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 TABLE 2. RECOVERY OF ALGINIC ACID CARBON FROM DIESEL PARTICULATE SAMPLES SPIKED WITH 10-:L ALGINIC ACID SOLUTION.

Mean Carbona, micrograms/cm2 (SD)

Sample Set unspiked

spiked

differenceb

Recoveryc (%)

A

22.94 (1.49)

34.90 (0.66)

13.47

96

B

22.25 (0.28)

36.38 (0.65)

14.14

101

C

22.61 (0.33)

38.01 (0.80)

15.39

110

All

22.56 (0.84)

36.06 (1.32)

13.49

97

a

Three unspiked samples per set. Seven spiked samples in sets A and B, and 3 in set C. b Spiked minus unspiked result. c Recovery based on mean result (13.98 µg/cm2 ) for 22 analyses of blank punches spiked with 10-:L aliquot of alginic acid solution. Analyses done over a 7-week period.

EC results for the three sample sets are listed in Table 3. Spiked sample results for two sets (A and C) were slightly higher, while those for a third set (B) were slightly lower. Differences between the mean EC loadings on the unspiked and spiked samples were not statistically different. Thus, an accurate correction was again made for the char formed through pyrolysis of alginic acid. Additional tests on spiked samples are ongoing.

TABLE 3. EC RESULTS FOR SPIKED AND UNSPIKED DIESEL PARTICULATE SAMPLES. Mean ECa, micrograms/cm2 (SD)

Sample Set unspiked

spiked

differenceb

A

4.24 (0.20)

4.36 (0.42)

0.12 (0.47)

B

3.88 (0.01)

3.78 (0.12)

-0.10 (0.12)

C

4.32 (0.14)

4.43 (0.12)

0.11 (0.18)

a

Three unspiked samples per set. Seven spiked samples in sets A and B; three spiked samples in set C. b Spiked minus unspiked results.

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NIOSH Manuual of Analytical Methods