CA1081994A

CA1081994A - Liquid dispenser with improved aspirating probe

Info

Publication number: CA1081994A
Application number: CA292,948A
Authority: CA
Inventors: Allen Reichler; Herman G. Diebler
Original assignee: Technicon Instruments Corp
Current assignee: Bayer Corp
Priority date: 1977-04-19
Filing date: 1977-12-13
Publication date: 1980-07-22
Also published as: GB1544767A; JPS53130090A; FR2388267A1; DE2816731C2; JPS626176B2; IT7867223A0; FR2388267B1; US4121466A; DE2816731A1; IT1108618B

Abstract

ABSTRACT OF THE DISCLOSURE
A metering apparatus is adaptable either as a dispenser or a sampler, the surface of the aspirating probe being coated with a thin film of liquid immiscible with the liquids to be aspirated. The thin immiscible film prevents contamination between segments of successively aspirated liquids and, also, their respective sources. Further, segments of the immiscible liquid can be aspirated between successive liquid segments, to maintain such liquid segments discrete.

Description

l~B~994 BACI~GROUND OF TH~ INVEN~ION
1. Field of the Invention This invention relates to metering apparatus for aspiratin~ discrete liquid volumes~ either for subsequent dispensing or passing to an analytical system, wherein contamination between successively aspirated volu~es is avoided~

2. Description of the Prior Art In prior art metering apparatus~ contamination between successively aspirated liquid volumes has been a major problem.
Such contamination can result, for example, from residue remaining on the probe surfaces from a previously aspirated liquid volume. The avoidance ofcQntamination is of particular concern where segments of sample liquids are successively aspirated, in preclse volumes~ for the analysis of dlfferent constituents of interest, for example, as in continuous-flow :
analytical systems of the type described in the Skeggs et al U. S Patent No 3,?41,432, issued on March 22, 1966 and in `~ the Smythe et al U. S, Patent No, 3,a79,141r issued on November 18, 1969. In such systems~ contamination has been ., significantly reduced by aspirating a segment wash liquid be-tween successive sample segmentsr adjacent sample segments being separated by a sequence of air-wash liquid-air segments.
To this end, the aspirating probe is immersed into a wash liquid reservoir between successive sample immersions, which serves to remove contaminants from both the interior and peripheral probe surfaces. Also, U. S. Patent No~ 3,479,141 teaches that contamination between successive sample liquids in continuous-flow analytical systems is very significantly reduced by introducing a liquid segment, e.g , silicone, which ,~ .

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1~819~4 iS immiscible with the aqueous sample segments and pre-feren-tial:Ly we-ts the interior surfaces of the probe and conduit system. In such event, the successive sample se~ments are, in e~fec-t, encased within the immiscible fluid~ and not in contact with the interior conduit surfacesl Also, in the case of metering apparatus of the dispenser-type, the aspirating probe is immersed into successive liquids, either samples or reagents, which are aspirated and dispensed, sequentially and in precise volumes.
Such dispensing is effected by the use of a pilot fluid, which serves.to "back-flush" contaminants from the interior surface of the probe system~ Again, possible contamination resulting from residues on the peripheral probe surfaces has been ~, .
: avoided by immersing the probe into a wash.liquid reservoir, . ~
and aspirating and dispensing such liquid to remove ~;
.......... contaminants from both.the interior and peripheral probe .;~
surfaces. : ~
~ The removal of contaminants from the peripheral probe ~ :
.: surfaces has required that the probe movement be other than :
rectilinearly, that is~to transport the probe from an aspirating station to a wash station~ Also, it is necessary that the probe surfaces, both interior and peripheral, be washed between successive aspirations. This need to actively wash the probe surfaces necessarily reduces the rate at which :
. precise liquid volumes can be aspirated or dispensed, and, also, requires a more complicated probe-driving mechanism, ~ :
` OBJECTS OF T~E INVENTION
Accordingly, an object of this invention is to provide - an improved metering system, wherein the problem of ,-,, ~:

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contamin~tion between successively aspirated samples is substantially avoicled~
Arlother objec-t o~ this invention is to provide an improved metering system, wherein the allowable aspi.rating rate is increased by avoiding the need to actively wash the probe system between successive liquid aspirations, A further object of this invention is to provide an improved metering system/ wherein a plurality of sample liquids can be aspirated successively into the probe system, without contamination between the aspirated sample liquids within the probe system or of the respective sources from which they have been aspirated, ~ nother object of this invention is to provide an improved metering system, wherein the probe system is inherently non-contaminating of the res~ective sources of liquids lnto which i.t is successively immersed.
These and other objects and features of the present - invention are achieyed by providing over the peripheral and internal surfaces of the probe proper a thin film of liquid which is characterized as being immiscible with the sample liquids to be aspirated and, also, which preferentially wets the internal and peripheral probe surfaces to the exclusion of such sample liquids, Such thin film can be defined, for example~ by flowing the immiscible liquid over the peripheral surfaces and aspirating the run-off along the probe or - immersing the probe into a reservoir of such liquid, The immiscible liquid may have a specific density which is greater or less than that of the liquids to be aspirated. For example~

in the preferred embodiment~ the immiscible liquid is flowed . . . .

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continuously down tile peripheral probe sur~ace at a rate substantlally equal to the aspiration rate of the probe system, such as to be eventually aspirated on probe inlet.
If desired, the flow of such immiscible liquid can be dlscontinued upon immersion of the probe inlet into a recep-tacl~ contalning liquid to be aspirated. During immersion, excess immiscible liquid on the peripheral probe surface is floated onto the surface of the liquid being aspirated, but a small film remains on such surface portion. Also, during aspiration of the liquid, a thin film of the immiscible liquid continously wets the interior probe surface. Accordingly, both peripheral and interior probe surfaces are constantly wetted and, hence, continuously protected by a thin film of the --immiscible liquid. As the probe is withdrawn, the flow of immiscible liquid may be commenced, so to be aspirated along - the probe immediately upon withdrawal of such probe from the liquid being aspirated. In such event, segments of the immiscible liquid and aspirated liquid segments are successively passed along the probe system, in turn, without the peripheral and internal surfaces of the probe being contacted by the aspirated liquid The aspirated liquid segment can be dispensed or, alternatively, a next receptacle containing a different liquid can be positioned under the probe, ;
in conventional fashion, whereby such liquid is aspirated upon immersion of the probe therein, for passage along the probe - system.
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Significantly, as an immiscible liquid segment is : ' :
- aspirated immediately prior and subsequent to each liquid segment passed into the probe system and preferentially wets ~

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10E~19Y14 bo~h the interior and peripheral surfaces, ~he successively a~pirated liquid segments are maintained discrete while passing along the probe system, e,g., to a continuous-flow analy-tical system, as shown. Accordingly~ there is no contamination between the aspirated li~uid segments passed along the probe system and, also, between their respective sources upon immersion of the probe therein, due to the presence of a thin protective film of immiscible liquid over the probe surfaces, Such result is achieved without the active washing of the interior and peripheral probe surfaces, BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view of a metering system ~'` ! , -: according to the present invention, which is adaptable either ' as a dispe~ser or sampler~
;; Figs. 2 and 3 further illustrate the operation of ~ -- the dispenser during the aspiration and discharge cycles.
Figs, 4, 5, and 6 are fragmentary views illustrating the liquid segments within the probe system~ during different operating cycles of the metering system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

' Referring more particularly to Fig. 1, a probe system, indicated as 10, comprises a tube 12 having an inlet end 14. An outer tube 16 is located concentrically about ~ tube 12, the upper end of tube 16 being sealed with the K peripheral surface of tube 12, as at 18, to define an annular ~- chamber 20 having a lower open end 22, ~'~ A probe-driving arm 24, affixed to tube 12, and a drive mechanism 25 are provided for moving the probe arrangement ~ 10 rectilinearly, as indicated by the arrows, to immerse and f~

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~f~: ' ~ ` ` ' ' ' " ` ' . ` ' -` ~L01~94 withdraw inlet end 1~ from a liquid receptacle 26 located at a take-off station beneath tube 12 ~t should be understood that a number of recep-tacles 26 can be automatlcally and successively positioned at the take-off station, as shown and described in the above-identified U S. Patent No. 3,241,432;
also, arm 24 can be adapted to impart a rotational movement to position inlet end 14 of tube 12 with respect to a plurality of liquid receptacles arranged in fixed relative position.
The outlet of tube 12 is connected along a conduit 28, having branch conduits 30, 32, 34, which are connected to pumps 36, 38, 40, respectively Also, the interior of annular chamber 20 is connected along conduit 42 to pump 44 Pumps 36, 38, 40 and 44 each have a predetermined pump rate and are independently operated in particular sequence by programmer 46, ; along leads 48, 50, 52 and 54, respectively.
As shown in Fig 1, probe arrangement 10 can be operated either as a dispenser, that is, in association with pumps 36, 38 and 40, or a sampler, in association with pump 40, to successively direct liquid samples of controlled volume to an analytical system 56. Analytical system 56 is shown connected ~` to the output of pump 40 along conduit 58 and may be of the type described in the above-identified U. S Patent No. 3,241,432.
With respect to dispenser operation, the outlet of pump 38 is connected along conduit 60 to waste, and the respective inlets of pumps 36 and 44 are connected along conduits 62 and 64 to a source 66 of immiscible liquid. The liquid contained in source 66 is characterized as being immiscible with liquid 68, whether a sample or reagent liquid, and as capable of preferentially wetting, to the exclusion of liquid 68, the bm:

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~19~4 yeriphera]. and internal surfaces 70 and 72, respectively, of tube 12 (see Figs. 4, 5 and 6), and the internal surfaces of conduits comprising the metering apparatus. For example, if such surEaces are formed of Te:Eloll~, either silicone oil or fluorocarbon oil can be employed as the immiscible liquid.
If such surfaces are formed oE polypropylene, a hydrocarbon oil, e.g. squalene, can be employed.
Initially, tube 12 is withdrawn from receptacle 26 -~ and pumps 38 and 44 are operating. ~peration of pump 44 fills chamber 20 with the immiscible liquid from source 66, excess liquid flowing from the lower end 22 of chamber 20 and downward as a thin film 74 along peripheral surface 70 of tube 12 (see Fig. 4). As a thin liquid film 74 reaches inlet 14, it tends to bead over the inlet end 14, so as to be as~i.rated upwardly along tube 12 and conduits 28 and 32 and passed to waste along conduit 60. As shown in Fig. 4, surface 70 of tube 12 is coated ` with a thin film 74 of the immiscible.liquid( the run-off forming a bead which is aspirated along tube 12.
To initiate the aspiration cycle, drive mechanism 25 20 is operated by programmer 46, along lead 76, to displace arm 24 ` downwardly and immerse inlet end 14 into receptacle 26 positioned ~ at the ~ake-off station. While inlet end 14 is immersed, programmer 46 deactivates pump 44, while continuing to operate pump 38 for a predetermined time interval, such as to aspirate ~;
.- liquid 68 into tube 12 (see Fig. ~)O As the immiscible Liquid `
:~ preferentially wets the surfaces of tube 12, to the exclusion .. of the liquid being aspirated, the aspirated liquid tends to . . ~
form a discrete segment 68' which is subsequently encased within -.~ such liquid 66 and prevented from contacting the interior surface .

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JIL()83L994 72 (see r i~ 6) ` ~lso, durin~ immersion, only a portion of thin film 7~ on peripheral surface 70 of tube 12 is wiped.
Accordingly, durin~ the immersion and aspiration cycles, the surfaces 70 and 72 of tube 12 are not in contact with-the liquid 68.
The specifie gravi-ty of the immiscible liquid may be greater or less than that of liquid 68, which is generally aqueous.
The immiscible liquid, e,g. fluorocarbon oil, wiped from peripheral surface 70 initially tends to form a thin film 77 10 over the surface of liquid 68 (See Fig, 5). When the weight of thin film 77 is sufficient to overcome the surface tension of liquid 68, such film tends to break-up as globules 73, which settle to the bottom of receptaele 26. Also, if the specifie gravity of the immiseible liquid is less than that of liquid 68, the thin film of immiseible liquid would remain over the surfaee ?
of ]iquid 68 as film 77, but would not interfere with, impede ;
or eontaminate successive aspirations of liquid 68.
When pump 38 has been operated for a period to aspirate a liquid segment 68' of predetermined volume, programmer 46 -20 deaetivates sueh pump and eontrols drive meehanism 25 to with-:- . .
draw tube 12 from reeeptaele 26, As tube 12 is being with-drawn, programmer 46 operates pump 44 to again flow immiseible liquid downwardly along peripheral surfaee 70 for aspiration along tube 12 by the aetion of pump 38 At sueh time, the aspirated liquid 68' of Fig 5 would be eneased within immiseible liquid 66, as shown in Fig. 6. As in Fig. 5, the spaeing between the aspirated liquid segments and the surfaee ~`
72 are exaggerated, for purposes of illustration.
Operating as a dispenser, a reeeiving reeeptaele 76 .: ~ . .

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~L081~94 is subs-titu~e~l a~ -tlle -take-o~f sta~ion, as shown in Fig. 3~
At such time, programmer 46 deactiva-tes pumps 38 and 44 and operates pump 36 to force immiscible liquid along conduits 30 and 28 and outwardl~ through tube 12~ forcing the liquid segment 68' into receptacle 76. Again, any immiscible liquid dispensed from tube 12 tends to sink within the dispensed liquid to form a thin layer 79 at the bottom of receptacle 76, such as not to inter~ere either with the addition of other liquids into receptacle 76 or with any reaction therebetween. When liquid segment 68' has been dispensed, programmer 46 deactivates pump 36 and operates pumps 38 and 44 to again flow immiscible liquid from source 68 along surface 70 for aspiration along tube 12.
As both peripheral and interior surfaces 70 and 72 are uncontamina~ed, the probe arrangement 10 is immediately `
available for a next subsequent dispensing operation . Also, the probe arrangement 10 can be adapted to aspirate and dispense multiple liquids in timed sequence without contamination therebetween For example, assume that liquid 68 is a first reagent and that segment 68' has been aspirated along :~ 20 tube 12 and that tube 12 has been withdrawn from receptacle 26, .~ as described. At such time, pumps 38 and 44 are operated and .
drive mechanism 25 displaces arm 24 to immerse tube 12 into :: a second receptacle 26', now positioned at the take-off station . and containing a liquid 69 While tube 12 is withdrawn, a first aspirated liquid segment 68' (See Fig. 6) is displaced along ~ tube 12 while immiscible liquid 66 is being aspirated along ;. tube 12, as described Upon immersion of tube 12 into liquid 69, programmer 46 controls pump 38 to aspirate a segment 69' of liquid 69 of predetermined volume along tube 12, concurrently, : bm: .

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proc3rammer 46 deactiv~tes pum~ ~, pump 36 being inactive. ~s shown in FicJ. 6, ]iquid segments 6~' and 69' are maintained discrete from each other ~y immiscible liquid which has been aspirated therebetween anc~ neither is in contact with the internal surface 72 of tube 12. It is evident that any number of liquids can be successively aspirated and maintained discrete along tube 12. Subsequently, pump 36 can be controlled by programmer 46, along lead 48 to dispense any number of successively aspirated liquid segments, e.g., 68' and 69', either in spaced-timed fashion, as desired, or in immediate sequence. However, dispensed, and referring to Fig. 3, the successively aspirated liquid segments can be intermixed, ;
immiscible liquid settling as a thin layer 73 at the bottom receptacle 76, so as to be effectively removed.

Alternatively, when probe arrangement 10 is operated -'' ::., as a sampler, receptacles 68, 68', etc., each containing a sample to be analyzed can be advanced to the take-off station, ~` in turn, by conventional apparatus. In such event, programmer 46 operates pump 40 continuously and operates pump 44 only during the wi~rawal cycle, to allow for the aspiration of immiscible liquid se~ments between successively aspirated samples. As illustrated in Fig 6, the successively aspirated sample liquids, e.g , 68' and 69', are passed by pump 40 along conduits 28, 34 and 58 to~analyzer 56! which analyzer is more I .
` particularly described in the above-identified U. S. Patent No 3,479,141.
With respect to the aspiration of successive samples, as described, an air bubble can be included between successive samples, as also taught in the above-identified U, S. Patent . ~ . . ~ .
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~)8~99 No 3,479,1~1, by operating programmer 46 to momentarily deactivate pump 4~ during the wlthdrawal cycle Accordingly, the flow of immiscible liquid -film 74 along surface ,0 of tube 12 is interrupted for a time sufficient to aspirate an air segm~nt along tube 12. In such event, adjacent segments 68, 68~,etc., of liquid samples are separated by a sequence of immiscible liquid - air - immiscible liquid segments, each liquid sample segment and air bubble being fully encased within the immiscible liquid and not contacting the internal surface 72 of tube 12 or the internal surfaces of conduits 28, 34 or 58 to analyzer 56, ; While the presently preferred forms of the metering apparatus have been described, it will be apparent, especially to those versed in the art, that the invention may take other forms and is susceptible of various changes in details without - departing from the principles of the invention.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A liquid metering system comprising:
a probe having an inlet end for immersion into a receptacle containing a first liquid to be aspirated, means for coating at least an outer peripheral surface, said probe with a second liquid, said second liquid being immiscible with said first liquid and which preferentially wets said surface of said probe to the substantial exclusion of said first liquid, means for immersing said probe into said first liquid, and means connected to an outlet end of said probe and operative while said probe is immersed in said first liquid for aspirating said first liquid.

2. A metering system as defined in claim 1, further including means for dispensing said aspirated first liquid along said probe.

3. A metering system as defined in claim 1, wherein the specific density of said second liquid is greater than that of said first liquid.

4. A metering system as defined in claim 1, wherein the specific density of said second liquid is less than that of said first liquid.

5. A metering system as defined in claim 1, wherein said second liquid is selected from the group consisting of fluorocarbon oil, hydrocarbon oil and silicone oil.

6. A metering system as defined in claim 1, wherein said coating means is operative to coat the internal surfaces of said probe with said second liquid.

7. A metering system as defined in claim 1, wherein said coating means includes means for flowing said second liquid along said outer peripheral surface of said probe.

8. A metering system as defined in claim 7, wherein said flowing means includes an annular chamber located concentrically about said probe, and means for pumping second liquid into said chamber, excess of said second liquid flowing along said outer peripheral surface to said inlet end of said probe.

9. A metering system as defined in claim 8, wherein said annular chamber is formed integrally with said probe.

10. A metering system as defined in claim 7, wherein said coating means includes means for flowing said second liquid along said outer peripheral surface to said inlet end of said probe.

11. A metering system as defined in claim 10, wherein said flowing means and said aspirating means being operative while said probe is withdrawn from said first liquid, such that at least a portion of said second liquid flowed along said outer peripheral surface is aspirated along said inlet end of said probe.

12. A metering system, as defined in claim 11, wherein said flowing means and said aspirating means have substantially the same flow capacity.

13. A metering system as defined in claim 1, further including means for immersing said probe into two or more successive receptacles containing different first liquids, said coating means and said aspirating means being operative while said probe is withdrawn from said receptacles, such that a segment of said second liquid is aspirated along said probe between successive segments of said different first liquids.

14. A metering system as defined in claim 13, further including means for selectively dispensing segments of said different first liquids aspirated along said probe in controlled time sequence.

15. A metering system as defined in claim 13, further including means for substantially concurrently dispensing said segments of said different first liquids aspirated along said probe.

16. A metering system as defined in claim 13, further including analytical means connected to the outlet of said probe for analyzing said first liquid segments, in turn, and means for passing said first liquid segments to said analytical means.

17. A metering system as defined in claim 13, further including means for deactivating said coating means while said probe is withdrawn, such that a segment of air is aspirated along said probe between said successive segments of said different first liquids.

18. A metering system as defined in claim 1, further including first and second conduits connected to said outlet end of said probe, first and second pumping means connected to said first and second conduits, respectively, said first pumping means being operative to aspirate along said probe and said second pumping means being operative to dispense along said probe, and programming means for controlling the operation of said first and second pumping means.

19. A metering system as defined in claim 18, said programming means is connected to said immersing means, said programming means being operative to control the relative operations of said immersing means and said first and second pumping means.