An Automatic Analyzer for Organic Compounds in Water Based on Solid-Phase Microextraction Coupled to Gas Chromatography

A Hybrid Stainless-Steel SPME Microneedle Electrode Sensor for Dual Electrochemical and GC-MS Analysis

A mechanically robust in-tube stainless steel microneedle solid phase microextraction (SPME) platform for dual electrochemical and chromatographic detection has been demonstrated. The SPME microneedle was fabricated by layer-by-layer (LbL) in-tube coating, consisting of carbon nanotube (CNT)/cellulose nanocrystal (CNC) film layered with an electrically conductive polyaniline (PANI) hydrogel layer (PANI@CNT/CNC SPME microneedle (MN)). The PANI@CNT/CNC SPME MN showed effective analysis of caffeine by GC-MS with an LOD of 26 mg/L and excellent precision across the dynamic range. Additionally, the PANI@CNT/CNC SPME MN demonstrated a 67% increase in sensitivity compared to a commercial SPME fiber, while being highly robust for repeated use without loss in performance. For electrochemical detection, the PANI@CNT/CNC SPME MN showed excellent performance for the detection of 3-caffeoylquinic acid (3-CQA). The dynamic range and limits of detection (LOD) for 3-CQA analysis were 75-448 mg/L and 11 mg/L, respectively. The PANI@CNT/CNC SPME MN was demonstrated to accurately determine the caffeine content and 3-CQA in tea samples and dark roast coffee, respectively. The PANI@CNT/CNC SPME MN was used for semiquantitative antioxidant determination and composition analysis in kiwi fruit using electrochemistry and SPME-coupled GC-MS, respectively.

Miniaturization of Analytical Methods

This chapter highlights miniaturization in sample preparation as a valuable alternative for green analytical chemistry. The current state of the art is discussed on the basis of examples selected from representative application areas, including biomedical, environmental and food analysis, and involving conventional instrumental techniques for final determination of the target compounds. The emphasis is on those techniques and approaches that have already demonstrated their practicality by the analysis of real-life samples, and in particular on those dealing with the accurate determination of minor organic components. The potential of recent developments in this field for sample treatment simplification and complete hyphenation of analytical processes are discussed and the most pressing remaining limitations evaluated.

An aniline-based fiber coating for solid phase microextraction of polycyclic aromatic hydrocarbons from water followed by gas chromatography-mass spectrometry

A fiber coating from polyaniline (PANI) was electrochemically prepared and employed for solid phase microextraction (SPME) of some polycyclic aromatic hydrocarbons (PAHs) from water samples. The PANI film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The applicability of this coating was assessed employing a laboratory-made SPME device and gas chromatography with mass spectrometry (GC-MS) for the extraction of some PAHs from the headspace of aqueous samples. Application of wider potential range in CV led to a PANI with more stability against the temperature. The homogeneity and the porous surface structure of the film were examined by the scanning electron microscopy (SEM). The study revealed that this polymer is a suitable SPME fiber coating for extracting the selected PAHs. Important parameters influencing the extraction process were optimized and an extraction time of 40 min at 40 degrees C gave maximum peak area, when the aqueous sample was added with NaCl (20%, w/v). The synthesis of the PANI can be carried out conveniently and in a reproducible manner while it is rather inexpensive and stable against most of organic solvents. The film thickness of PANI can be precisely controlled by the number of CV cycles. The resulting thickness was roughly 20 microm after 20 cycles. At the optimum conditions, the relative standard deviation (RSD) for a double distilled water spiked with selected PAHs at ppb level were 8.80-16.8% (n = 3) and detection limits for the studied compounds were between 0.1-6 pg mL(-1). The performance of PANI was, also, compared with a commercial solid coated-based SPME fiber, carbowax/divinylbenzene (CW/DVB), under similar experimental conditions.

Miniaturization in sample treatment for environmental analysis

The increasing demand for faster, more cost-effective and environmentally friendly analytical methods is a major incentive to improve the classical procedures used for sample treatment in environmental analysis. In most classical procedures, the use of rapid and powerful instrumental techniques for the final separation and detection of the analytes contrasts with the time-consuming and usually manual methods used for sample preparation, which slows down the total analytical process. The efforts made in this field in the past ten years have led to the adaptation of existing methods and the development of new techniques to save time and chemicals, and improve overall performance. One route has been to develop at-line or on-line and, frequently, automated systems. In these approaches, miniaturization has been a key factor in designing integrated analytical systems to provide higher sample throughput and/or unattended operation. Selected examples of novel developments in the field of miniaturized sample preparation for environmental analysis are used to evaluate the merits of the various techniques on the basis of published data on real-life analyses of trace-level organic pollutants. Perspectives and trends are briefly discussed.

Anodized aluminum wire as a solid-phase microextraction fiber

The efficiency of anodized aluminum wire was investigated as a new fiber for solid-phase microextraction (SPME). Aluminum wires were anodized by direct current in a solution of sulfuric acid at room temperature and were conditioned at 300 degrees C for 30 min. These fibers were used for the extraction of some aliphatic alcohols, BTEX, and petroleum products from gaseous samples. The extracted analytes were transferred to a GC injector using an (inhouse-designed) SPME syringe that also allowed for an easy change of SPME fibers. The results obtained prove the ability of anodized aluminum wire as a new fiber for sampling of organic compounds from gaseous samples. This behavior is due most probably to the porous layer of aluminum oxide, which is formed on the metal surfaces. In this work, the optimum conditions for the preparation and conditioning of fibers and the extraction of analytes from gaseous samples were obtained. In the optimum conditions, one fiber was used in several equal analyses and the relative standard deviations were below 5% (n = 5). However, fiber-to-fiber reproducibility was 8% (n = 5). This fiber is firm, inexpensive, and durable and can be prepared simply.

Solid-phase trapping of solutes for further chromatographic or electrophoretic analysis

Because of its simplicity, speed and effectiveness, solid-phase extraction (SPE) has become the preferred technique for concentration of selected analytes prior to chromatographic or electrophoretic analysis. In this review the historical development of SPE is briefly traced. Then the principles of SPE are reviewed in some detail. Numerous references are given on the format, sorbents, elution conditions, online techniques and automation with special emphasis on relatively recent developments. The principles and recent advances in solid-phase microextraction (SPME) are also reviewed. The final section on selected recent applications includes an extensive list of references to work published within the last three years. Future trends and developments are discussed briefly.