Assay Technology

AIR SAMPLER EVALUATION (ANSI 104-1998)

Part I - SUMMARY of TESTS – A Chlorofluorocarbon (bp 15° C)

Methods described here are referenced to numbered documents which specify details of the methods. Statistical results of the tests are reported in the following sections.

Sections 1 - 4 of ANSI/SEI 104-1998 are as follows:

  1. Purpose, Practice, Rationale and Scope
  2. Determination of Standard Compliance
  3. References
  4. Definitions

Sections 5 and 6 describe the test method and procedures of validation. Descriptions and related data follow.

5. Test Apparatus & Method (Method AT-EXP-2)

Stock standard gas was created by static dilution from 100% analyte, mixed volumetrically with input air pumped at a pre-set flow rate through an inert polypropylene chamber containing Diffusive Samplers under test. Flow was verified by in-line rotameter and analyte concentrations were verified by charcoal tube samples continuously drawn from locations in the chamber bracketing the Samplers under test. Assay Technology Sampler No 548 incorporating a polyacetal Sampling Grid with four (4) tubular sampling channels, a 200 mg charcoal (coconut) wafer, and a Wafer Dish and Sampler Cap made of polyester.

6.2 De-Sorption Efficiency (DE) (Method AT-DE-1)(forward)

Analyte recovery and de-sorption efficiency determined by analysis (Method AT541) of charcoal wafers "spiked" from standard analyte solutions in methylene chloride. Samplers were tested at several "spike" levels cor-responding to levels expected for 8-hr Sampler exposures at 0.1-2.0 times the internal Exposure Limit (EL) of 300 ppm. An average recovery for this chlorofluorocarbon from the Assay Technology charcoal sampler was 96%, over the range of 50-200 m g/sample. Results in Table 6.2.

Table 6.2 % Recovery

(De-Sorption Efficiency)

 

Analyte Name

Amount Spiked

Amount Recovered

% DE

Date

(ug/sample)

(ug/sample)

Chlorofluorocarbon

50.0

37.0

74%

Mar-00

0.1 x EL

50.0

37.0

74%

Mar-00

"

50.0

40.0

80%

Mar-00

"

50.0

45.0

90%

Mar-00

"

50.0

44.0

88%

Mar-00

"

50.0

44.0

88%

Mar-00

Average recovery

82%

Chlorofluorocarbon

253

252

100%

Mar-00

0.5 x EL

253

252

100%

Mar-00

253

251

99%

Mar-00

253

250

99%

Mar-00

Average recovery

96%

Chlorofluorocarbon

496

486

98%

Mar-00

1.0 x EL

496

487

98%

Mar-00

496

516

104%

Mar-00

496

518

104%

Mar-00

496

450

91%

Mar-00

496

441

89%

Mar-00

Average recovery

97%

Chlorofluorocarbon

908

971

107%

Mar-00

2.0 x EL

908

948

104%

Mar-00

908

1058

117%

Mar-00

908

1065

117%

Mar-00

908

936

103%

Mar-00

908

929

102%

Mar-00

Average recovery

108%

Table 6.2
(a) De-Sorption Method = Forward
(b) De-Sorption Solvent = 97% Carbon disulfide + 3% Benzyl alcohol
(c) De-Sorption Volume = 2 ml
(d) Media = Assay Technology Monitor AT548

 

6.3 Effect of Concentration/Time on Sampler Accuracy

Samplers were subject to chamber exposures as described in Section 5. then analyzed by Method AT541. Exposures were applied to Samplers in the range 1-8 hours and 0.1-2.0 times the EL of 300 ppm. For this evaluation, the sampling rate for this Chlorofluorocarbon using the Assay Technology sampler was determined to be 0.50 ml/minute. Results in Table 6.3.

 

Table 6.3 Uptake Rate Determination

Analyte:

CFC 

(bp 15° C)

134

= MW

RUN AVE

RUN

TIME

TIME

REF CONCN

Ref Exp

REF EXP

ug/MONITOR

REF EXP

ANALYTE

(min)

(hr)

(ppm)

(ppm-hr)

(ppm-hr)

(ug)

(ppt-min)

(uliter)

1

15

0.25

1366

342

        

15

0.25

1095

274

        
 

15

0.25

1011

253

        

15

0.25

1149

287

289

48

17.33

9
               

                 

2

120

2.00

1044

2088

        

120

2.00

1018

2036

        
 

120

2.00

1007

2014

        

120

2.00

1009

2018

2039

347

122.34

63
                 
 

464

7.73

1056

8166

        

3

464

7.73

967

7478

        

464

7.73

790

6109

        
 

464

7.73

719

5560

        

464

7.73

927

7169

6897

1087

413.80

196

15

0.25

189

47

        
 

15

0.25

172

43

        
 

15

0.25

173

43

45

8

2.67

2
                 
 

120

2.00

101

202

        

4

120

2.00

92

184

120

2.00

94

188

        
 

120

2.00

81

162

        
 

120

2.00

90

180

183

33

10.99

6

450

7.50

106

5

450

7.50

101

          

450

7.50

87

653

 

450

7.50

101

758

        

6

450

7.50

105

788

733

133

43.95

24
 

15

0.25

432

108

        
 

15

0.25

389

97

        

15

0.25

342

86

        
 

15

0.25

358

90

        

7

15

0.25

378

95

95

15

5.70

3

120

2.00

519

1038

 

 

120

2.00

490

980

 

120

2.00

506

1012

1010

163

60.60

29

8

450

7.50

348

2610

450

7.50

353

2648

450

7.50

333

2498

        
 

450

7.50

355

2663

        

9

450

7.50

359

2693

2618

458

157.05

83

 

Least Squares Calcns

REF EXP

Found

(ppt-min)

(uliter)

17.33

8.51

122.34

62.58

2.67

1.40

6.36

5.88

43.95

23.96

5.70

2.79

60.60

29.56

157.05

78.60

Slope=

Slope=

0.50

0.51

 

 

6.4 Bias Due to Reverse Diffusion

Samplers were subject to Exposure Pulse (> OSHA PEL) with a duration less than 50% of the Recommended Sampling Time (RST) followed by a Zero Exposure Period (ZEP) for the duration of the RST. The recovery of analyte from Samplers analyzed immediately following Exposure Pulse was compared with analyte recovery from identically-exposed Samplers analyzed at the end of the RST (i.e. following the Zero Exposure Period). The difference between these two recoveries is taken as the extent of Reverse Diffusion (i.e. evaporative loss as % of Sample) from the Sampler under the experimental conditions chosen.

In practice, Bias Due to Reverse Diffusion will depend on the extent and duration of actual Exposure Pulses in the environment being monitored which cannot be exactly predicted in a lab test. For this evaluation, Bias Due to Reverse Diffusion was estimated as the extent of Reverse Diffusion (evaporative loss as % of Sample) when an Exposure Pulse at 1.0 times the EL is applied for 25% of the duration of the RST (2 hr) followed by a Zero Exposure Period of 100% of the RST (8 hr). Results in Table 6.4.

Table 6.4 Recovery of Initial Vapor Spike

After Zero Exposure Interval

(% Loss = "Reverse Diffusion")

Hrs Exposure at 0.0 ppm =

0.00

8.00
       

Chlorofluorocarbon Found (ug) =

  

131.7

126.0

Std Deviation = +/-

  

5.75

5.96

Co-Eff Variation = +/-

  

4%

5%

Chlorofluorocarbon Recovery

100%

96%

 

 

6.5 Background (Blank) Determination

Unexposed Samplers analyzed by Method AT541 to determine background Analyte levels (if any) on the Sampler prior to sampling. For this evaluation, no significant background values were attributed to the sampler or analytical method for this Chlorofluorocarbon. In addition, the Claimed Detection Limit (CDL) for this Chlorofluorocarbon was determined to be 1.0 m g/sample, equivalent to 0.7 ppm for an 8 hour sampling period. Results in Table 6.5.

Table 6.5 Background (Blank) Determination

Replicate

ANALYTE

EXPOSURE

Chlorofluorocarbon

  

NO.

CONCN

TIME

FOUND in MONITOR

 

(ppm)

(hr)

(ug/sample)

(ppm)
       

8hr TWA
         

1

0

0

<1.0

<0.7

2

0

0

<1.0

<0.7

3

0

0

<1.0

<0.7

4

0

0

<1.0

<0.7

5

0

0

<1.0

<0.7

6

0

0

<1.0

<0.7

 

 

6.6 Effects of Air Velocity & Orientation

Samplers exposed to atmospheres of this Chlorofluorocarbon for 2 hrs at 1.0 times the EL (see Section 5) in a Chamber with 3 zones of different cross-sectional areas such that linear velocities of 20, 100, and 200 cm/sec, respectively, were generated. Samplers were placed in each zone with 50% of samplers placed normal to and 50% of Samplers perpendicular to the flow direction. When data were compared from these locations (representing normal air velocity and orientation variation in workplaces), no significant differences were found among the groups indicating the absence of an effect of Air Velocity & Orientation on Sampling Rate in the range 20-200 cm/sec. Results in Table 6.6.

Table 6.6 Effects of Air Velocity and Orientation

RUN

SAMPLE

ANALYTE

EXPOSURE

EVALUATION

  

TEST RESULTS

  

% OF

NO.

ID

CONCN

TIME

PARAMETERS

  

from MONITORS

  

REFERENCE
   

(ppm)

(hr)

Air Velocity

Values

Ave

(%)

(%)

(Ref Method)

and Orientation

(ppm)

(ppm)

(+/-)(CV)

Reference Value =

355

1

Sample 1

-

-

  

308

-

-

87%
 

Sample 2

-

-

20 cm/sec

307

-

-

86%
 

Sample 3

-

-

air velocity

305

-

-

86%
 

Sample 4

-

-

parallel to

366

-

-

103%
 

Sample 5

-

-

Monitor face

304

-

-

86%

Sample 6

-

-

325

-

-

92%

355

2.0

-

319

7.59

90%

Reference Value =

355

2

Sample 1

-

-

  

346

-

-

97%
 

Sample 2

-

-

100 cm/sec

336

-

-

95%
 

Sample 3

-

-

air velocity

326

-

-

92%
 

Sample 4

-

-

parallel to

331

-

-

93%
 

Sample 5

-

-

Monitor face

383

-

-

108%

Sample 6

-

-

346

-

-

97%

355

2.0

-

345

5.91

97%

Reference Value =

355

3

Sample 1

-

-

  

393

-

-

111%
 

Sample 2

-

-

200 cm/sec

361

-

-

102%
 

Sample 3

-

-

air velocity

372

-

-

105%
 

Sample 4

-

-

parallel to

364

-

-

103%
 

Sample 5

-

-

Monitor face

352

-

-

99%

Sample 6

-

-

555

-

-

156%

355

2.0

-

400

20.90

113%

Reference Value =

1966

4

Sample 1

-

-

2001

-

-

102%

Sample 2

-

-

20 cm/sec

2082

-

-

106%

Sample 3

-

-

air velocity

1813

-

-

92%

Sample 4

-

-

parallel to

2159

-

-

110%

Sample 5

-

-

Monitor face

1748

-

-

89%

Sample 6

-

-

1878

-

-

96%

1966

2.0

-

1947

8.23

99%

Reference Value =

1966

5

Sample 1

-

-

1940

-

-

99%

Sample 2

-

-

20 cm/sec

2014

-

-

102%

Sample 3

-

-

air velocity

2026

-

-

103%

Sample 4

-

-

perpendicular to

1751

-

-

89%

Sample 5

-

-

Monitor face

1961

-

-

100%

Sample 6

-

-

1896

-

-

96%

1966

2.0

-

1931

5.20

98%

 

 

6.7 Effect of Temperature & Humidity

Samplers were exposed to atmospheres of this Chlorofluorocarbon for 2 hrs at 1.0 times the EL in several Chamber runs in which nearly identical exposures were applied with variations in temperature and humidity as follows: 10oC/10%RH, 10oC/70%RH, 40oC/10%RH, 40oC/70% RH. When data from the four conditions (representing normal temperature & humidity variation) were compared, no significant differences among the groups were found, indicating the absence of an effect of Temperature & Humidity on Sampling Rate in the range 10-40oC and 10-70% RH. Results in Table 6.7.

 

Table 6.7 Effects of Temperature & Humidity

 

 

RUN

SAMPLE

ANALYTE

EXPOSURE

EVALUATION

  

TEST RESULTS

  

% OF

NO.

ID

CONCN

TIME

PARAMETERS

  

from MONITORS

  

REFERENCE
   

(ppm)

(hr)

Temperature

Values

Ave

(%)

(%)

(Ref Method)

& Humidity

(ppm)

(ppm)

(+/-)(CV)

Reference Value =

837

1

Sample 1

-

-

  

757

-

-

90%
 

Sample 2

-

-

T = 10oC

884

-

-

106%
 

Sample 3

-

-

  

802

-

-

96%
 

Sample 4

-

-

RH = 10%

845

-

-

101%
 

Sample 5

-

-

  

751

-

-

90%

Sample 6

-

-

821

-

-

98%

837

2.0

-

810

6.34

97%

Reference Value =

381

2

Sample 1

-

-

  

477

-

-

125%
 

Sample 2

-

-

T = 10oC

430

-

-

113%
 

Sample 3

-

-

  

379

-

-

99%
 

Sample 4

-

-

RH = 70%

478

-

-

125%
 

Sample 5

-

-

  

546

-

-

143%

Sample 6

-

-

448

-

-

118%

381

2.0

-

460

12.16

121%

Reference Value =

426

1

Sample 1

-

-

  

374

-

-

88%

1

Sample 2

-

-

T = 40oC

447

-

-

105%

1

Sample 3

-

-

  

400

-

-

94%

1

Sample 4

-

-

RH = 10%

488

-

-

115%

1

Sample 5

-

-

  

404

-

-

95%

1

Sample 6

-

-

431

-

-

101%

1

426

2.0

-

424

9.52

100%

Reference Value =

472

1

Sample 1

-

-

  

545

-

-

115%

1

Sample 2

-

-

T = 40oC

528

-

-

112%

1

Sample 3

-

-

  

466

-

-

99%

1

Sample 4

-

-

RH = 70%

456

-

-

97%

1

Sample 5

-

-

  

573

-

-

121%

1

Sample 6

-

-

470

-

-

100%

1

Monitor 541

472

2.0

-

506

107%

 

 

6.8 Effect of Storage Identical sets of Samples were exposed for 2 hours at 1.0 times the EL and 70% RH. One set was analyzed immediately, followed by subsequent analysis of samples stored under ambient (22ºC) conditions at 7, 14 and 21 days. When data were compared from the four storage periods, no significant differences were found among the four groups indicating no detectable loss of analyte occurs for up to 21 days under ambient storage. Recommended Sample Holding Time = up to 7 days. See Table 6.8.

 

Table 6.8 Effects of Storage

(CFC bp = 15° C)

 

RUN

SAMPLE

ANALYTE

EXPOSURE

EVALUATION

  

TEST RESULTS

  

% OF

NO.

ID

CONCN

TIME

PARAMETERS

  

from MONITORS

  

REFERENCE
   

(ppm)

(hr)

Storage

Values

Ave

(%)

(%)

(Ref Method)

after Sampling

(ppm)

(ppm)

(+/-)(CV)

Reference Value =

426

1

Sample 1

      

414

-

-

97%

1

Sample 2

      

466

-

-

109%

1

Sample 3

    

NO

374

-

-

88%

1

Sample 4

    

STORAGE

434

-

-

102%

1

Sample 5

436

-

-

102%

1

Sample 6

TIME (Days)

429

-

-

101%

1

2.00

0

-

426

7.14

100%

Reference Value =

426

1

Sample 1

488

-

-

115%

1

Sample 2

    

TEMP

466

-

-

109%

1

Sample 3

22oC

397

-

-

93%

1

Sample 4

      

412

-

-

97%

1

Sample 5

459

-

-

108%

1

Sample 6

TIME (days)

438

-

-

103%

1

2.00

7

-

443

7.76

104%

Reference Value =

426

1

Sample 1

386

-

-

91%

1

Sample 2

    

TEMP

422

-

-

99%

1

Sample 3

22oC

365

-

-

86%

1

Sample 4

      

380

-

-

89%

1

Sample 5

414

-

-

97%

1

Sample 6

TIME (days)

402

-

-

94%

1

Monitor 541

2.00

14

-

395

5.48

93%

Reference Value =

426

1

Sample 1

329

-

-

77%

1

Sample 2

    

TEMP

425

-

-

100%

1

Sample 3

22oC

376

-

-

88%

1

Sample 4

      

365

-

-

86%

1

Sample 5

394

-

-

92%

1

Sample 6

TIME (days)

379

-

-

89%

1

Monitor 541

2.00

21

-

378

8.40

89%

 

 

6.9 Sampler Integrity

Samplers in sealed standard aluminum foil pouch packaging exposed to 1.0 times the EL for 2 hours, then analyzed. Results from analysis were not significantly different from results for un-exposed Samplers (blank values) demonstrating the integrity of Sampler packaging. Results in Table 6.9.

 

Table 6.9 Sampler Integrity

Replicate

ANALYTE

EXPOSURE

Chlorofluorocarbon

  

NO.

CONCN

TIME

FOUND in MONITOR

  
 

(ppm)

(hr)

(ug/sample)

(ppm)

8hr TWA

1

198

2

<1.0

<0.7

2

198

2

<1.0

<0.7

3

198

2

<1.0

<0.7

4

198

2

<1.0

<0.7

5

198

2

<1.0

<0.7

6

198

2

<1.0

<0.7

 

 

Summary Comments

Sampler 548 was evaluated for sampling this Chlorofluorocarbon, because preliminary experiments suggested that Samplers 541 and 546 would not retain this very volatile compound (bp » 15oC) during reverse diffusion tests. The overall accuracy expressed as Maximum Total Error (95% confidence) for sampling using Monitor 548 was +15%.

Concentration Range 0.1-2.0 times the OSHA PEL; 0.2-5.0 times the OSHA STEL

Sampling Time 15 min - 8 hour

Air Velocity 15-150 cm/sec

Temperature 10-40oC

Humidity 30-70% RH

Based on estimated Sampler-to-Sampler variation of +5%, Laboratory variation of +3%, and Exposure Chamber Variation of Error + 7%, less than 5% of the Maximum Total Error is attributed to Bias (i.e. systematic error). We have estimated the Bias Due to Reverse Diffusion as < 5%.

It is recommended that Sampler 548 be used within the envelope of conditions studied, but, in general, minor excursions outside these limits would be expected to have only minor effects. Due to the detection limit of PFP, lower levels or shorter sampling times could not be accommodated. Due to lack of detectable Reverse Diffusion for 8 hr zero exposure interval, increases in Concentration, Sampling Time, or Humidity above the limits described here could probably to tolerated with minimal error.

 

Prepared by: CR Manning, PhD, May 2000

ã Assay Technology Inc