Simultaneous sampling and analysis for vapor mercury in ambient air using needle trap coupled with gas chromatography–mass spectrometry

Needle trap device technique: From fabrication to sampling

Needle Trap Device (NTD) as a novel, versatile, and eco-friendly technique has played an important role in analytical and environmental chemistry. The distinctive role of this interdisciplinary technique can be defended through the sampling and analysis of biological samples and industrial pollutants in gaseous and liquid environments. In recent years, significant efforts have been made to enhance the performance of the needle trap device resulting in the development of novel extraction routes by various packing materials with improved selectivity and enhanced adsorption characteristics. These achievements can lead to the facilitated pre-concentration of desired analytes. This review tries to have a comparative and comprehensive survey of the three important areas of NTD technique: I) Fabrication and preparation procedures of NTDs; II) Sampling techniques of pollutants using NTDs; and III) Employed materials as adsorbents in NTDs. In the packing-material section, the commercial and synthetic adsorbents such as carbon materials, metal-organic frameworks, aerogel, and polymers are considered. Furthermore, the limitations and potential areas for future development of the NTD technique are presented.

Battery-Operated and Self-Heating Solid-Phase Microextraction Device for Field Detection and Long-Term Preservation of Mercury in Soil

The application of headspace solid-phase microextraction (HS-SPME) for mercury preservation and detection still has several shortcomings, including the use of high-temperature desorption chamber, the consumption of expensive reagent (NaBEt4 or NaBPr4), and analyte loss during sample storage. Herein, a self-heating HS-SPME device using a gold-coated tungsten (Au@W) fiber was developed for the field detection of mercury in soil by miniature point discharge optical emission spectrometry (μPD-OES). Hg2+ was reduced to Hg0 with NaBH4 solution and then preconcentrated with the Au@W fiber. The adsorbed Hg0 could be rapidly desorbed by directly heating the fiber with a mini lithium battery and subsequently detected by μPD-OES. A limit of detection (LOD) of 0.008 mg kg-1 was obtained with a relative standard deviation (RSD) of 2.4%. The accuracy of the self-heating HS-SPME was evaluated by analyzing a soil certified reference material (CRM) and nine soil samples with satisfactory recoveries (86-111%). Compared to the conventional external heating method, the proposed method reduces desorption time and power consumption from 80 s and 60 W to 20 s and 2.5 W, respectively. Moreover, the self-heating device enables the μPD-OES system to remove the high-temperature desorption chamber, making it more compact and suitable for field analytical chemistry. Interestingly, the Au@W SPME fiber can be also used for the long-term preservation of mercury with a sample loss rate <5% after 30 days of storage at room temperature.

Proof of concept for a passive sampler for monitoring of gaseous elemental mercury in artisanal gold mining

Mercury emissions from artisanal gold mining operations occurring in roughly 80 developing countries are a major workplace health hazard for millions of people as well as the largest contributor to global mercury pollution. There are no portable, cheap, and rapid methods able to inform workers or health practitioners of mercury exposure on site in remote locations. In this work, a proof of concept for a miniaturized mercury sampler, prepared by the direct reduction of gold into the porous nanostructures of Vycor glass (PVG), is introduced. Mercury retention on the PVG/Au sampler induces significant color changes, due to the formation of Au-Hg amalgam that affects the surface plasmon resonance characteristics of the material. The color change can potentially be quantified by the analysis of pictures obtained with a cell phone camera rapidly and onsite. Laboratory experiments showed the viability of using PVG/Au as passive sampler for monitoring of Hg°. PVG/Au samplers were then deployed in an artisanal and small-scale gold mining (ASGM) operations in Burkina Faso and it was able to indicate personal mercury exposures. The amount of mercury quantified in the samplers for all miners was higher than the current personal exposure limit set by the US Occupational Safety & Health Administration (OSHA).

Detection of gaseous elemental mercury using a frequency-doubled green diode laser

We demonstrate a second-harmonic-generation (SHG) based method for the detection of gaseous elemental mercury by using a newly available green diode laser. Multimode ultraviolet radiation at 253.7 nm is generated through a process of SHG. Correlation spectroscopy is introduced into the scheme to guarantee the measurement accuracy. The limit of detection achieved is 0.6 μg/m³ (0.07 ppb) for 1-m pathlength and 10-s integration time. The measurement accuracy is estimated to be 1.2%. The linear response range is estimated to be 0~60 μg/m² (6.7 ppb·m), within which the linearity error is less than 1%. Real-time monitoring of mercury volatilization is demonstrated with a time resolution of 1 s. The results of performance characterization show that the proposed method has great potentials for mercury sensing in environmental and industrial fields.

Short duration needle trap sampling with gas chromatography analysis to determine nearly instantaneous concentrations of selected organic vapor contaminants

Needle trap device samplers were used for rapid (60 s) quantitative sampling of short-term exposure limit (STEL) and peak exposure standard concentrations using a manually operated pump to collect small volume (10 mL) gas phase samples containing methylene chloride, benzene, toluene, and tetrachloroethylene vapors. Solventless introduction of chemical samples for gas chromatography analysis with flame ionization detection yielded linear results (R(2) > 0.99) for vapor standard mixtures of the four target analytes ranging from 10% to 200% of their respective nominal STEL or peak exposure standard concentrations. Needle trap samplers showed ≥86% recovery (as GC-FID peak area responses) following 14-day storage at room temperature compared to the same samplers analyzed immediately, with better recovery values observed with shorter storage (≥95% at room temperature for seven days, except for methylene chloride) or with storage at 4°C. Calibration for quantitation of concentrations of benzene, toluene, and tetrachloroethylene was shown to be possible with the use of an internal standard to account for injector discrimination between the solventless NTD approach and injections of target analytes in carbon disulfide. Due to the simple sampling method (no field calibration and battery-free pumping) and the avoidance of solvent dilution, a needle trap sampling approach could simplify sample collection and analysis to chromatographically determine nearly instantaneous (1 min) exposure concentrations.

A rapid electrochemical procedure for the detection of Hg(0) produced by mercuric-reductase: application for monitoring Hg-resistant bacteria activity

In this work, gold microelectrodes are employed as traps for the detection of volatilized metallic mercury produced by mercuric reductase (MerA) extracted from an Hg-resistant Pseudomonas putida strain FB1. The enzymatic reduction of Hg (II) to Hg (0) was induced by NADPH cofactor added to the samples. The amount of Hg(0) accumulated on the gold microelectrode surface was determined by anodic stripping voltammetry (ASV) after transferring the gold microelectrode in an aqueous solution containing 0.1 M HNO(3) + 1 M KNO(3). Electrochemical measurements were combined with spectrofluorometric assays of NADPH consumption to derive an analytical expression for the detection of a relative MerA activity of different samples with respect to that of P. putida. The method developed here was employed for the rapid determination of MerA produced by bacteria harbored in soft tissues of clams (Ruditapes philippinarum), collected in high Hg polluted sediments of Northern Adriatic Sea in Italy.

Fundamentals and applications of needle trap devices: a critical review

The needle trap device (NTD) is an extraction trap that contains a sorbent inside a small needle, through which fluid can be actively drawn into and out of by a gas-tight syringe or pump, or analytes can be introduced passively to the trap by diffusion. The needle trap (NT) is a potentially solventless sampling technique/sample preparation and introduction device. Both fluid-borne analytes and particles can be trapped inside the needle and then adsorbed analytes are desorbed in an inlet of analytical instrument and introduced for identification and quantification. The fluid may be either gaseous or liquid. The objectives of this critical review are to summarize the theory of the sampling process for both active and passive time-average extraction modes in addition to outlining the evolution of the technology and main applications.