Washington Administrative Code › Title 296 - Labor and Industries, Department of › Chapter 296-62 - General occupational health standards › Part I - AIR CONTAMINANTS (SPECIFIC) › Section 296-62-07660 - Appendix D to WAC 296-62-076 - Sampling and analytical methods for MDA monitoring and measurement procedures

Current through Register Vol. 24-14, July 15, 2024
Measurements taken for the purpose of determining employee
				  exposure to MDA are best taken so that the representative average eight-hour
				  exposure may be determined from a single eight-hour sample or two four-hour
				  samples. Short-time interval samples (or grab samples) may also be used to
				  determine average exposure level if a minimum of five measurements are taken in
				  a random manner over the eight-hour work shift. Random sampling means that any
				  portion of the work shift has the same chance of being sampled as any other.
				  The arithmetic average of all such random samples taken on one work shift is an
				  estimate of an employee's average level of exposure for that work shift. Air
				  samples should be taken in the employee's breathing zone (air that would most
				  nearly represent that inhaled by the employee).
There are a number of methods available for monitoring
				  employee exposures to MDA. The method WISHA currently uses is included
				  below.
The employer, however, has the obligation of selecting any
				  monitoring method which meets the accuracy and precision requirements of the
				  standard under his/her unique field conditions. The standard requires that the
				  method of monitoring must have an accuracy, to a ninety-five percent confidence
				  level, of not less than plus or minus twenty-five percent for the select
				  PEL.
WISHA methodology.
Sampling procedure.
Apparatus:
Samples are collected by use of a personal sampling pump that
				  can be calibrated within ±5 percent of the recommended flow rate with
				  the sampling filter in line.
Samples are collected on 37 mm Gelman type A/E glass fiber
				  filters treated with sulfuric acid. The filters are prepared by soaking each
				  filter with 0.5 mL of 0.26N
				  H2SO4. (0.26 N
				  H2SO4 can be prepared by diluting
				  1.5 mL of 36N H2SO4 to 200 mL
				  with deionized water.) The filters are dried in an oven at 100 degrees C. for
				  one hour and then assembled into three-piece 37 mm polystyrene cassettes
				  without backup pads. The front filter is separated from the back filter by a
				  polystyrene spacer. The cassettes are sealed with shrink bands and the ends are
				  plugged with plastic plugs.
After sampling, the filters are carefully removed from the
				  cassettes and individually transferred to small vials containing approximately
				  2 mL deionized water. The vials must be tightly sealed. The water can be added
				  before or after the filters are transferred. The vials must be sealable and
				  capable of holding at least 7 mL of liquid. Small glass scintillation vials
				  with caps containing Teflon liners are recommended.
Reagents:
Deionized water is needed for addition to the vials.
Sampling technique:
Immediately before sampling, remove the plastic plugs from
				  the filter cassettes.
Attach the cassette to the sampling pump with flexible tubing
				  and place the cassette in the employee's breathing zone.
After sampling, seal the cassettes with plastic plugs until
				  the filters are transferred to the vials containing deionized water.
At some convenient time within ten hours of sampling,
				  transfer the sample filters to vials.
Seal the small vials lengthwise.
Submit at least one blank filter with each sample set. Blanks
				  should be handled in the same manner as samples, but no air is drawn through
				  them.
Record sample volumes (in L of air) for each sample, along
				  with any potential interferences.
Retention efficiency:
A retention efficiency study was performed by drawing 100 L
				  of air (eighty percent relative humidity) at 1 L/min through sample filters
				  that had been spiked with 0.814 microgram MDA. Instead of using backup pads,
				  blank acid-treated filters were used as backups in each cassette. Upon
				  analysis, the top filters were found to have an average of 91.8 percent of the
				  spiked amount. There was no MDA found on the bottom filters, so the amount lost
				  was probably due to the slight instability of the MDA salt.
Extraction efficiency:
The average extraction efficiency for six filters spiked at
				  the target concentration is 99.6 percent.
The stability of extracted and derivatized samples was
				  verified by reanalyzing the above six samples the next day using fresh
				  standards. The average extraction efficiency for the reanalyzed samples is 98.7
				  percent.
Recommended air volume and sampling rate:
The recommended air volume is 100 L.
The recommended sampling rate is 1 L/min.
Interferences (sampling):
MDI appears to be a positive interference. It was found that
				  when MDI was spiked onto an acid-treated filter, the MDI converted to MDA after
				  air was drawn through it.
Suspected interferences should be reported to the laboratory
				  with submitted samples.
Safety precautions (sampling):
Attach the sampling equipment to the employees so that it
				  will not interfere with work performance or safety.
Follow all safety procedures that apply to the work area
				  being sampled.
Analytical procedure:
Apparatus: The following are required for analysis.
A GC equipped with an electron capture detector. For this
				  evaluation a Hewlett Packard 5880 Gas Chromatograph equipped with a Nickel 63
				  High Temperature Electron Capture Detector and a Linearizer was used.
A GC column capable of separating the MDA derivative from the
				  solvent and interferences. A 6 ft X 2 mm ID glass column packed with three
				  percent OV-101 coated on 100/120 Gas Chrom Q or a 25 meter DB-1 or DB-5
				  capillary column is recommended for this evaluation.
A electronic integrator or some other suitable means of
				  measuring peak areas or heights.
Small resealable vials with Teflon-lined caps capable of
				  holding 4 mL.
A dispenser or pipet for toluene capable of delivering 2.0
				  mL.
Pipets (or repipets with plastic or Teflon tips) capable of
				  delivering 1 mL for the sodium hydroxide and buffer solutions.
A repipet capable of delivering 25 micro-L HFAA.
Syringes for preparation of standards and injection of
				  standards and samples into a GC.
Volumetric flasks and pipets to dilute the pure MDA in
				  preparation of standards.
Disposable pipets to transfer the toluene layers after the
				  samples are extracted.
Reagents:
0.5 NaOH prepared from reagent grade NaOH.
Toluene, pesticide grade. Burdick and Jackson distilled in
				  glass toluene was used.
Heptafluorobutyric acid anhydride (HFAA). HFAA from Pierce
				  Chemical Company was used.
pH 7.0 phosphate buffer, prepared from 136 g potassium
				  dihydrogen phosphate and 1 L deionized water. The pH is adjusted to 7.0 with
				  saturated sodium hydroxide solution.
4,4'-Methylenedianiline (MDA), reagent grade.
Standard preparation:
Concentrated stock standards are prepared by diluting pure
				  MDA with toluene. Analytical standards are prepared by injecting uL amounts of
				  diluted stock standards into vials that contain 2.0 mL toluene.
25 µL HFAA are added to each vial and the vials are
				  capped and shaken for 10 seconds.
After ten min, 1 mL of buffer is added to each vial.
The vials are recapped and shaken for ten seconds.
After allowing the layers to separate, aliquots of the
				  toluene (upper) layers are removed with a syringe and analyzed by GC.
Analytical standard concentrations should bracket sample
				  concentrations. Thus, if samples fall out of the range of prepared standards,
				  additional standards must be prepared to ascertain detector response.
Sample preparation:
The sample filters are received in vials containing deionized
				  water.
1 mL of 0.5N NaOH and 2.0 mL toluene are added to each
				  vial.
The vials are recapped and shaken for ten min.
After allowing the layers to separate, approximately 1 mL
				  aliquots of the toluene (upper) layers are transferred to separate vials with
				  clean disposable pipets.
The toluene layers are treated and analyzed.
Analysis:
GC conditions
Zone temperatures:
Column--220 degrees C.
Injector--235 degrees C.
Detector--335 degrees C.
C Gas flows, N2 Column--30
								mL/min
He Column 0.9 mL/min. (capillary) with
30 mL/min.
								ArCH4 (95/5) makeup gas
Injection volume: 5.0 uL
Column: 6 ft X 1/8 in ID glass, 3% OV-101 on
								100/120 Gas Chrom Q or 25 meter x .25 mm DB-1 or DB-5 capillary
Retention time of MDA derivative: 2.5 to
								3.5,
depending on column and flow
Chromatogram:
Peak areas or heights are measured by an integrator or other
				  suitable means.
A calibration curve is constructed by plotting response (peak
				  areas or heights) of standard injections versus ug of MDA per sample. Sample
				  concentrations must be bracketed by standards.
Interferences (analytical):
Any compound that gives an electron capture detector response
				  and has the same general retention time as the HFAA derivative of MDA is a
				  potential interference. Suspected interferences reported to the laboratory with
				  submitted samples by the industrial hygienist must be considered before samples
				  are derivatized.
GC parameters may be changed to possibly circumvent
				  interferences.
Retention time on a single column is not considered proof of
				  chemical identity. Analyte identity should be confirmed by GC/MS if
				  possible.
Calculations:
The analyte concentration for samples is obtained from the
				  calibration curve in terms of ug MDA per sample. The extraction efficiency is
				  one hundred percent. If any MDA is found on the blank, that amount is
				  subtracted from the sample amounts. The air concentrations are calculated using
				  the following formulae: Microgram/m3=(microgram MDA
				  per sample) (1000)/(L of air sampled)
				  ppb=(microgram/m3)
				  (24.46)/(198.3)=(microgram/m3)(0.1233) where 24.46
				  is the molar volume at 25 degrees C. and 760 mm Hg.
Safety precautions (analytical):
Avoid skin contact and inhalation of all chemicals.
Restrict the use of all chemicals to a fume hood if
				  possible.
Wear safety glasses and a lab coat at all times while in the
				  lab area.
Statutory Authority: Chapter 49.17 RCW. 93-04-111 (Order
					 92-15), § 296-62-07660, filed 2/3/93, effective
					 3/15/93.