Specifications
SKC Elemental Mercury Passive Sampler
Several methods for determining personal exposure levels of elemental
mercury vapor are available. Sampling methods that employ passive
samplers are desirable because they are simple to perform and eliminate
the need for sampling pumps. Unfortunately, most passive samplers
must be returned to the manufacturer for analysis by proprietary
procedures.
The SKC Passive Sampler for Elemental Mercury is specified in OSHA Method ID-140 for eight hour TWA sampling. A backup report by OSHA expands application of this sampler for long-term sampling up to 120 hours.
SKC, however, offers an elemental mercury sampler that is designed
for analysis using standard laboratory equipment; therefore, the
cost
per measurement
is kept to an absolute minimum compared to other samplers. The 520
Series Elemental Mercury Sampler measures worker exposure levels
as a time-weighted Average (TWA) and permits the positive analysis
of
elemental mercury vapor.
The OSHA Laboratory in Salt Lake City, Utah, conducted an evaluation
of the SKC elemental mercury sampler over a broad range of mercury
concentrations and sampling times. The evaluation consisted of the
following major
experiments: validation of the sampling rate, desorption efficiency,
precision and accuracy, storage stability, reverse diffusion, face
velocity dependence, and comparison of methods. The method of reference
for this evaluation is OSHA ID-140.
Mercury vapor enters the sampler by positive, controlled diffusion
so that a known sample volume is taken for a given period of time.
Mercury is completely adsorbed onto the solid sorbent. The sorbent
capsule is then taken to an accredited laboratory where the sorbent
is dissolved in acid and analyzed by flameless atomic absorption.
The sampler holder is cleaned and reused, thereby reducing sampling
costs.
Operation
- Remove a sorbent capsule from the plastic vial and insert it
into the sampler housing. Attach the sampler near the worker's
breathing zone.
- When sampling is completed, remove the sorbent capsule from the
holder and insert it into the provided ziploc bag for shipment
to an
accredited laboratory.
- Clean the housing and insert a new sorbent capsule
and foam disk. The sampler can then be reused.
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Interferences
Extensive field testing and chamber studies have shown that excellent
accuracy and precision can be achieved with these samplers without
interference from moisture or other gases, including chlorine.
Ambient Temperature
The sampling rate will vary with ambient temperature changes that
affect the diffusion rate. This effect is small, but may be significant
if sampling at unusually high or low temperatures. The diffusion
coefficient (D) is proportional to the temperature (T) to the 1.5
power (D a T1.5). This factor
is taken into account in the calculation used in the OSHA method.
Wind Velocity
The sampling rate will remain substantially constant
over a range of wind velocity from 25 to 750 ft/min. In very still
air conditions
(below 25 ft/min), the sampling rate will drop by up to 30%. If very
high wind velocities (in excess of 750 ft/ min) are expected, passive
samplers should not be used.
Ambient Pressure Changes
The sampling rate varies with ambient pressure changes that affect
the diffusion rate. The diffusion coefficient is inversely proportional
to the ambient pressure. This factor is taken into account in the
calculation used in the OSHA method.
Presence of Other Gases
Mercury sampling on this sorbent has been shown to be unaffected
by the presence of other gases, including chlorine. Note, however,
that complex interactions in the atmosphere may reduce the total
free elemental mercury present to be sampled.
References:
OSHA Method No. ID 140, Occupational Safety and Health Administration, Inorganics
Division, OSHA Technical Center, Salt Lake City, Utah.
A. O. Rathje and D. H. Marcero, "Improved Hopcalite Procedure
for the Determination of Mercury Vapor in the Air by Flameless Atomic
Absorption," Am. Ind. Hyg. Assoc. J. Volume 37 (1976), pp. 311-314.
Method MDHS 16/2, Health and Safety Executive (HSE), United Kingdom
