Liquid sampling apparatus with retention means

An apparatus for preparing a sample of liquid for examination and analysis. The apparatus includes a tube closed at one end and open at the other, and a pipette dimensioned for insertion into the tube. The pipette has a sealing surface which is slightly smaller in diameter than the inside diameter of the tube. Protruding from the sealing surface is a rib which is aligned along the longitudinal axes of the pipette and which engages a portion of the inside wall of the tube to maintain the pipette in the tube.

BACKGROUND OF THE INVENTION 
This invention relates to laboratory testing procedures and, more 
particularly, to apparatus for preparing liquid samples of urine and the 
like for examination. 
In the field of clinical testing, it is often important to isolate and 
accurately sample a specific volume of fluid. As an example, one type of 
routine medical test is an analysis of a patient's urine to determine the 
amounts of sugar, albumin, and solids present in the specimen. As part of 
this analytical procedure, microscopic studies are performed to determine 
the presence and amount of cellular elements such as erythrocytes, 
leukocytes, epithelial cells, casts, and crystals in the urine. In a 
standard procedure for making such determinations, a precise volume of 
urine is centrifuged to preferentially redistribute the cellular elements 
in the lower portion of a container tube, and then liquid from the lower 
portion is transferred to a slide for observation. 
In obtaining samples for microscopic observation, it is important that the 
nature of the sample finally placed onto the the microscopic slide not be 
dependent upon the individual technique of the person who prepares the 
samples. To this end, an approach and apparatus was developed for 
isolating a precise volume of liquid at the bottom of a tube initially 
having a larger volume of liquid, with a pipette having a diametrically 
enlarged chamber that seals against the inner wall of the container so as 
to isolate the sample. After the seal is formed, the portion of liquid 
above the seal is decanted by inverting the tube and pipette with the seal 
intact. The tube and pipette are righted, and then after mixing the 
sample, a portion is drawn into the chamber for transferring to the slide. 
This technique has proved highly successful and popular in standardizing 
the microscopic urine testing procedure. 
The above-described testing procedure has several drawbacks, however, 
particularly when used for large-scale laboratory testing wherein many 
samples are to be studied. Since the pipette is hollow and initially 
filled with air, it tends to float upwardly when placed into the 
liquid-filled tube, thereby breaking the seal between the outer portion of 
the chamber and the wall of the tube and allowing liquid circulation 
between the liquids being isolated from each other. Consequently, it is 
sometimes necessary to hold the pipette in place manually. Further, when 
the tube and pipette are inverted to decant the portion of the liquid to 
be removed, the pipette must be held in place manually to maintain the 
seal and thereby retain the small sample. With this constraint, it is 
impossible to decant multiple containers at one time, as for example by 
placing a large number of containers with inserted tubes into a rack and 
then partially inverting the rack to decant all of the containers at once. 
Finally, because the pipette must be held in place manually when 
decanting, it is possible that the hand may be splashed with a portion of 
the liquid being decanted, which is undesirable both hygenically and 
because of cross contamination of samples. 
There therefore exists a need for apparatus which allows the standardized 
preparation of a urine sample for microscopic observation, but also 
provides for the positive retention of the seal between the tube and the 
container wall during sampling. Further, such apparatus should be 
economical to manufacture and should allow rapid processing of samples in 
large numbers with minimal variation of the technique now well established 
in laboratories worldwide. The present invention fulfills this need, and 
further provides related advantages. 
SUMMARY OF THE INVENTION 
The present invention provides an apparatus and method for preparing liquid 
specimens, wherein a sample for analysis and observation may be isolated 
from a larger volume of liquid conveniently and reproducibly. Variation in 
the sampling and observation due to differences in the laboratory 
technique is minimized, and the preparation of large numbers of samples 
may proceed rapidly. Further, the chances of inadvertent mixing of the 
liquid sample and the liquid to be decanted is minimized. With this 
invention, accurate, reproducible analysis of the components of urine and 
other samples is possible in a large scale, production line fashion. 
The apparatus for preparing liquid specimens includes a tube for holding 
the liquid to be sampled and a pipette or other means for isolating and 
withdrawing a sample from a portion of the liquid. In accordance with the 
invention, the pipette or other means includes retention means for 
maintaining the seal between the pipette and the tube, thereby resisting 
the tendency of the pipette to float in the liquid and also holding the 
pipette in place when the container is inverted to decant the liquid to be 
discarded. 
In a preferred embodiment following a standardized test procedure, 12 ml of 
liquid such as urine to be analyzed is placed in an generally cylindrical, 
but tapered centrifuge tube. After capping, the tube is centrifuged to 
cause migration of the solid elements to the liquid volume at the bottom 
of the container. The container is removed from the centrifuge, and a 
pipette having a specialized configuration is inserted. The pipette is 
hollow with an open lower end or stem, an upper end closed by a bulb, and 
a diametrically enlarged chamber adjacent the stem. The outer wall of the 
chamber includes a sealing surface which seals against a corresponding 
surface on the inner wall of the tube to isolate a liquid specimen at the 
lower end of the container, the liquid specimen preferrably being 1 ml in 
volume. 
In a preferred embodiment, at least one outwardly projecting rib is 
provided on the wall of the chamber, the rib having a sufficiently great 
height that it frictionally engages the inner wall of the tube over a 
short range of axial movement of the pipette as the sealing surfaces are 
brought into contact. The wall of the chamber is of a relatively thin 
plastic construction, so that the contact between the rib and the inner 
wall of the tube flexes the wall of the chamber inwardly, thereby 
resiliently biasing the rib against the tube wall. In practice, it is 
found that, for conventionally sized apparatus having a chamber diameter 
of slightly less than 1/2 inch, provision of a pair of diametrically 
opposed ribs, each of height of about 0.005 inches, is sufficient to hold 
the pipette in place with the sealing surfaces in contact, against the 
buoyant force tending to cause the tube to float upwardly, and also holds 
the tube in place with the sealing surfaces in contact when the liquid in 
the upper portion of the tube is decanted by partially inverting the tube. 
It will be appreciated from the foregoing that the present invention 
represents an advance in the art of isolating and sampling liquid 
specimens, particularly where multiple samples must be prepared and 
evaluated. Where multiple samples are being prepared, a plurality of 
centrifuge tubes are placed into a rack, a pipette is inserted into each 
container to isolate a sample, the rack is partially inverted to decant 
the discarded portion, and then the samples are individually transferred 
to a slide for examination. Multiple samples may thereby be prepared 
rapidly, without the risk of contacting the decanted liquid or 
cross-contaminating the various tubes. Other features and advantages of 
the present invention will become apparent from the following, more 
detailed description, taken in conjunction with the accompanying drawings, 
which illustrate, by way of example, the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As is shown in the drawings for purposes of illustration, the present 
invention is embodied in an apparatus, indicated generally by the numeral 
20, for use in preparing a liquid sample for subsequent observation. As 
best illustrated in FIGS. 2 and 3, the apparatus 20 includes a tube 22 
having a closed lower end 24, an open upper end 26, and a tapered portion 
28, so that the cross-sectional area of the open end 26 is greater than 
that of the closed end 24. In the illustrated embodiment, a funnel section 
30 further increases the area at the open end. Volume indicia, as for 
example, circumferential marking lines 32 and associated numerals 34, may 
be provided to assist in measuring precise quantities of liquid. 
A pipette 36 is dimensioned for insertion into the tube 22. As used herein, 
a "pipette" is an elongated element preferably, but not necessarily, 
hollow, having isolation means for sealingly isolating a portion of liquid 
in the tube 22. The preferred pipette 36 includes an elongated portion 38 
having an upper end closed with a resiliently compressible bulb 40 
extending above the upper end 26 of the tube 22, when the pipette 36 is 
fully inserted into the tube 22. At its lower end, the pipette 26 includes 
a diametrically enlarged chamber 42 and a filling tube or stem 44 at the 
lowest portion of the pipette 36. 
At best illustrated in FIG. 3, the pipette 36 is inserted into the tube 22 
and pushed downwardly until the lower end of the stem 44 contacts the 
closed end 24 of the tube 22. As illustrated in FIG. 6, with the pipette 
36 in this position, there is a small gap 45, typically about 0.003 
inches, between a lower edge 46 of the outer wall of the chamber 42, and 
the corresponding sidewall 48 of the tube 22. The presence of the gap 45 
is desirable, in that it allows liquid to be forced out of an isolated 
volume of liquid 50 below the chamber 42 as the pipette 36 is inserted, 
avoiding a piston effect that would otherwise force liquid into the stem 
44. This small gap 45 effectively seals the isolated volume of liquid 50 
below the chamber 42 from a discarded volume of liquid 52 above the 
chamber 42, as the discarded volume of liquid 52 is decanted. When the 
tube 22 with the pipette 36 in its fully inserted position is partially 
inverted to decant the discarded volume of liquid 52, the surface tension 
of the isolated volume of liquid 50 in the gap 45 retains the isolated 
volume of liquid 50 without loss of liquid. Thus, used herein, the term 
"contacting" when applied to the positioning of surfaces refers to their 
proximate positioning to effect a seal, although the surfaces may not be 
in physical contact. 
To prepare a sample of liquid using this apparatus and a standardized 
format, 12 ml of urine is poured into the tube 22, and the upper end 26 is 
covered with a snap-fitting cap (not shown). The tube 22 is placed into a 
centrifuge and centrifuged at 400 times the force of gravity for 5 
minutes. This centrifuging process forces the denser elements of the 
liquid, including solid particles, toward the lower end 24 of the tube 22. 
The tube 22 is removed from the centrifuge, the cap is removed, and the 
pipette 36 is inserted in the manner illustrated in FIG. 2 until the stem 
44 contacts the lower end 24 of the tube 22, thereby sealing the isolated 
volume of liquid 50, containing most of the solid elements, from the 
discarded volume of liquid 52. In the standardized format, the isolated 
volume of liquid 50 is 1 ml. 
Because the interior of the pipette 36 is completely air filled at this 
point, it has a tendency to float upwardly so as to break the seal between 
the isolated volume of liquid 50 and the discarded volume of liquid 52. 
Care must be taken to avoid such floatation. 
The discarded volume of liquid 52 is then decanted by partially inverting 
the tube 22 with the pipette 36 held in the fully inserted position to 
maintain the seal and prevent loss of the isolated volume of liquid 50. 
After the discarded volume of liquid 52 is decanted, the tube 22 and 
pipette 36 are returned to the upright position. The liquid remaining in 
the tube 22 is mixed to a generally uniform mixture by swirling the tube 
22 or by using the pipette 36 as a stirring rod. Optionally, a stain may 
be added to the remaining liquid. The isolated volume of liquid 50 is 
transferred into the chamber 42 using the pipette 36 by compressing the 
bulb 40 to force air out of the chamber 42 through the stem 44 to create a 
partial vacuum in the chamber 42, and then releasing the bulb 40 to draw 
liquid into the chamber 42. The pipette 36 may then be removed from the 
tube 22 to deposit a sample of liquid on a microscope slide (not shown) 
for observation, by compressing the bulb 40 slightly to force a drop of 
liquid onto the slide. 
In accordance with the invention, retention means is provided to hold the 
pipette 36 in its fully inserted position to maintain the stem 44 in 
contact with the closed end 24. The sealing contact between the lower edge 
46 of the chamber 42 and the sidewall 48 of the tube 22 is maintained in 
spite of the tendency of the pipette 36 to float, even when the pipette 36 
and the tube 22 are partially inverted to decant the discarded volume of 
liquid 52. Without the presence of such retention means, the person 
preparing the liquid sample must sometimes hold his finger against the 
bulb 40 to conteract the tendency of the pipette 36 to float, and must 
nearly always use one finger to hold the pipette 36 in place during the 
decanting procedure. 
In a preferred embodiment of the retention means, at least one raised rib 
54 is provided on an outwardly facing wall 56 of the chamber 42. The rib 
54 has a height greater than the clearance between the outwardly facing 
wall 56 and a corresponding sidewall 58 of the tube 22, so that either the 
rib 54 or the outwardly facing wall 56 of the chamber 42 must deform 
inwardly to allow full insertion of the pipette 36 into the tube 22. In 
the preferred embodiment, the chamber 42 is formed of plastic having a 
wall thickness of about 0.015 inches. The outwardly facing wall 56 is 
therefore deformed inwardly by the contact of the rib 54 and the sidewall 
58 of the tube 22, in the manner illustrated in FIG. 6. This inward 
deformation of the outwardly facing wall 56 of the chamber 42 resiliently 
biases the rib 54 outwardly against the sidewall 58 of the tube 22. The 
resulting frictional force resists the tendency of the pipette 36 to float 
upwardly, and also holds the pipette 36 in place to maintain the sealing 
contact to retain the isolated volume of liquid 50 when the tube 22 is 
inverted to decant the discarded volume of liquid 52. 
Any configuration providing an increased periphery to the outer wall 56 of 
the chamber 42 will provide some of the benefits of the present invention, 
but the rib configuration is preferred. If the entire periphery of the 
chamber 42 is raised to give the chamber 42 a greater diameter, the 
frictional retention force tends to be too great and there may also be a 
piston effect created during insertion of the pipette 36. If only a single 
raised dot on the outer wall 56 is provided, it is found that the 
frictional force increases rapidly over a short distance of axial movement 
of the pipette 36 relative to the tube 22, resulting in a less desirable 
"feel" and a sense of positive engagement conveyed to the person 
performing the sampling procedures. Accordingly, the rib 54 having a 
raised portion elongated parallel to the axis of the pipette 36 is 
preferred, as illustrated in FIGS. 1 and 4. 
In the preferred embodiment, the entire pipette 36 is formed in a 
multiple-piece die using a blow molding process. To facilitate the blow 
molding process, two different sections of the die (not shown) are joined 
near a lower end of the largest diameter portion of the chamber 42. 
Consequently, a circumferential flash molding 60 is usually produced on 
the chamber 42. It is preferred that the rib 54 connect to, and be 
continuous with, the flash molding 60 in the manner illustrated in FIG. 4. 
When the rib 54 and the flash molding 60 are continuous, any air bubbles 
present in the rib 54 as the part is formed from liquid plastic are forced 
along the length of the rib 54, into the liquid plastic at the flash 
molding 60, and thence out of the part through the space between the dies. 
Soundness and dimensional reproducibility of the pipette 36 are thereby 
promoted. 
The rib 54 has a height which gradually increases from the end nearest the 
stem 44 toward the end nearest the bulb 40. This gradually increasing 
height allows the rib 54 to engage sidewall 58 of the tube 22 over a 
length of axial travel as the pipette 36 is inserted into the tube 22. 
This gradually increasing frictional force provides a proper "feel" to the 
insertion and a sense of positive engagement when the pipette 36 is fully 
inserted, thereby aiding the person preparing the sample in conducting the 
sampling. 
If a numeral "1" is formed as a raised portion 61 on the inside of the 
sidewall 58 of the tube 22, in some rotational positions of the pipette 36 
the raised rib 54 may undesirably contact the raised portion 61. In such a 
construction, it is preferred to configure the rib 54 as a first raised 
portion 62 of greater height and a second raised portion 64 of lesser 
height so that the second raised portion 64 provides clearance over the 
numeral. 
At least one rib 54 is desired, but additional ribs may be provided. In the 
preferred embodiment, two diametrically opposed ribs, each having a height 
of about 0.005 inches, are provided. 
A liquid sampling procedure utilizing an apparatus embodying the present 
invention is performed in a manner generally similar to that described 
previously. However, with an apparatus embodying the invention it is not 
necessary that the pipette 36 be held in place manually to prevent 
flotation, or during decanting of the discarded liquid. It will therefore 
be appreciated that, through the use of this invention, the sample 
preparation procedure may be greatly enhanced by allowing the simultaneous 
preparation of multiple tubes of liquid. Multiple tubes are placed into a 
rack, the pipettes are inserted, and then the entire rack is inverted to 
decant the discarded liquid from all of the tubes at one time. Whether a 
single tube or multiple tubes are prepared, the person conducting the 
sample preparation need not touch the liquid or risk cross contamination. 
Although a particular embodiment of the invention is described in detail 
for purposes of illustration, various embodiments may be made without 
departing from the spirit and scope of the invention. Accordingly, the 
invention is not to be limited except as by the appended claims.