U.S. patent number 3,798,973 [Application Number 05/271,901] was granted by the patent office on 1974-03-26 for sample method and arrangement for gas chromatograph.
This patent grant is currently assigned to The Perkin-Elmer Corporation. Invention is credited to Willard E. Estey.
United States Patent |
3,798,973 |
Estey |
March 26, 1974 |
SAMPLE METHOD AND ARRANGEMENT FOR GAS CHROMATOGRAPH
Abstract
A method for providing enhanced stream splitting is provided by
conveying a plug comprising a mixture of a sample material and
carrier gas to a stream splitting means and initially dividing a
leading portion of the plug during a relatively short interval of
time into a measurement component and into a discharge component.
The division or split ratio is automatically altered to a second
value according to which the remaining and principal portion of the
plug is divided by conveying the discharge component through a
discharge volume which is relatively small with respect to the
volume of the plug and through a flow restriction to atmosphere.
The measurement component of the plug is simultaneously conveyed
toward a chromatographic column. The second split ratio is thereby
maintained substantially constant for the passage of the remaining
and principal portion of the plug past a split station of the
stream splitting means. A chromatographic apparatus in accordance
with features of the invention comprises a stream splitting means,
means providing a flow channel communicating between a first outlet
of the stream splitting means and a separating column, and means
providing a second flow channel communicating between a second
outlet of the stream splitting means and a flow restrictor means
which is vented to atmosphere. The second flow channel has a
relatively small volume for providing that a discharge component of
the plug which flows therein after splitting is rapidly vented to
atmosphere. In a particular embodiment, the discharge volume is
substantially less in magnitude than the volume of the plug.
Inventors: |
Estey; Willard E. (Ridgefield,
CT) |
Assignee: |
The Perkin-Elmer Corporation
(Norwalk, CT)
|
Family
ID: |
23037566 |
Appl.
No.: |
05/271,901 |
Filed: |
July 14, 1972 |
Current U.S.
Class: |
73/863.43;
73/19.02; 73/23.35; 73/863.58; 73/864.81 |
Current CPC
Class: |
G01N
30/10 (20130101); G01N 2030/347 (20130101) |
Current International
Class: |
G01N
30/10 (20060101); G01N 30/00 (20060101); G01N
30/34 (20060101); G01r 001/10 () |
Field of
Search: |
;73/422GC,23.1 |
Foreign Patent Documents
Primary Examiner: Swisher; S. Clement
Attorney, Agent or Firm: Levinson; Daniel R.
Claims
What is claimed is:
1. A sample injection arrangement for a gas chromato-graph having
an open tubular separating column comprising:
an elongated generally tubular shaped housing member;
a stream splitting body positioned at one end of said housing
member and having an inlet aperture extending into a
frustro-conically shaped bore;
said stream splitting body including a thin-walled conically shaped
body positioned near a narrow portion of said frustro-conically
shaped bore and forming with said frustro-conically shaped bore a
stream splitting station;
means extending through said stream splitting body and
communicating with said thin-walled conically shaped body for
providing a flow passage between an inlet of said conically shaped
body and an open tubular column;
a channel formed in said stream splitting body between said
frustro-conically shaped bore and an outer surface of said
body;
a flow impedance; and,
an elongated body coupled between said aperture in said stream
splitting means and said flow impedance means;
said flow impedance means having an outlet aperture exposed to
atmospheric conditions.
2. The apparatus of claim 1 wherein said elongated body has a
volume which is substantially less than the volume of a sample
mixture adapted to be accommodated by said instrument.
3. The apparatus of claim 2 wherein said tubular housing has a
longitudinal axis, a recess formed in said body and extending in a
direction substantially parallel to said axis, and said elongated
body is positioned in said recess.
4. The apparatus of claim 1 including means positioned within said
tubular housing for mixing the sample and carrier gas, said means
comprising a plurality of disc segments extending in a generally
radial direction within said housing from different circumferential
locations within said housing and positioned at different
longitudinal sections in said housing.
5. The apparatus of claim 4 wherein a flow channel is provided for
conveying a sample quantity and carrier gas to said mixing chamber
and said disc segments are positioned circumferentially within said
housing for causing a carrier gas stream flowing therethrough to
repeatedly alter the direction of flow.
6. The apparatus of claim 5 wherein said disc segments are
assembled and secured to a rod and said assembly is adapted for
insertion and removal from said housing.
7. A method for supplying a relatively small portion of a mixture
of a sample material and a carrier gas to a chromatographic
separating column with apparatus having a conduit for conducting a
stream containing a given quantity of said mixture to stream
splitting means that splits the stream in a predetermined ratio
into a relatively small measurement component, which is carried by
a first channel to said column, and a relatively large discharge
component, which is carried by a second channel to flow restricting
means through which the discharge components is vented, said method
comprising:
providing a second channel whose volume between said splitting
means and said flow restricting means is substantially less than
the volume of said quantity of mixture supplied, and
selecting the amount of flow restriction of said flow restricting
means and said volume of the second channel in relation to each
other and in relation to the flow rate of said mixture to the
stream splitting means for the leading front of said discharge
component to pass through said second channel and said flow
restricting means in not more than 2 1/2 percent of the time it
takes for said quantity of said mixture to pass said stream
splitting means.
8. The method of claim 7 in which the time for the leading front of
the discharge component to pass through the second channel and flow
restricting means is about 1 percent of the time it takes for said
quantity of said mixture to pass said stream splitting means.
Description
This invention relates to gas chromatography. The invention relates
more particularly to an improved sample injection and stream
splitting method and arrangement for use with a gas
chromatograph.
A gas chromatograph, as is known, is an analytical instrument which
separates a sample material into constituents by conveying a plug
comprising a mixture of sample material in a vaporized state and a
substantially larger volume of carrier gas through a separating
column. The constituents which experience different transit times
through the column elute successively in time from the column to
provide a quantitative indication of the constituents of the
sample. An effluent of the column is coupled to a detection and
indicating means which senses the occurrence of generally bell
shaped peaks associated with each of the constituents and which
provides an indication of their height, area and shape.
Two general types of separating columns are presently utilized with
gas chromatographs. One form of chromatographic column comprises an
elongated capillary or open tubular column which is coated on an
inner surface thereof with a separating medium. Alternatively, a
support material is formed as an open tubular liner within the
capillary column, and the separating medium is deposited on the
support material. A second type of chromatographic column comprises
an elongated tube which is packed with a support material and upon
which the separating medium is deposited. Each of these types of
columns exhibits desirable characteristics which are useful in
separating the components of particular sample materials.
The capillary or open tubular column has an operating
characteristic which necessitates the introduction of a relatively
smaller plug quantity than can be accommodated by a packed column.
The plug volume which can be handled by a capillary column is
generally on the order of 1/10 to 1/10,000 of the quantity which is
applied to a packed column. The corresponding small sample quantity
renders the sample impractical to handle. In accordance with
present techniques, sample volumes within the range of about 0.5 to
10 microliters are introduced to the instrument at an injection
station and form substantially larger plug mixtures with the
carrier gas. The plug quantity is then automatically reduced by a
stream splitting means prior to entry onto a capillary column. The
stream splitting means divides the plug in accordance with a
predetermined split ratio into a relatively small quantity
measurement component which flows to the column and into a
relatively large quantity discharge component which is conveyed
through a discharge volume and flow restriction to atmosphere.
In order to provide meaningful analytical results, it is desirable
that the plug of sample material and carrier gas be substantially
fully homogenized before stream splitting occurs. When this
condition is not achieved, non-linearities which can be introduced
by the stream splitting means interefere with the separation and
reduce its accuracy. In practice, however, full homogenization is
not always achieved and attempts have been made to reduce stream
splitting non-linearities. More particularly, linearity occurs when
the flow rate of the plug sample mixture remains relatively
constant during the passage of the plug past the stream splitting
point or junction. In general, the carrier gas exhibits relatively
constant velocity or flow rate as it goes through the various flow
paths and channels of the inlet system of the chromatograph.
However, as the discharge component of the plug reaches a venting
flow restrictor, and goes through the restrictor to atmosphere, the
flow rate of the plug is altered. This variation in flow rate
represents a change in rate at which another portion of the plug
passes the split point. The result of this is an undesirable
alteration in the amount of sample or measuring component of the
plug which flows to the column after this variation in splitting
time occurs which differs with respect to the quantity of the
measuring component of the plug flowing to the column prior to the
plug passing the exit restrictor. Less than complete homogenization
of the plug prior to splitting in a non-linear system leads to
inaccurate results.
One stream splitting arrangement which overcomes this undesirable
non-linear affect includes a discharge channel having a volume
which is greater than the volume of the largest plug expected to be
handled by the instrument. The use of this relatively large
discharge volume then assures that the entire plug will have passed
the split station before a leading front of the discharge component
of the plug reaches the flow restriction and is vented to
atmosphere. The flow viscosity of the discharge component of the
plug and the downstream pressure is then maintained relatively
constant throughout the occurrence of the split. While this
arrangement has provided highly useful and advantageous results, it
necessitates the use of a relatively large discharge volume thereby
undesirably increasing the size of the injection and stream
splitting means. For example, although the sample quantities are on
the order of 0.5 to 10 microliters, the plug mixture for these
quantities can have a typical volume of 5 cc. Furthermore, the
instrument operator is required to limit the quantity of the plug
to a volume which is less than the volume of the discharge channel.
This can then limit the sample quantity and carrier flow rates
which can be employed. At times this requirement is not fulfilled
and the stream splitting ratio is disadvantageously affected.
In addition to relatively large size requirements for the open
tubular column injection and stream splitting means and an
accompanying relatively high cost, the replacement of a packed
column injection means with the open tubular injection and stream
splitting means has required a partial disassembly of the
instrument. This, of course, disadvantageously limits the ready
adaptability of the instrument.
Accordingly, it is an object of this invention to provide an
improved stream splitting method and arrangement for use with open
tubular gas chromatographic separating column.
Another object of the invention is to provide an improved injection
arrangement for a gas chromatograph.
Another object of the invention is to provide an improved
stream-splitting means for use with a gas chromatograph which
provides a substantially uniform splitting ratio during transit of
a plug past a stream splitting station.
Another object of the invention is to provide an improved injection
and stream-splitting arrangement for an open tubular column having
a size adapted which is readily interchangeable with packed column
injection and stream splitting means of present day
chromatographs.
Another object of the invention is to provide an improved open
tubular column injection and stream splitting arrangement having a
relatively small size, yet which provides substantial linearity in
stream splitting.
Another object of the invention is to provide a sample injection
and stream splitting arrangement for open tubular columns which can
be fabricated at substantially less cost than present day
arrangements.
A further object of the invention is to provide an improved
injection arrangement which provides enhanced sample-carrier gas
mixing and homogenization.
In accordance with the general features of the method of this
invention, a plug comprising a mixture of a sample material and
carrier gas is conveyed to a stream splitting means and a leading
portion thereof is initially divided during a relatively short
interval of time into a measurement component and into a discharge
component. The division is automatically altered to a second value
according to which the remaining and principal portion of the plug
is divided by conveying the discharge component through a
relatively small discharge volume and flow restriction to
atmosphere. The measurement component of the plug is simultaneously
conveyed toward a chromatographic column. The second split ratio is
thereby maintained substantially constant for the transit of the
remaining and principal portion of the plug past a split station of
the stream splitting means. The discharge component of the plug is
preferably vented to atmosphere simultaneously with the initial
splitting of the plug into measurement and discharge quantities.
However, a practical discharge volume must exhibit finite
dimensions, and a relatively short transit time is required for
conveying the dishcarge component from the split station to
atmosphere.
A chromatographic apparatus in accordance with features of the
invention comprises a stream splitting means, means providing a
flow channel communicating between a first outlet of the stream
splitting means and a separating column, and means providing a
second flow channel communicating between a second outlet of the
stream splitting means and a flow restrictor means which is vented
to atmosphere. The second flow channel has a relatively small
volume for providing that a discharge component of the plug which
flows therein after splitting is rapidly vented to atmosphere. In a
particular embodiment, the discharge volume is substantially less
in magnitude than the volume of the plug thereby providing a
substantially constant flow rate of the plug past the splitting
station.
In accordance with other features of the invention, mixing of the
sample and carrier gas to provide a sample plug of enhanced
homogenity is provided by a sample injector having a flow channel
formed by a cylindrically shaped body and a plurality of segments
of disc shaped stream diverting members supported within the
cylinder and extending into the cylindrical flow passage
alternatively from different circumferential locations on the inner
surface of the cylinder. The carrier stream flowing through the
cylinder thereby repeatedly alters its direction of passage and the
resulting turbulence enhances mixing of the sample material and
flowing carrier stream to provide a plug of enhanced
homogenization.
These and other objects and features of the invention will become
apparent with reference to the following specification and to the
drawings wherein:
FIG. 1 is a schematic diagram in block form illustrating a
chromatographic apparatus incorporating features of the present
invention;
FIG. 2 is a more detailed schematic view of a sample injection and
stream splitting arrangement of FIG. 1;
FIGS. 3a, 3b and 3c are diagrammatic representations illustrating
the transit of a plug mixture past a stream splitting station of a
prior art arrangement;
FIGS. 4a, 4b and 4c are diagrammatic representations illustrating
the transit of a plug mixture past a stream splitting station and
which is useful in describing the operation of the present
invention;
FIG. 5 is a side elevation view, partly in section, illustrating an
injector and stream splitting arrangement constructed in accordance
with features of the present invention;
FIG. 6 is a sectional view taken along lines 6--6 of FIG. 5;
FIG. 7 is a sectional view taken along lines 7--7 of FIG. 5;
FIG. 8 is a sectional view taken along lines 8--8 of FIG. 5;
and,
FIG. 9 is an enlarged view of a portion of the injector of FIG.
5.
Referring now to FIG. 1, the chromatographic instrument illustrated
therein includes a source of carrier gas 10. Carrier gas is
conveyed by a suitable tubulation 11 from the source 10 to an
injector and stream splitting means 12. The injector and stream
splitting means 12 is demountably supported by a heated injector
block 14 which maintains the injector and stream splitter at a
desired temperature. The injector is adapted for receiving,
vaporizing, and mixing a sample with the stream of the carrier gas.
The sample which typically has a volume on the order of 0.5 to 10
microliters is introduced into the injector means 12 from a syringe
16. The sample thus inserted forms a mixture or plug of vaporized
sample material and carrier gas, a measurement portion or component
of which is conveyed to an open tubular chromatographic column 18
and a discharge portion or component of which is conveyed to
atmosphere through a vent 20. The sample measurement component is
transported through the column 18 and is separated into
constituents which experience different transit times in the
column. An effluent of the column is coupled to a detector 22. The
detector 22 which comprises, for example, an ionization detector,
senses the occurrence of constituent peaks and provides an
electrical indication thereof. This electrical indication is
applied to an indicator, as for example, a strip chart recorder,
which forms a chromatogram having a series of bell shaped peaks,
the areas of which are indicative of the concentration of the
associated constituents of the sample.
The injector and stream splitting means 12 is schematically
illustrated in greater detail in FIG. 2. The syringe 16 includes a
probe 24 which extends through a septum 26 into a relatively narrow
bore tube 28. Carrier gas from the source 10 flows through a
channel formed between the bore 28 and a concentrically located
tube 29. The carrier gas flows into the bore 28 where it picks up
the sample which is ejected by the probe 24. The sample thus
deposited in the flowing carrier stream is transported to a mixing
chamber 30 where the sample is mixed with the carrier gas to
provide a homogenized plug 31. The plug 31 will have a volume which
is principally determined by the duration of injection and the
carrier gas flow rate. For example, at a 5cc/second carrier gas
flow rate a one second injection time, and a one microliter sample
quantity, the plug will have a volume of about 5cc. The plug
flowing from the mixing chamber 30 flows toward a stream splitting
station referenced by the dotted line 32. The plug is divided at
the station 32 into a measurement component 33 which flows along a
portion of a first channel 34 to the chromatographic column and
into a discharge component 35 which flows through a discharge
volume 36 to a flow restricting means 38. The effluent of this flow
restricting means is vented to atmosphere. Atmospheric conditions
for the purposes of this application represents the external
environmental conditions under which an analytical instrument
operates. The plug 31 is divided at the split station 32 in
accordance with a predetermined ratio R. In general, the ratio R
will have a value within the range of about 1/10 to about 1/10,000.
The ratio R is determined principally by the flow restriction of
the column connected to the channel 34, and the flow restriction
provided by the flow restricting means 38 connected to channel
36.
As indicated hereinbefore, the split ratio R is disadvantageously
subject to variation when the discharge component of a plug is
vented to atmosphere before substantially the entire volume of the
plug has completed its transit past the splitting station 32.
Stated alternatively, the plug is undesirably subjected to a
variation in flow rate during its transit at the splitting station.
A prior arrangement for avoiding this variation in R is illustrated
and described with respect to FIGS. 3a, 3b and 3c. The plug of
sample material 31 is represented by the cross-hatched section.
FIG. 3a illustrates the location of the plug as it reaches the
stream splitting station 32. FIG. 3b illustrates the division of
the plug shortly after a leading front 42 of the plug has passed
the station 32. It will be observed that at this time a portion of
the measurement component 33 of the plug has entered the channel 34
on its passage to the open tubular chromatographic column.
Similarly, a portion of relatively larger discharge component 35
has entered the discharge volume 36 on its passage toward the flow
restriction 38. In FIG. 3c, the plug has fully passed the split
station 32 and a leading front 43 of the discharge component 35,
which is fully located within the discharge channel 36 has not
reached the flow restriction 38. As indicated hereinbefore, when
the leading front 43 of the discharge plug component 35 flows
through the restrictive means 38 while a portion of the plug is
simultaneously in transit at the split station 32, then the flow
rate of the plug is altered as it passes through orifice 38 because
it has a viscosity different than the carrier which precedes the
plug through the discharge channel. This alters the time in which
sample is being split in a variation in the total amount of sample
which flows to the column. The split ratio R is thus effectively
altered. This is overcome as illustrated by the arrangement of FIG.
3c wherein the discharge volume 36 extending between the split
station 32 and the orifice 38 is made substantially larger than the
volume of the plug 31.
In accordance with the present invention, and as illustrated in
FIG. 4, a discharge component 35 of the plug is very rapidly
conveyed to atmosphere upon passing the split station 32. By
immediately conveying the discharge portion 35 of the plug to the
flow restriction 38 and to atmosphere, the flow rate of the
discharge component 35 is immediately altered from an initial value
to a second substantially constant value corresponding to the
downstream venting of the discharge component. It is noted that
after this condition is achieved, the split ratio R will remain
substantially constant throughout the interval while the remainder
and principal portion of the plug is in transit past the split
station 32. This advantageously provides for an enhanced split
operation in that the split ratio R changes immediately from an
initial value R.sub.1 to a second vaue R.sub.2 which value remains
substantially constant throughout the transit of the remainder and
principal portion of the plug past the split station 32. This rapid
initial variation in split ratio is accomplished by providing a
relatively small discharge volume 36. Preferably, the discharge
volume 36 is substantially less than the volume of the plug. Its
small size is limited by the practical requirements for providing a
venting means of finite dimensions which is adapted for supporting
the flow restriction 38 and does not create greater flow impedance
in conjunction with the restriction 38 than can be tolerated for
the desired split ratio. In addition to enhancing the linearity of
operation, the relatively small discharge volume further
contributes significantly to an overall reduction in size of the
injector and stream splitting means thereby rendering it
interchangeably mountable with injector means for packed column and
substantially reducing its cost of fabrication.
A particular embodiment of an injector and stream splitting means
constructed in accordance with this invention is illustrated in
FIGS. 5 through 8. The chromatographic injector station includes
the heater block 14 having an integral injector heater and support
segment 50. The segment 50 includes a bore extending longitudinally
therethrough for receiving an injector assembly. A radially
extending bore is formed in the heater block segment 50 for
receiving a carrier gas inlet tubulation 52. The injector assembly
which is demountably positioned in the segment 50 includes an
elongated generally tubular shaped housing 54 having an integrally
formed generally rectangular shaped segment 56 positioned at one
end of this housing. As is indicated in greater detail hereinafter,
the rectangular shaped segment 56 supports a flow restricting means
and shut-off valve for conveying a discharge portion of a plug to
atmosphere. Concentrically positioned in the injector housing 54 is
a liner assembly which includes an elongated tubular shaped body 58
extending from an inlet or right hand end of the injector as viewed
in FIG. 5 toward a central location within the injector housing 54.
The liner assembly further comprises an elongated concentrically
located liner body 60 which is formed of glass and which includes a
generally conically shaped outlet end surface 62 which is seated
against a conforming surface of an insert body 64 near one end of
the cylindrical body 58. The liner body 60 includes a
longitudinally extending bore 65 which extends between an injection
station and the insert 64. As indicated in greater detail
hereinafter, carrier gas flows through a channel which includes the
bore 65 and a bore 66 which is formed in the insert body 64. The
conically shaped surface 62 is secured against a conforming surface
of the insert 64 by a helical spring 68 which is positioned about
the body and contacts a shoulder segment 70 thereof and by an
elongated tubular sleeve 72 which is positioned about the liner 60.
This assembly inhibits carrier gas from leaking from the tube 52
directly to the bore 66 without sweeping past the sample injection
station. The assembly of the liner body 60, the sleeve 72, and the
cylindrical body 58 extend through a tubular shaped member 74 to a
probe entry or injection station. The member 74 is fitted and
brazed into a bore formed in the ring 56. An enlarged threaded
outer surface 78 is formed near one end of the member 74 and a
septum cap 79 engages this threaded surface. A probe penetrable
cylindrically shaped septum 80 formed of rubber, for example, and
an optionally used disc shaped septum shield 81 formed, for
example, of Teflon are positioned within the cap 79. When the cap
is mounted, the Teflon disc bears against one end of the sleeve 72
thereby exerting a force on the spring which seats the liner 60
against the insert 64. The septum 80 provides a probe penetrable
seal through which the syringe needle or probe 24 (FIG. 2) is
introduced. The probe which is initially introduced through a bore
84 in the cap 79, through the septum 80, through the shield 81 and
through a bore 86 in the sleeve 72, extends into the bore 65 of the
liner 60.
Carrier gas flows to this injector assembly through the tubulation
52 and a bore 88 formed in the injector housing 54. The gas flows
from the bore 88 to a concentrically located ring shaped channel
formed between an inner surface of the housing 54 and an outer
surface of the body 58. Carrier gas then flows through and from
this ring shaped channel via a plurality of apertures 90 formed in
the body 58 to a ring shaped channel extending between the inner
surface of the body 58 and an outer surface of the sleeve 72 toward
the spring 68. A ring shaped flow channel extends between an outer
surface of the liner 60 and an inner surface of the sleeve 72.
Carrier gas flowing toward the right as viewed in FIG. 5 through
this ring shaped channel flows into the bore 65 of the liner 60 and
reverses its direction of flow. An outlet orifice of the probe 24
(FIG. 2) extends into the bore 65 and discharges a quantity of
sample material into this flowing carrier stream. The carrier
stream sweeps this mixture of sample and carrier through the bore
65 and toward a mixing chamber. The carrier gas conveys the sample
quantity through the bore 66 of the insert 64 and through a spacer
ring 104 to the mixing chamber 100, referenced generally as
100.
The mixing chamber 100 is formed with a relatively wide
cross-sectional area and a relatively short length in comparison
with present day arrangements employed with open tubular columns.
In order to provide a homogenized plug or mixture of carrier gas
and sample, turbulence, the duration of mixing and the length of
plug travel is effectively increased by providing an insert
assembly of baffle members 102 which are positioned within the
housing 54. These baffle members 102 comprise segments of discs
which are secured to a rod 103 and extend from opposite sides of
the inner surface of the injector housing 54. They have a segmented
disc shape which conforms to a portion of the inner circumference
of the housing 54 and a flat 105. A flow passage 106 is provided
between the flat 105 of each member 102 and the inner surface of
the housing 54. The flats 105 of adjacent members are alternately
oppositely positioned. The direction of travel of the plug and
carrier stream is thereby repeatedly altered by this baffle
assembly and the transit time of the plug is thereby increased. An
enhanced mixing and homogenization of the plug is thus
provided.
The flowing carrier gas stream and plug which exit from the mixing
chamber pass through a ring shaped spacer body 107, similar to 100,
into a stream splitting member 108 having an outer diameter thereof
which extends within the bore of the injector housing 54 and which
is secured thereto by brazing, for example. The splitting member
108 has integrally formed therein a conically shaped bore 110 and a
cylindrically shaped bore. A thin walled injector tube assembly 112
extends through the cylindrical bore toward the conical bore 110.
The tube 112 includes a conically shaped tip 116 having an inlet
orifice 118. The tube 112 further includes a shoulder 114 of
enlarged cross-section which locates the tube 112 against a
shoulder formed near the junction of the integral, cylindrical and
conical bores of the body 108 and provides accurate locating of the
tip 116. A conventional swage lock means 119 secures the tube 112
within the split body 108. Carrier gas and the measurement
component which flow in the tube 112 enter this tube through the
origice 118 of the conical segment 116. A transverse plane,
provided by the section lines 6--6 at the orifice, represents a
stream split station equivalent to the split station 32 of FIGS.
2-4. The measuring plug component and carrier gas which flow
through the orifice 118 is conveyed through the tube 112 and
through a tubulation 120 and a column coupling means 122 to an open
tubular separating column.
The discharge component of the plug is conveyed about the outer
surface of the cone shaped member 116 and through a thin-walled
tubulation 132 which is fitted into a radially extending bore 133
in the member 108. A recess 134 (FIG. 7) is formed in and extends
longitudinally through the wall of the housing 54. This recess is
adapted for receiving and positioning the tubulation 132. The
tubulation 132 extends along the length of the housing 54 within
the recess 134 and extends into a bore 135 which communicates with
an open space 136 formed in the rectangular shaped segment 56 of
the injector housing 54. A cylindrically shaped flow restrictor
support block 140 is positioned in the space 136 which is formed at
an angle with respect to the axis of the injector and the
rectangular shaped segment 56. This block which is brazed to the
segment 56 includes an internal bore 142 threaded along a portion
of its length for receiving and engaging a flow restrictor 144. The
flow restrictor is generally cylindrically shaped and includes a
longitudinal bore extending therethrough of predetermined
dimensions for establishing a desired flow impedance to the
discharge component of the carrier gas and plug. The flow
restrictor is threaded about an outside surface thereof and engages
the internally threaded segment of the bore 142. The discharge
component of the plug flows successively through the tubulation
132, and the bore 135, space 136, bore 142 and the bore of flow
restrictor 144.
A vent control is provided for alternatively providing a
substantially unobstructed flow passage between the outlet of the
restrictor 144 and atmosphere or for establishing a bleed vent for
conserving carrier gas when a sample analysis is not in progress.
The vent control includes a tubular shaped vent port body 150
having internal threads which engage external threads formed on an
outer surface of the block 140. An 0 ring 152 provides a gas-tight
seal at this union. A valve block 154 is fitted about the port body
150 at one end thereof and a gas-tight seal is provided
therebetween by an 0 ring 156. The port body 150 includes an
internal conically shaped end segment which converges to a bore 158
communicating with a bore 160 in the valve block 154. The valve
block, which is annular shaped, includes a sliding valve member
162. This valve member is adapted to be positioned in a valve bleed
position, as illustrated in FIG. 5, or in a vent position. In the
bleed position, the bore 160 communicates with a bore 164 in the
slide body. A cylindrical bore 166 of enlarged cross-section is
formed in the slide body 162 and a body of sintered material 168 is
positioned therein. The carrier gas and discharge plug component
flow from the restrictor 144, through the bores 158, 160 and 164
and through the sintered material 168 to atmosphere. The sintered
material establishes a flow impedance creating a back pressure
which reduces the carrier flow and conserves the carrier gas when a
sample analysis is not in progress. As an analysis is about to be
initiated, the instrument operator actuates the slide 162 by
pressing it in a generally upward direction thereby longitudinally
translating the slide member and transferring a bore 170 and an
outlet venting tube 172 into communication with the bore 160 and
the valve body 154. The discharge component of carrier gas and the
plug which flow from the restrictor 144 thereby flow through a
relatively unobstructed flow passage to atmosphere.
The injector and stream splitting assembly are secured in the
heater block 14 by a clamp 145 which engages the rectangular
segment 56 of the housing 54 and which is screw mounted to the
heater block segment 50. The assembly is thereby readily
demountable by decoupling the column flow cover 122 and by removing
the clamp 145.
The discharge component of the plug is conveyed to atmosphere
almost immediately after passing the splitting station 32 by
providing a relatively small discharge volume. The discharge volume
comprises the volume between the outlet port 133 and the split
station, the volume of the port 133, the volume of the tubulation
132, the volume of the port 135 and the space 136 leading to the
flow restrictor 144. By providing a discharge volume which is
relatively small, the discharge component of the plug is rapidly
vented to atmosphere and the change in split ratio from R.sub.1 to
R.sub.2 occurs immediately. The discharge volume is relatively
small when this volume is substantially smaller than the volume of
the plug. This is in contrast with prior arrangements wherein the
discharge volume was made substantially larger than the volume of
the plug.
As indicated hereinbefore, it is desirable to provide an injection
and stream splitting means for an open tubular chromatographic
column which is relatively smaller than present day arrangements.
In this regard, an interval of time, T.sub.2, during which the
carrier gas and the sample which is injected into the carrier gas
stream are mixed is significant because of the necessity of
obtaining a homogeneous mixture prior to splitting. On the other
hand, it is desirable to maintain relatively short flow channels in
order to provide a relatively compact injector system. In
accordance with another feature of the invention, the mixing
chamber of FIG. 5 provides a mixing time interval comparable with
present day mixing chambers while still providing a relatively
compact structural arrangement. This is accomplished by providing a
relatively short mixing chamber length of relatively wide
cross-section and by providing the flow diverting and turbulence
disc members 102. These members in addition to creating the
increased turbulence which enhances the mixing of the carrier gas
in the sample also effectively elongate the path over which this
mixing occurs thereby increasing the interval of time during which
mixing can occur over than which would be provided by a mixing
chamber with this relatively shorter length.
In a particular embodiment of the invention, the discharge volume
has a magnitude which at a predetermined carrier flow rate and
within a range of split ratios, provides for the transit of a
leading front 43 of the plug discharge component through the
discharge volume in an interval of time equal to about 1 percent of
the time required for the plug to traverse the split station and
generally not exceeding about 2 1/2 percent of this interval of
time.
A particular injector and stream splitting arrangement not deemed
limiting in any respect includes a mixing chamber 100 having a
length of about 5.49 centimeters, a diameter of about 0.952
centimeters and a discharge volume principally composed of the
elongated tube 132 having a length of about 10.8 centimeters and a
diameter of about 0.0635 centimeters. With an injector having a
mixing chamber and discharge volume of these approximate
dimensions, two samples were injected into the system. A first
sample comprises a standard test mixture of C.sub.7 to C.sub.10
straight chain hydrocarbons with a boiling point range of from
about 93.5.degree. to about 159.degree.C. Sample sizes ranging in
size from 0.5 to 10.0 microliters and a range of split ratios from
1:16 to 1:418 were employed and were separated on a 300 foot by
0.01 inch inside diameter wall coated column AP-L at split ratios
of 1:74 to 1:418 as well as a 50 foot long 0.02 inch inside
diameter support coated column AP-L with a split ratio of 1:16.
Relatively good reproducible quantitative results were obtained. A
second sample comprises a mixture of C.sub.9 to C.sub.25 straight
chain hydrocarbons having a boiling point range of about
144.degree.C. to a vapor pressure of 40 MM at 282.degree.C. A gas
chromatographic column oven was programmed during the examination
of this sample. The sample injection quantities which ranged from
0.5 to 8.0 microliters at relatively low split ratios were
separated on a 50 foot long by 0.02 inch inside diameter support
coated open tubular column OV-1. In one test, the split ratio was
1:13 while in a second test the split ratio was 1:33. Good
reproducible quantitative results were also obtained. In addition,
no significant "ghost" peaks were produced with either of the
examples.
There has thus been described an improved chromatographic injection
and stream splitting method and apparatus wherein the stream
splitting ratio of measurement to discharge plug components is
initially altered and is then maintained substantially constant.
The arrangement is further advantageous in that it is relatively
compact in size and is readily interchangeable with present day
packed column injectors. The arrangement is economical in that it
can be fabricated at a substantial cost savings over present day
injection and stream splitting arrangements for open tubular
columns.
While I have described particular embodiments of the invention, it
will be apparent to those skilled in the art that variations may be
made thereto without departing from the spirit of the invention and
the scope of the appended claims.
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