High accuracy calibration of a dynamic vapor sorption instrument and determination of the equilibrium humidities using single salts

Abstract

We present a procedure for accurately calibrating a dynamic vapor sorption (DVS) instrument using single salts. The procedure accounts for and tailors distinct calibration tests according to the fundamental properties of each salt. Especially relevant properties influencing the calibration are the heat of solution, heat of condensation, and the kinetics connected to the salt phase transition, as these influence the microclimate surrounding the salts during calibration. All these issues were dealt with to obtain precise calibration results. The DVS instrument comprises two control modes to generate and measure the relative humidity (RH). Both control modes were separately examined and combined to overcome the shortcomings of each of the two control modes and thereby obtain the most accurate results. Repeated calibration testing with the single salts (LiCl, MgCl2, Mg(NO3)2, NaCl, and KNO3) enables five discrete sorption isotherm measurements within the range of 11%–93%RH. The equilibrium RH of the solution for LiCl, MgCl2, Mg(NO3)2, NaCl, and KNO3 was determined with a standard deviation of 0.06%-0.15% (0.45% for KNO3) RH. By comparing the measured calibration values with the well-known equilibrium RH of each salt solution, the presented method’s results are both accurate with significant agreement and precise with small variation.

Direct Measurements of the Deliquescence Relative Humidity in Salt Mixtures Including the Contribution from Metastable Phases

“…To improve the accuracy of the RH eq for single-salt results, a methodology was developed that took the properties of single salts into account. 22 This work was extended to include salt mixtures, and some preliminary examinations were reported in ref ( 23 ).…”

Direct measurements of the RHeq in salt mixtures including the contribution from metastable phases

“…Furthermore, since each salt differs in atomic composition, thereby resulting in different sizes, atomic structures, etc., each salt also differs in its properties, namely, their water absorption and desorption properties. Therefore, individual salt calibration tests were combined together with the specified salt preparation method in [21] to perform a highly accurate calibration. The salt calibration methods incorporate the following salt properties that influence calibration: the heat of solution, heat of condensation, and kinetics connected to the salt phase transition.…”

“…This work was extended to include salt mixtures, and some preliminary examinations were reported in [22]. The present work makes use of the highly accurate calibration of the DVS instrument described in [21] to obtain a highly accurate and direct measurement of RHeq for salt mixtures of NaCl, NaNO3, Na2SO4 and (NH4)2SO4 -Na2SO4. The determination of the RHeq of salt mixtures of NaCl, NaNO3, and Na2SO4 salts are chosen since these results can be compared with results from the literature [11][12], [15][16] just as results from the thermodynamically based ECOS-Runsalt program and the improved model presented in [23] based on an extended Pitzer formalism on the ion interaction for calculating water activity.…”

Quantifying the hygroscopic properties of cyclodextrin containing aerosol for drug delivery to the lungs

“…DVS is an analytical tool used to determine humidity isotherms and the moisture content of inorganic and organic compounds 19 under controlled environmental conditions of RH and temperature. It is a technique commonly used to determine the stability of pharmaceutical and food products in different atmospheres to optimise storage conditions, 20 and ideally suited for comparison with aerosol measurements.…”

“…1,15,16 The hygroscopicity of microscopic sized aerosol droplets is determined on a single droplet basis using Raman tweezers 17,18 and compared with dynamic vapour sorption (DVS) humidity isotherm measurements. 19,20 As an excipient, 2-HP-b-CD is used in developing environmentfriendly formulations removing polycyclic aromatic hydrocarbons (PAHs) from soil 21 and has shown to complex with heavy metals, 6 small organic guest molecules 22 and acetanilides. 23 In ref.…”