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These procedures were designed and tested for internal use by OSHA personnel. Mention of any company name or commercial product does not constitute endorsement by OSHA.

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Introduction

The general procedure for collection and analysis of air samples for phosphine is described in OSHA Method No. ID-180 (11.1). Phosphine is collected on a solid sorbent composed of beaded activated carbon impregnated with potassium hydroxide (KOH). The sampling and analytical procedure is based on the following proposed chemical reaction:

3 PH3 + 6 OH¯ + 5 O2 -------> 6 H2O + HPO4 + 2 HPO3

For every 3 moles of phosphine, 1 mole of phosphate (HPO4 ) and 2 moles of phosphite (HPO3) are produced. The collected phosphine is extracted from the carbon bead using 30% hydrogen peroxide (H2O2) and analyzed as phosphite by ion chromatography (IC).  An additional analytical confirmation by IC for phosphate was not performed. The KOH used for impregnating the sorbent contained high background levels of phosphate.

This method has been validated for a 36-L, 240-min sample based on a pump flow rate of approximately 0.15 L/min. All solid sorbent tubes used during the validation contained single sections consisting of approximately 1.5 g of treated carbon. The majority of tubes used were prepared in-house; exceptions are noted where commercially prepared tubes were used. Two different size tubes (9-mm and 5-mm o.d.) were obtained from a commercial source (SKC Inc., Eighty Four, PA). A significant difference in recoveries between the different size tubes was not noted during side-by-side testing.

A cylinder of phosphine (1.02% phosphine in nitrogen, certified, Air Products Co.) was used for generating test atmospheres. An evaluation (11.2) of the cylinder concentration using the phosphomolybdate method of analysis (11.3) indicated the manufacturer's stated concentration was accurate. The stated concentration was used for all calculations of theoretical (taken) concentrations. A dynamic generation system (described in Section 2 and Figure 1) was used for all experiments except for the detection limit and field evaluation tests. Detection limit tests were performed using sodium phosphite spikes. Samples for all experiments were analyzed IC (11.1).

The method validation consisted of the following experiments and summaries:

  • 1. An analysis of 22 spiked samples to determine desorption efficiency and analytical precision and accuracy.
  • 2. An analysis of 22 samples collected from dynamically generated test atmospheres to determine overall precision and accuracy.
  • 3. A determination of the sampling media collection efficiency.
  • 4. Determinations of breakthrough when sampling time or concentration is increased or when sampling in low humidity environments.
  • 5. An evaluation of the room temperature storage stability of 38 samples taken at the OSHA Permissible Exposure Limit (PEL) of 0.3 ppm. An additional evaluation of the effects of refrigeration on storage stability.
  • 6. A determination of any significant change in recovery when sampling at different humidities.
  • 7. A study of the shelf-life of stored sorbent tubes.
  • 8. A determination of the qualitative and quantitative detection limits.
  • 9. A field evaluation of sampling media at a grain processing mill. 
  • 10. An assessment of the method and summary.

An Addendum describing a comparison of different lots of carbon bead, and samples generated at the STEL are included at the end of this backup report. The study of different lots was conducted when it was discovered that some lots of the carbon bead were less efficient at collecting phosphine than previously expected.

Results were calculated using concentration-response curves and were statistically examined for outliers and homogeneity of variance. Possible outliers were determined using the Treatment of Outliers test (11.4). Homogeneity of variance was determined using the Bartlett's test (11.5).

  1. Analysis

    Twenty-two samples were prepared by adding known amounts of phosphine to treated solid sorbent tubes to determine desorption efficiency (DE) and recoveries for the analytical portion of the method. An active method of spiking was used with low flow (0.01 to 0.02 L/min) sampling pumps to determine the amount of gas collected and not necessarily the sampling capability at the low flow rate.

    1. Procedure:

      Sampling tubes containing treated carbon bead were spiked by a procedure similar to that described in reference 11.6. The phosphine source mentioned in the Introduction was diluted to approximately 50 ppm using the system shown in Figure 1. Calibrated low flow-rate pumps were connected to the sampling manifold and were used to deliver the spikes for measured time periods. Air used to dilute the phosphine source was tempered to 50% RH and 25°C. Pumps used for this experiment were Model No. 222-3-12 (SKC, Eighty Four, PA) and were calibrated to collect samples at 0.010 to 0.020 L/min. Spikes were approximately 6, 12, and 24 µg phosphine. These levels are approximately 0.5, 1, and 2 times the PEL for a 36-L air sample.

    2. Results:

      Recoveries are presented in Table 1. For the analytical section of the method, the overall DE was 96.8%, and the analytical precision (CV1 pooled) was 0.030. One result was omitted as an outlier (1 × PEL group). Results for the three test levels passed the Bartlett's test and were pooled.

  2. Sampling and Analysis

    To determine the precision and accuracy of the method, known generated samples were prepared and analyzed.

    1. Procedure:
      1. The phosphine gas source mentioned in the Introduction was used to generate test atmospheres of phosphine. This source was diluted with filtered, humidified air using the system shown in Figure 1.
      2. Dynamic generation system - A Miller-Nelson Research Inc. (Model HCS-301) flow, temperature and humidity control system was used for air flow control and conditioning. All generation system fittings and connections were Teflon. A glass mixing chamber was used to mix the tempered, filtered air with the contaminant gas. The system was set to generate test atmospheres at 50% RH and 25 °C.
      3. The phosphine and diluent air flow rates were adjusted using mass flow controllers. Flow rates were also measured using a dry test meter (diluent air) and a soap bubble flow meter (phosphine gas).
      4. Samples were taken from the sampling manifold using constant flow pumps. Calibrated Du Pont P125 pumps were used. Pump flow rates were approximately 0.12 to 0.15 L/min and sampling times ranged from 240 to 360 min. Sample concentrations were approximately 0.5, 1, and 2 times the OSHA PEL for 30- to 50-L air samples.
    2. Results:

      Results are shown in Table 2. The precision and accuracy data, based on NIOSH statistical protocol (11.5), is presented in Tables 1 and 2. The generated sample (Sampling and Analysis) results passed the Bartlett's test and were pooled. The pooled coefficients of variation are as follows:

      CV1(pooled) = 0.030

      Cv2(pooled) = 0.039

      CVT(pooled) = 0.041

      There was insignificant overall bias and the overall error was ±8.3%. Overall error (11.7) was calculated using the equation: Overall error % = ±(|mean bias| + 2CVT ) × 100 (95% confidence)

  3. Collection Efficiency

    Procedure:
    Efficiency was determined for in-house and commercially prepared tube

    1. In-house Tubes

      The collection efficiency at the upper validation limit was determined using double sampling tubes. Two sampling tubes were connected in series. These tubes were prepared at the OSHA laboratory. Eight double tubes were connected to the sampling manifold to collect samples at approximately 2 times the OSHA PEL for 210 min (50% RH and 25°C). Pump flow rates were 0.12 to 0.15 L/min.

    2. Commercial Tubes

      Six double tubes were also used to collect samples at 0.67 ppm for 240 min. Pump flow rates, humidity and temperature were the same as mentioned in Section 3.1. Tubes prepared by SKC Inc. (Eighty Four, PA.) were used.

    3. The amount of phosphine vapor collected in the first and second tubes was determined. The collection efficiency was calculated by dividing the amount collected in the first tube by the total amount of phosphine collected in the first and second tube.

    Results:
    Results shown in Table 3 indicate a collection efficiency of 100.0% when sampling at approximately 2 times the OSHA PEL for 210 or 240 min. No breakthrough was evident during the collection efficiency study.

  4. Breakthrough

    Three different breakthrough experiments were conducted to assess potential breakthrough:

    Increased sampling time
    Increased concentration
    Sampling in low humidity environments

    1. Increased Sampling Time - Procedure: A preliminary study using solid sorbent tubes and phosphine detector tubes (Model No. CH31101, Dräger, Pittsburgh, PA) as colorimetric, qualitative indicators of breakthrough was conducted. The Dräger tubes were chosen because of the very stable, reproducible indication, large size, loose packing, and small pressure drop when attached to a sampling pump. Two lots of Dräger detector tubes had been previously tested at low concentration ranges when using detector tube pumps (11.2). Additional testing was conducted with continual flow pumps (DuPont P125) to assess the possibility of using these detector tubes for identification of breakthrough. These tubes were found capable of producing a noticeable colorimetric indication after sampling 0.3 ppm phosphine for 15 min at a flow rate of 0.1 L/min (approximately 0.6 µg phosphine). The detector tubes were attached between the sampling tubes and pumps. Six samples were taken for 360 min at 0.6 ppm and a flow rate of 0.12 to 0.15 L/min (50% RH and 25°C).
    2. Increased Concentration - Procedure: Two sampling tubes containing treated carbon bead were attached to each other and five of these double tube samples were taken to determine breakthrough at a concentration level of 1.9 ppm phosphine. Commercially prepared (SKC Inc.) tubes were used for this experiment.
      1. Samples were collected at a flow rate of approximately 0.15 L/min, a concentration of 1.9 ppm phosphine, 25°C and 50% RH. Samples were taken for 240 min.
      2. Breakthrough was assessed by analyzing both tubes and dividing the amount collected in the second solid-sorbent tube by the total amount collected in both tubes.
    3. Decreased Humidity - Procedure: An experiment was conducted to determine if breakthrough exists at 30% RH. Sampling at this humidity had given lower recoveries than expected (See Section 6. for further details). This experiment should establish whether these low recoveries are due to breakthrough or an incomplete or unanticipated reaction of phosphine with the treated sorbent. To determine breakthrough, sampling tubes, detector tubes, and pumps were connected together as mentioned in Section 4.1. Samples were taken for 90 min at flow rates of 0.115 to 0.135 L/min. The generation system parameters were 1 ppm phosphine, 25°C, 30% RH.

    Results:
    Detector tube color indications were not observed after increasing the sampling time 360 min at 2 times the PEL. As shown in Table 4, increasing the sampling concentration to 1.9 ppm (240-min sampling time) produced breakthrough; however, the amount was less than 5%. When sampling without a humidifier at 30% RH, breakthrough was evident after a 6-µg sample load (Table 4). Humidifiers are necessary at low RH (<40%) to prevent premature breakthrough.

  5. Storage Stability

    A study was conducted to assess the stability of phosphine collected on the treated solid sorbent.

    1. Procedure - storage assessment at room temperatures of 20 to 25°C.
      1. Thirty-eight samples were collected using the generation system previously described in Section 2. Samples were collected at the PEL, 50% RH, and 25°C.
      2. Samples were stored at room temperature (20 to 25°C) on a lab bench.
      3. Six to eight samples were analyzed after various periods of storage (0, 5, 12, 18, and 32 days).
    2. Procedure - refrigeration assessment
      1. Thirty-five samples were collected in an effort to determine the effect of refrigeration on sample storage stability. Twenty-four samples were collected at the PEL and 11 at 2 times the PEL. The 11 samples were taken using commercially prepared tubes while the other tubes were prepared in-house.
      2. Twelve samples taken at the PEL and four taken at 2 times the PEL were analyzed immediately after generation.
      3. Nine samples were stored at room temperature (20 to 25°C) and ten were refrigerated (7°C). Twelve samples were analyzed after a 12- to 13-day storage period. The remaining seven samples were analyzed after 30 days.
    3. Results:

      Results of this stability study are shown in Table 5 and Figure 2. The mean of samples (stored at 20 to 25°C) analyzed was 81% of the known concentration after 12 days, 64% after 18 days, and 48% after a 32-day storage period. Results indicate samples may be stored at typical laboratory temperatures up to 12 days after sampling. Sample refrigeration reduces sample loss. Samples refrigerated for 13 days (7°C) showed no apparent loss while those refrigerated for 30 days displayed a slight loss in recovery. Samples should be refrigerated whenever possible. Since it is difficult to control the temperature of samples after field collection and during shipment, samples should be analyzed within 12 days of collection regardless of laboratory refrigeration.

  6. Humidity Study

    A study was conducted to determine any significant effect on recoveries when sampling at different humidities. Test atmospheres were generated at 23, 30, 40, 50, and 80% RH. Samples were taken for 360 min at flow rates of approximately 0.15 L/min. Results are listed in Table 6 and displayed in Figure 3. As shown, samples collected at relative humidities less than 40% result in unacceptably low phosphine recoveries. This loss can be resolved by sampling with an in-line humidifier.

    The following techniques were used in an attempt to humidify samples taken in areas having less than 40% RH:

    1. Deionized water (0.75 mL) was added to the end of a cellulose filter plug (Rainin Instrument Co., Woburn, MA; part no. 23534/B) contained inside a glass tube. This tube was used as a humidifying pre-tube. The 0.75 mL spike should not cause water saturation to the treated sorbent and should provide continuous humidification for up to 6 h of sampling at a flow rate of 0.15 L/min.
    2. A 25-mL impinger containing approximately 5 mL of deionized water was also used as a humidification device.
    3. Procedure:

      Two different experiments were conducted. The first experiment was performed at the PEL while the second was performed at a higher concentration (1.042 ppm). The second experiment was performed to evaluate the potential for humidifier failure or breakthrough at higher concentration levels. Sampling rates for both experiments were 0.11 to 0.15 L/min. Samples were taken for 300 min during the first experiment and 120 min for the high concentration test.

    4. An additional test was conducted to assess any change in recovery if the humidifier is used at high humidity levels. Three samples with an in-line humidifier and two samples without the humidifier were taken at about 2 times the PEL. Sampling conditions were 25°C and 80% RH.

    Results:
    Results for either humidifier are shown in Table 6. As shown, acceptable recoveries are noted when the relative humidity is equal to or greater than 40% (25°C). The results demonstrate the recovery was approximately 55% at 30% RH, and a 46% net recovery was noted at 23% RH. It is, therefore, concluded that the relative humidities below 40% definitely result in low phosphine recoveries. Results using a humidifier (Table 6) show acceptable recoveries when sampling in low humidity environments; therefore, in-line humidifiers are necessary for accurate assessments of phosphine when sampling in low humidities (<40% RH).

    The collection of samples with an in-line humidifier at 80% RH was compared to samples taken without a humidifier. Both approaches gave comparable recoveries. Average recoveries were 107.6% and 112.5% for samples collected at 80% RH with a humidifier and for samples collected without one, respectively. For added convenience, humidity levels do not have to be determined if a humidifier is used.

  7. Shelf Life Study

    A shelf life study of the treated sampling tubes was conducted.

    Procedure:
    Sampling tubes were prepared in-house and sealed with plastic caps. After 68 days, the tubes were used to collect samples from the generation system previously mentioned in Section 2. Commercially prepared tubes were also set aside and used after a period of 6 months. These tubes were then used for the 0 day storage test (Table 5 - Refrigeration vs. Room Temperature - 2 × PEL data).

    Results:
    Commercially prepared tubes stored for 6 months and then used to collect samples gave an average recovery of 113.7%. Sealed tubes can be stored at typical laboratory temperatures (20 to 25°C) for at least 6 months and then used for sampling.

  8. Detection Limits

    Procedure:
    Detection limits were determined by statistically examining the analytical results of spiked samples and blanks. Low concentration samples were prepared by spiking solutions of deionized water with sodium phosphite. Concentrations of 0.14, 0.28, and 0.57 µg/mL phosphite were used. Analysis of detection limit samples was performed with a full scale detector output setting of 3 microsiemens. A 50-µL sample loop was used for all injections.

    1. Qualitative Detection Limit - The Rank Sum Test (11.8) was used for the determination of the qualitative limit.
    2. Quantitative Detection Limit - A modification or derivation of the International Union of Pure and Applied Chemistry (IUPAC) detection limit equation (11.9) was used to calculate the quantitative limit. At the sensitivity level tested, blank readings and the standard deviation of the blank were equal to zero. The lack of a blank signal does not satisfy a strict interpretation of the IUPAC detection limit when using the equation shown in Table 8. The quantitative detection limit for this method is calculated using the standard deviation of a standard below the range of the expected detection limit as a substitute for the blank readings.

    Results:
    The results are listed in Table 8 and graphically displayed in Figure 4. The qualitative detection limit is 0.14 µg/mL. The quantitative detection limit is 0.23 µg/mL (both limits are calculated as HPO32¯). Using a 36-L air volume and a 5 mL sample volume, the qualitative limit is 0.009 ppm and the quantitative limit is 0.015 ppm phosphine (Table 8).

  9. Field Evaluation

    A field evaluation at a grain processing mill was conducted using a number of different sampling devices.

    Procedure:
    A Teflon sampling manifold was set-up with two exhaust pumps (DuPont P4000 pumps calibrated at 3 L/min) at one end of the manifold. These pumps continually drew the workplace air-phosphine mixture through the sampling manifold. Side-by-side samples were taken from the manifold during a 3-h sampling period in which Magtoxin (magnesium phosphide) was used to fumigate an area in which grain is packaged and stored.

    Mercuric cyanide-impregnated silica gel tubes manufactured by SKC and Supelco as well as commercially prepared carbon bead tubes were used. Carbon bead samples were taken with two different size tubes. One tube had an outer diameter of 5 mm (thin) while the other was 9 mm (large). Both tubes contained approximately 1.5 g of treated sorbent. The thin tube was tested since it could be used at higher humidity levels (without the humidifier) and provide more convenience during use. The thin tube is easier to break open and connect to a pump than the larger tube. The 9-mm o.d. tube is used with the humidified filter tube since the dimensions of both tubes are similar and are easily connected together with flexible tubing.

    Results:
    Results are listed in Table 9. The field validation indicated good agreement between the mercuric cyanide-treated silica gel tubes and the KOH-impregnated carbon bead samples with in-line humidifiers. The results of the non-humidified carbon bead samples are similar to the laboratory recoveries for low humidity sampling (Table 6). A significant amount of breakthrough was noted for the treated silica gel tubes at the apparent concentration of 1.4 to 1.5 ppm phosphine. The SKC tubes had less breakthrough than the Supelco tubes at this concentration.

  10. Summary

    The results indicate the method meets the NIOSH criteria for accuracy and precision (11.5).

    A side-by-side method comparison was not performed; however, detector tube and mercuric cyanide-treated silica gel samples were taken during the same period and under the same generation conditions as the carbon bead tube. Recoveries for the silica gel samples were within accepted limits (see reference 11.2 for further details).

    Method No. ID-180 has the disadvantage of low recoveries at low humidities if a humidifier is not used. Unacceptable recoveries are also noted if samples are stored at ambient temperatures longer than 12 days before analysis. However, the overall method offers a simple, accurate and precise assessment of phosphine concentrations if the appropriate steps are taken:

    • 1) When sampling in low humidity environments, a humidifier is necessary. Humidifiers can be used regardless of the humidity at the sampling site.
    • 2) Analyses should be performed within 12 days and samples should be refrigerated during this time period.

    Experiments have been conducted after this backup report was written. Please consult the Addendum at the end of this report for further information.

  11. References
    1. Occupational Safety and Health Administration Technical Center: Phosphine in Workplace Atmospheres by J.C. Ku (OSHA-SLTC Method No. ID-180). Salt Lake City, UT. Revised, 1991.
    2. Occupational Safety and Health Administration Analytical Laboratory: Phosphine Detector Tubes (PE-4). Salt Lake City, UT. 1987.
    3. National Institute for Occupational Safety and Health: Manual of Analytical Methods. 2nd. ed., Vol. 5 (Method No. S332) (DHEW/NIOSH Pub. No. 79-141). Cincinnati, OH: National Institute for Occupational Safety and Health, 1979.
    4. Mandel, J.: Accuracy and Precision, Evaluation and Interpretation of Analytical Results, The Treatment of Outliers. In Treatise On Analytical Chemistry, 2nd Ed., edited by I. M. Kolthoff and P. J. Elving. New York: John Wiley and Sons, 1978. pp. 282-285.
    5. National Institute for Occupational Safety and Health: Documentation of the NIOSH Validation Tests by D. Taylor, R. Kupel and J. Bryant (DHEW/NIOSH Pub. No. 77-185). Cincinnati, OH: National Institute for Occupational Safety and Health, 1977.
    6. National Institute for Occupational Safety and Health: Backup Data Report No. S332 for Phosphine, Attachment A. Cincinnati, OH: National Institute for Occupational Safety and Health, 1977 (unpublished).
    7. Occupational Safety and Health Administration Analytical Laboratory: Precision and Accuracy Data Protocol for Laboratory Validations. In OSHA Analytical Methods Manual. Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.
    8. Dixon, W.J. and F.J. Massey, Jr.: Introduction to Statistical Analysis. 2nd ed. New York: McGraw-Hill Book Co., Inc., 1957. pp. 289-292, 445-449.
    9. Long, G.L. and J.D. Windfordner: Limit of Detection, A Closer Look at the IUPAC Definition. Anal. Chem. 55: 712a-724a (1983).

Table 1
Analysis

Level* 

0.5 × PEL

1 × PEL

2 × PEL

µg
taken

µg
found


DE

µg
taken

µg
found


DE

µg
taken

µg
found


DE

5.19

5.62

1.083

11.99

11.11

0.927

24.04

(LIA)

-

5.17

5.00

0.967

12.98

12.21

0.941

25.83

25.39

0.983

5.17

4.99

0.965

13.46

12.44

0.924

26.55

25.42

0.957

5.14

5.11

0.994

12.70

12.55

0.988

25.06

24.69

0.985

5.10

5.10

1.000

11.82

11.20

0.948

23.84

22.35

0.938

5.02

4.97

0.990

12.75

12.18

0.955

25.78

24.75

0.960

13.20

12.38

0.938

26.57

24.83

0.935

12.39

10.18

0.822**

25.09

23.89

0.952

      
   n

6      

7      

7      

   Mean

1.000

0.946

0.959

   Std Dev

0.043

0.022

0.020

   CV1

0.043

0.023

0.021

CV1 (pooled) = 0.030
Ave. DE = 0.968

* Levels are approximate
** Excluded from statistical analysis as an outlier
LIA = Lost In Analysis
DE = Desorption Efficiency

Table 2
Sampling and Analysis

Test Level

--------- Found ---------

Taken

Recovery

µg

Air Vol (L)

ppm

ppm

percent

0.5 × PEL

8.85

41.0

0.155

0.152

102.0

9.39

42.3

0.160

0.152

105.3

10.76

47.7

0.162

0.152

106.6

8.40

37.1

0.163

0.152

107.2

11.68

51.1

0.164

0.152

107.9

9.40

41.9

0.161

0.152

105.9

10.12

44.1

0.165

0.152

108.6

8.56

38.6

0.160

0.152

105.3

      

n

8

Mean

0.161

106.1

Std Dev

0.003

CV2

0.019

   
 

1 × PEL

18.47

45.1

0.295

0.284

103.9

16.95

44.1

0.276

0.284

97.2

13.95

39.0

0.257

0.284

90.5

15.80

37.7

0.301

0.284

106.0

19.52

51.1

0.275

0.284

96.8

17.59

41.2

0.307

0.284

108.1

17.37

42.9

0.291

0.284

102.5

16.72

41.7

0.288

0.284

101.4

     

n

8

Mean

0.286

100.8

Std Dev

0.016

CV2

0.057

     

2 × PEL

28.35

35.1

0.581

0.666

87.2

23.55

28.6

0.592

0.666

88.9

27.22

31.8

0.616

0.666

92.5

26.21

30.2

0.624

0.666

93.7

27.80

32.9

0.608

0.666

91.3

26.57

30.6

0.624

0.666

93.7

    

n

6

Mean

0.608

91.2

Std Dev

0.018

CV2

0.029

      
* Excluded from statistical analysis as an outlier

CV2 (pooled) = 0.039

CVT (pooled) = 0.041

Bias = 0.1%

Overall Error = ±8.3%

Table 3
Collection Efficiency
50% RH, 25°C

-------- ppm Phosphine --------

Sample No.

First Tube

Second Tube

% Collection Efficiency

1

0.49

ND

100

2

0.55

ND

100

3

0.58

ND

100

4

0.58

ND

100

5

0.51

ND

100

6

0.54

ND

100

7

0.52

ND

100

8

0.57

ND

100

9

0.58

ND

100

10

0.59

ND

100

11

0.62

ND

100

12

0.62

ND

100

13

0.61

ND

100

14

0.62

ND

100

Note:

(1) Samples 1 to 8 were taken at 0.12 to 0.15 L/min flow rate for 210 min. These tubes were prepared at the OSHA lab. Samples 9 to 14 are commercially prepared tubes used to take samples for 240 min and at the same flow rates as the in-house tubes.

(2) ND = None detectable < 0.015 ppm phosphine

(3) Samples 1 to 8: Generation concentration = 0.6 ppm phosphine
Samples 9 to 14: Generation concentration = 0.67 ppm phosphine

Table 4
High Concentration Breakthrough
50% RH, 25°C

------- µg PH3 Found -------

Sample No.

1st

2nd

% Breakthrough

1

83.07

3.34

3.9

2

82.60

1.22

1.5

3

71.92

2.22

3.0

4

81.84

2.37

2.8

5

77.80

3.00

3.7

Ave:

3.0

Note:

(1) 1st and 2nd = Commercially prepared (SKC) sampling tubes 
(2) Sample rate = approximately 0.15 L/min flow rate for 240 min 
(3) Generation concentration 1.90 ppm phosphine

Low Humidity Breakthrough
30% RH, 25°C

----- µg PH3 Found -----

Sample No.

1st

2nd*

% Breakthrough

1

5.69

3.90

40.6

2

5.45

2.50

31.5

3

5.62

3.20

36.3

4

5.66

1.88

24.9

5

5.61

3.13

35.8

    

 n          

5

5

Mean    

5.61

2.92

33.8

Std Dev

0.093

0.76

 CV        

0.017

0.26

Note:

(1) 1st = Sampling Tube; 2nd = Dräger phosphine detector tube
(2) Sampled at 0.115 to 0.135 L/min flow rate for 90 min 
(3) Generation concentration = 1 ppm phosphine
* Results obtained using calibrated detector tubes. These results are approximate.

Table 5
Storage Stability Test
Ambient (20 - 25°C) Storage

(1 × PEL)

--------- Found -----------

Taken

%

Storage

µg

Air Vol (L)

ppm

ppm

Recovery

Day 0

18.47

45.1

0.295

0.284

103.9

16.95

44.1

0.276

0.284

97.2

13.95

39.0

0.257

0.284

90.5

15.80

37.7

0.301

0.284

106.0

19.52

51.1

0.275

0.284

96.8

17.59

41.2

0.307

0.284

108.1

17.37

42.9

0.291

0.284

102.5

16.72

41.7

0.288

0.284

101.4

    

n

8

Mean

0.286

100.8

Std Dev

0.016

CV

0.057

  

Day 5

16.70

44.0

0.273

0.284

96.1

16.85

45.2

0.268

0.284

94.4

16.15

42.8

0.271

0.284

95.4

12.08

39.4

0.220

0.284

*

19.33

52.0

0.267

0.284

94.0

15.86

42.1

0.271

0.284

95.4

  

n

5

Mean

0.270

95.1

Std Dev

0.002

CV

0.009

  

Day 12

12.90

41.4

0.224

0.300

74.7

14.19

42.4

0.241

0.300

80.3

16.63

47.8

0.250

0.300

83.3

13.27

37.4

0.255

0.300

85.0

16.99

50.3

0.243

0.300

81.0

13.54

41.0

0.237

0.300

79.0

15.28

43.2

0.254

0.300

84.1

16.60

37.9

0.315

0.300

*

  

n

7

Mean

0.243

81.0

Std Dev

0.011

CV

0.045

* Excluded from statistical analysis as outliers

Table 5 (Continued)
Storage Stability Test
Ambient (20 - 25°C) Storage

(1 × PEL)

---------- Found -----------

Taken

Storage

µg

Air Vol (L)

ppm

ppm

% Recovery

Day 18

12.55

44.2

0.204

0.280

72.9

11.88

43.7

0.195

0.280

69.6

10.96

41.7

0.189

0.280

67.5

9.58

38.6

0.178

0.280

63.6

11.53

51.1

0.162

0.280

57.9

9.87

41.5

0.171

0.280

61.1

9.08

43.4

0.150

0.280

53.6

11.55

42.8

0.194

0.280

69.3

  

n

8

Mean

0.180

64.4

Std Dev

0.018

CV

0.102

  

Day 32

7.92

44.1

0.129

0.284

45.4

7.97

44.8

0.128

0.284

45.1

7.70

42.8

0.129

0.284

45.4

7.19

38.9

0.133

0.284

46.8

10.87

53.1

0.147

0.284

51.8

8.61

41.6

0.149

0.284

52.5

7.61

43.0

0.127

0.284

44.7

9.08

43.3

0.151

0.284

53.2

  

n

8

Mean

0.137

48.1

Std Dev

0.010

CV

0.077

Samples listed above were collected at 1 × PEL, 25°C and 50% RH.

Table 5 (Continued)
Storage Stability Test
Refrigeration (7°C) vs. Room Temperature (20 to 21°C)

---------- Found -------------

Taken

ug

Air Vol (L)

ppm

ppm

% Recovery

Day 0

15.37

38.65

0.286

0.309

92.6

11.96

39.09

0.220

0.309

*

(1 × PEL)

16.13

38.80

0.299

0.309

96.8

15.80

38.78

0.293

0.309

94.8

14.14

36.72

0.277

0.309

89.6

15.58

38.11

0.294

0.309

95.1

16.11

38.62

0.300

0.309

97.1

16.75

40.84

0.295

0.309

95.5

16.65

38.88

0.308

0.309

99.7

16.44

38.27

0.309

0.309

100.0

15.42

34.98

0.317

0.309

102.6

15.99

37.58

0.306

0.309

99.0

  

n

11

Mean

0.299

96.6

Std Dev

0.011

CV

0.038

  

25.75

31.82

0.582

0.525

110.9

(2 × PEL)

26.53

31.62

0.603

0.525

114.9

25.58

30.88

0.596

0.525

113.5

26.54

31.37

0.608

0.525

115.8

n

4

Mean

0.597

113.7

  

Std Dev

0.011

CV

0.019

*Tubing connecting the pump and sampling tube disconnected during sampling. This result was not used in statistical calculations.

Day 0 samples were desorbed and analyzed immediately af ter collection. In-house prepared tubes were used for 1 × PEL samples; commercial tubes were used for 2 × PEL samples.

Table 5 (Continued)
Storage Stability Test
Refrigeration (7 °C) vs. Room Temperature (20 to 21°C)

---------- Found----------

Taken

%

µg

Air Vol (L)

ppm

ppm

Recovery

Day 13

16.37

39.11

0.301

0.309

97.4

Refrigerated

15.77

36.95

0.307

0.309

99.4

(1 × PEL)

16.94

39.16

0.311

0.309

100.6

16.59

37.75

0.316

0.309

102.3

15.59

34.80

0.322

0.309

**

15.93

37.31

0.307

0.309

99.4

   

n

5

Mean

0.308

99.8

Std Dev

0.006

CV

0.018

  

Day 12

14.00

39.16

0.257

0.309

83.2

Room Temperature

13.47

36.56

0.265

0.309

85.8

(1 × PEL)

1

4.61

39.79

0.264

0.309

85.4

13.55

37.20

0.262

0.309

84.8

11.97

34.17

0.252

0.309

81.6

13.78

37.25

0.266

0.309

86.1

  

n

6

Mean

0.261

84.5

Std Dev

0.005

CV

0.021

  

Day 30

19.81

30.99

0.460

0.523

88.0

Refrigerated

22.48

31.35

0.516

0.523

98.7

(2 × PEL)

20.47

29.01

0.508

0.523

97.1

21.29

29.80

0.514

0.523

98.3

  

n

4

Mean

0.500

95.5

Std Dev

0.027

CV

0.053

  

Day 30

17.28

31.63

0.393

0.523

75.1

Room Temperature

13.47

30.84

0.314

0.523

60.0

(2 × PEL)

15.94

29.65

0.387

0.523

74.0

  

n

3

Mean

0.365

69.7

Std Dev

0.044

CV

0.121

             

Table 6
Humidity Experiments (25°C)

%RH

23

30

40

50

80

ppm PH3 Taken

0.309

0.298

0.307

0.284

0.294

   

ppm PH3 Found

0.148

0.169

0.302

0.295

0.257

0.134

0.181

0.306

0.276

0.262

0.133

0.175

0.315

0.257

0.272

0.151

0.192

0.308

0.301

0.271

0.159

0.105

0.301

0.275

0.267

0.135

0.195

0.307

0.274

0.198

0.291

0.158*

0.105

0.288

0.268

  

n

6

8

5

8

7

Mean, ppm

0.143

0.165

0.306

0.286

0.267

Std Dev, ppm

0.011

0.038

0.006

0.016

0.006

CV

0.076

0.232

0.018

0.057

0.022

Ave Recovery

46.4%

55.3%

99.8%

100.8%

90.9%

* Excluded from statistical analysis as an outlier
Samples were taken for 360 min at a flow rate of approximately 0.15 L/min.

Low Concentration

Table 6 (Continued)
Humidifier vs. No Humidifier
25°C & 30% RH

------- ppm Phosphine Found ------

Sample Type

Humidifier

No Humidifier

FP

0.33

0.26

FP

0.44

0.22

IMP

0.34

0.28

IMP

0.34

0.28

  

n

4

4

Mean

0.36

0.26

Std Dev

0.052

0.028

CV

0.143

0.109

% Recovery

90

65

  
Generation concentration = 0.4 ppm phosphine
Sampling rate = 0.11 to 0.15 L/min
Sampling time = 300 min

High Concentration

---------- ppm Phosphine Found -----------

---- Humidifier ----

No Humidifier

Sampling No.

FP

IMP

1

0.9196

0.9608

0.3524

2

1.0271

0.9675

0.3413

3

1.0194

1.0221

0.2509

4

1.0314

0.9980

0.3460

5

1.0239

1.1107

0.3827

6

0.9186

1.0417

0.3191

  

n

6

6

6

Mean

0.990

1.017

0.332

Std Dev

0.055

0.055

0.045

CV

0.056

0.055

0.135

% Recovery

95.0

97.6

31.9

  
Generation concentration = 1.042 ppm phosphine
Sampling rate = 0.11 to 0.15 L/min, Sampling time = 120 min

FP = cellulose plug was wetted with DI water prior to sampling and used as pre-tube (Section 6.1).
IMP = an impinger containing 5 mL DI water was placed in front of sampling tube (Section 6.2).

Table 7
Shelf Life

------ Found ---------

Taken

Storage

µg

Air Vol (L)

ppm

ppm

% Recovery

Day 0

18.63

42.9

0.312

0.297

105.1

16.38

37.4

0.315

0.297

106.1

18.76

41.4

0.326

0.297

110.0

15.09

37.6

0.289

0.297

97.3

   

n

4

Mean

0.310

104.5

Std Dev

0.016

CV

0.051

   

Day 68

17.33

42.0

0.297

0.297

100.0

20.88

48.0

0.313

0.297

105.4

22.09

50.3

0.316

0.297

106.4

19.15

43.2

0.319

0.297

107.4

  

n

4

Mean

0.311

104.7

Std Dev

0.010

CV

0.032

Eight blank sampling tubes were prepared in the laboratory. Four tubes were used to take samples from the generation system (1× PEL, 25°C, 50% RH) and then immediately analyzed (Day 0). The other 4 blank sampling tubes were stored at 20 to 25°C for 68 days. Samples were then collected using the same conditions as the Day 0 samples.

Commercial tubes were stored for 6 months on a lab bench and then used for sampling. These tubes were used to collect samples for the 0 Day Storage Stability experiment (See Table 5 - Refrigerated vs. Room temperature, 0 Day Storage, 2 × PEL for data). Four samples were collected at 2 times the PEL, 25°C and 50% RH. Recoveries were 113.7% and the CV was 0.019.

Table 8
Qualitative Detection Limit
Rank Sum Test
For n(s) = n (b) = 6

   

-------- STD Concentration (as HPO3) -------

   

0.14 µg/mL

0.28 µg/mL

0.57 µg/mL

Rank

PA

SAM

PA

SAM

PA

SAM

1
2
3
4
5
6
7
8
9
10
11
12

0.00
0.00
0.00
0.00
0.00
0.00
1.42
2.09
2.17
2.22
2.22
2.30

RBL
RBL
RBL
RBL
RBL
RBL
STD
STD
STD
STD
STD
STD

0.00
0.00
0.00
0.00
0.00
0.00
3.87
4.00
4.06
4.06
4.23
4.47

RBL
RBL
RBL
RBL
RBL
RBL
STD
STD
STD
STD
STD
STD

0.00
0.00
0.00
0.00
0.00
0.00
8.54
8.60
8.63
8.64
8.73
8.73

RBL
RBL
RBL
RBL
RBL
RBL
STD
STD
STD
STD
STD
STD

  

Blank rank sum =

21

21

21

   

Confidence level =

99.9%

99.9%

99.9%

Qualitative detection limit for phosphine = 0.14 µg/mL or 0.70 µg (5 mL sample volume). This corresponds to a 0.009 ppm phosphine concentration for a 36-L air volume at 0.15 L/min sampling rate.
Note: SAM denotes sample type:
(1) RBL = Reagent Blank
(2) STD = Standard

PA = Integrated Peak Area (HPO3)/100,000

Table 8 (Continued)
 Quantitative Detection Limit (IUPAC Method)

------- STD Concentration (as HPO3) --------

Sample No.

0.14 µg/mL
PA

0.28 µg/mL
PA

0.57 µg/mL
PA

1
2
3
4
5
6

n
Mean
Std Dev
CV

1.42
2.09
2.17
2.30
2.22
2.22

6
2.07
0.33
0.16

4.47
4.06
4.06
4.23
4.00
3.87

6
4.12
0.21
0.05

8.63
8.73
8.64
8.54
8.73
8.60

6
8.65
0.07
0.01

   
PA = Integrated Peak Area ( HPO3)/100,000

The mean blank reading and standard deviation (Std dev) were equal to zero. 

Using the equation:  Cld = k(sd)/m

Where:

Cld = the smallest reliable detectable concentration an analytical instrument can determine at a given confidence level.
k = 10, thus giving greater than 99.9% confidence that any detectable signal will be greater than or equal to an average blank (or low standard) reading plus ten times the standard deviation (area reading $ Blave + 10sd). 
sd = standard deviation of low standard readings.
m = analytical sensitivity or slope as calculated by linear regression. 
Cld = 10(0.33)/14.397 = 0.23 µg/mL
Quantitative detection limit = 0.23 µg/mL (as HPO3) or 1.15 µg (5-mL sample volume). This corresponds to 0.015 ppm phosphine for a 36-L air volume at 0.15 L/min sampling rate.

Table 9
Field Evaluation - Grain Processing Mill

Sampling conditions: 26 to 30 % RH, 2°C
Sampling system: Samples were taken side-by-side using a Teflon sampling manifold and two exhaust pumps.
Sampling time: 3 h
Pumps: Du Pont P4000
Sampling rates: 0.11 to 0.14 L/min
Tube Type

n

Average Results

CV

Supelco MC tube
SKC MC tube
IBC large tube and humidifier
IBC large tube (no humidifier)
IBC thin tube (no humidifier)

3
3
3
3
3

1.41 ppm
1.51 ppm
1.43 ppm
0.63 ppm
0.56 ppm

0.098
0.044
0.13
0.048
0.11

Supelco MC and SKC MC tubes contain silica gel impregnated with mercuric cyanide. Sampling and analysis for the silica gel tubes were performed using the NIOSH phosphine method S332 (11.3) with some modifications. 

IBC = Impregnated Beaded Carbon. The thin tube is approximately 170-mm long and 5-mm o.d. The large tube is approximately 110-cm long and 9-mm o.d. Both tubes contain 1.5 g of treated sorbent. All IBC tubes were sampled and analyzed according to reference 11.1. 

The humidifier is a cellulose filter plug saturated with 0.75 mL deionized water.


The Supelco MC and SKC MC tubes exhibited some breakthrough; results listed above represent both A (front) and B (backup) sections. The amount found in each section is shown:

Sample #

ppm A

ppm B

SKC MC 1
SKC MC 2
SKC MC 3
Supelco MC 1
Supelco MC 2
Supelco MC 3

1.34
1.38
1.30
0.94
1.19
1.06

0.10
0.15
0.27
0.37
0.38
0.30

The block diagram of the major components of the generation system is shown below. This system provided a means of generating dynamic test atmospheres. The system consists of four essential elements:

1) Flow, temperature, and humidity control system
2) Phosphine vapor generating system 
3) Mixing chamber 
4) Active sampling manifold

Figure 1

Figure 1

Figure 2 
Storage Stability - Collected Samples

Figure 2 - Storage Stability - Collected Samples

Figure 3 
Effects of Humidity on Phosphine Sample Collection

Figure 3 - Effects of Humidity on Phosphine Sample Collection

Figure 4 
Detection Limit Curve

Figure 4 - Detection Limit Curve

Addendum 1

Comparison of Different Lots of Carbon Bead

The original evaluation of the treated carbon bead was conducted with bead obtained from Union Carbide [(Tonawanda, NY) Note: The carbon bead was called "Purasieve" by Union Carbide]. More recent lots have been obtained from Kureha Chemical, MY. Recent lots of carbon bead have been less efficient in collecting phosphine when using the sampling and analytical parameters described in the method (11.1). A series of experiments, were conducted to determine phosphine recoveries for different lots and to find a lot that gave adequate recoveries.

Procedure:
A generation system as mentioned in Section 2 was used to generate dynamic atmospheres of phosphine. Sampling tubes were prepared at the laboratory or were obtained commercially from SKC Inc. (Eighty Four, PA) or Supelco (Bellefonte, PA). All samples were collected using the following conditions:

80% RH, 25°C, sample flow rate of approximately 0.15 L/min

Results:
As shown below, the Union Carbide bead and the Kureha Chemical Co. lot no. 820601 and 15161 carbon bead gave acceptable recoveries for the collection of phosphine. The Supelco bead recovery was slightly low at approximately 75%.

Experiment #

Results

1

OSHA-New

OSHA-Old

ppm, PH3

0.74

2.68


Sampling time = 60 min
Theoretical PH3 concentration = 2.70 ppm

2a

SKC-567

SKC-646

SKC-537

ppm, PH3

0.23

0.26

0.66

   
 
   

2b

SKC-567

SKC-646

SKC-537

ppm, PH3

0.17

0.18

0.41


Sampling time = 120 min
Theoretical PH3 concentration:
  2a = 0.70 ppm
  2b = 0.40 ppm

Addendum (Continued)
Comparison of Different Lots of Carbon Bead

Experiment #

Results

3

  

Supelco

OSHA-Old

ppm, PH3

0.52

0.70


Sampling time = 240 min
Theoretical PH3 concentration = 0.70 ppm

4

 

JKC

SKC-537

ppm, PH3

0.56*

0.61

Average value, n = 4


Sampling time = 240 min
Theoretical PH3 concentration = 0.60 ppm

5

 

JKC2

SKC-537

ppm, PH3

1.25**  
1.40***

1.41

** Sampling rate 0.3 L/min
*** Sampling rate 0.15 L/min, n = 2


Sampling time = 120 min
Theoretical PH3 concentration = 1.40 ppm
Identities Source
OSHA-New:
OSHA-Old:
SKC-537:
SKC-567:
SKC-646:
Supelco:
JKC:
JKC2:
Kureha Chemical Co. lot no. G270R 77137
Union Carbide, lot no. unknown; used to validate method ID-180
Same as OSHA-Old
Same as OSHA-New
From SKC Inc., lot no. unknown
From Supelco, lot no. 765-93, 20/40 mesh.
Kureha Chemical Co. (Japan) Grade MU-AZ, lot no. 820601
Kureha Chemical Co. (Japan) Grade MU-AZ, lot no. 15161

The "OSHA, Supelco, and JKCII designated sampling tubes were impregnated with potassium hydroxide and prepared in-house. The "SKC" sampling tubes were prepared by SKC Inc. The "SKC 646" series is assumed to be carbon bead recently obtained from Kureha and is similar to OSHA-Nev.

Summary: The Kureha Chemical Co. lot no. 820601 carbon bead appears acceptable to use for phosphine sampling after it is impregnated with potassium hydroxide. The lot obtained from Union Carbide is no longer available. Presumably, this lot had also originated from Kureha Chemical.

Further testing using electron microscopy and X-ray fluorescence to determine if any significant physical differences existed among the lots of carbon bead have been inconclusive. Subtle differences in physical structure and sulfur content were noted between the lots. Greater collection efficiency was noted for those lots showing the presence of small amounts of sulfur. Examination of the physical character of the beads with a scanning electron microscope revealed less surface fissures and cracks, and more smooth surface indentations for the more efficient beads; however, at this point in time it is unknown as to why lot differences exist for the collection retention of phosphine. Personnel at Kureha Chemical Co. indicated the pitch used in the bead production sometimes varies widely.

Addendum 2

An additional study was conducted to assess the ability of the Kureha Chemical Co. lot no. 820601 carbon bead to collect samples near the STEL concentration of 1 ppm PH3 The bead was impregnated with KOH and prepared as mentioned in the method. The generation system as described in Section 2 was used to produce a dynamic atmosphere of approximately 1.3 ppm PH3 at 25°C and 80% RH. Samples were taken from the system first at different flow rates to determine the potential for breakthrough. Two sampling tubes were connected in series and samples were taken for 15-min at each of the flow rates. Results are shovn below.

--ppm PH3 Found---

Sample

Flow Rate, L/min

1st Tube

2nd Tube

% Breakthrough

1
2
3
4

0.15
0.30
0.50
1.00

1.22
1.22
1.03
1.07

ND
ND
ND
0.07

0
0
0
6.1

ND = None detectable < 0.012 ppm PH3

The amount of breakthrough and sensitivity of the analytical instrument for the amount of PH3 collected for 15-min was assessed. The sampling flow rate of 0.3 L/min and a sampling time of 15-min was considered acceptable for STEL determinations of PH3

Seven samples were then taken from the generation system using the conditions mentioned above. A sampling flow rate of approximately 0.3 L/min was used for 15-min.

Sample

PH3 ppm Found

PH3 ppm Taken

% Recovery

1
2
3
4
5
6
7

1.18
1.21
1.21
1.27
1.17
1.21
1.30

1.30
1.30
1.30
1.30
1.30
1.30
1.30

90.8
93.1
93.1
97.7
90.0
93.1
100.0

  

n = 7
Mean = 1.22
Std Dev = 0.047
CV2 = 0.039


94.0

  

Overall Error (STEL) = 13.8%

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