2.3 Field Methods
57
2.3.2 Sample Collection
Sample bottles should be labeled using label tape and indelible ink. Information
on the bottle label should also be recorded on a multipart chain-of-custody
record (provided in Appendix D), along with information about the desired
analyses and the identity of the sample collector. A field logbook should be
kept in which station identification codes, date and time of sampling, and all
field data are recorded. Notes on any unusual conditions at the sample sites or
any circumstances that may have caused deviation from normal procedures
should be recorded on the Lake or Stream Water-Sampling Record (provided
in Appendix D) and described in the field data logbook.
Each sample should be labeled uniquely with site identifier, date, and sample ID/bar code in the field. An additional lab number is typically added at a
later time to each aliquot in the laboratory. The sampler completes the process of filling out the bottle label at the time of sample collection. The chainof-custody record form should include sample name, date, time of day, tests
requested, comments, and appropriate signatures. Collection time should
include whether the time recorded was daylight savings time or standard time.
Most electronic data recording, including stream stage, is recorded in standard time, year-round. Therefore, this information is needed to relate the water
sample to the electronic data.
Water sample aliquots should be collected in the field in sealed syringes or
glass bottles with septum caps for some analytes to minimize contact with the
atmosphere in the event that the dissolved CO 2 partial pressure is considerably
higher than that of the atmosphere. This is a common occurrence in surface
waters. Collection into a bottle having a septum cap is done by immersing and
capping the bottle under water. Syringes or bottles with septum caps are used
because the concentration of some analytes can change if the water sample
equilibrates with atmospheric carbon dioxide partial pressure prior to analysis. DIC concentrations and pH are the measurements that are typically analyzed without contact with the atmosphere. Monomeric Al measurements are
also sometimes made in this way, although the effects of CO 2 degassing on Al
measurements are expected to be small. We therefore do not recommend collection of sample aliquots for Al analysis in syringes or septum-capped bottles.
We do, however, recommend that aliquots of samples be collected in
syringes or glass bottles with septum caps along with the standard bottles, and
that the syringe or septum-capped samples be used for analysis of pH and DIC.
This precaution is considered to be more important for streams than it is for
epilimnetic samples from lakes. If samples for these analyses are collected into
bottles (with or without septum caps) in the field, it is especially important that
no headspace be left in the bottle (fill completely to top) and that laboratory
procedures limit the opportunity for CO 2 degassing in the laboratory prior to
57
2.3.2 Sample Collection
Sample bottles should be labeled using label tape and indelible ink. Information
on the bottle label should also be recorded on a multipart chain-of-custody
record (provided in Appendix D), along with information about the desired
analyses and the identity of the sample collector. A field logbook should be
kept in which station identification codes, date and time of sampling, and all
field data are recorded. Notes on any unusual conditions at the sample sites or
any circumstances that may have caused deviation from normal procedures
should be recorded on the Lake or Stream Water-Sampling Record (provided
in Appendix D) and described in the field data logbook.
Each sample should be labeled uniquely with site identifier, date, and sample ID/bar code in the field. An additional lab number is typically added at a
later time to each aliquot in the laboratory. The sampler completes the process of filling out the bottle label at the time of sample collection. The chainof-custody record form should include sample name, date, time of day, tests
requested, comments, and appropriate signatures. Collection time should
include whether the time recorded was daylight savings time or standard time.
Most electronic data recording, including stream stage, is recorded in standard time, year-round. Therefore, this information is needed to relate the water
sample to the electronic data.
Water sample aliquots should be collected in the field in sealed syringes or
glass bottles with septum caps for some analytes to minimize contact with the
atmosphere in the event that the dissolved CO 2 partial pressure is considerably
higher than that of the atmosphere. This is a common occurrence in surface
waters. Collection into a bottle having a septum cap is done by immersing and
capping the bottle under water. Syringes or bottles with septum caps are used
because the concentration of some analytes can change if the water sample
equilibrates with atmospheric carbon dioxide partial pressure prior to analysis. DIC concentrations and pH are the measurements that are typically analyzed without contact with the atmosphere. Monomeric Al measurements are
also sometimes made in this way, although the effects of CO 2 degassing on Al
measurements are expected to be small. We therefore do not recommend collection of sample aliquots for Al analysis in syringes or septum-capped bottles.
We do, however, recommend that aliquots of samples be collected in
syringes or glass bottles with septum caps along with the standard bottles, and
that the syringe or septum-capped samples be used for analysis of pH and DIC.
This precaution is considered to be more important for streams than it is for
epilimnetic samples from lakes. If samples for these analyses are collected into
bottles (with or without septum caps) in the field, it is especially important that
no headspace be left in the bottle (fill completely to top) and that laboratory
procedures limit the opportunity for CO 2 degassing in the laboratory prior to