WAC 296-155-17347
Appendix D to WAC 296-155-173--Sampling and analytical methods for MDA
monitoring and measurement procedures. 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 OSHA
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
her or his 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% 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 (80% relative humidity) at 1 L/min through sample filters
that had been spiked with 0.814 micro-g 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% 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%. 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%.
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 3% 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. An 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
2.9 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
micro-L amounts of diluted stock standards into vials that
contain 2.0 mL toluene. 25 micro-L HFAA are added to each
vial and the vials are capped and shaken for 10 seconds. After 10 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 10 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. Gas flows, N2 Column--30
mL/min He Purge--Column 0.9 mL/min. (capillary) with 30
mL/min. ArCH4 (95/5) make up 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 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 micro-g 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 micro-g MDA per sample. The
extraction efficiency is 100%. 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. micro-µg/m3 = (micro-µg MDA per sample) (1000)/(L
of air sampled) ppb = (micro-µg/m3)
(24.46)/(198.3) = (micro-µg/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), § 296-155-17347, filed 2/3/93, effective 3/15/93.]