Sample Transport and Storage - Field Sampling: Principles and Practices in Environmental Analysis - page 205

Negative/blank A sample known not to contain the component of interest is included with
samples collected in the field. Can be either a field or trip blank.

Positive
(spiked)

A sample that contains more component of interest than is commonly found in
samples.

Surrogate A sample containing a compound similar to that of interest is included with

samples.

Reference Soil samples taken from similar soil in a different location known not to be

contaminated with the component of interest.

and storage procedures. Three other common types of controls are the negative and
positive or spiked (component of interest is added to the sample) and a sample containing
a surrogate compound.
A negative control would contain all the components found in the sample except the
one of interest and can be of two types—field and transport. A field control follows the
whole path of samples, while transport controls are used as checks of the transportation
portion of the path of samples to the commercial laboratory. These allow for isolation of
the source of contamination problems if they occur. Negative controls are important for
two reasons. If they contain any of the component of interest serious contamination has
occurred, and this is the most serious concern. Any component detected in the negative
control that was not present originally also indicates a serious problem, however, and
makes the samples suspect. In such cases the analytical results should only be used after
verification by using other samples that they are representative of the field conditions.
A positive control contains the component of interest in a known concentration. If a
positive control has less of the component than it did in the field, it has lost material.
Again this means that all the samples taken, stored, and transported with this sample have
probably lost some of this component. One nice aspect of positive controls is that if they
all show a similar loss this can be used to estimate the loss from the samples. In this way
the original concentration of the component of interest in the samples can be estimated.
The sample information thus obtained may be useful; however, such samples and their
analytical results must be used with caution due to estimating the concentration of
components of interest using a “fudge” factor.
In some cases a surrogate is added to samples in place of the actual component of
interest. This is done when the component of interest is particularly toxic or otherwise
hard to handle. The surrogate is similar to the component of interest both chemically and
physically. Again it is assumed that if the surrogate concentration is unchanged during
storage and transportation, no loss of sample has occurred.
As discussed in previous chapters, controls consisting of samples adjacent to the
contaminated area need to be taken and sent through the storage and transportation
process. Also included would be samples from similar soils that are not from adjacent
areas. Both of these types of controls need to go through the same process.
Another type of control to consider is the archived sample. These are samples from
each step or stage of the sampling plan that are stored for later reference. They are
extremely useful if a question about analytical results or transport conditions arises later