Thermo-responsive polymer coated fiber-in-tube capillary microextraction and its application to on-line determination of Co, Ni and Cd by inductively coupled plasma mass spectrometry (ICP-MS)

Direct Coupling of SPME to Mass Spectrometry

Solid-phase microextraction devices are normally analyzed by gas or liquid chromatography. Their use has become increasingly widespread since their introduction in 1990, and nowadays most analytical laboratories use or have used SPME as an efficient and green method to perform analyte extraction and sample clean-up in one step. The SPME technique is intrinsically flexible, and allows for a high degree of optimization with regard to the extracting phase, as well as the way sample is analyzed. Since its introduction, researchers have been trying different ways to transfer analytes extracted from the solid phase to a mass spectrometer, with the aim to increase throughput and reduce solvent, gas usage and costs associated with conventional chromatographic techniques. Furthermore, but not less important, for pure fun of developing new, more efficient and sensitive analytical strategies! This chapter aims at providing a comprehensive overview of the most relevant non-chromatographic mass spectrometric approaches developed for SPME. Technical aspects of each SPME-MS approach will be discussed, highlighting their advantages, disadvantages and future potential developments. Particular emphasis will be given on the most recent direct coupling approaches using novel ionization approaches, and a concise overview of the existing applications will also be provided.

Trends in microextraction approaches for handling human hair extracts - A review

The complementary role of hair in testing scenarios has expanded across the spectrum of toxicological and clinical monitoring investigations and, over the last 20 years, hair analysis has gained increasing attention and recognition. Moreover, a great deal of attention has been paid to the miniaturisation of extraction procedures, minimising/eliminating toxic organic solvents consumption, making them user-friendly and rapid, in addition to maximising extraction efficiency. The aim of this work is to provide a critical review of the advances observed over the last 5 years in the use of miniaturised approaches for sample clean-up and drug pre-concentration in hair analysis. There have been major improvements in some well-established microextraction approaches, such as liquid phase microextraction, mainly through the use of supramolecular and ionic liquids. In addition, new developments have also been reported in solid phase microextraction, driven by d-SPE applications. In the last 5 years, a total of 69 articles have been published using some type of microextraction technique for hair specimens, thus justifying the relevance of a critical review of innovations, improvements and trends related to these miniaturised approaches for sample preparation.

Magnetic dispersive solid-phase extraction using ZSM-5 zeolite/Fe2O3 composite coupled with screen-printed electrodes based electrochemical detector for determination of cadmium in urine samples

A novel, simple, fast, sensitive and environmentally friendly approach is presented to determine cadmium in urine samples, combining magnetic dispersive solid-phase extraction (MDSPE) for sample preparation and screen-printed carbon electrodes (SPCEs) for square-wave anodic stripping voltammetry. This association involves the miniaturization of sample preparation and measurement process. Firstly, cadmium was extracted directly from urine samples employing a ZSM-5/Fe₂O₃, then, the composite enriched with cadmium was deposited onto the SPCE and finally covered with a suitable electrolyte for electrochemical detection. Thereby, the elution and detection of cadmium were carried out in a single step. To optimize experimental parameters affecting MDSPE, a two-step multivariate strategy has been employed. The method has been evaluated under optimized extraction/elution conditions (i.e., type of sorbent, ZSM-5/Fe₂O_3; amount of sorbent, 10 mg; sample pH, 6.8; extraction time, 5.5 min; and HCl concentration, 0.5 M) using standard addition calibration. Standard addition calibration curves gave a good linearity in the range from 0 to 30 μg L^-1 with correlation coefficients ranging from 0.997 to 0.998 (N = 7). The limit of detection, evaluated empirically and statistically, ranged from 0.5 to 1.0 μg L^-1 and from 0.4 to 0.8 μg L^-1, respectively, which are lower than the threshold level established by the Ministry of Labour and Social Affairs (Spain) and World Health Organization for normal cadmium content in urine (i.e., 3.4 and 4.0 μg L^-1, respectively). The repeatability of the proposed method was evaluated at 5 and 20 μg L^-1 spiking levels obtaining coefficients of variation ranged between 12 and 15% (n = 6). A certified reference material (REC-8848/Level II) was analyzed to assess method accuracy finding 92% and 1.3 μg L^-1 as the recovery (trueness) and standard deviation values, respectively. Finally, the method was applied to spiked urine samples, obtaining good agreement between spiked and found concentrations (recovery ranged from 89 to 98% and CV values ranged from 7% to 14%). Therefore, this is a new and successful contribution to the portable total analytical systems.

Application of stimuli-responsive materials for extraction purposes

Stimuli-responsive materials, frequently designated as "smart/intelligent materials", can modify their structure or properties by either a biological, physical, or chemical stimulus which, if properly controlled, could be used for specific applications. Such materials have been studied and exploited in several fields, like electronics, photonics, controlled drugs administration, imaging and medical diagnosis, among others, as well as in Analytical Chemistry where they have been used as chromatographic stationary phases, as part of sensors and for extraction purposes. This review article pretends to provide an overview of the most recent applications of these materials (mostly polymeric materials) in sample preparation for extraction purposes, as well as to provide a general vision of the current state-of-the-art of this field, their potential use and future applications.

A monolithic copolymer prepared from N-(4-vinyl)-benzyl iminodiacetic acid, divinylbenzene and N,N'-methylene bisacrylamide for preconcentration of cadmium(II) and cobalt(II) from biological samples prior to their determination by ICP-MS

A capillary monolith consisting of poly[N-(4-vinyl)-benzyl iminodiacetic acid-co-divinylbenzene-co-N,N'-methylene bisacrylamide), referred to as poly(VBIDA-DVB-Bis), has been prepared. It is shown to be an efficient sorbent for the enrichment of Co(II) and Cd(II). The two ions are completely retained by the monolith in the pH range from 4.0 to 9.0. The breakthrough curve tests were adopted to evaluate the adsorption performance of the monolith towards Co(II) and Cd(II). A dose-response model was used to describe the breakthrough curves of the two ions at different initial concentrations. The adsorption capacities for Co(II) and Cd(II) are 1.54 and 1.73 mg·m^-1 at a concentration level of 2.5 mg·L^-1, respectively. The enrichment factor is 100, and the required sample volume is 5 mL. Following elution of the two ions with 0.5 M HNO₃, they were quantified by ICP-MS. The limits of detection in a 1 mL sample are 0.35 ng·L^-1 for Co(II) and 0.44 ng·L^-1 for Cd(II). The method was applied to the determination of Co(II) and Cd(II) in spiked rice, human urine and seawater samples. Graphical abstract Schematic representation of a monolithic copolymer prepared from N-(4-vinyl)-benzyl iminodiacetic acid (VBIDA), divinylbenzene (DVB) and N,N'-methylene bisacrylamide (Bis) and its application for selective capturing of cadmium(II) and cobalt(II) from complex sample matrices prior to their determination by ICP-MS.

Determination of Cadmium in Brown Rice Samples by Fluorescence Spectroscopy Using a Fluoroionophore after Purification of Cadmium by Anion Exchange Resin

Simple analytical methods are needed for determining the cadmium (Cd) content of brown rice samples. In the present study, we developed a new analytical procedure consisting of the digestion of rice using HCl, Cd purification using anion exchange resin, and then determining the Cd content using fluorescence spectroscopy. Digestion with 0.1 M HCl for 10 min at room temperature was sufficient to extract Cd from the ground rice samples. The Cd in the extract was successfully purified in preference to other metals using Dowex 1X8 chloride form resin. Low concentrations of Cd in the eluate could be determined using fluorescence spectroscopy with a fluoroionophore. Overall, the actual limit of quantification value for the Cd content in rice was about 0.1 mg-Cd/kg-rice, which was sufficiently low compared with the regulatory value (0.4 mg-Cd/kg-rice) given by the Codex Alimentarius Commission. We analyzed authentic brown rice samples using our new analytical procedure and the results agreed well with those determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Since the fluoroionophore recognized Zn²⁺ and Hg²⁺ as well as Cd²⁺, a sample containing high concentration of Zn²⁺ or Hg²⁺ might cause a false positive result.

Hydrogel Nanofilaments via Core-Shell Electrospinning

Recent biomedical hydrogels applications require the development of nanostructures with controlled diameter and adjustable mechanical properties. Here we present a technique for the production of flexible nanofilaments to be used as drug carriers or in microfluidics, with deformability and elasticity resembling those of long DNA chains. The fabrication method is based on the core-shell electrospinning technique with core solution polymerisation post electrospinning. Produced from the nanofibers highly deformable hydrogel nanofilaments are characterised by their Brownian motion and bending dynamics. The evaluated mechanical properties are compared with AFM nanoindentation tests.

On-line sample processing involving microextraction techniques as a front-end to atomic spectrometric detection for trace metal assays: a review

Within the last decade, liquid-phase microextraction (LPME) and micro-solid phase extraction (μSPE) approaches have emerged as substitutes for conventional sample processing procedures for trace metal assays within the framework of green chemistry. This review surveys the progress of the state of the art in simplification and automation of microextraction approaches by harnessing to the various generations of flow injection (FI) as a front end to atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS) or inductively coupled plasma atomic emission spectrometry or mass spectrometry (ICP-AES/MS). It highlights the evolution of flow injection analysis and related techniques as vehicles for appropriate sample presentation to the detector and expedient on-line matrix separation and pre-concentration of trace levels of metals in troublesome matrices. Rather than being comprehensive this review is aimed at outlining the pros and cons via representative examples of recent attempts in automating green sample preparation procedures in an FI or sequential injection (SI) mode capitalizing on single-drop microextraction, dispersive liquid-phase microextraction and advanced sorptive materials including carbon and metal oxide nanoparticles, ion imprinted polymers, superparamagnetic nanomaterials and biological/biomass sorbents. Current challenges in the field are identified and the synergetic combination of flow analysis, nanotechnology and metal-tagged biomolecule detection is envisaged.