Enhancing LOD determination in gas chromatography: Validating the Hubaux-Vos method for gas concentration measurement.

The limit of detection (LOD) is a crucial measure in analytical methods, representing the smallest amount of a substance that can be distinguished from background noise. In the realm of gas chromatography (GC), however, determining LOD can be quite subjective, leading to significant variability among researchers. In this study, we validate the Hubaux-Vos method, an International Standards Organization(ISO)-approved approach for determining LOD in gas concentration measurements, using a GC equipped with a discharge ionization detector (DID) and a dynamic dilution system. We employ a gas mixture certified reference material (CRM) of CO, CH4, and CO2 at various concentrations to generate calibration curves for each gas. Subsequently, we estimate the LODs for each gas using the Hubaux-Vos method. Surprisingly, our findings indicate a notable difference between the LODs calculated using the Hubaux-Vos method and those confirmed through experiments. This highlights the importance of critically examining the theoretical foundations of LOD determination. We strongly recommend researchers to scrutinize the principles guiding LOD determination. The method proposed in this study offers an effective way to rigorously validate theoretical approaches for estimating LODs in gas concentration measurements using GC.

Investigation of adsorption characteristics of four toxic gases (nitric oxide, nitrogen dioxide, sulfur dioxide, and hydrogen chloride) on the inner surface of nickel-coated manganese steel cylinders and aluminum cylinders.

To develop standard toxic gas mixtures, it is essential to identify adsorption characteristics of each toxic gas on the inner surface of a gas cylinder. Thus, this study quantified adsorbed amounts of the four toxic gases (nitric oxide [NO], nitrogen dioxide [NO2], sulfur dioxide [SO2], and hydrogen chloride [HCl]) on the inner surface of aluminum cylinders and nickel-coated manganese steel cylinders. After eluting adsorbed gases on the inside of cylinders with ultrapure water, a quantitative analysis was performed on an ion chromatograph. To evaluate the reaction characteristics of the toxic gases with cylinder materials, quantitative analyses of nickel (Ni), iron (Fe), and aluminum (Al) were also performed by inductively coupled plasma optical emission spectrometry (ICP-OES). It was found that the amounts of NO, NO2, and SO2 adsorbed on the inner surface of aluminum cylinders were less than 1.0% at the level of 100 µmol/mol mixing ratio, whereas the signal for most heavy metal elements were below their respective detection limits. This study found that the amounts of HCl adsorbed on the inner surface of nickel-coated manganese steel cylinders were less than 5% at the level of 100 µmol/mol mixing ratio, whereas Ni (86 µmol) and Fe (28 µmol) were detected in the same cylinders. It was revealed that the adsorption mainly took place via the reaction of HCl with inner surface material of nickel-coated manganese steel cylinders. On the other hand, in the case of aluminum cylinders, the amounts of the adsorption were determined to be less than 1% at the level of HCl 100 µmol/mol mixing ratio, whereas most of Ni, Fe, and Al were detected at levels similar to their limits of detection. As a result, this study found that aluminum cylinders are more suitable for preparing HCl gas mixtures than nickel-coated manganese steel cylinders. Implications: To develop a standard toxic gas mixture, it is essential to understand the adsorption characteristics of each toxic gas inside a gas cylinder. It was found that the amounts of NO, NO2, and SO2 adsorbed inside aluminum cylinders were less than 1.0% at the level of 100 µmol/mol mixing ratio. The amounts of HCl adsorbed inside nickel-coated manganese steel cylinders were less than 5% at the level of 100 µmol/mol mixing ratio, whereas those inside aluminum cylinders were less than 1%, indicating that aluminum cylinders are more suitable for preparing HCl gas mixtures.

A chelate complex-enhanced luminol system for selective determination of Co(II), Fe(II) and Cr(III).

A determination method for Co(II), Fe(II) and Cr(III) ions by luminol-H2 O2 system using chelating reagents is presented. A metal ion-chelating ligand complex with a Co(II) ion and a chelating reagent like ethylenediaminetetraacetic acid (EDTA) produced highly enhanced chemiluminescence (CL) intensity as well as longer lifetime in the luminol-H2 O2 system compared to metals that exist as free ions. Whereas free Cu(II) and Pb(II) ions had a strong catalytic effect on the luminol-H2 O2 system, significantly, the complexes of Cu(II) and Pb(II) with chelating reagents lost their catalytic activity due to the chelating reagents acting as masking agents. Based on the observed phenomenon, it was possible to determine Co(II), Fe(II) and Cr(III) ions with enhanced sensitivity and selectivity using the chelating reagents of the luminol-H2 O2 system. The effects of ligand, H2 O2 concentration, pH, buffer solution and concentrations of chelating reagents on CL intensity of the luminol-H2 O2 system were investigated and optimized for the determination of Co(II), Fe(II) and Cr(III) ions. Under optimized conditions, the calibration curve of metal ions was linear over the range of 2.0 × 10(-8) to 2.0 × 10(-5) M for Co(II), 1.0 × 10(-7) to 2.0 × 10(-5) M for Fe (II) and 2.0 × 10(-7) to 1.0 × 10(-4) M for Cr(III). Limits of detection (3σ/s) were 1.2 × 10(-8) , 4.0 × 10(-8) and 1.2 × 10(-7) M for Co(II), Fe(II) and Cr(III), respectively.

Preparation and characterization of an electrogenerated chemiluminescence sensor by electrochemical grafting of 4-nitrophenyl diazonium salts onto a glass carbon electrode.

An ECL sensor was fabricated by immobilization of a tris(2,2'-bipyridyl)ruthenium (II) complex (Ru(bpy)3(2+)) to an amine group-modified GC electrode (NH2-GC electrode). Here, the NH2-GC electrode was prepared by electrochemical reduction of a nitro group-modified GC electrode in 0.1 M KCl ethanol solution under H2 gas, which was followed by electrochemical grafting of 4-nitrophenyl diazonium salts in 0.1 M NBu4BF4 acetonitrile solution onto the GC electrode. The prepared ECL sensor was successfully confirmed via cyclic voltammetry, contact angle, scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and ECL spectrometry. The contact angle for the surface of the GC electrode, NO2-GC electrode, and NH2-GC electrod was 88.4 degrees, 67.4 degrees, and 52.4 degrees, respectively. The stability of the ECL sensor was investigated under continuous cyclic potential scanning for 55 cycles and the ECL intensity remained at 55%. The prepared ECL electrode can be expected to immobilize enzymes for preparation of the ECL biosensor to detect target molecules.

Fabrication of chemiluminescence sensor based on conducting polymer@SiO2/Nafion composite film.

Tris(2,2'-bipyridyl)ruthenium (II) (Ru(bpy)2+) electrogerated chemiluminescence (ECL) sensor was fabricated by immobilization of Ru(bpy)2+ complex on conducting polymer@SiO2/Nafion composite film on surface of glassy carbon electrode. The conducting polymer@SiO2 nanocomposites were prepared by coating polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh) on the surface of the SiO2 sphere. The conducting polymer@SiO2 nanocomposite was characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and atomic force microscopy (AFM). The sensitivity and reproducibility of the prepared ECL sensor to tripropylamine (TPA) was evaluated. As a result, the PPy@SiO2 composite electrode exhibited high sensitivity and good reproducibility compared to that obtained with PANI@SiO2 and PTh@SiO2 composite electrodes because of the strong interaction between PPy@SiO2 and Ru(bpy)2+ complex.

Preparation of Pt-Ru@ polypyrrole-MWNT catalysts by gamma-irradiation and chemical reduction and their adsorption capacity for CO.

With the objective to prepare electrocatalysts with high efficiency, the Pt-Ru@PPy-MWNT catalysts were prepared by different approaches. First, the polypyrrole (PPy) as anchoring materials was coated on the surface of multi walled carbon nanotubes (MWNT) by in situ polymerization. Subsequently, Pt-Ru nanoparticles were deposited onto PPy-MWNT composite by different methods like the reduction of metal ions by gamma-irradiation and chemical reduction using formaldehyde as reducing agent assisted with stirring of magnetic bar, and assisted with microwave irradiation, and assisted with ultrasonic irradiation, in order to prepare electrocatalyst for fuel cell. The catalytic efficiency of Pt-Ru@PPy-MWNT catalyst was examined for CO stripping.

Fabrication of functional poly(thiophene) electrode for biosensors.

Three-type polymer electrodes such as poly(Th), poly(Th-AP) and poly(Th-AP-TAA) were fabricated, respectively, by electro-oxidative polymerization of thiophene (Th), mixture of Th and 2-aminophenol (AP), and mixture of Th, AP and 3-thiopheneacetic acid (TAA) on the surface of indium tin oxide (ITO) glass by cyclic voltammetry (CV). The polymer electrodes were electrodeposited by cycling the potential between -1.0 and +2.5 V in acetonitrile containing 50 mM tetrabutylammoniumhexafluorophosphate (TBAF(6)P). The surface morphology of polymer electrodes was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. The surface morphology of the poly(Th) showed typical roughness and fractal-like growth patterns, and the morphologies of poly(Th-AP) and poly(Th-AP-TAA) were dramatically changed. The water contact angle at the poly(Th-AP-TAA) (23 degrees) is lower in comparison to poly(Th) (47 degrees ). The functional groups (-OH) and carboxylic acid (-COOH) group play an important role. Horseradish peroxidase was loaded onto poly(Th-AP-TAA) surface and used to test the sensing of H(2)O(2).

Horseradish peroxidase immobilized on poly(thiophene-2-aminophenol-3-thiopheneacetic acid) film electrode with Au nanoparticle-fabrication and evaluation as hydrogen peroxide sensor.

Enzyme immobilized electrode was fabricated by two methods. In one of the methods, gold-nanoparticles (Au-NPs) prepared by gamma-irradiation were loaded into the copolymer film and horseradish peroxidase (HRP) was immobilized into the Au-NPs loaded copolymer film through physical entrapment. In the other method, the Au-NPs was prepared by electrochemical reduction of Au ions on the surface of poly(Th-AP-TAA) and HRP was immobilized into the Au-NPs. The enzyme immobilized electrodes were tested for electrocatalytic activities towards sensing of H2O2.