In analytical science, precision is non-negotiable. Yet, one silent contaminant can distort results and jeopardize data integrity — carryover.

What is Carryover?
Carryover is the unintentional transfer of analyte from one sample injection to the next. Even trace residues can cause:

False positives

Inflated concentrations

Poor reproducibility

Regulatory non-compliance

Where Does It Come From?

Autosampler needle – inadequate washing

Syringe/injection port – especially in GC

Tubing and valves – adsorptive surfaces

Column or detector flow cell – strong retention

MS ion source – memory effects in LC-MS/MS

How to Detect It

Inject blanks after high-concentration samples

Watch for baseline drift or ghost peaks

Apply bracketing standards during validation

How to Prevent It

Use strong wash solvents with multiple rinses

Run a blank between critical samples

Select low-adsorption components (e.g., PTFE tubing)

Optimize autosampler wash/dwell times

Use column backflush or switching valves in GC

Apply divert valves or clean the source in LC-MS

Regulatory Perspective
Carryover evaluation is a required step in method validation as per ICH Q2(R1) and FDA/EMA guidelines.

Key Takeaway
Carryover may be subtle, but its consequences are serious. Prevent it with proper cleaning, smart method design, and strict validation practices.

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