Table 5. Syringe dilution study--precision and accuracy

Table 5. Syringe dilution study--precision and accuracy.

Volunteer AAP

(#2†)

(#1*)

(#3**)

TNT concentration

TNT concentration DNT concentration

(mg/L)

Concentration relative to that obtained

by serial dilution.

* 1:10000 = 2 L to 20 mL.

† 1: 2000 = 10 L to 20 mL.

** 1: 5000 = 4 L to 20 mL.

dard deviation (RSD), was 2.41%. For Volunteer sample #2, a 10.0-L sample of filtered extract was

diluted to 20 mL and the calculated RSD was 0.80%. For Volunteer #3, a 4-L sample was diluted to

20 mL and the RSD was 2.72% for TNT and 2.83% for 2,4-DNT. In all cases, the random error intro-

duced using syringe dilution is minor compared with that due to short-range heterogeneity in soil

(Jenkins et al. 1996). Likewise, the concentration estimates for TNT and 2,4-DNT were 106% of

estimates using serial dilution, indicating that no significant bias would be introduced using this

approach.

Based on these results, we believe that extracts to be analyzed to determine whether soils are

heavily contaminated with secondary explosives can be successfully diluted using a 10-L syringe

Table 6. Recommended modifications of methods for commercial kits for high-level determination

of explosives.

Concentration

Additional

of TNT in extraction

Solvent

extract dilution

TYPE

solvent for soil sample

diluent

required for

Resulting concentration

Method

containing 10% TNT

recommended

linear range of test

and estimated detector response

Colorimetric

A ≈ 0.35*

EnSys

20 g/L

Acetone

1:10000

2 mg/L

Stain length ≈ 28 mm

Erickson

30 g/L

Methanol

1:10000

3 mg/L

A ≈ 0.377

Jenkins

20 g/L

Acetone

1:10000

2 mg/L

A ≈ 0.28**

Medary

17.1 g/L

Methanol

1:2500

6.8 mg/L

Immunoassay

50 L/15 mL

0.71 g/g ≈ 50 on DTechtor

50 L/15 mL

EM Science (D TECH)

64.6 g/mL

Acetone (1/300)

Bottle B (1/300)

100 L/10 mL

5 g/g ≈ 50% B/Bo†

100 L/4 mL

Idetek (Quantix)

25 g/mL

Acetone (1/40)

MQ (1/100)

Diluent tube

100 L/10 mL

4 g/g ≈ 40% B/Bo

100 L/25 mL

Millipore (EnviroGard)

25 g/mL

Acetone (1/250)

MQ (1/100)

user supplied

1.6 g/g ≈ 40% B/Bo

100 L/25 mL

Ohmicron

50 g/mL

MeOH (1/250)

Buffer (1/250)

Diluent tube

* Absorbance.

** Estimated for 25-mL cuvette.

† Absorbance of test vs. absorbance of control.

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