral infections, both in virus survival, and in the activation of the host's immune system, which depends on the presence of micronutrients to maintain the integrity of its functions. In this sense, the metallome can be an important object of study for understanding viral infections. Therefore, this work presents an overview of the role of trace elements in the immune system and the state of the art in metallomics, highlighting the challenges found in studies focusing on viral infections.

Direct immersion single-drop microextraction of semi-volatile organic compounds in environmental samples: A review

Single-drop microextraction (SDME) techniques are efficient approaches to pretreatment of aqueous samples. The main advantage of SDME lies in the miniaturization of the solvent extraction process, minimizing the hazards associated with the use of toxic organic solvents. Thus, SDME techniques are cost-effective, and represent less harm to the environment, subscribing to green analytical chemistry principles. In practice, two main approaches can be used to perform SDME - direct immersion (DI)-SDME and headspace (HS)-SDME. Even though the DI-SDME has been shown to be quite effective for extraction and enrichment of various organic compounds, applications of DI-SDME are normally more suitable for moderately polar and non-polar semi-volatile organic compounds (SVOCs) using organic solvents which are immiscible with water. In this review, we present a historical overview and current advances in DI-SDME, including the common analytical tools which are usually coupled with DI-SDME. The review also focuses on applications concerning SVOCs in environmental samples. Currents trends in DI-SDME and possible future direction of the procedure are discussed.

Speciation of chromium in waters using dispersive micro-solid phase extraction with magnetic ferrite and graphite furnace atomic absorption spectrometry

The combination of a solid-phase microextraction process with graphite furnace atomic absorption spectrometry provides a very sensitive determination method for determining chromium in waters. Freshly prepared ferrite particles are used to retain the chromium species, and then separated by a magnet without the need for a centrifugation step. The solid phase is suspended in water and directly introduced into the graphite furnace to obtain the analytical signal. The complexation of Cr(III) with ethylenediaminetetraacetate allows the selective retention of Cr(VI), and thus the speciation of the metal. The procedure is sensitive (0.01 µg L⁻¹ detection limit when using a 10 mL sample aliquot) and reproducible (5% relative standard deviation for five consecutive experiments at the 0.3 µg L⁻¹ level). The reliability of the procedure is verified by analysing five certified water samples.

Rapid liquid-phase microextraction of analytes from complex samples on superwetting porous silicon for onsite SALDI-MS analysis

To simplify the pretreatment process of complex samples is a key step for rapid detection. Herein, we report a single-step method to rapidly extract analytes with liquid-phase microextraction (LPME) from complex samples on a superwetting porous silicon (PSi) for onsite detection with surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The operation time is less than 3 min with this simple method. The limit of detection (LOD) of malachite green in lake water is lowered to 10^-13 M, that of verapamil and methadone in whole blood is down to 10^-11 M and 10^-13 M, in urine is 10^-13 M and 10^-14 M, respectively; and the ranges of quantification is up to 8 or 9 orders of magnitude with high precision (coefficients of determination (R²) > 0.98) for the complex samples. This method could provide an approach to directly extract target compounds from complex samples on substrate for SALDI-MS analysis.

Colorimetric determination of Hg2+ in environmental water based on the Hg2+-stimulated peroxidase mimetic activity of MoS2-Au composites

A colorimetric assay is described for sensitive determination of Hg²⁺ ions based on the MoS₂-Au composites as peroxidase mimetics, which are synthesized by microwave-assisted solvothermal method. The addition of Hg²⁺ stimulates their peroxidase-like activity, along with lower Michaelis constant toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with H₂O₂, allowing the composites for direct determination of Hg²⁺. A broad linear response is obtained ranging from 20 nM to 20 μM with a detection limit (LOD) of 5 nM. The superior peroxidase-like activity is attributed to the large surface area of MoS₂ nanosheets and the synergistic catalytic effect of MoS₂ and Au. The Hg²⁺-stimulation effect implies the strong interaction between Hg²⁺ and MoS₂-Au, where the XPS results confirm the presence of metallic Hg⁰, indicative of an Au-Hg amalgam. This colorimetric assay is successfully applied for the determination of Hg²⁺ in environmental water (tap water and Yellow River water) with excellent selectivity over interfering cations.