Source: https://guthlabs.ai/docs/instruments/ph-henderson-hasselbalch-calculator/mechanism/

instrument mechanism / verified-clean

# pH / Henderson-Hasselbalch Calculator mechanism

The inspectable method record for pH / Henderson-Hasselbalch Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The chemistry formula is valid under its stated assumptions, and the existing educational/not-medical-advice label is appropriate. Review is required to define the buffer-capacity note and to specify whether blood calculations accept dissolved CO2 concentration or PCO2, including the required units and coefficient.

- pH=pKa+log10([A-]/[HA]) is the standard Henderson-Hasselbalch equation for a conjugate acid-base pair, provided the ratio is dimensionless and concentrations are positive.

- The claimed 'buffer capacity note' has no definition or formula, so that output cannot be verified or reproducibly generated.

- The phrase 'acid-base blood parameter estimate' is ambiguous: clinical bicarbonate systems commonly use pH=6.1+log10([HCO3-]/(0.03×PCO2)) when PCO2 is supplied in mmHg, whereas the stated concentration-ratio formula requires dissolved CO2 concentration as [HA].

## Units and conventions

- log means base-10 logarithm.

- [A-] and [HA] must be expressed in the same concentration units, or converted before division; their ratio is dimensionless.

- pKa is dimensionless and must correspond to the specified acid-base pair and relevant temperature, ionic strength, and chemical conditions.

- For bicarbonate blood calculations using PCO2 rather than dissolved CO2 concentration, the applicable coefficient and PCO2 units must be explicitly specified.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "pKa": 4.76,
    "conjugate_base": "0.100 mol/L acetate",
    "conjugate_acid": "0.100 mol/L acetic acid"
  },
  "expected_outputs": {
    "pH": 4.76
  },
  "working": "A-/HA = 0.100 mol/L ÷ 0.100 mol/L = 1. pH = 4.76 + log10(1) = 4.76 + 0 = 4.76."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

A zero conjugate-acid concentration causes division by zero, making the pH undefined; the instrument must reject the input rather than force a numeric result. There is also a convention hazard if the ratio direction or logarithm base is not made explicit.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/ph-henderson-hasselbalch-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/ph-henderson-hasselbalch-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/ph-henderson-hasselbalch-calculator/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`