Hemoglobin P50 from the Dissociation Curve

Standard pH / T / pCO₂. Measure saturation S at several pO₂ and recover P50 from a Hill linearization: ln(S/(1−S)) versus ln pO₂.

University / research· 22 min·Related simulator: Biophysics, Fluids & GeoscienceOxygen-Hemoglobin Dissociation Curve

Goal

Determine P50 from S = pO₂ⁿ / (P50ⁿ + pO₂ⁿ). A plot of ln(S/(1−S)) versus ln pO₂ has intercept −n ln P50, so P50 = exp(−intercept / slope).

Equipment

Blood tonometer
Oximeter
pO₂ control
Standard pH / T / pCO₂

Experiment

Blood tonometer at standard conditions. No live S on the bench — the oximeter answers only after you record.

Standard conditions are fixed: pH 7.40, 37 °C, pCO₂ 40 mmHg. Half-saturation and the Hill order are not shown on the bench. You only change pO₂.

Partial pressure pO₂pO₂ = 27 mmHg

Oximeter: no reading

Record at least 6 points. Keep measured S roughly in the range 0.15–0.85.

Measurements

№	pO₂ mmHg	S	ln(S/(1−S))	ln pO₂
No measurements yet — take your first reading.

Data processing

Add at least 2 measurements to compute the fit.

Uncertainty

Lab report

Opens the system print dialog — choose “Save as PDF” or your printer. Header and footer are hidden when printing.

One click opens the print dialog — choose “Save as PDF”.

Hemoglobin P50 from the Dissociation Curve

Generated: 24 Aug 2026, 22:28

Goal

Determine P50 from S = pO₂ⁿ / (P50ⁿ + pO₂ⁿ). A plot of ln(S/(1−S)) versus ln pO₂ has intercept −n ln P50, so P50 = exp(−intercept / slope).

Measurement table

#	pO₂ (mmHg)	S	ln(S/(1−S))	ln pO₂
No measurements yet — take your first reading.

Fit and derived value

Add at least 2 measurements to compute the fit.

Conclusion

The fitted P50 agrees with the hidden standard adult value. Main uncertainties: oximeter noise and the Hill-equation idealization.

PhysSandbox virtual lab — values come from your session; add your own discussion of error sources.

Theory

The Hill plot is linear in log–log coordinates. The bench hides effective P50, n and any “right/left shift” label. Conditions are standard (pH 7.40, 37 °C, pCO₂ 40 mmHg) so you recover the usual adult P50.

Procedure

pH, temperature and pCO₂ are fixed at standard values. P50 is hidden. You only change pO₂.
Record the oximeter saturation S (as a fraction). Small noise is added. There is no live P50.
The notebook computes ln(S/(1−S)) and ln pO₂. Use points with S roughly between 0.15 and 0.85.
Repeat for at least 6 oxygen tensions from about 12 to 70 mmHg.
Fit the Hill plot; P50 = exp(−intercept / slope). Compare with the reference.

Conclusion

The fitted P50 agrees with the hidden standard adult value. Main uncertainties: oximeter noise and the Hill-equation idealization.