Eric D. Salin

Direct detection of mercury in single human hair strands by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

Single shot laser ablation ICP-MS has demonstrated the potential to detect Hg in single human hairs with a resolution corresponding to less than one day of growth and with a detection limit of approximately 0.2 μg g−1.

Direct solid sample analysis using furnace vaporization with Freon modification and inductively coupled plasma atomic emission spectrometry-I. Vaporization of oxides and carbides

A modified electrothermal vaporization (ETV) furnace was used as a high temperature reaction chamber and a vaporizer for direct solid sample analysis with inductively coupled plasma atomic emission spectrometry (ICP-AES). At temperatures ranging from 1000 to 2400°C, pure oxides and carbides were converted to lower boiling point halides and evaporated. The samples were deposited as 10 μl of 1% slurries of the powdered samples in distilled water. Experimental results showed that, with the use of Freon-12 as a gas phase halogenation reagent, near 100% vaporization was achieved for the powdered samples studied, Al2O3 (b.p. 2980°C, <10 μm), SiO2 (b.p. 2230°C, <44 μm), ZrO2 (b.p. 5000°C, <74 μm) and TaC (b.p. 5500°C, typically 5 μm). The same was true for WC (b.p. 6000°C, <10 μm) if BaCl2 was used as a second halogenation reagent. The approach appears to have the potential to vaporize a wide variety of samples with inorganic matrices. Probably the importance of our work does not lie in the fact that we vaporized tungsten carbide. Rather, it lies in the fact that tungsten carbide is one of the most refractory compounds known to man.

Pneumatically pumping fluids radially inward on centrifugal microfluidic platforms in motion.

This paper describes a pumping technique applicable to centrifugal microfluidic platforms, involving the use of a regulated stream of compressed gas to pump liquid radially inward and toward the center of the platform while spinning. This technique provides a noncontact method for pumping fluids and is highly efficient, requiring only approximately 60 s to reach completion. This pumping operation can be attained with an applied gas flow rate of 58.8 L min(-1), while the platform is rotated at frequencies less than 180 rpm (3.0 Hz).

Miniaturised centrifugal solid phase extraction platforms for in-field sampling, pre-concentration and spectrometric detection of organic pollutants in aqueous samples.

Great variations in pollutant concentrations are observed in the environment and pre-concentration is often required to detect trace contaminants in water samples. This paper presents a novel solid phase-extraction device integrated onto a centrifugal microfluidic platform for rapid on-site pre-concentration and screening of organic contaminants in aqueous samples. In-column fluorescence and absorbance measurements are obtained directly from an analyte trapped on the top of a solid phase extraction microcolumn. Results are presented for the representative fluorophore fluorescein and the polycyclic aromatic hydrocarbon anthracene. An absolute detection limit of 20 ng was obtained for anthracene using a simple light emitting diode for fluorescence excitation. One of the main advantages of this device is that only a simple motor is needed to induce liquid flow, making simultaneous on-site extraction and measurement of multiple samples easy while minimizing sample losses and contamination.

Speciation of chromium by high-performance thin-layer chromatography with direct determination by laser ablation inductively coupled plasma mass spectrometry.

It is of considerable importance to be able to distinguish metallic species because their toxicity depends on their chemical form. Therefore, the analysis of environmental samples can be enhanced by the combination of high-performance thin-layer chromatography (HPTLC) with laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). In this study, Cr (3+) and Cr (6+) were separated on silica gel HPTLC plates using aqueous mobile phases. Separation was achieved in seconds with retardation factors ( R f ) of 0 and 1 for Cr (3+) and Cr (6+), respectively. LA was used to volatilize the chromium species directly from the chromatographic material prior to ICPMS detection. A linear calibration was obtained, and detection limits (3sigma) of 6 ng for Cr (6+) and 0.4 ng for Cr (3+) were achieved with precision ranging from 3 to 40% at the 95% confidence level. The silicon present in the stationary phase was used as an internal standard. This procedure allows for a rapid separation and quantification, requires only 0.5 muL of sample, and lower detection limits can be achieved through preconcentration.

Pre-concentration of trace metals on centrifugal microfluidic discs with direct determination by laser ablation inductively coupled plasma mass spectrometry

Solid Phase Extraction (SPE) is commonly used for pre-concentration and matrix removal in trace metal determinations. We present a novel centrifugal microfluidic device for field sampling and on-site pre-concentration of water samples. Metal-8-hydroxyquinoline complexes are adsorbed onto miniature C18-bonded silica gel columns on centrifugal microfluidic discs. Laser Ablation (LA) is used to directly vaporize the analytes from the column, instead of eluting the pre-concentrated analytes for introduction in an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) by conventional solution nebulization. Absolute detection limits ranging between 0.1 and 12 ng were obtained for Ni, Cu, V, Pb and Co in drinking water Certified Reference Materials (CRMs). These centrifugal devices require only 1–600 µL samples and necessitate no more than a simple motor to actuate fluid flow. The discs can be used to perform multiple extractions simultaneously as well as allowing the easy storage of samples before transport to the laboratory for LA-ICP-MS analysis.

Enzyme Inhibition-Based Determination of Pesticide Residues in Vegetable and Soil in Centrifugal Microfluidic Devices

Pesticide residue is of concern as an environmental pollutant when present at medium to high concentrations. Such residue was quantified in both vegetable and soil samples by an enzyme inhibition technique. The multistep reactions were integrated into centrifugal microfluidic devices allowing automated simultaneous analysis of several samples or of replicates. The small sample size inherent to microfluidic devices allowed for less reagent to be used including less of the expensive enzyme which is key to this method. Liquid-solid magnetically actuated extraction, filtration, sedimentation, and detection were all integrated on the same device. Several parameters were optimized including the concentration of enzyme, substrate, chromatic agent, and reaction time. In this environmental application of centrifugal microfluidics, the percent inhibition of enzyme activity is logarithmically proportional to the demonstration pesticide concentration (in this case carbofuran). This meant that as the pesticide concentration increased in the samples, the reaction was more inhibited and the final product absorbed less light at 525 nm. Two versions of the centrifugal microfluidic devices were made. One version was designed for the analysis of vegetable samples (cabbage) and the other for the analysis of soil samples. Each version provided results that were statistically similar to the conventional benchtop method with a carbofuran limit of detection of 0.1 ppm or 0.1 μg g(-1) (5 ng absolute limit of detection).

Rapid stopped-flow microwave digestion system

A prototype system for stopped-flow microwave assisted wet digestions has been developed. A coiled Teflon PFA tube serves both as a sample container and as a digestion vessel. A sample plug, consisting of a water slurry mixed with an acid mixture, is pumped into the coil. Sample flow is stopped, the coiled tube is sealed (by closing an input and an output valve) and microwave power is applied for 2 min for digestion of the sample. Methodology was developed using powdered botanical reference samples and was tested with powdered botanical and biological reference materials. The digests were analysed by inductively coupled plasma atomic emission spectrometry. In addition to comparisons with certified values, the results were compared with those obtained by conventional open-vessel hot-plate digestions, by open-vessel microwave digestions and by digestions taking 32 min by using the coiled tube system. Precise, and in many instances, quantitative digestions were obtained using a net digestion time of 2 min. Elemental recoveries were sample type and digestion time dependent and were found to be comparable with, and sometimes, superior to those obtained when using a 3 h long hot-plate digestion. In this preliminary study, characteristics, limitations and future directions are discussed.

Spectrophotometric determination of aqueous sulfide on a pneumatically enhanced centrifugal microfluidic platform.

A pneumatically enhanced centrifugal microfluidic platform was developed for rapid spectrophotometric determination of aqueous sulfide. This platform performs an automated analysis based on the reaction between hydrogen sulfide and N,N-dimethyl-p-phenylenediamine in the presence of iron(III) chloride to form Methylene Blue. The platform design minimizes the number of integrated valves required, compared to other centrifugal systems, significantly improving the ease of fabrication. The sequential analytical procedure and spectrophotometric analyses were performed directly on-disk, demonstrating significant advantages in portability and cost over conventional analytical methods. This method allows for rapid and precise determination of aqueous sulfide in the concentration range of 0.4-2.0 mg L(-1), which can be extended by a pneumatically induced, on-disk serial dilution to 6.0 mg L(-1). A detection limit of 0.4 mg L(-1) was calculated for this pneumatically enhanced method.

Pneumatic flow switching on centrifugal microfluidic platforms in motion.

This paper describes a flow switching technique applicable to centrifugal microfluidic platforms, using a regulated stream of compressed gas. This pneumatic flow switching technique allows for flow control at a T-shaped junction between one inlet channel and two outlet channels. This technique provides a noncontact, robust, and efficient method for switching the direction of fluid flow while a disk is rotating at relatively low frequencies. The switching operation can be implemented reproducibly with applied gas flow rates between 17 and 58 L min(-1) and rotational frequencies between 400 rpm (6.6 Hz) and 1200 rpm (20 Hz).