Coulometric Analysis Research Articles

Evaluation of the Corrosion Resistance of Watch Links from 316L and 904L Austenitic Stainless Steels Obtained by the Metal Injection Molding (MIM) Technique Intended to Be in Contact with Human Skin

Watchmaking manufacturers obtain their bracelet links from machining drawn metal profiles. But, today, there is another process that represents an alternative to manufacture them: metal injection molding using metal powders (MIM technology). This process is less expensive than the machining of drawn metal profiles. The aim of this study was to evaluate the corrosion behavior and the nickel cation release of two stainless steel alloys: 316L MIM and 904L MIM. The general corrosion behavior was evaluated by the rotating electrode technique; the galvanic corrosion measurements were conducted with a 316L AISI bulk coupling partner. The pitting corrosion behavior was evaluated in FeCl3 0.5 M media (according to ASTM G48-11). For comparison, a complementary study was conducted on 316L and 904L bulk alloys. The Ni cation release tests were conducted on 316L and 904L MIM and bulk samples according to EN 1811. Different electrochemical parameters were measured and calculated (open circuit potential, polarization resistance, corrosion current and Tafel slopes, coulometric analysis). Generally, if MIM steels are compared with conventional steels, their corrosion resistance behavior is inferior. In the couplings studied, the galvanic currents generated are very important. The shape of the curves also reveals the presence of localized corrosion phenomena. According to tests in ferric chloride, MIM steels were noted to have inferior behavior compared to conventional steels. MIM type 904L steels are comparable in behavior to conventional type 316L steels. The quantities of nickel released according to EN 1811 were very significant (2 mg cm−2 week−1 up to 24 mg cm−2 week−1) and did not meet the requirements of the European directive (0.5 µg cm−2 week−1). In conclusion, conventional steels studied under the same experimental conditions revealed a better behavior compared to MIM steels independently of the phenomenological parameters chosen.

Electrochemical Stimulation of Monopolar Electrodes

Changes in the electrostatic potential within an aqueous acidic solution induced by the passage of current between the Au disk of a stationary Au|Au ring disk electrode and a distant counter electrode, Idisk made it possible to stimulate the reduction of selenite to elemental selenium at the concentric Au ring electrode polarized at Eringo just positive to its otherwise expected onset. This effect was ascribed to variations in the surface overpotential, and, thus, in the rates of selenite reduction along the ring, we define, hereafter, as a monopolar electrode. The stimulation efficiency could be accurately determined from a coulometric analysis of the peak for Se oxidation observed by subsequently scanning the ring linearly toward positive potentials to yield selenite. Shown in the figure below is a series of linear scan \\voltammograms, LSV, recorded at a scan rate of 50 mV/s for the ring polarized at Eringo in the range 0.39 - 0.45 V (see legend) following Nstim = 40 between Edisk = 0.75 and 1.00 V, where the black curve corresponds to the LSV recorded without any prior stimulation under otherwise identical conditions. As clearly indicated the stripping charge associated with the oxidation of elemental Se increases as the potential at which the ring is polarized is decreased. Excellent quantitative agreement was obtained between the current flowing through the ring, Iring , and Eringo as a fucntion of Idisk and theoretical simulations employing COMSOL using parameters extracted from independent measurements performed under otherwise identical experimental conditions. This novel tactic is expected to open new prospects for gaining insight into surfacediffusion and other interfacial dynamics phenomena.AcknowledgementsThis work was supported by the US NSF Award 1808592Literature Cited1) Han, Q.; Georgescu, N. S.; Gibbons, J.; Scherson, D. Electrochim. Acta 2019, 325, 134957 Figure 1

Assessment of Drimia delagoensis (Jessop) Baker Total Phenol, Flavonoids Content and Antioxidant Activity of Both Bulb and Leaves.

Drimia delagoensis has been utilized for its medicinal properties since antiquity. The bulb and leaves are predominantly composed of secondary metabolites that exhibit biological activity. The quantification of total phenolic and flavonoid content, as well as the assessment of antioxidant activity was conducted using the Folin-Ciocalteus method, coulometric analysis, DPPH and the FRAP assays. The ethyl acetate, aqueous, and hexane extracts of the bulb exhibited significantly high total phenolic contents (167.9000±0.3376 μg GAE/mg, 56.2500±0.0043 μg GAE/mg, and 26.4000±0.0198 μg GAE/mg, respectively) compared to the ethyl acetate (49.4400±0.1341 μg QE/mg), aqueous (9.5200±0.1274 μg QE/mg), and hexane leaf extracts (1.8091±0.0049 μg QE/mg). On the other hand, the ethyl acetate leaf extract exhibited the highest antioxidant and free radical scavenging activity. The ethyl acetate extract of D. delagoensis, was identified as a significant source of natural antioxidants, and its use in the management of diabetic foot ulcers linked with oxidative stress is supported.

(Keynote) Electrode Stimulation: Ohmic Microscopy and the Monopolar Electrode

In a recent communication (1), we described a novel method of controlling the electrostatic potential in the solution neighboring a working electrode, we have dubbed the monopolar electrode , ME, polarized at a constant potential, EME, using a potentiostat. This tactic involved passing current between a second or stimulating electrode , SE, placed in front, and at a relatively small distance from the ME, and a distant auxiliary electrode, AE. Depending on the polarity of the current flowing through the SE, the electrostatic potential just outside the ME could be modified so as to increase or decrease the surface overpotential, and, thus modulate the rates of redox reactions at the ME|electrolyte interface. This presentation will review critical aspects of ohmic microscopy, and illustrate with two examples the electrode stimulation effect, using a ring disk electrode, RRDE, in which current flowing through the disk acting as the SE, is employed to induce reactions on the ring, acting as the ME, namely: i. the oxidation of adsorbed carbon monoxide on Pt using a Pt|glassy carbon RRDE and ii. the reduction of selenite to elemental Se on Au in aqueous 0.1 M HClO4 using a Au|Au RRDE. In both these cases, the stimulation current was generated by scanning the potential of SE within its double layer region, so as to minimize any changes in the actual composition of the solution adjacent to the ME, while monitoring the current flowing through the ME, IME . Under these conditions, the electrostatic potential in solution follows the primary current density. The efficiency of the stimulation process was determined by coulometric analysis of the CO oxidation current and in the case of selenite via a coulometric analysis of the current due to the oxidation of elemental Se produced by the reduction of selenite. The stimulation efficiency, in this latter case, could be accurately determined from a coulometric analysis of the peak for Se oxidation observed by subsequently scanning the ME linearly toward positive potentials to yield selenite. Excellent quantitative agreement was obtained between IME and EME as a function of Idisk and theoretical simulations employing COMSOL using parameters extracted from independent measurements performed under otherwise identical experimental conditions. This overall approach will open new prospects for gaining insight into the rates of surface diffusion and other interfacial dynamics phenomena.AcknowledgementsThis work was supported by a grant from NSF, CHE-1412060 References Han, Q.; Georgescu, N. S.; Gibbons, J.; Scherson, D. Acta 2019, 325, 134957.

On the nature of adsorbed species on platinum single-crystal electrodes

The dependence of voltammetric currents on multiple parameters (concentration, pH, temperature, etc) has become a primary source of information in interfacial studies of noble metal electrodes. Peak potential, charge, and width are intimately related to surface structure and reactivity. However, this interpretation usually neglects the complexity of the redox processes involved. For the so-called hydrogen adsorption region in platinum, anion competitive adsorption plays an important role that is usually overlooked. While charge displacement already demonstrated decades ago the existence of anion adsorption contributions, only recently a combination of several surface-sensitive techniques has proven unambiguously the presence of OH adsorbed on step site at potentials much lower than usually considered. This information must not be neglected when analysing the properties of complex catalysts such as those composed of nanoparticles since it is of great importance for understanding its overall reactivity, for comparing with computational results, and for performing coulometric analysis.

Electrochemical contributions: Hans Wenking (1923–2007)

Electrochemical contributions: Hans Wenking (1923–2007)

Quantification of electron transfer on carbon nanotubes: Effect of edge defects on electro-oxidation of glycerol catalyzed by platinum

It is still an ongoing challenge to quantitatively determine the number of transferred electrons from carbon supports to metallic catalysts, which is highly related to their catalytic performance. In this work, a facile method combining electrochemical and spectroscopic technologies was proposed to evaluate the electron transfer (ET) reaction rate on carbon nanotubes (CNTs) with defects. Using 7,7,8,8-tetracyanoquinonedimethane (TCNQ) as an electron-accepting molecule, the transferred electrons from CNTs were quantitatively determined through the Beer-Lambert law and coulometric analysis. It was revealed that the edge defects on CNTs are beneficial for the ET reaction rate, due to the lower local work function. Hence, the defective CNTs supported Pt nanoparticles (Pt/d-CNTs) performed the higher activity in the electrooxidation of glycerol, suggesting the influence of the ET ability of d-CNTs on the electronic metal-support interaction. This scenario is supported by density function theory calculation and X-ray photoelectron spectroscopy. Our results pave a new way to the facile evaluation of electronic metal–carbon interaction.

Calibration-free coulometric sensors for operando electrolytes imbalance monitoring of vanadium redox flow battery

It is necessary for vanadium redox flow battery (VRFB) to become more cost-effective due to long-term stable operation with minimal life-cycle maintenance for its further development. Despite the absence of self-discharge in idle mode, the available capacity of VRFB gradually decreases during the battery cycling. The capacity decrease is attributed to side reactions appearance, which increase the average oxidation state (AOS) of vanadium electrolyte. This negative effect can be minimized by periodic electrolyte capacity recovery. However, it is crucial to have reliable information on the electrolytes composition to conduct rebalancing efficiently and timely. Various methods for vanadium electrolyte assessment have been previously proposed, however, none of them can be used coupled with industrial VRFBs. In this work, we present an operando coulometric analysis of an electrolyte sample in a VRFB cell and its subsequent return to the bulk solution. The proposed approach outperforms other methods due to sensitivity of the signal to the overall vanadium content and AOS and stable performance under imbalance conditions. The analysis of AOS was verified by three methods – coulomb-counting, ex-situ spectrophotometry, and coulometry. Therefore, this method can be successfully used not only in lab-scale VRFB studies, but can also be coupled with industrial VRFB stacks.

Effect of the interfacial electric field on the HER on Pt(111) modified with iron adatoms in alkaline media

The study of the hydrogen evolution reaction (HER) aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy. In previous works, laser-induced temperature jump (LITJ) experiments on Pt(111) modified with Ni(OH)2 in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER. It was hypothesised that small amounts of Ni(OH)2 cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution. In this work, to test the validity of this hypothesis, the study has been extended to Pt(111) surfaces modified with Fe(OH)2. The modified surfaces have been studied voltammetrically, and the voltammetric charges have been analysed. The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II) to Fe(0). In agreement with the coulometric analysis, the voltammetric features in the OH adsorption region would be related with the oxidation to the +3 valence state. The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules, shifting the potential of maximum entropy away from the onset of the HER. Hence, the most catalytic surface is the one with the lowest Fe coverage.

Highly Efficient Electrochemical Oxidation of Alcohols in a Flow Electrochemical Column Cell Modified with Au Nanoparticle Catalyst

Electrosynthesis is a powerful means for obtaining a variety of useful chemical products without employing toxic or otherwise hazardous chemical reagents and under relatively mild conditions. However, conventional batch-type cells suffer from a low productivity due to narrow two-dimensional reaction fields in the electrochemical system. To overcome this problem, we utilized continuous-flow column cell[1]. Although it was developed for a highly sensitive coulometric analysis of trace chemical substances in 1968, it is also expected to conduct rapid and quantitative bulk electrolysis due to its large electrode area and continuous-flow system. This flow cell consisted of a working electrode compartment and a counter electrode compartment, separated by an ion permeable Vycor® glass tube (Figure 1 (a)). A bundle of carbon fiber threads was tightly packed as a working electrode in the continuous-flow column cell, and a Pt spiral wire was used as a counter electrode. During several decades, the bulk gold has been considered as less active material, but at nanoscale, it exhibits surprisingly physicochemical and catalytic properties[2]. Therefore, in this work, the carbon fiber surface was also functionalized with Au nanoparticle catalyst to promote an electrochemical oxidation of alcohols.As a result, we have successfully demonstrated an efficient electrocatalytic oxidation of benzyl alcohol to provide benzaldehyde and benzoic acid with high current efficiencies in alkaline media. Moreover, it was also found that the selectivity of benzaldehyde was influenced by the added base amounts, and increased up to 97% by decreasing the amounts. We will also report the results of electrochemical oxidation of other alcohols.

Обоснование применения ёмкостей «Акваспектр» для насыщения водных сред активным водородом с использованием биохимического показателя суммарной антиоксидантной активности

The article presents the results of a biochemical study of aqueous environments with molecular hydrogen by antioxidant activity. Activated hydrogen has selective antioxidant activity against dangerous free radicals for the human body and animals. In addition, its anti-inflammatory, anti-apoptotic, anti-allergic properties were found and it stimulates energy metabolism in cells. This problem is currently relevant due to the great interest in activated hydrogen as an antioxidant over the past ten years, but its quantitative metabolic parameters have not yet been assessed at a sufficient scientific level. The total antioxidant activity of aqueous systems saturated with hydrogen was studied using coulometric analysis. It has been shown that their total antioxidant activity increases depending on the quality of aqueous media and the operating time of the “Aquaspectr Hydrogen Mug Mug for Activating Water” device: for Arkhyz mineral water, 20 times after 26 minutes of hydrogen saturation, drinking natural oxalis Kristalia with mineral drinking medicinal water DonatMg (in volume ratio) 31 times after 55 minutes and DonatMg mineral drinking medical water 44 times after 28 minutes. The total antioxidant activity was determined using electrically generated bromine, the samples were analyzed on a certified Expert-006 coulometer (Econix-Expert LLC, Russia) according to a certified method. In the work it was shown that saturation of water systems, in particular mineral and drinking water, by the method of hydrogen evolution on the surface of containers from environmentally friendly magnesium alloys, can be quite an effective way to activate various liquid media with antioxidants used in environmental medicine. In addition, our results can be useful in solving scientific and technical problems in the development of alternative energy sources.

Сравнение посевных, урожайных и антиоксидантных свойств семян и проростков полевицы гигантской (Agrostis gigantea Roth) после воздушной сушки и термодегидратации

The study of the biological characteristics of feed crops and the use of modern methods in the study of the processes of their selection is relevant for the intensification of feed production. The article presents the results of a biochemical study of the giant VIK-2 (Agrostis gigantea Roth) field birch seed, their sowing and yield properties after thermal dehydration (drying of air-dried samples at 105 oС to constant weight), as well as their total antioxidant activity during germination in the dark. The total antioxidant activity of seeds and seedlings was studied using coulometric analysis and determined using electrogenerated bromine, the samples were analyzed on a certified couponometer Expert-006 (LLC Econix-Expert, Russia) using a certified method. The work shows that, compared with air drying after thermohydration, there is a decrease in the viability and yield properties of seeds. Seed germination decreased by 5.5%, the height of plants at the end of the germination period (on the 14th day after sowing) by 9.4%, the mass of 100 sprouts – by 21.3%, the yield of green mass (microgreen) also by 21.3%. The antioxidant activity of seeds after thermal dehydration also decreased by 21.4%. For the first time, data were obtained on the viability, formation of microgreen biomass and a change in the total antioxidant activity of the seeds of the VIK-2 giant cultivar after thermal dehydration (drying the initial seeds) in the test at 105 °C to constant weight. It was shown that thermal dehydration of seeds at 105 °C significantly affects the viability of seeds and seedlings of a bent field, which is associated with the characteristics of metabolism, forms and state of water activity in cells and tissues of plants.

Chronoamperometric and coulometric analysis with ionophore-based ion-selective electrodes: A modified theory and the potassium ion assay in serum samples

The behavior of the same ion-selective electrode (ISE) under three measurement modes: potentiometric, chronoamperometric and coulometric is compared using valinomycin-based K+-ISE as model system. The ISE response to decrease and to increase of the K+ ion activity is studied systematically. It is shown that the theoretical description of the time dependencies of current and of charge must take the concentration polarization in consideration, and the respective equations are presented. The concentration of K+ ion in blood serum samples is measured in the potentiometric, in the chronoamperometric and in the coulometric mode, and satisfactory results are obtained in all three cases.

Determination of Low Chlorine Content in Organic Compounds and Polymers Using an Expert-006 Coulometer

A method of visual mercurimetric titration of chloride ions is widely used in elemental microanalysis for determination of chlorine content in organic substances after their combustion in an oxygen-filled flask. However, when the chlorine content is less than 0.5%, the mercurimetric method fails to provide sufficient accuracy, and a more sensitive method of chlorine coulometric titration by electrogenerated silver ions appears preferable. We consider the possibility of determining microgram contents of chloride ions in solutions using a digital coulometric analyzer (Expert-006 produced by Econics-Expert (Moscow)) supplemented with an electrolytic cell with silver electrodes. The coulometer was tested in different operating modes to select the optimal electrochemical parameters of ion chloride titration and develop a technique for coulometric determination of chloride ions which in combination with the preliminary burning of the analyzed substances in an oxygen-filled flask provides determination of the residual chlorine in organic matrices at a level of 0.1–0.5%. The proposed technique was used to determine the residual chlorine in a number of polymers. The relative error did not exceed 5% at chlorine concentrations of 0.16–0.28%.

Кластерная характеристика вод по величине их суммарной антиоксидантной активности

The article presents the results of a biochemical study of aqueous media in terms of antioxidant activity, which was studied by coulometric analysis using electrogenerated bromine, the samples were analyzed on the coulometer "Expert-006" (LLC "Econix-Expert", Russia) by a certified method. Modern ideas about the properties of water are based on its cluster structure, which is devoted to a significant number of theoretical and experimental works. They indicate that the structure of water is formed by clusters that are constructed from water molecules held by hydrogen bonds. The 9 clusters of water differing in a set of characteristics are allocated. It is shown that oligotrophic waters with low organic matter content and aligned and simplified community structure of aquatic organisms characterized by a complex cluster structure of water and the lowest values of antioxidant activity and water production characteristics differ by a stable, simplified cluster structure with high values of antioxidant activity of the water. Following the research it is revealed that, water has various cluster structure. The most complex in terms of cluster composition is spring water (5 clusters) and artesian water (4 clusters). The most simple composition was the water of the seas and fisheries ponds-1-2 clusters. It was discovered, that oligotrophic waters with low organic matter content and aligned or simplified community structure of aquatic organisms characterized by a complex cluster structure of water and the lowest values of antioxidant activity and water production characteristics differ by a stable, simplified cluster structure with high values of antioxidant activity of the water.

Антиоксидантные свойства водных сред с молекулярным водородом используемых в экологичной медицине

The article presents the results of the biotechnological study of aquatic environments with molecular hydrogen by antioxidant activity. Molecular hydrogen has selective antioxidant activity against dangerous free radicals. It has anti-inflammatory, anti-apoptotic, anti-allergic effects and stimulates energy metabolism. The problem is urgent nowadays because of the great interest to molecular hydrogen as an antioxidant over the past ten years, but its quantitative metabolic parameters have not been estimated yet. The total antioxidant activity of aquatic systems saturated by hydrogen have been studied using coulometric analysis. It was shown that their antioxidant activity of aquatic systems increase of 8-10 times depending on the operating conditions and time of the "H2 Inhaler" device and 3 times when using a mineral generator active Hydrogen "Aquaspectr Mineral". The effect of molecular hydrogen have been studied by changing the antioxidant status of the human body, which was determined by changing the total antioxidant activity of urine and oral fluid during inhalation of hydrogen and oral administration of hydrogen-saturated water. The synergistic effects has been revealed in determining the total antioxidant activity of the oral fluid in the range from 14.02 to 17.59% rel. and synergism/antagonism of urine in the range from 37.17 to 27.62% rel., compared with control measurements. The total antioxidant activity was determined using electro-generated bromine, the samples were analyzed on an Expert-006 coulometer (Econix-Expert LLC, Russia) according to our certified method.

Electrochemical Synthesis of Individual Core@Shell and Hollow Ag/Ag2S Nanoparticles.

This letter presents an electrochemical methodology for structure-tunable synthesis, characterization, and kinetic monitoring of metal-semiconductor phase transformations at individual Ag nanoparticles. In the presence of HS- in aqueous solution, the stochastic collision and adsorption of Ag nanoparticles at a Au microelectrode initiates the partial anodic transformation of Ag to Ag2S at each particle. A single continuous current transient is observed for each Ag nanoparticle reacted. The characteristic shapes of the transients are distinct from previously reported amperometric recordings of electrochemical reactions involving single nanoparticles and are highly uniform at a constant applied potential. The average maximum current increases while the event duration decreases as a function of increasing potential. Independent of applied potential, the electrochemical transformation event abruptly stops after converting ∼80% of the Ag in the nanoparticle to Ag2S, a self-terminating process that does not occur for bulk Ag electrodes under similar conditions. The resulting products are a mixture of core@shell Ag@Ag2S nanoparticles with and without voids in the core, as characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). Both the frequency and size of voids increase at more positive potentials. The average size of the core@shell nanoparticles determined by coulometric analysis of the current transients agrees well with TEM measurements.

Determination of low chlorine content in organic compounds and polymers using an «Expert-006» coulometer

A method of visual mercurimetric titration of chloride ions is widely used in elemental microanalysis for determination of chlorine content in organic substances after their combustion in an oxygen-filled flask. However, when chlorine content is less than 0.5%, the mercurimetric method fails to provide essential accuracy, and a more sensitive method of chlorine coulometric titration by electrogenerated silver ions appeared favorable. We consider a possibility of determining the microgram content of chloride-ions in solutions using a digital coulometric analyzer («Expert-006» produced by «Econics-Expert» (Moscow)) supplemented with an electrolytic cell with silver electrodes. The coulometer was tested in different operation modes to select the optimal electrochemical parameters of ion chloride titration and develop a technique for coulometric determination of chloride ions which in combination with the preliminary burning of the analyzed substances in an oxygen-filled flask provides determination of the residual chlorine in organic matrices at a level of 0.1 – 0.5%. The proposed technique was used to determine the residual chlorine in a number of polymers. The relative error did not exceed 5% at chlorine concentrations of 0.16 – 0.28%.

Utilization of an environmentally-friendly monomer for an efficient and sustainable adrenaline imprinted electrochemical sensor using graphene

Generally, the toxic and mutagenic functional monomers are employed to synthesize the MIP films. This work demonstrates the fabrication of molecular imprinted polymer (MIP) based electrochemical sensor for adrenaline using a green functional monomer, nicotinamide. The adrenaline imprinted film was electropolymerized over reduced graphene oxide (rGO) modified glassy carbon electrode (GCE) by cyclic voltammetry (CV). The as-synthesized sensors were characterized by SEM. The electrochemical analysis showed that the graphene-modified electrode exhibited excellent electrocatalytic activity toward adrenaline and the over-potential of adrenaline decreased significantly as compared to bare GCE which can be attributed to graphene's unique physical and chemical properties such as subtle electronic characteristics, attractive π–π interaction, and strong adsorptive capability of MIP film. The thickness of MIP was estimated to be 1.97 nm by coulometric analysis. This electrochemical sensor displays high selectivity owing to specific imprinted cavities for adrenaline and worked well over a wide linear concertation range of adrenaline between 0.015 μM and 40 μM with a detection limit (LOD) of 3 nM. The sensor offered good reproducibility (Relative standard deviation of 3.44%) and retained 94.6% of its initial response for over 40 days. Finally, excellent recoveries from 96.0% to 100.7% were obtained for two different samples of urine and adrenaline ampoules. Thus, this work holds great promise with numerous advantages including easy fabrication, high sensitivity and selectivity, high throughput and satisfactory reproducibility for adrenaline.

Novel Calibration Technique for a Coulometric Evolved Vapor Analyzer for Measuring Water Content of Materials

Evolved vapor coulometry is a measurement technique that selectively detects water and is used to measure water content of materials. The basis of the measurement is the quantitative electrolysis of evaporated water entrained in a carrier gas stream. Although this measurement has a fundamental principle—based on Faraday’s law which directly relates electrolysis current to amount of substance electrolyzed—in practice it requires calibration. Commonly, reference materials of known water content are used, but the variety of these is limited, and they are not always available for suitable values, materials, with SI traceability, or with well-characterized uncertainty. In this paper, we report development of an alternative calibration approach using as a reference the water content of humid gas of defined dew point traceable to the SI via national humidity standards. The increased information available through this new type of calibration reveals a variation of the instrument performance across its range not visible using the conventional approach. The significance of this is discussed along with details of the calibration technique, example results, and an uncertainty evaluation.