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The Role of Internal Standards and their Interaction with Soils Impact Accuracy of Volatile Organics Determinations
Citation:
HIATT, M. H. The Role of Internal Standards and their Interaction with Soils Impact Accuracy of Volatile Organics Determinations . ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 90(8):591-604, (2010).
Impact/Purpose:
The level of uncertainty in environmental analyses is of concern for those who use analytical data to make environmental decisions [1, 2]. Soil is a complex medium that can influence the behavior of volatile organic analytes (VOAs) as general matrix effects (such as organic phase uptake), biological activity and even varying kinetics (fast and 10 slow) adding to the difficulty in assessing the viability of VOA determinations [3, 4]. Soil has been difficult to prepare as a reference material for VOAs. Researchers have used vapor addition of analytes to dry soils for developing performance soils [5]. It has also been found that volatile analytes react with the reference soil matrix after their addition [6]. Just how the soil matrix might impact the accuracy of volatile organic determinations is poorly understood.
Description:
Both US Environmental Protection Agency (EPA) SW-846 Methods 8260C/5035 and 8261A include mixing soil with water and addition of internal standards prior to analyses but the equilibration of internal standards with the soil is not required. With increasing total organic carbon (TOC) and no effort to equilibrate internal standards with the matrix, results are less likely to be accurate. Adding internal standards to soils prior to diluting the sample with water gives more accurate determinations but less reliable quality control (QC). Extending times for equilibration of internal standards improves accuracy but is conducive to analyte degradation not normally observed during analyses. Soil-matrix effects on analytes can be greatly understated using a single internal standard as described in Method 8260C while the use of multiple internal standards as described in Method 8261A is more accurate. Method 8261A’s reporting error when spiking soils before adding water provides confidence intervals with accuracy near the experimental rule (75.2, 95.7, and 99.5%) with the exception of two analytes that require overnight equilibration.