Hair Analysis Panel Discussion: Section 3.4
3.4 Other Methodological Considerations
The group discussed a number of other issues that influence the analytical results and should be considered when choosing methods and evaluating analytical data.
What amount of hair is needed for reliable analyses?
CDC has used between 500 and 1,000 milligrams of hair in its studies
(DP). Another panelist commented that the amount selected depends
on the analytical method used, but he is more accustomed to sample
sizes in the 50 milligram range (TC). Down the road, there may be
an interplay between the sensitivity of the method and the quantity
of hair needed for analysis.
To what extent should multi-element analytical approaches be used? The group agreed that a targeted (single-chemical) approach is preferable when analyzing hair for a particular environmental contaminant. The analytical method selected needs to be considered in the specific context of the substance and exposure situation under evaluation; both time and element need to be targeted (RB, MG, MK).
Serious interference problems can exist with instruments that
test for a spectrum of metals (e.g., ICP instruments) (DP). According
to one panelist's observations, laboratories do not always appear
to account for these interferences: inconsistencies in approaches
are seen across laboratories using ICP-MS and ICP-OES (SS). When
performing OES, one must take a lot of care in choosing the emission
wavelength used in the measurement. Interferences from other elements
can occur and must be considered. This is particularly true when
one uses ICP-MS for elements with masses less than 80. Peaks can
be the result of molecules made in the process of generating the
ions. These can interfere with the peaks you are trying to measure
(e.g., argon chloride and arsenic, both with nominal masses of 75
atomic mass units). A high-resolution MS, however, can resolve two
such peaks (DP).
Other interferences. Metals in acid solutions, as well
as paint, dusts, gloves, etc. in the laboratory setting can be detected
by the instruments used for hair analysis. Looking at low-level
metals in a hair sample is therefore not a simple exercise (RB).
These interferences might potentially overwhelm the amount that
you may be seeking to measure in the hair sample (MK).
What about organic compounds? A hair assay for benzene
is being developed that is evaluating metabolic products in hair
(data are proprietary). Such an assay may have a great impact on
determining the feasibility of using hair analysis for organic chemicals
Quality assurance and quality control. It is the responsibility of the laboratory to demonstrate its quality control procedures, such as standardizing procedures, running blank measurements, calibrating equipment, and verifying measurements externally through proficiency testing programs.