Inertial impaction air sampling device

An inertial impactor to be used in an air sampling device for collection of respirable size particles in ambient air which may include a graphite furnace as the impaction substrate in a small-size, portable, direct analysis structure that gives immediate results and is totally self-contained allowing for remote and/or personal sampling. The graphite furnace collects suspended particles transported through the housing by means of the air flow system, and these particles may be analyzed for elements, quantitatively and qualitatively, by atomic absorption spectrophotometry.

BACKGROUND OF THE INVENTION 
The present invention relates generally to an inertial impaction air 
sampling device which is small-sized for portability and self-contained 
allowing for remote or personal sampling, and more particularly, to a 
portable, personal air sampling device capable of collecting respirable 
organometallic particulates in room environment air and direct analysis 
for providing immediate results. 
The collection and analysis of elemental containing particulates, 
especially organometallic particulates in the presence of additional 
organic sample components, in ambient air is becoming increasingly 
important as maximum permissable exposure to toxic agents decreases. 
Accordingly, the relationship between the sampling method and the 
analytical method is becoming increasingly important. The particular 
analyte to be determined, as well as the particular sampling method 
chosen, will generally dictate the analytical procedure that can be used, 
and conventional sampling devices have not always proved satisfactory for 
providing the information desired. 
Several air sampling devices are commonly known for collecting particulates 
in room air. Bulk or wipe samples do not yield useful information about 
airborne concentrations of contaminants. Filter sampling is not always 
reliable since filter loading can occur rapidly with membrane filters, and 
contaminants or oversized particles can be collected that would suggest 
higher than actual exposure. Also, no particle size distribution is 
obtainable without further analysis by electron microscopy or some other 
analytical technique. Further, filter samples generally require extensive 
treatment prior to the analysis, a process that is time consuming, 
expensive, and subjects the entire procedure to increased probability of 
errors. 
Atomic absorption spectrometry offers advantages in the analysis of 
elemental containing particulates because it can provide low detection 
limits (more sensitive detection) and precise determinations for a wide 
variety of elements, and is thus very popular for non-real-time 
determinations. However, real time sampling would be optimum and would 
eliminate the potential problems associated with sample collection 
methods, sample transport, and sample preparation, and real time sampling 
has heretofore not been possible with atomic absorption spectrometry. Real 
time sampling would require, first, that an atomic absorption spectrometer 
be present in the vicinity of the sample being collected and, second, that 
multiple instruments be available should several sites be needed to be 
sampled simultaneously. This is neither economical or practical where the 
determination of occupational exposure must be made from a breathing zone 
sample, the "breathing zone" being commonly known as the space within one 
foot of the mouth and nose of the worker in an occupational environment. 
Also, traditional atomic absorption methods utilize the sample in the form 
of a solution. Airborne particulates, however collected, must be subjected 
to a dissolution procedure, usually requiring acid digestion and a 
dilution process. These processes cause undesirable sample losses as do 
the pretreatment processes for filter sampling. 
Additionally, specific methods for sampling and analysis using atomic 
absorption spectrophotometry have suffered from various specific 
disadvantages. Impinger samplers used with UV/VIS Absorption 
Spectrophotometry have been plagued with matrix interferences which 
preclude sensitive and precise detection of various organometallic 
elements, for instance hexaphenyl dilead in the presence of styrene. 
Filter collection methods used with Flame Atomic Absorption have been 
shown to have excessive loss of the sample. Because of the additional 
losses in the sample preparation for analysis, the overall efficiency of 
this method is less than 25% with poor precision. 
The most precise and sensitive analytical method for sampling and detecting 
organometallic constituents in ambient air is inertial impaction sampling, 
a method which collects the sample in such a way that it can be deposited 
directly into the analytical measurement system, e.g. the spectrometer 
sample cell, combined with Graphite Furnace Atomic Absorption (GFAA) 
analysis. Compared with flame atomic absorption, this method of analysis 
offers low detection units, electrothermal atomization, more absorption, 
more sensitive detection--results using this method are approximately 
three orders of magnitude better than detection using flame atomic 
absorption--and the elimination of all sample pretreatment steps. However, 
in the past, inertial impaction has been limited to quantitative rather 
than qualitative analysis. Also, when inertial impaction samplers have 
been combined with graphite furnace impaction substrates, the furnace 
itself has been permanently mounted in the electrothermal atomization 
atomic absorption spectrometer, and a tapered collection device was 
inserted into the furnace for analysis. While this method is useful in the 
development of an area monitoring system for a workplace environment, it 
is not useful in the case of the determination of occupational exposure 
where samples must be collected in the breathing zone of the worker. 
Nevertheless, inertial impaction has been shown to be extremely efficient 
in the collection of respirable size particles (1-20 .mu.m aerodynamic 
diameter), with entry losses in the range of 8-16% for particles from 1-7 
.mu.m aerodynamic diameter, and inertial impaction sampling plus GFAA 
analysis has proved to be the best sampling and analysis method for the 
determination of airborne organometallic particulates. 
There is an existing need for a reliable and economical air sampling device 
to be used for both quantitative and qualitative analysis of materials in 
the environment. 
Also, there is an existing need for an inertial impaction device designed 
as a personal breathing zone sampler, capable of size selective sampling 
of respirable size particles in the ambient environment (1-20 microns in 
diameter), low detection limits, and rapid, direct analysis without the 
need for extended sample preparation procedures. 
There is a further need for a personal breathing zone sampler that is 
portable and attachable to an individual in the workplace, and that 
operates at a flow rate which closely approximates the rate of human 
respiration (2.0 L/min.). 
There is still a further need for a personal breathing zone sampler device 
using a graphite furnace as the impaction substrate. 
SUMMARY OF THE INVENTION 
In view of the above-described needs, it is an object of this invention to 
provide a portable inertial impaction sampling device with remote 
capability which is capable of quantitative and qualitative analysis of 
solid aerosol particulates in gas efficiently and sensitively and capable 
of providing an impacted sample for analysis which is not removed from the 
substrate and requires no sample preparation process. 
It is also an object of this invention to provide a portable inertial 
impaction sampling device which may be attached to an individual for 
providing a breathing zone sample. 
It is another object of this invention to provide a portable inertial 
impact sampling device that may utilize a graphite furnace as the 
impaction substrate. 
Additional objects, advantages, and novel features of this invention will 
become apparent to those skilled in the art upon examination of the 
following description or may be learned by the practice of the invention. 
The objects and advantages of the invention may be realized and attained 
by means of the instrumentalities and combinations particularly pointed 
out in the appended claims. 
To achieve the foregoing and other objects and in accordance with the 
purpose of the present invention, as embodied and broadly described 
herein, there is provided a portable inertial impact sampler for detection 
and collection of solid aerosol particulates in gas, i.e. anything with 
mass suspended in a gas, including dust, vapor droplets, molecules or 
organometallic particulates. The sampler includes a cylindrical sample 
probe at one end for receiving, collimating, and expelling the gas flow, a 
tube arranged perpendicular to the expelling end of the probe and to the 
gas flow, a continuous sample collecting surface inside the perpendicular 
tube, and a removable mount for holding the probe and tube in a fixed 
position relative to each other during the collection of the sample. The 
mount may be adjusted for spacing the collection surface appropriately in 
relation to the end of the probe to allow for the collection of a 
particular size of particulate, because the size of particulate to be 
collected is controlled by this spacing, as well as the size of the end of 
the probe and the flow rate of the gas. The sampler arrangement according 
to the invention, where the tube containing the sampling surface is held 
in contact with the sample probe during collection and is removable for 
analysis, allows the direct size-selective collection of particles as an 
impacted sample that is not removed from the substrate for preparation, 
but may be analyzed according to the chosen method immediately and 
directly.

DETAILED DESCRIPTION OF THE INVENTION 
As shown in the figures, one embodiment of the portable inertial impact 
sampler 1 includes a converging sample probe 10, mount 20, and tubular 
flow diverter 30, and a sample collector 40. 
A preferred embodiment of inertial impact sampler 1 includes the use of a 
graphite tube as tubular diverter 30, the interior surface 31 of which is 
also sample collector 40. FIGS. 1 and 2 depict this preferred embodiment 
for the tubular diverter; in FIG. 1, tubular diverter 30 is shaded for 
clarity. Graphite tube 30 has a continuous inner surface 31 having a 
diameter of 6 millimeters for collection of the sample. The wall of 
tubular diverter 30 includes entry port 32 having a 2 millimeter diameter 
for introduction of the sample into the furnace. The size of the graphite 
tube or furnace is selected to be compatible with prior art devices for 
Graphite Furnace Atomic Absorption (GFAA) for single elemental analysis, 
or Inductively Coupled Plasma Atomic Emission (ICP) if a multi-elemental 
analysis is desired. 
Although the preferred embodiment is described for an inertial impacter 
using a graphite furnace as the sample collector, persons reasonably 
skilled in the art will immediately recognize that alternative sample 
collectors with different dimensions are possible and may, under 
appropriate circumstances, be preferable. In fact, there are numerous 
possibilities for an impaction substrate to be utilized with the sampler 
of this invention; the material to be used for the substrate as well as 
the dimensions of the sampler structure may be chosen to fit the study to 
be performed and the analytical technique to be used. 
For example, where xray fluorescence is the chosen method of analysis, the 
interior surface 31 of tubular diverter 30 will not be the sample 
collector as is the case with GFAA or ICP (which utilize the graphite 
furnace). In this case, as illustrated by FIG. 3, diverter 30 may be made 
of plastic, copper, or other suitable material with an interior surface 
structured to receive a removable plate sample collector 40 made of TEFLON 
(trademark), defined as Du Pont's tradename denoting all of its 
fluorocarbon resins, including PTFE, FEP, and various copolymers in 
Whittington's Dictionary of Plastics, Second Edition, Technomic Publishing 
Co., Inc., 1978, page 309, or other suitable, stable polymer or 
hydrocarbon material that is basically inert to the chemical process of 
the invention, which has a top surface 41 to directly receive the sample. 
For other types of analyses, silicon chips may be used as sample 
collecting surfaces. 
FIG. 3 is a three-quarter cutaway view of the tubular diverter 30 
containing a distinct sample collector 40 showing the use of support 
structure 34 in the interior wall 31 of tubular diverter 30. Preferably, 
in an arrangement where the sample collector 40 is a distinct structure 
from the tubular diverter 30, grooves will be used as support devices 34 
for a sample collecting plate 40. Again, persons of reasonable skill in 
the art will recognize that may support devices other than grooves may be 
used according to the scope of the invention. 
Referring again to FIGS. 1 and 2, probe 10 includes a cylindrical input end 
11 of diameter D1 for receiving the flow of gas, and an interior surface 
12. This cylindrical input end 11 increases inlet efficiency by 
significantly reducing turbulence in and around the vicinity of the inlet. 
Diameter D1 of the input end extends as the diameter of the interior 
surface 12 from input end 11 to a point 17 at one-half the length of probe 
10 from input end 11 to an output end 13. At point 17, halfway down the 
length of probe 10, interior surface 12 tapers at an angle of 
approximately 55.degree.-65.degree. from the axis to output end 13, 
preferably at about 60.degree.. This particular angle is important to this 
invention as it has been found to provide the optimum collection of 
particles by minimizing the effects of particle bounce from tapered 
surface 12, thus minimizing entry losses. Output end 13 preferably 
includes a jet 14 having a length-to-width ratio of 3 or greater, which 
collimates the flow of gas and particles into a stream along the axis of 
collector 10. This length-to-width ratio of jet 14 is important as it has 
been found to achieve laminar flow at 3 or greater. The tip of jet 14 is 
directed towards, and may be inserted into, port 32 for allowing the gas 
flow to contact sample collecting surface 40. 
Mount 20 includes an open end 21 for being connected to the output end 13 
of probe 10, which may be threaded to secure the connection; the 
connecting point between probe 10 and mount 20 is preferably vacuum sealed 
against the environment by some appropriate means, such as Teflon or a 
suitable polymer tape. A transverse cylindrical bore 23 centrally disposed 
and extending completely through mount 20 perpendicular to its axis and 
located just prior to the closed end 22. Tubular diverter 30 is inserted 
into and removed from mount 20 through bore 23. The connection between 
open end 21 and output end 13 allows for adjusting the spacing between 
sample collecting surface 40 and output end 13 to effect collection of a 
chosen size of particulate. Mount 20 also includes window opening 24 in 
one wall opposite and aligned with bore 23 to allow the inserted tubular 
diverter 30 to be viewed for observation and orientation with output end 
13 of probe 10. This is particularly helpful when jet 14 is to be inserted 
into entry port 32. Window opening 24 is preferably vacuum sealed by some 
appropriate covering 25, such as glass. Mount 20 further includes a flat 
set screw 26 in closed end 22 to hold tubular diverter 30 in a fixed 
position. 
Tubing 50 is connected to each end of the diverter tube 40 and extends 
outside sampler 1. The two sections of tubing 50 are connected with 
T-connector 51 and air flow through the tube is regulated with a personal 
sampling pump. This pump is not shown, but it may preferably be a vacuum 
pump attached to the individual where the breathing zone sample is being 
tested. 
The connections 33 between the diverter tube 30 and the tubing 50 and 
connections 52 between the tubing 50 and the T-connector 51 are vacuum 
sealed with some appropriate means, such as with TEFLON(trademark) or or a 
suitable synthetic resin polymer tape, and may also be threaded to effect 
the connection. 
Finally, FIG. 2 also shows a clip 2, connected to the exterior surface of 
input end 11 of probe 10, by which the sampler 1 may be attached to an 
individual for collecting an ambient air sample. 
The basic operation of the invention is now apparent. In accordance with 
the preferred embodiment of the invention, the sampler 1 is attached by 
clip 2 to an individual for taking a breathing zone sample. Air flow is 
generated through tubes 50 which are attached to a vacuum pump on a belt 
pack of the individual wearing the sampler. Vacuum pump and belt pack are 
not shown but are standard items; the vacuum pump is typically a Gilian 
pump at a standardized flow rate. Air is pulled into inlet end 11 of probe 
10 at a flow rate of 2 L/min., corresponding to the breathing rate of a 
human being. The flow is tapered in interior surface 12 and passes through 
jet 14 into tubular diverter 30 by entry port 32 to contact sample 
collector 40. Air flow then changes direction and passes out of each end 
of tubular diverter 30 through tubes 50, leaving an impacted, concentrated 
sample on the collector 40 which may be immediately analyzed without 
further sample preparation. In the case of the preferred embodiment, where 
a graphite tube or furnace in tubular diverter 30, the method used for 
immediate analysis is either Graphite Furnace Atomic Absorption for single 
elemental analysis, or Inductively Coupled Plasma Atomic Emission for a 
multi-elemental analysis. 
Materials used in the sampler 1 may be aluminum for probe 10, typically 
QQ-A-225/8 Aluminum or 6061-P651 Aluminum, and brass or "half-hard" brass 
for mount 20, typically Type C 36000 ASTMB-16 halfhard brass. It is 
contemplated that future assemblies may use a great variety of materials. 
In one embodiment, the length of probe 10 is approximately 75 mm and the 
diameter is 41 mm. Jet 14 is 1.1 millimeter in diameter and is 4 
millimeters in length. A 6 millimeter distance is allowed between the exit 
of jet 14 and the exterior wall of tubular diverter 30 for the preferred 
embodiment where a graphite tube is used for tubular diverter 30 as well 
as sample collector 40. The graphite tube itself is commercially available 
from Perkin-Elmer, with a 6 millimeter inner diameter and a 2 millimeter 
hole in its wall to be used as an entry port. Where a platform or plate 40 
is used inside tubular diverter 30 to collect the sample, the distance 
between jet 14 and tubular diverter 30 is 3.5 millimeters. Tubing 50 
through the air flow passes is typically TYGON(trademark), defined as a 
tradename for a series of vinyl compounds used as linings, coatings, 
adhesives, tubing and extruded shapes for chemical process equipment as 
corrosion protection, in Hawley's The Condensed Chemical Dictionary, Tenth 
Edition, Van Nostrand Reinhold Company, 1981, page 1065, with a 1/4 inch 
inner diameter. 
A prototype of this invention has been constructed and tested for 
performance. Using the parameters described above, test results showed 
that the sampler according to the invention allows size selective sampling 
of respirable size particles of 1-20 microns in diameter; using the 
preferred embodiment with the graphite furnace, results showed the 
invention to be approximately six orders of magnitude more sensitive for 
lead analysis than filter sampling that has typically been used. Prior to 
this invention, the current detection limit has only been 1 .mu.g/m.sup.3 
at best. This increased sensitivity is primarily due to the rapid analysis 
time allowed because extended sample preparation procedures are 
eliminated, as well as to the decrease in sample loss afforded by the use 
of the invention because of the basic design of the sampler, again, the 
elimination of inherently lossy sample preparation procedures, and the use 
of the metal as the sample collector which dissipates the static charge on 
the charged particles. Previous sampling techniques using plastic devices 
get a increased sample loss due to migration of the particles. 
Other advantages, not previously discussed, include the small portable 
nature of the invention, which allows the sample collector itself to be 
sent through the mail for analysis, and which also affords the device the 
versatility to be used as a process sampler, a personal sampler and an 
environmental sampler. Not least among the advantages is its practicality 
and economy: the jet 14 of the invention may be of any material, rather 
than tantalum which is expensive but was previously required for jets used 
for this purpose so the equipment could withstand the 4000.degree. heat of 
the absorption spectrometer; and the graphite tube of the preferred 
embodiment no longer has to be discarded after analysis but can be cleaned 
and reused after the burnout that occurs during the analysis, thus 
bringing the cost of this sampling method into the range of gas badges or 
charcoal tube sampling. 
The particular sizes and equipment discussed above are cited merely to 
illustrate particular embodiments of the invention. It is contemplated 
that use of this invention may involve components having different 
sensitivities and sizes as long as the principle described herein is 
followed. An inertial impaction sampler, constructed in accordance with 
the present invention, will provide accurate, reliable quantitative and 
qualitative sampling of solid aerosol particulates in gas with unusual 
speed, low detection limits, and versatility. It is intended that the 
scope of the invention be defined by the claims appended hereto.