quantification of heavy metals in Active Pharmaceutical Ingredients (APIs), excipients, and finished pharmaceutical products using techniques such as ICP-MS, AAS, or colorimetric wet chemistry.

2. Scope

This SOP applies to the Analytical Method Development (AMD) department for testing heavy metals including lead, cadmium, arsenic, and mercury in raw materials and formulations, in accordance with pharmacopeial (USP <232>, <233>, IP) and ICH Q3D Elemental Impurities guidelines.

3. Responsibilities

• Analytical Scientist: Performs method development, sample digestion, instrumental analysis, and documentation.
• Reviewer: Verifies data accuracy and ensures adherence to specifications.
• QA: Reviews and approves method validation records and ensures compliance with regulatory standards.
• Head – AMD: Ensures method robustness, reproducibility, and readiness for regulatory submission.

4. Accountability

The Head of AMD is accountable for ensuring all heavy metals test methods are developed and validated in accordance with ICH Q3D and pharmacopeial requirements and are suitable for use in release and stability testing.

5. Procedure

5.1 Method Selection

1. Select appropriate technique based on required sensitivity and matrix:
   • ICP-MS (Inductively Coupled Plasma–Mass Spectrometry) – preferred for multi-elemental trace analysis
   • AAS (Atomic Absorption Spectrophotometry) – suitable for single-element analysis
   • Colorimetric Wet Chemistry (USP <231>) – legacy method, limited use
2. Define target elements and permitted daily exposure (PDE) limits per ICH Q3D.
3. Record rationale in Annexure-1: Method Development Justification Sheet.

5.2 Sample Preparation and Digestion

1. Weigh 100–500 mg of sample into a digestion vessel.
2. Add nitric acid (65%) or HNO₃/H₂O₂ mixture.
3. Digest using:
   • Microwave digestion (preferred)
   • Hot plate digestion (for simple matrices)
4. Cool and dilute to volume with Type I water.
5. Filter through 0.45 µm membrane if necessary.
6. Document process in Annexure-2: Sample Digestion Log.

5.3 Instrument Calibration and Setup

1. Prepare calibration standards for each element using traceable certified reference standards.
2. Run blank, standards, and system suitability (e.g., recovery from spike).
3. Verify R² ≥ 0.999 for linearity.
4. Perform instrument tuning and record performance in Annexure-3: Instrument Calibration Sheet.

5.4 Method Execution

1. Inject digested samples into ICP-MS/AAS and quantify against calibration curve.
2. For wet chemistry, compare sample color to standard lead/cadmium solution after hydrogen sulfide treatment.
3. Ensure analytical run includes:
   • Blank
   • Spiked recovery sample
   • Matrix-matched standard
4. Calculate elemental concentration (µg/g or ppm).
5. Document raw data and final results in Annexure-4: Heavy Metal Result Sheet.

5.5 Method Optimization

1. Optimize:
   • Digestion parameters (acid volume, temperature, duration)
   • Instrument parameters (RF power, nebulizer gas flow, etc.)
   • Matrix-matching of standards and samples
2. Perform trial runs to assess recovery and reproducibility.
3. Log optimization trials in Annexure-5: Optimization and Feasibility Record.

5.6 Method Validation

1. Validate per ICH Q2(R1) and USP <233>:
2. Specificity: Absence of interference in blank and placebo matrices.
3. Accuracy: Spike recovery 80–120% of known additions.
4. Precision: RSD ≤ 15% for 6 replicates.
5. LOD/LOQ: Based on standard deviation of blank (if applicable).
6. Linearity: 5 concentration levels; R² ≥ 0.999.
7. Robustness: Evaluate with slight changes in digestion conditions and instrument settings.
8. Summarize validation in Annexure-6: Validation Summary Report.

6. Abbreviations

• ICP-MS: Inductively Coupled Plasma–Mass Spectrometry
• AAS: Atomic Absorption Spectrophotometry
• PDE: Permitted Daily Exposure
• QA: Quality Assurance
• AMD: Analytical Method Development

7. Documents

1. Method Development Justification Sheet – Annexure-1
2. Sample Digestion Log – Annexure-2
3. Instrument Calibration Sheet – Annexure-3
4. Heavy Metal Result Sheet – Annexure-4
5. Optimization and Feasibility Record – Annexure-5
6. Validation Summary Report – Annexure-6

8. References

• ICH Q3D – Guideline for Elemental Impurities
• USP <232> – Elemental Impurities Limits
• USP <233> – Elemental Impurities Procedures
• Ph. Eur. 2.4.8 – Heavy Metals
• ICH Q2(R1) – Validation of Analytical Procedures

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Method Development Justification Sheet

Sample	Elements Targeted	Technique Selected	Reason	Prepared By
API-A	Pb, Cd, As, Hg	ICP-MS	Trace-level detection	Sunita Reddy

Annexure-2: Sample Digestion Log

Date	Sample	Acid Used	Digestion Method	Analyst
03/05/2025	Excipent-B	HNO3/H2O2	Microwave	Ajay Mehra

Annexure-3: Instrument Calibration Sheet

Element	Concentration Range (ppb)	R² Value	Status
Lead (Pb)	0–100	0.9996	Pass

Annexure-4: Heavy Metal Result Sheet

Sample	Element	Observed (µg/g)	Limit (µg/g)	Status
API-A	Cd	0.43	0.5	Pass

Annexure-5: Optimization and Feasibility Record

Parameter	Condition	Observation	Conclusion
Digestion Temp	190°C	Complete digestion	Accepted

Annexure-6: Validation Summary Report

Parameter	Acceptance Criteria	Results	Status
Precision	RSD ≤ 15%	10.2%	Pass
Accuracy	80–120%	98.6%	Pass

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Incorporated ICH Q3D elements and ICP-MS optimization	Regulatory Alignment