Principles, Practices, and Equipment for …...Incomplete Recovery-Decomposition 50% 60% 70% 80% 90%...

Principles, Practices, and Equipment for

Maria D.R. Peralta, PhD and C.R. Manning, PhD, CIH

Performance Evaluation of Personal Monitoring

Badges

Personal Samplinghas arisen …

In response to the

Occupational Safety and Health Act of 1970 OSHA Rules 29CFR1910.1000 & later

placed limits on time-averaged

chemical concentrations

within employees personal breathing zones

Two types of Samplers:Active & Diffusive

• Active Sampling• Tubes

• Pump Delivers Analyte to Sorbent

• Less work to validate (4 tests)

• Diffusive Sampling• Badges

• Diffusion Delivers Analyte to Sorbent

• More work to validate (7 tests)

Published ProtocolsDescribed Evaluation Parameters

for Diffusive Samplers

• NIOSH Draft Protocol

• CEN EN 838 (Europe)

• ANSI/ISEA 104-2009

• ASTM D6246

• MDHS 27 (UK)

Personal SamplerEvaluation Parameters

• Analytical Recovery & Blank

• Sampling (uptake) Rate

• Reverse Diffusion

– Breakthrough

• Velocity/Orientation Effects

• Humidity Effects

• Temperature Effects

• Storage Stability

Analytical Recovery & Blank(Desorption Efficiency)

• Add Analyte to each Sampler

• Add Analyte to Extraction Fluid

• 5x replicates

• 3 concentrations: low, medium, high

• Blank

– Breakthrough

• Temp Effects

• Analyze Samplers & Calculate Recovery

% Recovery = DE = (Qty Found, Sampler) – (Blank)

(Qty Found, Fluid)

Possible Causes of Low DE

- Weakly attracted to sorbentRe-evaporation

- Strongly Held on SorbentIncomplete Recovery

- Decomposition

Sorbent ASorbent BSorbent C

– Breakthrough

• Temp Effects

Analytical Recovery & Blank(Desorption Efficiency)

– Breakthrough

• Temp Effects

Analytical Recovery & BlankEquipment Needed

Sampling Rate Test

• In a dynamic (flowing) exposure chamber:

• Generate Analyte– Constant concentration

• Expose Diffusive & Active Samplers– Active sampler is reference method

– Set period of time

• Analyze Samplers– Qty found on each sampler

• Sampling Rate =

Qty Found (diffusive) x Sample Volume (active)

Qty Found (active) x Sampling Time

– Breakthrough

• Temp Effects

2 4 6 8

Sampling Time, hr .Q

10 ppm

30 ppm

Non-IdealAnalyte Uptake: • Linear

– Time

– Concentration

• Slope ~ Sampling Rate

– Breakthrough

• Temp Effects

Sampling Rate Test

TestCell

HeatedVaporizer

SyringePump

Miller-NelsonAtmosphereGenerator

Source

CalVessel

CompressedAir

Solvent Flowat __ mL/min

Air at 100 L/min25oC, 20-85%RH

SamplingTubes

Personal Monitoring Badges

15-200cm/sec

DynamicExposure Chamber

Critical OrificeSampling

Sampling Rate Test(schematic)

Sampling Rate Test Set-UpPhoto

Critical OrificeSampler

Badges

Syringe Pump

Exposure Chamber

Vaporizer

AirRecirculatesIn Mini-Chamber

AtmosphereGas Flow

FanRecirculatingMini-Chamber

Sampling Rate Test Set-UpClose-up showing tubes and badges

AirOut

Miller-NelsonAtmosphere Conditioner

Syringe Pump

Critical Orifice Sampler

Reverse Diffusion Test(evaporative loss during/after sampling)

• Expose 10 Diffusive Samplers• Highest Expected Concentration for short time

• Remove & Cap 5 Samplers (A)• Store Cold & Analyze Later

• Leave 5 Samplers Open (B)• Expose to Zero Air (several hours)

• Analyze All Samplers Together

• Compare: Analyte Found (B)

Analyte Found (A)

Difference (A – B) due to Reverse Diffusion

– Breakthrough

• Temp Effects

2 4 6 8

Time in Zero Air (hr)Q

20 ppm

40 ppm

40ppm Non-Ideal

Reverse Diffusion

- Causes:

- Exceeding Capacity of

Sorbent

- Weak association

between analyte and

- This test determines the Maximum Sampling Time (MST) for each Analyte

– Breakthrough

• Temp Effects

Reverse Diffusion Test(evaporative loss during/after sampling)

Air Velocity Test

• Expose 5 Samplers @ V = 15 cm/sec (30 ft/min)

• @ V = 50 cm/sec

• @ V = 100 cm/sec

– Breakthrough

• Temp Effects

• Compare Analyte recovered on all Samplers for different air velocities

• Sampling Rate should be unaffected by air velocity when V ≥ minimum required air velocity

Fixed %RH, Time, Concentration

Air Velocity Test Looks for Differences

at 15 cm/sec vs higher flows

(15 cm/sec = 30 ft/min … lowest typical air velocity in workplaces)

Air Velocity Effects

Air Velocity EffectsAt some air velocity, Sampling Rate will begin to decrease

With proper design, Sampler “works” down to 15 cm/sec

Results for a particular Sampler will be similar for many analytes

10 20 30 40 40 50

Air Velocity, cm/secQ

Non-Ideal @ 2ppm

Ideal @ 2ppm

Ideal @ 4 ppm

Non-Ideal @ 4 ppm

– Breakthrough

• Temp Effects

Humidity Effects(typical experiment)

30 40 50 60 70 80 90% RH

50% RH

80% RH

• Expose 15 Samplers at Fixed Concentration, Temp, Time

• 5 at 20% RH

• 5 at 50% RH

• 5 at 80% RH

• Analyze All Samplers

• Compare Amt Found for Different Humidity Exposures

– Difference Due to Evaporative Loss Arising from Moisture Taking Up Sorbent Capacity

– Breakthrough

• Temp Effects

Miller-NelsonAtmosphere Conditioner

Supplies air at controlled flow, temp, and %RH

– Breakthrough

• Temp Effects

• Expose 5 Samplers at 0 °C

• 25 °C

• 40 °C

Temperature Effect Test(Sampling Rate increases with Temp)

• Compare Analyte Recovery on All Samplers

– Breakthrough

• Temp Effects

Fixed %RH, Time, Concentration

0 25 40

Test Temp (deg C)

10 ppm

20 ppm

40 ppm

Typical S.R. Increase:

3% per 10 °C

Temp Test Set-Up

Temperature Test

Critical Sampler

Chamber inIncubator

Heater& Cooler

– Breakthrough

• Temp Effects

Storage Stability Test(analyte loss on storage)

• Expose 30 Diffusive Samplers• At Fixed Concentration, Temp, Time

• Remove & Cap 10 Samplers • Store at Room Temp (25ºC)

• Remove & Cap 10 Samplers • Store In Freezer (-20ºC)

• Remove & Cap 10 Samplers • Store in Refrigerator (2-8ºC)

– Breakthrough

• Temp Effects

Analyze Stored Samplers:

- 15 after 1 week storage

- 15 after 2 week storage

5 10 15 20

Holding Time, days%

ecovere

FreezerRefrigRoomTemp

Causes for decreased storage stability

– Analyte Loss• Evaporation

• Migrates into packaging

– by Decomposition

– Breakthrough

• Temp Effects

Storage Stability Test(analyte loss on storage)

Evaluation Criteria

o Several OSHA Rules & most NIOSH criteria suggest an overall uncertainty of + 25% is acceptable for personal monitoring tests.

o Taking a 25% accuracy criterion, you would accept evaluation results as validation of a sampler provided test variation stay within + 25% overall system variation.

o In some cases in conformance with accuracy requirements, you may place procedural limits on (for example):

(a) Allowed %RH or Temperature Range in which Sampler is used

(b) Allowed Holding Time or Storage Conditions after sampling

(c) Allowed Sampling Time (< 8 hr)

Summaryo Diffusive Samplers are easy to use, but difficult to evaluate.

o 7 types of tests are needed to evaluate a Personal Monitoring Badge (Diffusive Sampler).

o Complex Sampling Rate evaluations for Badges replace use of the Sampling Pump. (Sampling Rates can be predicated with some accuracy.)

o Desorption efficiency (DE) tests, humidity effects, and sample stability tests are similar for both Diffusive or Active samplers.

o Diffusive Samplers can suffer evaporative losses (Reverse Diffusion) if maximum sampling time is exceeded, but MST is large for most analytes.

o Temperature & Air Velocity affects are simple and similar for many analytes, so they need be performed only 1 time per each type of Sampler.

Principles, Practices, and Equipment for …...Incomplete Recovery-Decomposition 50% 60% 70% 80% 90%...

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