*Analytical Chemistry - Advancement, Perspectives and Applications*

The two size alleles of human keratin 1 are due to a deletion in the glycine-rich carboxyl-terminal V2-subdomain. Journal of Investigative Dermatology. **99**:697-702.

[47] Korge, B. P., Gan, S. Q., McBride, O. W., Mischke, D., and Steinert, P. M. (1992b) Extensive size polymorphism of the human keratin 10 chain resides in the carboxy-terminal V2-subdomain due to variable numbers and sizes of glycine loops. Proceedings of the National Academy of Sciences**. 89**:910-914.

**197**

**Chapter 11**

**Abstract**

studies

**1. Introduction**

Considerations for Stability of

for Long-Term Studies

ation by the environmental research community.

surface water and drinking water [3–10].

position, chemical transformation, or loss/gain.

Environmental Samples in Storage

*Susan Marie Viet, Maire S.A. Heikkinen and Michael Dellarco*

It is often advantageous to store collected environmental samples for future retrospective analyses. However, information about sample stability is necessary to determine if there will be analyte loss or gain or degradation under the specified storage conditions and storage period. Failure to evaluate stability could result in inaccurate results and biased exposure assessments. As part of the National Children's Study pilot, we considered which types of environmental samples could be stored for extended periods of time. We conducted an extensive literature review and considered the conduct of long-term stability studies for environmental samples. We present our findings and experience below as guidance for consider-

**Keywords:** Sample stability, Sample storage, Environmental samples, Long-term

For long-term environmental studies, such as for prospective epidemiology studies, it is often advantageous to store collected environmental samples for future retrospective analyses. Traditionally, stored environmental samples have included human tissue and fluids, animal and plant tissues, soils, sediments, and ice cores [1]. Such samples can be used to evaluate results of government policies, health of an animal population, or temporal trends in ecosystems or exposures [2]. In longitudinal studies, this also permits spreading costs of analyses over time – an important consideration as analysis for environmental contaminants can be expensive. Additionally, it provides more flexibility to analyze subsets of samples in nested case–control studies for specific health outcomes or for inclusion of new target analytes or analysis methods. For instance, concern about the presence of pesticides, pharmaceuticals and personal care products (PPCPs) has heightened over the past several years due to the presence of these chemicals in wastewater, groundwater,

Information about sample stability in long-term studies is critical to determine, if there will be analyte loss or gain or degradation under specified storage conditions and storage period. Failure to evaluate stability could result in inaccurate results and biased exposure assessments due to partial or complete analyte decom-
