PQL: Practical Quantitation Limit
The lowest concentration that can be reliably achieved within specified limits of precision and accuracy during routine laboratory operating conditions. For many analytes, the PQL is the lowest non-zero standard in the calibration curve.

MDL: Method Detection Limit
Minimum concentrations of a substance that can be measured and reported with 99% confidence that the value is above zero. The sample is carried through the entire method under ideal conditions. This is performed on an annual basis by the laboratory.

where:	S	Standard deviation of the replicate analyses.
		the Student’s t-value appropriate to a 99% confidence level and a standard deviation estimate with n -1 degrees of freedom.

M: Matrix
The component or substrate (e.g., surface water, drinking water, soil) which contains the analyte of interest.

LCS: Laboratory Control Sample
A known matrix spiked with compound(s) representative of the target analytes. This is used to document laboratory performance. The LCS must be a secondary source.

MS: Matrix Spike
An aliquot of sample spiked with a known concentration of target analyte(s). The spiking occurs prior to sample preparation and analysis. A matrix spike is used to document the bias of a method in a given sample matrix.

MSD: Matrix Spike Duplicate
A second aliquot of the same matrix as the matrix spike that is spiked in order to determine the precision of the method.

MB: Method Blank
An analyte-free matrix to which all reagents are added in the same volumes or proportions as used in sample processing. The method blank should be carried through the complete sample preparation and analytical procedure. The method blank is used to document contamination resulting from the analytical process.

RPD: Relative Percent Difference
The ratio of the difference of two readings over its average. This is a means of determining the precision between two numbers.

QA: Quality Assurance
A planned system of activities (program) whose purpose is to provide assurance of the reliability and defensibility of the data.

QC: Quality Control
A routine application of procedure for controlling the monitoring process. QC is the responsibility of all those performing the hands-on operations in the laboratory.

Accuracy
The nearness of a result or the mean of a set of results to the true or accepted value.

Precision
Measure of the reproducibility of a set of replicate results among themselves or the agreement among repeat observations made under the same conditions.

Initial Calibration
Analysis of analytical standards for a series of different specified concentrations; used to define the linearity and dynamic range of the response of the detector to the target compounds.

Continuing Calibration
Analytical standard run to verify the initial calibration of the system at a specified time frame.

%R: Percent Recovery
The numerical ratio of the amount of analyte measured by the laboratory method divided by the known amount of analyte added to the matrix to be analyzed.

%D: Percent Difference
To compare two values, the percent difference indicates both the direction and magnitude of the comparison, i.e, the percent difference may be either negative, positive, or zero.

SD: Standard Deviation
The square root of the variance of a set of values.
S =

Contamination
A component of a sample or an extract that is not representative of the environment source of the sample. Contamination may stem from other samples, sampling equipment, while in transit, from laboratory reagents, laboratory environment, or analytical instruments.

USEPA, Contract Laboratory Program, Statement of Work for Organic Analysis,
Multi-Media, Multi-Concentration, OLM03.0.

USEPA, Contract Laboratory Program, Statement of Work for Inorganic Analysis,
Multi-Media, Multi-Concentration, ILM04.0.

USEPA, Test Methods for Evaluating Solid Waste,
Chapter 1 - Quality Control, Volume 1B, Update IIIB, July 1992.