Protocol for Obtaining Reference Isotherms Using BAM-P109 and Water.

*

Materials: The adsorbent is a certified reference material, BAM-P109 (nanoporous carbon).

‡

The sample mass to be used should be optimized to achieve the best signal-to-noise ratio,

according to the experimental parameters of the instrument being used. The adsorptive, water, 

should be LC/MS grade, and carrier gas, molecular nitrogen, should have purity ≥ 99.999 %.

Sample pretreatment: The nanoporous carbon should be outgassed in vacuum at room temperature, 

then heated over a period of 1 h to 200 °C and held at that temperature for 3 h under vacuum with 

continuous pumping (final pressure < 0.1 Pa). If the outgassing is performed in a separate manifold, 

minimize exposure to air when transferring to the analysis port and re-outgas in the instrument to 

140 °C for at least 6 h to remove any adsorbed gases.

Measurement of adsorption isotherms: Water (H2O) adsorption and desorption isotherms are to be

measured on BAM-P109 at 25 C as a function of P/P0 or percent RH. It is recommended that data 

be recorded at the following interval: 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 

0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 P/P0, or 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 

80, 85, 90, and 95 % RH. The same measurement is also to be done without the adsorbent to 

perform a “blank correction.” This blank should be subtracted from the adsorption isotherm.†

Comparison to the empirical reference isotherm data: Measured isotherms should fall within the 

95% uncertainty interval of the reference isotherms for pure water and water entrained in nitrogen 

shown in the Tables 1 and 2, respectively. 

* H. G. T. Nguyen et al., Reference isotherms for water vapor sorption on nanoporous carbon: results of an 

interlaboratory study, Adsorption 29 (2023) 113−124. Available On-line.

‡ D. Panne & A. Thünemann (2010). Certified Reference Material BAM-P109. Available On-line.

† H. G. T. Nguyen, J. C. Horn, M. Thommes, R. D. van Zee, L. Espinal, Experimental Aspects of Buoyancy 

Correction in Measuring Reliable High-pressure Excess Adsorption Isotherms Using the Gravimetric Method, Meas. 

Sci. Technol. 28 (2017) 125802. Available On-line.
Table 1. The reference isotherm for pure water/BAM-P109 along with the associated 95 % lower 

(l95) and upper (u95) uncertainty bounds.

Adsorbed amount v. (P/P0 × 100): adsorption 

band

Adsorbed amount v. (P/P0 × 100): desorption 

band

P/P0 × 100 (mmol/g) l95 u95 P/P0 × 100 (mmol/g) l95 u95

5 0.041 0.027 0.055 95 23.622 23.345 23.899

10 0.072 0.054 0.090 90 23.295 23.074 23.516

15 0.107 0.084 0.130 85 23.024 22.853 23.196

20 0.148 0.126 0.169 80 22.754 22.588 22.920

25 0.222 0.191 0.254 75 22.483 22.275 22.691

30 0.287 0.259 0.316 70 22.213 21.936 22.490

35 0.416 0.381 0.452 65 21.978 21.552 22.404

40 0.683 0.620 0.745 60 21.217 20.646 21.789

45 1.215 1.105 1.325 55 15.310 12.512 18.109

50 2.331 2.063 2.599 50 4.685 3.131 6.238

55 5.213 4.599 5.827 45 1.804 1.240 2.368

60 11.748 11.100 12.396 40 1.027 0.660 1.393

65 17.470 16.643 18.297 35 0.702 0.363 1.041

70 20.391 19.755 21.027 30 0.560 0.309 0.811

75 21.813 21.445 22.182 25 0.479 0.259 0.699

80 22.540 22.132 22.947 20 0.418 0.222 0.615

85 22.866 22.441 23.290 15 0.380 0.194 0.567

90 23.322 23.021 23.623 10 0.351 0.171 0.530

95 23.622 23.345 23.899 5 0.338 0.049 0.627
Table 2. The reference isotherm for water in nitrogen/BAM-P109 relative humidity measurements 

along with the associated 95 % lower (l95) and upper (u95) uncertainty bounds.

Adsorbed amount v. RH: adsorption band Adsorbed amount v. RH: desorption band

RH (%) (mmol/g) l95 u95 RH (%) (mmol/g) l95 u95

5 0.041 0.026 0.055 95 22.475 21.963 22.987

10 0.073 0.054 0.093 90 22.220 21.794 22.646

15 0.107 0.079 0.134 85 21.944 21.557 22.331

20 0.149 0.110 0.187 80 21.696 21.333 22.058

25 0.206 0.149 0.263 75 21.461 21.113 21.808

30 0.289 0.202 0.376 70 21.194 20.841 21.547

35 0.431 0.295 0.568 65 20.884 20.523 21.245

40 0.700 0.470 0.930 60 20.419 20.045 20.794

45 1.252 0.875 1.630 55 15.667 12.319 19.015

50 2.385 1.764 3.006 50 5.244 2.446 8.041

55 5.337 3.495 7.180 45 1.683 1.358 2.008

60 11.233 8.863 13.604 40 0.958 0.774 1.142

65 16.674 15.059 18.289 35 0.609 0.498 0.721

70 19.903 19.187 20.619 30 0.409 0.341 0.476

75 21.106 20.660 21.552 25 0.288 0.244 0.332

80 21.592 21.213 21.970 20 0.210 0.180 0.239

85 21.871 21.512 22.231 15 0.154 0.133 0.175

90 22.095 21.729 22.462 10 0.111 0.092 0.130

95 22.475 21.963 22.987 5 0.074 0.053 0.095
To reiterate, the following recommendations for measurements of static pure BAM-P109/H2O 

sorption isotherm are offered:

• Sample Activation: Sufficiently complete sample activation is crucial. As noted 

above, the nanoporous carbon must be activated at 200 °C for 3 h under high vacuum 

(≤0.1 Pa) to realize the reported reference isotherm. If the sample is activated ex-situ,

minimize exposure to air and moisture to obtain the correct sample mass and re-outgas in the 

instrument at 140 °C for at least 6 h to remove any physiosorbed gases.

• Sample Volume Determination: Proper determination of sample volume is needed both 

for buoyancy correction in a gravimetric system, as well as the void volume 

determination in a volumetric system. When required in data analysis, a skeletal density 

of 2.18 g/cm3should be used for BAM-P109.

1

• Buoyancy Correction/Void Volume Correction: A buoyancy correction must be applied 

when using a gravimetric system. Although less important at low-pressures, buoyancy 

effects are significant for high-pressure measurements and cannot be overlooked. This is 

analogous to the use of void volume in a volumetric instrument to determine surface 

excess uptake, and the effect of using the wrong volume also becomes more significant 

with increasing pressure.

• Equation-of-State: In general, identify the equation-of-state used to calculate fluid 

density, and use critically evaluated equations, such as those contained in the NIST 

Reference Fluid Thermodynamic and Transport Properties Database (REFPROP). The 

Wagner and Pruss equation of state2should be used for H2O at 25 °C to replicate the 

reference data.

• T, P, and m: Ensure good control and measurement of temperature, pressure, and 

sample mass, as these are important in accurate determination of the uptake.

• Blank Correction: A blank run subtraction should be performed whenever possible, as it 

corrects for small uncompensated transducer nonlinearities, effects of temperature 

heterogeneities coupled with the compressibility of the adsorptive, and other 

experimental effects.

1BAM (2020). Safety Data Sheet for CRM BAM-P109.

2W. Wagner and A. Pruss, The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water 

Substance for General and Scientific Use," J. Phys. Chem. Ref. Data, 31(2002) 387. Available On-line.
To reiterate, the following recommendations for measurements of dynamic BAM-P109/H2O in N2

sorption isotherm are offered:

• Sample Activation: Sufficiently complete sample activation is crucial. As noted 

above, the nanoporous carbon must be activated at 200 °C for 3 h under high vacuum 

(≤0.1 Pa) to realize the reported reference isotherm. If the sample is activated ex-situ,

minimize exposure to air and moisture to obtain the correct sample mass and re-outgas in 

the instrument at 140 °C for at least 6 h to remove any physiosorbed gases.

• Carrier gas: The carrier gas used is extremely important and will affect the data 

obtained. Nitrogen gas should be used to obtain reference data associated with RH 

experiments using nitrogen as carrier gas. Helium should be used if like-pure water 

vapor sorption data is desired.

• T, RH, and m: Ensure good control and measurement of temperature, relative 

humidity, and sample mass, as these are important in accurate determination of the 

uptake. In general, calibration of relative humidity sensors is highly recommended. 

Common calibration materials include salts with known deliquescent point. Mass flow 

controllers should also be calibrated, if possible.

• Blank Correction: A blank run subtraction should be performed whenever possible, as

it corrects for small uncompensated effects.