Packed column thermal reactor for an analytical instrument

An elongate straight column for use as a reactor in an analytical instrument. The column contains inert packed material which provides for the necessary flow path length for a fluid stream entering the reactor. Fittings are incorporated onto the ends of the column in such a manner that their width is no larger than the width of the column. The column configuration for a reactor allows more versatility in the type of temperature regulator mechanisms used to heat and cool the reactor.

BACKGROUND OF THE INVENTION 
The present invention is directed to automated analyzers and, more 
specifically, is directed to a transport delay mechanism for use in a 
flowing stream reactor that may comprise part of an automated analyzing 
instrument. Color development in the detection system of an amino acid 
analyzer has been selected as a representative application. 
In some amino acid analysers, a very small or micro chromatographic column 
is used as a specialized application of a liquid column chromatographic 
separation technique, utilizing ion exchange resin as the stationary phase 
and eluting buffers of varying pH and salt concentration as the moving 
phase. Amino acids contained in a sample are introduced at the top of the 
column and are separated from each other as they are eluted through the 
resin bed which comprises the column packing. For amino acid analysis, the 
method for detecting the amino acids in the effluent stream has been to 
combine the column effluent with a reagent that is metered into the stream 
at a flow rate proportional to that of the column eluent. When the reagent 
combines with the amino acids present in the stream, compounds are formed 
which, when subjected to further development process, can be detected by 
specific changes in optical properties such as absorption or fluorescence. 
One of the classical detection methods in amino acid analyzer systems is 
that developed by Spackman and Moore, wherein the reagent used is 
ninhydrin dissolved in a suitable solvent/buffer solution. Under this 
process, the column effluent/reagent solution is heated in a reactor to a 
fixed temperature for a specified period of time. The compound developed 
as a result of this process will have specific colors, the intensities of 
which are proportional to the amounts of compounds contained in the 
flowing stream. The optical density of these compounds is measured at 
specific wavelengths. 
Important to the calibration of the analyzer in terms of its specific 
sensitivity to detect amino acids is that the fluid/reagent mixture be 
maintained at a constant elevated temperature for a fixed period of time. 
It is critical to the stability of the instrument calibration that the two 
parameters of temperature and exposure time remain constant during the 
color development process. Classically, this has been accomplished by 
causing the effluent to pass through a TFE Teflon capillary coil which is 
normally suspended in a boiling water bath to act as the reactor in the 
amino acid analyzer system. 
The separation techniques employed in early analyzers required several 
hours to complete a single analysis. In such systems, it became common 
practice to retain the flowing stream within the reactor for as long as 
fifteen minutes to complete the color development. Newer techniques have 
increased the performance of these analyzers to permit the same analyses 
to be completed in the order of twenty minutes. It has then becomd 
necessary to provide increased color development in a much shorter period 
of time. Reference is made to FIG. 1 showing empirical results of studies 
which relate the optical densities of compounds formed by mixtures of 
ninhydrin and amino acids as a function of development time and 
temperature. 
It may be noted that maximum sensitivity and improved resolution can be 
obtained by operating the color development reactor at temperatures 
significantly above 100.degree. C. However, operation at these elevated 
temperatures obviates the use of TFE Teflon capillaries immersed in 
boiling water as has been done in prior analyzers. It then becomes 
necessary to develop a transport delay system within a heated zone for the 
flowing liquids which will withstand both the elevated temperature and the 
corrosive nature of the flowing stream. The elevated temperatures plus the 
fact that the pH of the solutions alternate between bases and acids 
increases the corrosive attack by the liquids. Also, at these high 
temperatures, it is important that the reactor not be damaged by the heat; 
therefore, the system must provide rapid cooling of the reactor in the 
event there is some type of catastrophic loss of fluid flow caused by a 
loss of control in a system. 
In most prior art the transport delay for the reactor has been a capillary 
coil that was usually wrapped in a cylindrical or spiral shape and located 
in some type of temperature control mechanism. The internal bore and 
length of this coil were of the proper dimensions to provide a suitable 
transport time within the heated zone at the flow rates prevailing in the 
analyzer. However, this type of configuration for the reactor does result 
in certain limitations with respect to the type of heating that can be 
used. In most instances, some type of heated bath surrounding the 
capillary coil has been used. A primary disadvantage with these types of 
heating systems for reactors is the fact that the cooling capability is 
not sufficient to provide the protection at higher temperatures against 
possible boiling of the flowing stream or against damage to the reactor 
materials themselves. 
Because of the numerous disadvantages accruing to the use of a heated 
reactor in which liquid is used as the heat exchange medium, the design of 
a reactor using a solid state heat exchange medium has been pursued. In 
such a development, it soon becomes apparent that the formation of a 
capillary system into a shape which will permit it to be thermally bonded 
to a solid state heat exchanger is both difficult and costly. In addition, 
the cost of fabricating such capillaries from materials which will 
withstand the gross of nature of the fluids to which they will be 
subjected in the analyzers is prohibitive for all but the most exotic 
applications. 
Attention is directed to ex,emplary prior systems such as shown in the U.S. 
Pat. No. 3,806,321 wherein FIG. 5 shows the reaction coil that is used to 
provide the color development. Another type of reactor is shown in U.S. 
Pat. No. 4,233,030 wherein the coils are longitudinally doubled back over 
each other. The U.S. Pat. No. 3,918,907 patent refers to the conventional 
type of means used to heat the reactor as a reaction coil in an 
electrically heated boiling bath. Similarly, in U.S. Pat. No. 3,926,800 
the color reaction or development coil 23 is placed in a heated bath 24 to 
develop the color of the column effluent and reagent delivered to the 
coil. 
Attention is directed to copending application entitled "Analytical 
Instrument Reactor Temperature Regulator", Ser. No. 327,378, filed on Dec. 
4, 1981 in the name of Donald E. Stephens and assigned to the assignee of 
the present patent application. This referenced patent application 
discloses an alternate method of heating a color development reactor which 
is in the form of a column. 
SUMMARY OF THE INVENTION 
The present invention relates to the use of a straight elongated column as 
a transport delay for a heated reactor in an automated analyzer. The 
column is packed with an inert material having a small particle size (70 
microns) of limited size distribution. The packing ensures a uniform fluid 
velocity across a section of the column, hence avoiding the problem of 
laminar flow and its degrading effects upon the resolution of the 
analyzer. The packed column provides the same requirements which the small 
bore capillary coils of the prior art supply relative to the transport 
delay of the flow path within the reactor and the necessary limitation of 
laminar flow of the flowing stream. 
When operating a color development reactor at temperatures above 
100.degree. C., the choice of materials that are able to stand such high 
temperatures and the range of pH involved is essentially limited to the 
use of noble metals, certain precious metal alloys and possibly a few 
difficult to fabricate exotic alloys. Consequently, the use of a short, 
comparatively large bore column which can be internally plated with or 
possibly constructed from a noble metal will provide a highly desirable 
reactor for use at high temperature. Also, the configuration of the column 
packed with an inert material provides a device that can be fabricated at 
a cost considerably below that of drawn capillary tubes which would have 
to be made of suitable noble metal materials. 
The use of a column configuration which provides both the necesary 
transport delay as well as the necessary linear front of the flowing 
stream allows much more flexibility in the type of heating system utilized 
for the reactor. Because of the use of the column configuration, numerous 
heating systems could be used such as the prior approach of boiling water, 
the reactor type heating arrangements as discussed in U.S. Pat. No. 
4,294,799, and the apparatus discussed in the previously referenced 
copending patent application entitled "Analytical Instrument Reactor 
Temperature Regulator". 
Pursuant to the development of this invention, it has been demonstrated 
that a transport delay for a flowing stream can be formed by utilizing a 
short, relatively large bore column packed with a suitable fine grain 
material having a particle size distribution of narrow range. This column 
can be made to have superlative performance to a capillary coil with 
regard to process stream resolution while providing appreciably longer 
transport delay time than a capillary coil. The form factor of the column 
lends itself well to being heated and cooled by solid state heat exchange 
medium, and its fabrication from materials that will withstand the high 
temperature and corrosive nature of the process is relatively easily 
managed.

DETAILED DESCRIPTION OF THE INVENTION 
For exemplary purposes, the application of the present invention will be 
discussed with respect to its use in an amino acid analyzer system. In 
such a system it is necessary to control the temperature of the thermal 
reactor to provide desirable color develop ment relating to the flowing 
stream. 
Attention is directed to FIG. 2, showing a schematic view of an overall 
amino acid analyzer system. A sample table 10 receives the various samples 
for introduction into the automated system which are sequenced through the 
conduit 12 to the sample injector valve 20. An eluting buffer 14 is 
transferred through the conduit 16 by the buffer pump 18 into the sample 
injector valve 20. The sample injector valve 20 is automatically operated 
by the analyzer controller 22 in order to sequence the sample in 
conjunction with the eluting buffer for introduction into the 
chromatographic column 24. As explained previously in the Background of 
the Invention, the liquid column chromatographic separation technique uses 
an ion exchange resin as a stationary phase with eluting buffers of 
varying pH and salt concentration as the moving phase. The resin base is 
packed into the column 24 for receipt of the eluting buffer in conjunction 
with the sample. The column 24 has a temperature regulator apparatus 26. A 
control system 28 is utilized to regulate the temperature in the column 
24. 
After the eluting stream exits the bottom of the column 24, it enters into 
a mixing tee 30 which is in fluid communication with a reagent pump 32 
that is designed to pump the reagent 34 into the mixing tee 30. A solvent 
36 is also used by operation of the valve 38 to pump solvent into the 
system which is done during shutdown procedures. 
The reagent mixture with the eluting buffer 14 from the liquid 
chromatographic column 24 flows through the conduit 40 into a flow path in 
the reaction chamber or column 42. The compounds produced by the reagent 
mixing with the amino acids from the sample are subjected to further 
development in the reaction chamber where the mixed flowing stream is 
heated to a specific temperature for a specific time. The presence of 
these compounds is detected by noting specific changes in optical 
properties of the stream. The optical density at specific wavelengths will 
indicate the amounts of compounds present in the flowing stream. The 
photometer 46 is used to observe these colors and intensities while the 
recorder 48 provides a documented record. 
Reference is made to FIG. 1 showing the results of some empirical studies 
made of the color development produced in ninhydrin/amino acid compounds 
under varying conditions of time and temperature. The graphical 
representation in FIG. 1 is a plot of optical density versus exposure time 
for a family of curves produced at different temperatures. This chart 
shows that maximum color development at 100.degree. C. requires a dwell 
time approaching fifteen minutes within the reactor. However, equivalent 
development may be realized by heating the mixture to higher temperatures 
for shorter periods of time, for example, one minute at 135.degree. C. 
Attention is directed to FIG. 3 showing the column reactor 42 which is an 
elongated straight column preferably made of stainless steel or other 
corrosive resistant metals and having threaded ends 50 and 52 for 
interface with a fitting 58 shown in FIG. 4. The fitting 58 has a column 
receptacle end 60 and a flow line receptacle end 62. The interior of the 
column receptacle end 60 has an internal threaded cavity 64 for engagement 
with the threaded end 50 of the column 42. The flow line receptacle end 62 
of the fitting 58 has an internal threaded cavity 68 for connection with a 
threaded connector screw 72. The center of the connector screw 72 has a 
bore 76 which is designed to receive the capillary line 40 which is in 
fluid communication with the mixing tee 30 as shown in FIG. 2. 
Adjacent the bottom 78 of the internal threaded cavity 68 of the fitting 58 
in FIG. 4 is a ferrule 80 which is designed to engage with the 
frustoconical recess 82 in the bottom 78 of the fitting flow line end 62. 
The ferrule 80 provides sealing of the capillary line 40 to the fitting 
58. Movement of the connector screw 72 toward the bottom 78 of the cavity 
will compress the resilient ferrule and establish a tight seal. 
Located adjacent the bottom 84 of the cavity 64 in the column end 60 of the 
fitting is a packing support disc 86 which is held in place by the edge 88 
of the threaded end 50 of the column 42. While only one packing disc 86 is 
shown in FIG. 4, it should be understood that another packing support disc 
86 is located at threaded end 52 of column 42. Attention is directed to 
FIG. 5 showing in more detail the column packing support 86 which has an 
annular solid portion 90 that is designed to provide a seal between the 
fitting 58 and the edge 88 of the threaded end 50 of the column. In the 
center portion 92 of the column packing support 86 in FIG. 5 are a 
plurality of perforations which are small enough to retain the column 
packing which is placed in the column, but are large enough to permit 
passage of the chromatographic effluent from the capillary path 40. 
As shown in FIG. 4, the reactor or column 42 has an internal bore or 
passage 96 in which is placed a plurality of packing material such as 
diamond grit which has an approximate seventy micron size. It should be 
noted that diamonds have excellent thermal conductivity characteristics 
and do not insulate the heat being generated. This packing is placed in 
uniformity within the bore 96 to ensure a uniform velocity profile across 
the column section. The uniform arrangement of the packed particles will 
establish small passages which in total are smaller in cross section than 
the cross section of a capillary coil. This uniform arrangement in 
conjunction with the continual flow of the stream into the reactor will 
promote uniform travel or velocity of the stream throughout the cross 
section of the packed reactor bore, i.e., a uniform velocity profile. 
It should be noted that the column 42 for use in a reactor in one 
application is, for example, 0.250 inches in diameter and approximately 
2.4 inches long with a bore 96 of approximately 0.125 inches. Also, the 
interior surface of the column bore 96 is treated by electro-plating a 
noble metal such as platinum onto its surface. 
With respect to the type of heating arrangements to which the present 
column is applicable, one approach for providing heat to a color 
development reactor is disclosed in the above referenced U.S. Pat. No. 
4,294,799 which explains in detail the type of configuration shown in FIG. 
6 of the present application for a packed column reactor. In the present 
invention, with respect to FIG. 6, the reactor 42 is placed within a 
heated core 100 which is preferably made of copper and is heated by a 
resistance element heater 102. A plurality of fins 104 is attached to the 
core element 100 to conduct heat into a flowing air stream which is drawn 
through the bottom opening 108 by the fan 110 during the cooling 
operation. By the control of the solenoid 112 and the damper mechanism 
114, the lid 116 is lifted from the housing 118 to provide cooling by the 
circulating air when the reactor must be cooled. It should be noted that 
the column 42 is easily adapted for use with the core 100 by the 
construction of a cylindrical bore 120. This is especially true with 
respect to the fact that the fittings 58 and 122 are designed so that 
their diameter is no larger than the diameter of the column 42. This 
arrangement of a straight elongated column for placement in the heating 
mechanism greatly simplifies the heat transfer process as opposed to using 
a long capillary coil which must be either in the form of a spiral or in 
the form of some type of folded arrangement to provide the necessary 
transport delay in the reactor. 
Attention is directed to FIGS. 7-9 showing in more detail the arrangement 
of using thermoelectric elements for heating and cooling the reactor 
column. FIG. 7 shows more detail of the temperature regulator assembly 130 
for the reactor 42. The reactor 42 is clamped to a thermal bar 132 by the 
use of the plate 134 shown in FIG. 9. The rear face 136 of the thermal bar 
132 is ground flat and polished to provide an excellent thermal junction 
between the bar and two thermoelectric modules or devices 138 and 140 
which are held in compression between the thermal bar 132 and a heat sink 
element 142. It should be noted that the face 144 of the heat sink is also 
polished smooth to provide a good thermal junction between the 
thermoelectric modules 138 and 140 and the heat sink. As shown more 
clearly in FIG. 8, three identical insulated mounting screws 146 are used 
to clamp the thermoelectric modules between the heat sink and the thermal 
bar 132. These mounting screws are stainless steel and are insulated from 
the heat sink by insulating sleeves 148 in FIG. 9. Compression washers 150 
are also used on the mounting screws 146 to provide a calibrated force to 
the thermoelectric modules when the arrangement is assembled. 
As shown in FIGS. 7 and 9, the reactor 42 and thermal bar 132 with the heat 
sink 142 are inserted through an aperture 152 in the mounting plate 154. 
Each end of the thermal bar 132 is attached to a mounting bracket 156 by 
stainless steel screws (not shown) inserted through insulators 158. This 
arrangement provides thermal isolation between the thermal bar 132 and the 
mounting plate 154. A flexible seal 160 is then inserted to cover the gap 
between the heat sink and the mounting plate. This construction provides 
that the thermal bar 132 is suspended from the mounting plate 154 while 
the heat sink is, in turn, suspended from the thermal bar. This type of 
support will remove all lateral stresses from the thermoelectric modules 
138 and 140. 
Once this overall system has been attached to the support wall 162, the 
heat sink 142 will protrude through a cutout opening 164 in the support 
wall 162. The plurality of heat exchange fins 166 in the heat sink member 
will be located in a plenum chamber 168 formed by the duct 170. Air 
leakage to the block is prevented by the seal 160. A cover member 172 
having insulation material 174 is attached and surrounds the reactor and 
thermal bar as shown in FIGS. 7 and 9. A thermistor 176 is located in the 
central portion of the thermal bar 132 for sensing the temperature of the 
bar and to serve as a detector for the electrical control system which 
will control the operation of the thermoelectric modules 138 and 140. More 
specific detail relating to the control and operation of this temperature 
regulator is found in the previously referenced copending patent 
application entitled "Analytical Instrument Reactor Temperature Regulator" 
which is incorporated herein by reference. 
Although various configurations have been shown with respect to the type of 
heating arrangements that can be utilized with a column reactor, it is 
envisioned that other types of heating arrangements could be utilized to 
conform with the unique versatility in using the present invention of a 
column for the reactor. Similarly, although one particular fitting 
arrangement has been shown, it is envisioned that other types of fittings 
could be designed to provide adequate sealing connection between the thin 
or small capillary line and the ends of the column reactor. Such other 
types of fittings could also be made wherein their overall diameter is no 
greater than that of the column itself.