Field samples - CR98_020018

Feasibility of SPE and GC-ECD for explosives

Table 11. Recovery and repeatability of GC and HPLC determinations of analyte concentrations in spiked water samples

CR98_02
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Table 10. Effect of residual water in acetonitrile on peak heights of

various analytes.

Mean peak height (n = 2)

5% water 10% water 15% water

Figure 6. TNT peak heights for acetonitrile solutions containing

10% water vs. solutions without water. Concentrations of TNT were

2.5, 5, 10, 20, and 30 g/L.

prior to analysis.) We found good recovery for all

Problems such as low recovery of the nitramines

the analytes by both methods. In general, repeat-

and interfering peaks in HPLC chromatograms

ability was better using HPLC-UV. Overall, the

have been solved (Jenkins et al. 1995). We per-

formed an initial spike recovery study using the

results indicated that SPE with acetonitrile elu-

two SPE protocols that are expected to be includ-

tion was a feasible sample preparation procedure

ed in SW-846 Update IV for Method 8330A. These

prior to GC-ECD.

protocols specify preconcentration with Empore

SDB-RPS (47-mm-diameter) disks or the Water

Field samples

Sep-Pak Vac Porapak RDX cartridges, and analyte

We analyzed several solid-phase extracts of

elution with acetonitrile. The purpose of this ini-

water samples collected from various explosives-

tial spike recovery was to determine whether a

contaminated sites. These included extracts from

solid-phase extract prepared for analysis by

LAAP in which 500-mL samples were preconcen-

Method 8330 could also be analyzed by GC-ECD.

trated using Porapak RDX cartridges and eluted

Using both disks and cartridges, we precon-

with 5 mL acetonitrile. These extracts were pre-

centrated duplicate 50-mL samples spiked at

pared and analyzed by HPLC at the U.S. Army

5-g/L aqueous concentration for most of the

Engineer Waterways Experiment Station (Vicks-

analytes (Table 11). We divided each 5.0-mL ace-

burg, Mississippi). Water samples from Umatilla

tonitrile extract and analyzed each by GC-ECD

Army Depot and CFB-Valcartier were precon-

and HPLC-UV. (The portion of acetonitrile extract

centrated at CRREL using either cartridges or Em-

used for HPLC was mixed 1/1 v/v with water

pore disks, with the HPLC analysis performed at

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