Dynamic Gravimetric Method Research Articles

RISE Test Facilities for the Measurement of Ultra-Low Flow Rates and Volumes with a Focus on Medical Applications

In the framework of the ongoing EMPIR JRP 18HLT08 Metrology for Drug Delivery (MeDDII), a main task is to improve dosing accuracy and enable traceable measurements of volume, flow and pressure of existing drug delivery devices and in-line sensors operating, in some cases, at ultra-low flow rates. This can be achieved by developing new calibration methods and by expanding existing metrological infrastructure. The MeDDII project includes, among other issues, investigations on fast changing flow rates, physical properties of liquid mixtures and occlusion phenomena to avoid inaccurate measurement results and thus improve patient safety. This paper describes the extension of an existing measurement facility at RISE and the design and construction of a new measurement facility to be able to carry out such investigations. The new measurement facility, which is based on the dynamic gravimetric method, is unique worldwide in respect of the lowest measurable flow rate. The gravimetric measuring principle is pushed to the limits of what is feasible. Here, the smallest changes in the ambient conditions have a large influence on the measurement accuracy. The new infrastructure can be used to develop and validate novel calibration procedures for existing drug delivery devices over a wide flow rate range. The extension of the measurement facilities also enables inline measurement of the pressure and the dynamic viscosity of Newtonian liquids. For this purpose, it is ensured that all measurements are traceable to primary standards.

Electrodialytic Enrichment and Matrix Conversion for the Determination of Trace Metals in Ultra-Pure Water.

The presence of trace contaminants in ultra-pure water (UPW) used in fabrication process can greatly affect the yield and quality of industrial products. In the present study, the electrodialytic enrichment of metal cations as a means of continuously monitoring the UPW quality was studied. A newly designed electrodialytic enrichment device (EED) was used to quantitatively transfer metal ions from samples to dilute nitric acid, which was then directly introduced into an inductively coupled plasma—mass spectrometry (ICP–MS) instrument. This process could be performed without contamination of the sample, and the enrichment factor was solely dependent on the flow rate ratio of the sample and acceptor solutions. The transference of analytes into the acidic solution improved the responsivity of the ICP–MS analysis, especially at low concentrations of less than 1 μg/L. Blank solutions to support the analysis of UPW could be produced using the EED effluent, from which metal ions were quantitatively removed. In addition, calibration curves with concentration ranges of several nanograms per liter were obtained by preparing standards using a dynamic gravimetric method while employing a single bottle and continuous mass monitoring to avoid any contamination from the volumetric flasks. The sensitivities associated with the ICP–MS analysis of a number of trace metal ions were improved by one or two orders of magnitude. The data show that the present EED is able to continuously produce enriched analyte solutions to allow the ongoing monitoring of UPW quality.

The primary dynamic gravimetric system for gas mass flow measurement

High accuracy mass flow measurement is an enabling technology at the base of many industries. HORIBA STEC Co., Ltd. developed its own primary gas mass flow measurement system. We employed the dynamic gravimetric method in a vacuum chamber, and we use only mass and time information for mass flow rate calculation, with no correction for temperature, pressure and humidity. The system achieved 0.036% uncertainty as lowest of results with satisfactory performance of proficiency testing with NIST (National Institute of Standards and Technology). Then the laboratory has been granted ISO/IEC 17025 accreditation since 2017. This paper describes the system details and uncertainty analysis.

Propriedades termodinâmicas da polpa de cajá (Spondias mombin L.)

Spondias mombin L. é um fruto nativo do Brasil, há uma variação da espécie nativa no Cerrado. Seus frutos são utilizados na produção de alimentos para fabricação de geléias, sorvetes e sucos e as folhas são utilizadas na medicina popular para tratar doenças inflamatórias. Objetivou-se analisar o comportamento termodinâmico e as propriedades da polpa de cajá em pó em diferentes temperaturas durante o processo de dessorção. A análise foi realizada pelo método dinâmico-gravimétrico. Os frutos de cajá com atividade de água entre 16,96 e 57,43 foram usados para as análises termodinâmicas. A dessorção da camada fina do fruto foi observada em diferentes temperaturas (10, 20, 30 e 40° C) e níveis de atividade da água, variando de 0,17 a 0,57, até o produto chegar ao teor de umidade de equilíbrio na condição de ar especificada. As propriedades termodinâmicas da polpa de cajá foram afetadas pelo teor de temperatura e umidade. A teoria isocinética pode ser comprovada para o processo de dessorção e esta é controlada pela entalpia. A dessorção de água em frutos de cajá é um processo não espontâneo.

Water collection techniques at very low flow rates including strong capillary effects

Milli-, micro- and nano-flow calibrations are important in several areas of pharmaceutical, flow chemistry and health care applications where volumetric dosage or delivery at given flow rates are crucial for the process. After developing a facility for the micro-flow range, METAS has developed a facility for flow rates from 50 nL/min up to 400 mL/min. The continuous collection of the flowing water into a beaker on a balance without having droplet formation for a continuous increase of the weighing values is a challenge (dynamic gravimetric method). This technique is often used to determine the flow rate over several orders of magnitude. In this paper, we describe the newly developed METAS piston provers and focus on the water collection techniques used for the flow rate determination of very low flow rates going as low as 50 nL/min by means of the dynamic gravimetric method. One water collection technique is to immerse the outlet needle into the water in the beaker. To reduce evaporation either a saturated environment is created or a layer of oil is added on top of the water. Another water collection technique is applied at the METAS facilities, where the outlet needle is positioned just over glass filters on top of the beaker to collect the water by means of a constant water bridge obtained independently of the flow rate. These two techniques are investigated for comparing the stability of the flow rate determination and the influence of the capillary forces acting due to the water or water-oil surface on the outlet needle and on the water bridge between the outlet needle and glass filters. The technique applied at METAS with the water bridge between outlet needle and glass filter reveals to be more stable for the flow rate determination and corrections due to capillary forces acting on the outlet needle can be neglected compared to the water collection technique with the immersed needle.

Reference Gas Mixtures of Formaldehyde in Nitrogen: Preparation by a Dynamic Gravimetric Method

The preparation of formaldehyde gas mixtures required for metrological assurance of air pollution control is an urgent task. Methods for the preparation of gas mixtures of formaldehyde for metrological purposes are considered. The 2 μmol/mol-level gas mixtures of formaldehyde in nitrogen have been obtained by a dynamic-gravimetric method with the depolymerization of trioxane vapor. The efficiency of the trioxane conversion process was experimentally studied. The sources of uncertainty are analyzed in detail. The reference gas mixtures obtained were used for the formaldehyde mole fraction measurements during the CCQM-K90 key comparison. The relative expanded uncertainty of the measurement U = 3.3% was achieved, confi rmed by the comparison results.

Thermal and moisture adsorption/desorption properties for a selection of vegetal insulation materials

Natural, or ‘green’ insulation materials, have become more popular for the ‘ecologisation’ of construction activities. The ecological aspects for such materials are being widely analysed, but experimental data about their physical properties when installed in building constructions remains lacking. In this study, pressed samples of three locally wild grown agricultural materials – rye, reed, and hemp – are analysed. Thermal conductivity measurements were carried out using the hot plate device. Comparison with widely used mineral insulation materials shows that thermal conductivity for simple pressed materials are roughly three times higher, and are comparable to plywood and cross-laminated timber insulation properties. Additional experiments regarding such materials include measurements of hygroscopic sorption properties (adsorption/desorption), determined using the dynamic gravimetric method at different temperatures and a wide, relative humidity range. The results obtained show that the difference in all studied materials appeared only at high humidity values; the rye straw and reed spikelets adsorbed more water than other materials, which is important for potential indoor air humidity assessment.

Reference gas mixtures of formaldehyde in nitrogen: preparation by a dynamic-gravimetric method

Reference gas mixtures of formaldehyde in nitrogen: preparation by a dynamic-gravimetric method

Improving Process Quality by Means of Accurate and Traceable Calibration of Flow Devices with Process-oriented Liquids.

Calibration of flow devices is important in several areas of pharmaceutical, flow chemistry and health care applications where volumetric dosage or delivery at given flow rates are crucial for the process. Although most of the flow devices are measuring flow rates of process-oriented liquids, their calibrations are often performed with water as calibration liquid. It is recommended to perform the calibrations of the flow devices with process-oriented liquids as the liquid itself might influence the performance of the flow devices. Therefore, METAS has developed facilities with METAS flow generators to address the issue of measuring with process-oriented liquids for flow rates from 400 ml/min down to 50 nl/min with uncertainties from 0.07-0.9 %. Traceability is guaranteed through the calibration of the generated flow rates of the METAS flow generators by means of the dynamic gravimetric method where a liquid of well-known density and a well-controlled evaporation rate is used. The design of the milli-flow facility will be discussed as well as first measurement results of the METAS flow generators in the range of micro-flow and milli-flow using water and other liquids.

Dynamic behavior analysis of drug delivery devices using a dynamic gravimetric method

The calibration of drug delivery devices is essential for accurate dose control. In this study, drug delivery devices, namely infusion and syringe pumps, were assessed using a dynamic gravimetric method. The flow rates caused by the syringe pump, infusion pump, and pressure-based pump were measured at various flow rates (0.5–60 mL/h) by simultaneously using a dynamic gravimetric method and flow meter. The measurement error uncertainty of the pumps were obtained using the dynamic gravimetric calibration method. The pulsation period and amplitude were obtained with respect to the flow rate to analyze the pulsating flow of the syringe pump and infusion pump. The pump error increased in the following order: the pressure-based pump, syringe pump, and infusion pump based on the flow rate. The measurement error uncertainty of the syringe pump increased slightly when the flow rate decreased, whereas the infusion pump exhibited significant increases in the error and uncertainty when the flow rate decreased. The flow stability of the pulsating flow from each pump was analyzed according to the flow rate. Thus, we discussed the characteristics of the pulsating flow from each drug delivery device. We confirmed that the pumps had different flow stability, error, and measurement uncertainty because of their different working principles.

Hydric and structural approaches for earth based materials characterization

The earth-based material considered in this work is called Stabilized Earth Bick (SEB). Two distinguish type of SEB were examined: SEB5-Tu and SEB5-Te; their difference refers to the freestone, or the red earth composition. Firstly, a morphological characterization has been done by comparing two different approaches: the water porosity test and the mercury porosimetry which provide access to the material porosity and the pore size distribution.Then, the sorption-desorption isotherm were carefully evaluated for each SEB type. The dynamic gravimetric method was selected for such measurement. Further, theoretical modeling of the sorption desorption isotherm was investigated; here the model parameters allow more accurate interpretation of experimental results.Most of these measurements provided the hygric and structural characteristics relating to the SEB materials and a comparison of their characteristics depending on the variation of their compositions.

<b>Thermodymnamic properties of crambe fruits

This study aimed to determine and evaluate the thermodynamic properties of crambe fruit at different equilibrium moisture contents. The dynamic-gravimetric method was used to collect experimental data. Crambe fruits with an initial moisture content of approximately 26% db (dry basis) were used. The thin-layer desorption of the product was conducted at different controlled temperatures (25, 30, 35, 40, and 45°C) and at water activity levels ranging from 0.10 to 0.89 until the product reached the equilibrium moisture content at the specified air condition. In conclusion, the thermodynamic properties of crambe fruit are affected by temperature and moisture content. The isokinetic theory is valid for the desorption process, which is controlled by enthalpy, and the Gibbs free energy is positive at all of the tested temperatures, which indicates that water desorption is not a spontaneous process.

Adsorption Isotherms of Propan-2-ol, Methylbenzene, and Tetrachloromethane on Selected Activated Carbons

This work reports adsorption isotherms of propan-2-ol, methylbenzene, and tetrachloromethane vapors on commercial activated adsorbents: Norit RB4, Sorbonorit 3, and Sorbonorit 4. The adsorption isotherms were measured at 293.15, 323.15, 355.15, 373.15, 393.15, and 413.15 K and pressures up to component saturation pressures at 293.15 K. The isotherms were measured using the dynamic gravimetric method. The data obtained from experiments were correlated with following multitemperature adsorption isotherms equations: Toth, Langmuir–Freundlich, and Dubinin–Astakhov.

Thermal and thermodynamic characterization of a dye powder from liquid turmeric extracts by spray drying

This study aimed to evaluate the thermodynamic properties of sorption isotherms and glass transition temperature (Tg) and the thermal properties of a dye powder obtained from turmeric extracts using spray drying. The sorption isotherms were evaluated at 15, 25 and 35 °C using the dynamic gravimetric method, wherein the isotherm data of the experiment were fit to GAB and BET models. Likewise, the Tg was measured using differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) was used to determine the mass loss, and the thermal properties (heat capacity, diffusivity and thermal conductivity) were determined using transient flow method. The results demonstrated that the GAB model best fit the adsorption data. The DSC analysis presented a glass transition temperature of 65.35 °C and a loss of volatiles at 178.07 °C. The TGA analysis indicated a considerable mass loss starting at 193 °C, resulting in degradation of the product. The thermal properties demonstrated a heat capacity of 2.45 J/g °C, a thermal conductivity of 0.164 ± 0.001 W/mK and a thermal diffusivity of 8.7x10-8 ± 0.000 m2/s.

Solubility of β-diketonates, cyclopentadienyls, and cyclooctadiene complexes with various metals in supercritical carbon dioxide

The solubility of a variety of metal acetylacetonate, tetramethylheptanedionate, cyclopentadienyl and cyclooctadiene complexes in supercritical carbon dioxide was measured. The complexes included the metals potassium, rubidium, titanium, zirconium, vanadium, chromium, manganese, iron, ruthenium, osmium, cobalt, rhodium, nickel, palladium, platinum, copper, silver, and zinc. The solubility experiments were carried out with a dynamic-gravimetric method at 333 K in the pressure range from 10 MPa to 30 MPa. The pressure dependence of solubility is presented and the influence of the ligand is discussed. The influence of the metal on solubility was investigated systematically in terms of the oxidation state of the metal, the size of the metal atom and the magnetic moment. The solubility of metal complexes depends on the ligand as well as on the metal atom. An increase in solubility can be observed with increasing number of ligands per centre atom and with increasing oxidation state. In an identical complex structure, solubility is influenced by the molecular size and the valence electron configuration of the metal centres.

Isotermas e calor isostérico de sorção do feijão

O teor de água de equilíbrio dos grãos de feijão foi determinado pelo método dinâmico-gravimétrico para temperaturas entre 25 e 55 °C e atividades de água para cada temperatura, entre 0,20 e 0,75. Observou-se que o teor de água decresce com o aumento da temperatura para uma dada atividade de água à semelhança dos produtos higroscópicos. Aos dados experimentais foram ajustados diversos modelos matemáticos disponíveis na literatura (Brunauer-Emmett-Teller, Chung Pfost, Copace, Guggenhein-Anderson-de Boer, Halsey Modificado, Henderson, Henderson Modificado, Oswin, Sabbah e Sigma Copace). Segundo os parâmetros estatísticos de análise, o modelo de Halsey Modificado foi o que descreveu melhor a higroscopicidade do feijão. A partir dos resultados obtidos calculou-se o calor isostérico para cada teor de água de equilíbrio. Observou-se que o calor isostérico aumenta com a diminuição do conteúdo de água do produto, indicando que a redução do teor de água aumenta a energia necessária para a remoção de água. Os valores de calor isostérico para os grãos de feijão na faixa de umidade de 10,10 a 21,71 (% b.s.), variam de 3961 a 2718 kJ kg-1.

Adsorption Equilibria of Butan-1-ol, Toluene and Water Vapour onto Sorbonorit 4 Activated Carbon and the Co-Adsorption of Organic Compounds and Water Vapour onto SKT Activated Carbon

The results of both experimental and theoretical investigations are presented. The results of experimental investigations of adsorption equilibria for the pure components butan-1-ol, toluene and water vapour onto Sorbonorit 4 activated carbon are first reported, with measurements having been undertaken using a dynamic gravimetric method. The results for butan-1-ol and toluene were correlated using the Langmuir, Freundlich, Redlich–Peterson, Toth and Dubinin–Astakhov models, while the results for water vapour were correlated using the equations of Dubinin and Serpinsky and of Barton and Barton and co-workers. A simple model enabling the prediction of the adsorption equilibria of butan-1-ol/water vapour and toluene/water vapour mixtures on SKT activated carbon is then presented. Such predictions were made on the basis of data for the pure components, with the equilibrium data for both pure components and mixtures being taken from the literature. The model, which is simple to simulate and verify using experimental data, is based on the Polanyi theory and the Dubinin–Astakhov isotherm equation. With this model, fairly good agreement was observed between predicted and experimental binary mixture adsorption data for the systems examined.

Comparative study of the dynamic gravimetric and pulse chromatographic methods for the determination of Henry constants of adsorption for VOC–zeolite systems

In this paper, we propose a comparative study between a gravimetric apparatus operating under dynamic conditions and a pulse chromatographic device developed for the determination of Henry constants of adsorption for VOC–zeolite systems. In both cases, we provide a description of the experimental set-up and procedure, as well as a complete report on the treatment of the rough experimental data. The experimental errors are also discussed. The comparison work is based on the study of the adsorption of toluene on a NaY zeolite (Si/Al 2.43) for temperatures ranging from 503 to 623 K. The maximal discrepancy found between the experimental Henry constants was 15.0%. The pulse chromatographic method is only dedicated to high-temperature measurements. For low-temperature experiments, the rough data cannot be treated in an efficient way, and it is not possible to obtain reliable Henry constant values. The dynamic gravimetric method is not temperature limited. It is however time-consuming, especially when low-temperature measurements (not presented in this paper) are concerned. Both methods are complementary if the determination of Henry constants is required in a wide temperature range.

Adsorption Equilibrium Moisture Contents of Flax Straw, Hemp Stalks and Reed Canary Grass

The quality of fibres obtained from flax, hemp and reed canary grass is dependent on the moisture characteristics of the crops. In this study, the adsorption equilibrium moisture contents of un-retted and dew-retted flax straw, un-retted and frost-retted hemp stalks and spring-harvested reed canary grass were determined using the dynamic gravimetric method at different temperatures (5, 15, 25 °C) for relative humidities in the range 35–95%. Non-linear regression was used to fit five commonly used three-parameter isotherm models [the modified Henderson model, the modified Chung–Pfost model, the modified Halsey model, the modified Oswin model and the modified Guggenheim–Anderson–de Boer (GAB) model] to the data obtained. The goodness-of-fit of the models was compared using the mean relative percentage deviation, the standard error of estimate and residual plots. The modified Halsey model was considered the best for predicting the equilibrium moisture content of un-retted flax and spring-harvested reed canary grass, and the modified Oswin model for predicting the equilibrium moisture content of dew-retted flax and un-retted hemp, while the Chung-Pfost model was the best for predicting the equilibrium moisture content of frost-retted hemp. For flax and hemp, there were statistically significant differences between un-retted and retted plant materials, whereas the differences between varieties were small.

Continuous dynamic-gravimetric preparation of calibration gas mixtures for air pollution measurements

The preparation of calibration gas mixtures for air pollution measurements by the dynamic-gravimetric method was investigated using sulphur dioxide in nitrogen as a model. The target mole fraction was 200×10–9 mol/mol, with the option of also getting smaller mole fractions. Thermal mass flow meters calibrated with reference mass flows were used to measure the dilution gas flow (nitrogen). The relative standard uncertainty of the dilution gas flows between 10 mg/s (approx. 500 ml/min) and 40 mg/s (approx. 2000 ml/min) was 0.15%. The mass flow of the target component measured as the permeation rate was determined via the quasi-continuous observation of the loss in the permeation tube mass during the measuring time. A magnetic coupling system and an adapted microbalance were used for this purpose. The results presented show permeation rates measured over the lifetime of a tubular permeation source. The measurement cycles took between 3 days and 7 h at least. The relative standard uncertainty of the mixture composition did not exceed 2%. First comparisons with gas mixtures prepared by the static-gravimetric method show compatibility. The applicability of the system is not restricted to the SO2/N2 mixture. It can also be used for preparing other gas mixtures in this field of application.