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Summary Report Hair Analysis Panel Discussion Exploring The State Of The Science

Hair Analysis Panel Discussion: Section 3.4

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Section 3
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 (MG).

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.

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