Biology Reference
In-Depth Information
between samples. Because it is important to ensure that all collagen-preparation glassware is
free of carbon from one sample to the next, it is important to thoroughly clean each piece after
each use. While multiple approaches for mitigating reuse exist, an effective method involves
rinsing each piece of glassware in a sulfuric acid bath and then heating each piece in
a commercial kiln used for firing ceramics (S. Ambrose, personal communication, 2007).
An ideal laboratory setup might involve dedicating two distinct spaces for staging
collagen and biological apatite extractions. In this setting, a “dry lab” would be dedicated
for preliminary processing of samples. For example, if archaeological matrix is present, it
is removed in the dry lab under a dedicated fume hood. Samples might be ground or
drilled to a powder in this space and then removed to the “wet lab” for chemical
treatment.
Once all wet chemistry is complete, all samples must be analyzed on a mass spectrometer,
typically in dedicated core facilities having specialists with expertise in
mass spectrometry.
Stable Isotopes and Mass Spectrometry
In typical projects that involve analysis of stable isotopes, the step following collagen and
biological apatite extraction utilizes instrumentation called
isotope ratio mass spectrometers
(IRMS).
The IRMS typically have four components: a combustion chamber, an ion source,
a mass analyzer, and series of ion detectors. These components act to detect subtle differences
in various isotopes, for example
13
C and
12
C, by initially combusting the sample and then
automatically transferring the converted gas into the mass spectrometer for analysis. Upon
entering the mass spectrometer, the gas is ionized so that it can be directed into the mass
analyzer where it is measured against known standards in the ion detectors (sometimes
called Faraday collectors). Interested skeletal biologists are encouraged to consult other sour-
ces for more detailed descriptions of the process of analyzing samples via IRMS (i.e.,
Barrie
and Prosser, 1996; Katzenberg, 2008; Brown and Brown, 2011
). Moreover, to fully understand
the complexities of the instrumentation, and to perhaps gain experience operating this type
of laboratory equipment, individuals are encouraged to seek out specialists to gain practical
skills in this area, even if this means temporarily relocating, taking an additional course
outside of the traditional skeletal biology curriculum, or volunteering as a laboratory assis-
tant at any IRMS core facility.
In addition to understanding the basic principles of the IRMS, skeletal biologists should
have some awareness about how stable isotope ratios are calculated on the mass spectrometer.
As mentioned above, the mass spectrometer analyzes both the sample and a known
standard. The standards are regulated on an international level by such agencies as
the United States National Institute of Standards and Technology (NIST), sometimes referred
to as the National Bureau of Standards (NBS), and by the International Atomic Energy
Agency (IAEA). A list of common standards can be found by accessing the following website:
any IRMS core facility will be well versed in NIST/IAEA standards and interested
researchers should familiarize themselves with the protocols of their particular laboratory.
As research projects progress beyond the analytical stage to scientific presentations and publi-
cations, explicitly discussing which standards were used in any stable isotope project is
compulsory.
