
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 nonzero 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 tvalue 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 analytefree 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.
where: 
C1 = the larget of the two observed values
C2 = the smaller of the two observed values 


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 handson 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 =
where: 
S = Standard Deviation
Yi = measured value of replicate
Y = mean of replicate measurements
n = number of replicates 


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. 