Lab Prep Calculations

Source: https://github.com/aipoch/medical-research-skills

When to Use

• Preparing a working solution from a concentrated stock and needing exact pipetting and solvent volumes.
• Planning a solid-to-solution preparation (weighing + dissolution) with molecular weight and purity corrections.
• Designing a serial dilution scheme when a single-step dilution factor is impractical or exceeds pipetting limits.
• Converting and preparing percentage-based solutions (w/v, v/v, w/w), including density-based mass-volume conversions.
• Generating an executable lab protocol (steps, equipment list, and warnings) before running an experiment.

Key Features

• Dilution calculations using C1V1 = C2V2, including solvent volume determination.
• Automatic suggestion/structuring of serial dilution steps when dilution factors are large.
• Solid preparation calculations using m = C × V × MW, with purity/content correction.
• Percentage concentration conversions (w/v, v/v, w/w) and density-aware conversions when applicable.
• Unit normalization (e.g., M/mM/µM; L/mL/µL) and sanity checks (e.g., V1 ≤ V2).
• Protocol-style outputs: calculation summary, step list, equipment/materials, and risk notes.

Dependencies

• None (documentation-only skill; no runtime dependencies specified).

Example Usage

Goal: Prepare 50 mL of 10 mM NaCl from a 1.0 M NaCl stock.

Inputs

• Target concentration (C2): 10 mM
• Target final volume (V2): 50 mL
• Stock concentration (C1): 1.0 M
• Solute/solvent: NaCl stock in water; dilute with water

Calculation (C1V1 = C2V2)

• Convert units: 1.0 M = 1000 mM
• ( V1 = \frac{C2 \times V2}{C1} = \frac{10\ \text{mM} \times 50\ \text{mL}}{1000\ \text{mM}} = 0.5\ \text{mL} )
• Solvent volume to add:
  • ( V_{\text{solvent}} = V2 - V1 = 50.0\ \text{mL} - 0.5\ \text{mL} = 49.5\ \text{mL} )

Executable Protocol

1. Label a clean 50 mL tube or volumetric container: "10 mM NaCl, 50 mL".
2. Pipette 0.50 mL of 1.0 M NaCl stock into the container.
3. Add ~45 mL of water and mix.
4. Bring to final volume by adding water to 50.0 mL total (or add 49.5 mL water if using a graduated vessel and not accounting for mixing losses).
5. Mix thoroughly (invert or stir) until homogeneous.

Equipment & Materials

• Micropipette (range covering 0.50 mL) and compatible tips
• 50 mL tube or volumetric flask/cylinder
• 1.0 M NaCl stock solution
• Water (or specified buffer)
• Marker/label

Checks / Warnings

• Ensure pipette accuracy at 0.50 mL (use an appropriate pipette range).
• Confirm the stock concentration and that the solvent/buffer matches experimental requirements.

Implementation Details

• Requirement confirmation

  • Target: concentration, final volume, solute, solvent/buffer.
  • Known parameters (as applicable): stock concentration, molecular weight (MW), purity/content, density.
  • Constraints: solubility limits, minimum weighable mass, pipetting range, available glassware.

• Dilution

  • Core equation: C1V1 = C2V2
  • Outputs: required stock volume V1 and solvent addition volume V2 − V1
  • Validation: enforce V1 ≤ V2; normalize units before computation.

• Serial dilution

  • Trigger: dilution factor too large for a single step (e.g., impractical pipetting volume or equipment limits).
  • Method: factor the overall dilution into multiple steps; for each step output:
    • step dilution factor
    • aliquot volume to transfer
    • solvent volume to add

• Solid preparation / dissolution

  • Mass from molarity: m = C × V × MW
  • Purity/content correction: m_adj = m / purity (purity as a fraction, e.g., 0.98)
  • Protocol notes may include dissolution aids (heating, sonication, pH adjustment) based on solubility/constraints.

• Percentage concentrations

  • Support conversions among w/v, v/v, w/w
  • If density is provided, perform mass-volume conversions to produce weigh/measure instructions.

• Verification and output formatting

  • Normalize units (M/mM/µM; L/mL/µL; g/mg).
  • Sanity checks: volumes non-negative; final volume matches target; step volumes within equipment ranges.
  • Output structure guidance and verification checklist: see references/guide.md.
  • Reusable structured output template: assets/lab_prep_calc_template.md.

When Not to Use

• Do not use this skill when the required source data, identifiers, files, or credentials are missing.
• Do not use this skill when the user asks for fabricated results, unsupported claims, or out-of-scope conclusions.
• Do not use this skill when a simpler direct answer is more appropriate than the documented workflow.