2024, Zelinka, Samuel L., Glass, Samuel V., Lazarcik, Eleanor Q. D., Thybring, Emil E., Altgen, Michael, Rautkari, Lauri, Curling, Simon, Cao, Jinzhen, Wang, Yujiao, Künniger, Tina, Nyström, Gustav, Dreimol, Christopher Hubert, Burgert, Ingo, Uyup, Mohd Khairun Anwar, Khadiran, Tumirah, Roper, Mark G., Broom, Darren P., Schwarzkopf, Matthew, Yudhanto, Arief, Subah, Mohammad, Lubineau, Gilles, Fredriksson, Maria, Strojecki, Marcin, Olek, Wiesław, Majka, Jerzy, Pedersen, Nanna Bjerregaard, Burnett, Daniel J., Garcia, Armando R., Verdonck, Els, Dreisbach, Frieder, Waguespack, Louis, Schott, Jennifer, Esteban, Luis G., Garcia-Iruela, Alberto, Colinart, Thibaut, Rémond, Romain, Mazian, Brahim, Perre, Patrick, Emmerich, Lukas, Li, Ling

AbstractAutomated sorption balances are widely used for characterizing the interaction of water vapor with hygroscopic materials. These instruments provide an efficient way to collect sorption isotherm data and kinetic data. A typical method for defining equilibrium after a step change in relative humidity (RH) is using a particular threshold value for the rate of change in mass with time. Recent studies indicate that commonly used threshold values yield substantial errors and that further measurements are needed at extended hold times as a basis to assess the accuracy of abbreviated equilibration criteria. However, the mass measurement accuracy at extended times depends on the operational stability of the instrument. Published data on the stability of automated sorption balances are rare. An interlaboratory study was undertaken to investigate equilibration criteria for automated sorption balances. This paper focuses on the mass, temperature, and RH stability and includes data from 25 laboratories throughout the world. An initial target for instrument mass stability was met on the first attempt in many cases, but several instruments were found to have unexpectedly large instabilities. The sources of these instabilities were investigated and greatly reduced. This paper highlights the importance of verifying operational mass stability of automated sorption balances, gives a method to perform stability checks, and provides guidance on identifying and correcting common sources of mass instability.

2025, Zelinka, Samuel L., Glass, Samuel V., Farkas, Natalia, Thybring, Emil E., Altgen, Michael, Rautkari, Lauri, Curling, Simon, Cao, Jinzhen, Wang, Yujiao, Künniger, Tina, Nyström, Gustav, Dreimol, Christopher Hubert, Burgert, Ingo, Roper, Mark G., Broom, Darren P., Schwarzkopf, Matthew, Yudhanto, Arief, Subah, Mohammad, Lubineau, Gilles, Fredriksson, Maria, Olek, Wiesław, Majka, Jerzy, Pedersen, Nanna Bjerregaard, Burnett, Daniel J., Garcia, Armando R., Dreisbach, Frieder, Waguespack, Louis, Schott, Jennifer, Esteban, Luis G., García‑Iruela, Alberto, Colinart, Thibaut, Rémond, Romain, Mazian, Brahim, Perré, Patrick, Emmerich, Lukas

Abstract Automated sorption balances are widely used for characterizing the interaction of water vapor with hygroscopic materials. This paper is part of an interlaboratory study investigating the stability and performance of automated sorption balances. A previous paper in this study investigated the mass, temperature, and relative humidity (RH) stability of automated sorption balances by looking at the mass change of a non-hygroscopic sample over time. In this study, we examine the mass stability of wood samples held at constant RH for seven to ten days after a step change. The reason for the long hold times was to collect data to “operational equilibrium” where the change in mass is on the order of the inherent operational stability of the instrument. A total of 80 datasets were acquired from 21 laboratories covering absorption with final RH levels ranging from 10 to 95%. During these long hold times, several unusual behaviors were observed in the mass-vs-time curves. Deviations from expected sorption behavior were examined by fitting the data to an empirical sorption kinetics model and calculating the root mean square error (RMSE) between the observed and smoothed behavior. Samples that had a large RMSE relative to the median RMSE of the other datasets often had one of several types of errors: abrupt disturbances, diurnal oscillations, or long-term mass decline during an absorption step. In many cases, mass fluctuations were correlated with changes in the water reservoir temperature of the automated sorption balance. We discuss potential errors in sorption measurements on hygroscopic materials and suggest an acceptable level of RMSE for sorption data.