Accuracy of pH Measurements in Blood‐Free Balanced Salt Solutions with and without Bovine Serum Albumin—with Four Devices (ABL80, i‐STAT®, pH Paper, and pH Probe)
Authors: Hees Josephine E. , Cleveland William J. , Lotze Felicia P. , Pille Johannes A. , Salzman Michele M. , Balzer Claudius , Riess Matthias L. 
Published: June 2021

Introduction

Accurate and precise measurements are vital in research. Discrepancies between the actual values and values measured by a device can have serious implications on the design and results of an experiment. Thus, it is critical to know what devices provide reliable values. The aim of this study was to compare four different devices commonly used to measure pH in the absence and presence of Bovine Serum Albumin (BSA).

Methods

A balanced salt solution (NaCl 119 mM, NaHCO3 24 mM, Glucose 5.5 mM, CaCa2 1.6 mM, KCl 4.7 mM, MgSO4 1.17 mM, NaPO4 1.18 mM) with or without 4% BSA was bubbled with different CO2 percentages (2.5%, 3.8%, 5%, 7.5 %, 10%), 30% O2 and N2 as the balance gas using a gas mixer. After a steady state pH was reached, judged by the pH probe, four samples were taken simultaneously, and 3 replicate measurements with each of the four devices were made. The devices used in this study were the ABL 80 FLEX (RADIOMETER, blood gas analyzer), VetScan i‐STAT® 1, pH paper (Macherey‐Nagel, pH range 6.4 – 8.0) and a pH probe (OAKTON®, pH700). Measured pH values were plotted against the expected pH values for a given concentration of CO2 according to the Henderson–Hasselbalch equation (pH = pKa + log10 ([A−]/[HA]). Linear regression ± SEM was done for each device with and without BSA and the coefficient of determination and regression coefficients were calculated. The mean and difference of each measurement by device were then calculated and used to create Bland‐Altman plots (right lower corner in each panel) to assess the agreement of the measuring device with the expected pH.

Results

Except for the pH paper, all devices showed a strong agreement with the expected pH for each CO2 percentage. The addition of BSA to the solution resulted in a trend to more acidic readings and to be even more in agreement with the expected pH for all four devices.

Conclusion

The blood gas analyzer, i‐STAT®, and pH probe all proved to be suitable devices for use in measuring the pH of a balanced salt solution in the chosen pH range. The pH paper appeared to be unsuitable to measure the pH within physiological ranges. Additionally, throughout all measurements, the solutions with 4% BSA tended to provide even more accurate values than the solutions without BSA.

Support or Funding Information

This work was supported, in part, by institutional funds, NIH grant (5R01 HL123227), and a Merit Review Award (I01 BX003482) from the U.S. Department of Veterans Affairs Biomedical Laboratory R&D Service.

Regression lines for the measured pH with all devices compared to the expected pH and Bland‐Altman‐plots

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Regression lines for the measured pH with all devices compared to the expected pH and Bland‐Altman‐plots

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.