Sampling and Laboratory Analysis for Solvent Stabilizers - Environmental Investigation and Remediation - page 201

4.3.5 A ZEOTROPIC D ISTILLATION
EPA Method 5031 uses azeotropic distillation to separate nonpurgeable, water-soluble, and VOCs,
such as 1,4-dioxane, in aqueous samples or leachates from solid matrices. An azeotrope is a liquid
mixture of two or more substances that behaves like a single substance: it boils at a constant tem-
perature, and its vapors have a constant composition. 1,4-Dioxane forms a homogeneous pressure-
maximum azeotrope with water in a completely miscible system at 87.8°C where 1,4-dioxane
comprises 47.2% of the vapor-phase mass (Lide, 2008). Azeotropic distillation capitalizes on the
ability of selected organic compounds to form binary azeotropes with water to facilitate separation
of the compounds from a complex matrix. Extraction by azeotropic distillation was used as early as
1992 for the analysis of 1,4-dioxane (Bruce et al., 1992). After 2 min of fractional distillation of the
40 mL samples, the i rst 100 L of distillate was collected for analysis by GC-FID. Recoveries

were determined by comparison with standards injected directly prior to distillation. An MDL of
7 ppb was achieved for 1,4-dioxane. Azeotropic microdistillation was judged superior to the PT
extraction method for analysis of water-soluble VOCs (Bruce et al., 1992). EPA Method 8015 for
VOC analysis by GC-MS uses Method 5031, azeotropic distillation, as a preparatory step. Methods
reporting limits for 1,4-dioxane analyzed following the standard application of EPA Method 8015B
are summarized in Table 4.4 (from USEPA, 2006c).

μ

4.3.6 S AMPLE E XTRACTION
EPA Method 5035 is used in most analyses of solid environmental samples (soil and other solid
media) for solvent extraction of organic compounds with methanol. The solvent and surrogates used
to calibrate the GC-MS instruments are added to the soil sample at the same time. For soils with
low concentrations of the water-soluble target analytes ( g/kg), 5 mL of reagent grade water

is added to a weighed soil sample together with surrogates and internal standards, prior to proceed-
ing with PT.

< 200 μ

4.3.6.1 Liquid-Liquid Extraction
Liquid environmental samples require a protocol different from that used for solid samples. Method
3510C, separatory funnel liquid-liquid extraction (separatory funnel LLE), and Method 3520C,

TABLE 4.4
Results of EPA Method 8015B for Analysis of 1,4-Dioxane at Different Concentrations
and in Different Sample Types

Low Concentration
(25 μg/L)

Medium Concentration
(100 μg/L)

High Concentration
(750 μg/L)

Sample Type Recovered (%) RSD (%) Recovered (%) RSD (%) Recovered (%) RSD (%)

Groundwater 124 16 96 10 99 8

TCLP leachate 103 20 103 16 102 7

Solid matrices 106 a 19 a 105 b 10 b - -

Source: U.S. Environmental Protection Agency (USEPA), 1996a, Method 8015B: Non-halogenated organics using GC/
FID. U.S. Environmental Protection Agency.
Notes: Method detection limits for 1,4-dioxane in 25 μg/L spiked samples of aqueous matrices: reagent water—12 ppb,
groundwater—15 ppb; TCLP leachate from aqueous matrix—16 ppb. All values at each concentration of nonpurge-
able volatiles are the average from seven replicate analyses by azeotropic microdistillation (EPA Method 5031).
TCLP = Toxicity Characteristic Leaching Procedure, an EPA extraction protocol. RSD = relative standard deviation.

a Incinerator ash (low concentration; 0.5 mg/kg).
b Kaolin (medium concentration; 25 mg/kg).