Methodology and Quality Assurance/Quality Control of Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 122

analytical batch. Whenever possible, always do a calibration curve within
that analytical batch on a daily basis.
A perfect 100% recovery is probably not achievable in the real world for
most analytes in complex matrices. Whether a certain percentage recovery is
satisfactory depends on the analyte, the sample matrix, and the method. For
example, the acceptable surrogate standard limit for VOCs in water and soil
samples is approximately 85-115% and 80-120%, respectively. The same
limits for base/neutral SVOCs are approximately 30-120% and 20-125% for
water and soil samples, respectively (Popek, 2003).
For qualitative purposes (chemical identification), it is suggested that compar-
ison to an authentic standard is the only acceptable criteria for positive
identification. Otherwise, ''tentative'' identification is the term used when an
authentic standard is not used or it is unavailable, and the analysis is based
solely on retention times for chromatography and spectral libraries.

EXAMPLE 5.3. Calculation of recovery from a matrix spike QC sample. Pyrene in soil
samples was extracted by sonic extraction followed by analysis using HPLC. A stock solution
of pyrene (50 mL, 100 mg/L) in acetonitrile was spiked in a clean soil (0.5 g) and was extracted
with 10 mL hexane. A portion of the extract (10 mL) was injected to HPLC and the
concentration of the extract was determined to be 0.45 mg/L. Calculate the percentage
recovery of the extraction.

SOLUTION: First, we calculate the amount of pyrene added (true value) as follows,

100mg
L 50 mL

1L
10 6

True value ¼

mL ¼ 0:005mg

We then calculate the amount of pyrene measured (analytical value):

10mL
10 3 mL ¼ 0:0045mg, therefore we use Eq. 2.5:

0 : 45mg
L

Analytical value ¼

Analytical value
True value 100 ¼

0 : 0045mg
0:005mg ¼ 90%

Percentage recovery ¼

REFERENCES

American Society of Testing and Materials (2005), Annual Book of ASTM Standards (a total of 77
volumes) West Conshohocken, PA.
C LEMENT R, Y ANG PW (2001), Environmental Analysis. Anal. Chem., 73:2761-2790.
C SUROS M (1994) Environmental Sampling and Analysis for Technicians, Lewis Publishers, Boca Raton,
FL.
*L EE CC (2000), Sampling, Analysis, and Monitoring Methods, 2nd edition, Government Institute,
Rockville, MD.
National Water Quality Monitoring Council (2005), National Environmental Methods Index (NEMI)
(http://www.nemi.gov).
N ELSON P (2003), Index to EPA Test Methods, April 2003 revised edition. US EPA New England Region
1 Library, Boston, MA (http://www.epa.gov/region01/info/testmethods/pdfs/testmeth.pdf).