When you receive your analytical report, you might notice several additional quality assurance and quality control (QA/QC) samples listed alongside your project data. These quality checks are not just routine - they are critical for validating data integrity, identifying potential interferences, and demonstrating defensibility in environmental decision-making.
Below is a closer look at the most common QA/QC samples analyzed in environmental laboratories and what they can tell you about your data quality.
Matrix Spike (MS) and Matrix Spike Duplicate (MSD)
A Matrix Spike (MS) is an actual field sample spiked with known concentrations of target analytes before sample preparation and analysis. This test evaluates how the sample’s unique matrix may affect recovery and accuracy. A Matrix Spike Duplicate (MSD) is a second spiked sample prepared in the same way, used to assess precision and reproducibility. The Relative Percent Difference (RPD) between the MS and MSD results provides a quantitative measure of consistency. Together, MS/MSD recoveries and RPD values help determine whether any matrix effects are influencing analytical performance.
Laboratory Control Sample (LCS) and Laboratory Control Sample Duplicate (LCSD)
The Laboratory Control Sample (LCS) is prepared using a clean control matrix—typically deionized water or a uniform material such as sand—spiked with target analytes. This test demonstrates the laboratory’s ability to accurately recover analytes when matrix effects are absent. The Laboratory Control Sample Duplicate (LCSD) is a replicate of the LCS used to confirm analytical precision. Comparing LCS and LCSD results through RPD and recovery limits ensures that the analytical process remains in statistical control.
Surrogate Spikes
Surrogate spikes are compounds added to organic samples analyzed by GC, GC-MS, or HPLC methods. They behave similarly to target analytes during extraction and analysis but are not typically found in the environment. Surrogate recovery results provide a direct measure of method performance for each sample, indicating both laboratory accuracy and potential matrix interference.
Method Blanks
A method blank consists of a contaminant-free matrix (such as deionized water) processed alongside your project samples. Method blanks verify that the entire preparation and analytical process is free from contamination. Ideally, all results in the method blank should be non-detect. Detectable concentrations may suggest potential laboratory contamination and prompt data review.
Field Duplicates
Field duplicates are collected at the same location and time as the primary sample to check the precision and consistency of the sampling and analysis processes. It is used to assess field variability and ensure reliable results. Field duplicates are typically handled and analyzed as separate samples independently, as a quality tool to document the accuracy of the sampling method and the analytical procedures.
Equipment Rinse Blanks
An Equipment Rinse Blank is a volume of laboratory-grade water that is used to rinse sampling equipment after decontamination. The rinse water is collected and tested to verify that sampling equipment is not contaminated. Equipment blank samples are collected to verify the effectiveness of the decon procedures on sampling equipment. The resulting rinse water is submitted for analysis to verify that the decon process was effective and that no carryover contamination remains from previous samples. Elevated results in an equipment rinse blank can indicate inadequate decontamination and the potential for false positives in field samples.
Field Blanks
Field blanks are typically prepared using laboratory-supplied, contaminant-free water and are opened and handled at the sampling site — but no environmental sample is collected. Field Blanks are collected to check for cross-contamination that may occur during sample collection, processing, and transport. Field blanks are processed and analyzed for the same parameters as field samples. If a field blank shows elevated results, it may indicate cross-contamination and trigger data qualification or resampling.
Why QA/QC Samples Matter
Each QA/QC component serves as a checkpoint in the analytical process, ensuring the data you receive are both accurate and defensible. Understanding these results allows environmental professionals to:
Assess the reliability of reported data,
Identify possible matrix or contamination issues, and
Make informed decisions based on sound analytical evidence.
Merit Laboratories’ QA/QC program is designed to meet regulatory requirements and provide clients with transparent, defensible data. If you have questions about interpreting QA/QC results or would like more information about our quality program, please contact our team.
Merit Laboratories is one of the nation’s leading environmental testing laboratories, analyzing air, soil, wastewater, groundwater, drinking water, and other sample matrices for a diverse range of analytical parameters. Merit is designated as a Small Business Enterprise (SBE) and Woman-Owned Business Enterprise (WBE).