Method and apparatus for automatically performing series analyses

Automatic sample preparation method and apparatus for making successive measurements with an analyzer by picking up with a single stepwise movable metering probe, in a first measuring cycle, a sample for measurement from a sample container and a small volume of air; introducing this sample and the air into the inlet of the analyzer; picking up with the same metering probe, in a secondary measuring cycle, a sample for measurement from the same sample container and a small volume of air, and picking up with said metering probe a metered quantity of liquid additive and a second small volume of air; and thence introducing said sample, said liquid additive and said air picked up in the secondary measuring cycle into the inlet of the analyzer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to sampling method and apparatus for analytical 
equipment and, in particular, to such method and apparatus that is adapted 
for automatically performimg series analyses. 
2. Description of the Prior Art 
In U.S. patent application Ser. No. 660,194 filed on Feb. 20, 1976 and 
assigned to the Assignee of the present application, there is disclosed 
apparatus wherein samples to be measured are taken up from successive 
sample containers and sequentially supplied to an atomic absorption 
spectrometer. Means are provided to prevent errors in the measured results 
due to carry-over of the sample material or other contaminations. The 
automatically controlled sequence of the individual operating steps 
permits series analyses to be performed, whereby the measured signals may 
be evaluated in a data processor. 
It will be appreciated that such a method of analysis, however, will not 
always yield reliable measuring results, particularly if the signals 
obtained depend on detector sensitivity or sample composition. Thus, for 
instance, the indicator sensitivity of thermionic detectors in gas 
chromatography which respond selectively to halogen, phosphorus or 
nitrogen containing compounds are dependent on ageing effects. In sample 
liquids like blood, substances which are inherently present may affect the 
signal measured so that a calibration curve obtained for one liquid sample 
may not be applicable to the same sample of different origin. In such 
cases it is, therefore, necessary to conduct separate reference 
measurements for each individual sample. 
In methods of measurement responsive to the quantity of the component to be 
determined in the sample, i.e., gas chromatography and atomic absorption 
spectroscopy, the procedure is to perform at least one additional 
measurement with the same sample, with a known amount of the component to 
be determined being added to the sample. Said known amount is added as a 
metered quantity of a liquid additive containing the desired component 
dissolved in a solvent. Additionally, a corresponding quantity of the pure 
solvent is added to the sample being measured, per se, before taking its 
measurement. The respective dilution is then taken into consideration in 
the subsequent evaluation of the measured signals. See, for example, the 
publication entitled, "Analysentechnische Berichte", Vol. 32, (1974) page 
10. 
SUMMARY OF THE INVENTION 
The basic and general object of the present invention is the provision of 
sampling methods and apparatus which are improvements over the known prior 
art systems. 
An object to be achieved by the invention resides in the provision of an 
automatic operating method of analysis and analysis apparatus wherein, 
independent of the method of measurement employed, in addition to the 
actual sample measurement, one or more reference measurements are made to 
thereby render the results obtained with the analysis apparatus 
independent of the composition of the sample liquid and variations in the 
apparatus response characteristics. 
To the accomplishment of the foregoing objectives, and additional object 
and advantages, which will become apparent as this description proceeds, 
the invention contemplates in one form thereof the provision of a new and 
improved method for making successive measurements with an analyzer 
comprising, for each complete cycle of operation, in controlled sequence, 
the steps of: picking up with a single stepwise movable probe, in a first 
measuring cycle, a sample for measurement from a sample container and a 
small volume of air. The next steps in the method comprise: introducing 
said sample and the small volume of air into the inlet of the analyzer; 
picking up with the same metering probe, in a secondary measuring cycle, a 
sample for measurement from the same sample container and a small vlume of 
air, and then picking up with the metering probe a metered quantity of 
liquid additive and a second small volume of air; and thereafter 
introducing said sample, said liquid additive and said air picked up in 
the secondary measuring cycle into the inlet of the analyzer. 
According to one aspect of the invention, there are a plurality of 
secondary measuring cycles in which different, respective, liquid 
additives are picked up by the metering probe and introduced into the 
inlet of the analyzer, and according to another aspect preselected amounts 
of the same liquid additive are picked up in the secondary measuring 
cycles, respectively. 
Further, according to another aspect of the invention, the liquid additive 
in each secondary measuring cycle contains a predetermined concentration 
of a solvent of the component to be determined in the sample. 
In the simplest case, wherein the dilution by the liquid additive does not 
affect the signal measured, there is obtained one, or a number of signals 
from measurements in which a predetermined, known quantity of the desired 
component has been added. At least one reference measurement is therefore 
obtained for each measurement taken of a sample 
In cases in which the addition of the liquid additive affects the measured 
signal, a quantity of solvent may be taken up in the first measuring 
cycle, which is equal to the added quantity of liquid additive in the 
secondary measuring cycles. Also, with different amounts of liquid 
additive added in the secondary measuring cycles, different quantities of 
solvent may be taken up, corresponding to the respective quantities of 
liquid additive in each of the secondary cycles. 
In both of the cases just discussed, it is immaterial whether or not the 
measurements of the samples, with or without the added solvent, are taken 
prior to or after the measurement with the liquid additive. Equal 
quantities of the liquid additives containing different amounts of the 
desired components in the same solvent may be employed and also, different 
quantities of the same liquid additive containing a predetermined amount 
of the desired component in a solvent may be added. Nevertheless, the 
measured results may be corrected in a known manner in such a way as to be 
comparable. 
In one form thereof, the invention provides new and improved automatic 
sample preparation apparatus for making successive measurements with an 
analyzer which comprises, in combination, a base plate; a rotatable table 
for receiving a plurality of sample containers mounted for rotation on the 
base plate, and means for controlling the advance of the table in a 
stepwise manner in accordance with the number of measuring cycles in a 
complete cycle of operation. In addition, the apparatus of the invention 
includes a rinse fluid container mounted on the base plate; a liquid 
additive container mounted on the base plate adjacent the rinse fluid 
container; and means mounting the base plate for pivotal movement between 
a fixed stop and a variable stop means, respectively. A metering probe is 
provided which has a capillary tip, and means are provided for mounting 
the probe for pivotal movement about two mutually normal axes to dip the 
tip into said containers one at a time and into the inlet of the analyzer. 
Pumping means, including a stepping motor, serve to pass rinse fluid 
through the metering probe to the rinse container and for picking up 
metered quantities of liquid in said capillary tip from the sample 
containers and from the liquid additive container for delivery to the 
inlet of the analyzer. A central control unit serves to coordinate the 
movement of the base plate, rotatable table, metering probe and pumping 
means. 
It will be appreciated that by means of the apparatus according to the 
invention, the base plate may be pivoted in such a way underneath the 
metering probe that a sample for measurement can be taken up, that the 
metering probe can then be rinsed or washed externally, that subsequently 
liquid additive can be taken up, and that finally after further external 
rinsing the liquid so picked up is delivered to the inlet of the analyzer. 
In addition, a small volume of air is taken up into the metering probe 
between each respective pick up of liquid and liquid additive. The 
variable stop means for the base plate enables the pivoting thereof to be 
controlled in accordance with a predetermined program. The employment of 
stepping motors in the pumping system has the advantage that the pick up 
and delivery of liquid into and from the metering probe can be very 
precisely controlled. 
The time sequence of the steps in the method may be controlled by the 
central control unit. Also, the number of steps of the stepping motors may 
be adjusted by this unit. A data processor may be provided for evaluation 
of the signals measured, which is in communication with the central 
control unit. The data processor may consitute a microcomputer built into 
the apparatus, and the time-programmed control as well as the number of 
steps employed in the pump stepping motors may be stored therein. This 
system optimally controls the cooperation of the members of the apparatus 
according to the invention, as well as the sequence of the individual 
operational steps. 
According to one aspect of the invention, the variable stop means includes 
a rotatable ratchet wheel having a plurality of alternately disposed teeth 
and stop faces, and a pawl linked to the base plate for coacting with the 
ratchet wheel in operative relationship, the number of stop faces on the 
ratchet wheel being equal to the number of pivoting movements of the base 
plate in one measuring cycle. 
According to another aspect of the invention, the means for controlling the 
advance of the rotatable table includes a cam rotatable with the ratchet 
wheel of the variable stop means, a stop latch engageable with serrations 
on the rotatable table, and linking means coupling the cam and the stop 
latch to thereby control the advance of the rotatable table in accordance 
with the number of measuring cycles in a complete cycle of operation. 
Advantageously, the metering probe according to the invention is externally 
rinsed prior to the take-up of liquid additive and prior to the delivery 
to the inlet of the analyzer. Further, according to an aspect of the 
invention, the metering probe is rinsed internally and externally between 
each complete cycle of operation. 
It is within the concept of the invention, with respect to both the method 
and apparatus, that each of the samples to be measured may be taken up by 
the metering probe and initially delivered to an intermediate vessel, from 
which it may then be supplied one or more times to the inlet of the 
analyzer. 
There has been thus outlined rather broadly the more important features of 
the invention in order that the detailed description thereof that follows 
may be better understood, and in order that the present contribution to 
the art may be better appreciated. There are, of course, additional 
features of the invention that will be described hereinafter and which 
will form the subject of the claims appended hereto. Those skilled in the 
art will appreciate that the conception upon which the disclosure is based 
may readily be utilized as a basis for the designing of other method and 
apparatus for carrying out the several purposes of the invention. It is 
important, therefore, that the claims be regarded as including such 
equivalent method and apparatus as do not depart from the spirit and scope 
of the invention. 
Specific embodiments of the invention have been chosen for purposes of 
illustration and description, and are shown in the accompanying drawings, 
forming a part of the specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in detail, there is illustrated apparatus for 
automated series analysis of sample liquid such as, for example, blood or 
urine for a specific component, utilizing an analyzer such as, for 
example, an atomic absorption spectrometer. Initially, the invention will 
be described in its simplest form, wherein in the first or primary 
measuring cycle the sample only is analyzed and in the second or secondary 
measuring cycle the sample plus a liquid additive is analyzed. In this 
example the sample is independent of the amount of solvent contained 
therein, as in a graphite tube assembly the solvent evaporates prior to 
the actual measurement. Later in the description, disclosure will be made 
of installations wherein it is necessary to add solvent to the liquid 
sample, usually in an amount equal to the amount in the liquid additive. 
As best seen in FIG. 1, the apparatus includes a metering probe 10 having 
an inlet end portion 12 with a capillary tip 71 which, in operation, is 
periodically dipped into vessels 14, 16 and 17 and moved to a sample 
introduction means 18 of an atomic absorption spectrometer 20. Vessel 14 
is a container for rinse fluid and vessel 16 is a container for the sample 
being analyzed, while vessel 17 is a container for liquid additive. As 
indicated by arrow 80 in FIG. 1, the container arrangement is mounted for 
movement in such a manner as to bring one container at a time underneath 
the intake end 12 of the metering probe 10, as will be discussed more 
fully hereinafter. It is noted that the rinse fluid container 14 is 
provided with a drain line 46 that leads to a collector vessel 50. The end 
opposite the inlet 12 of the metering probe is connected to a pump system, 
which includes a stepping motor driven rinse fluid pump 24, having an 
inlet connected to a rinse fluid reservoir 22 by a line containing a check 
valve 30. The discharge of this pump is connected to a second pump 36 via 
a line containing a check valve 32 so that the rinse fluid delivered by 
pump 24 is unidirectional. The second pump 36 is driven by a stepping 
motor 36' controlled by central control unit 84 in such a manner that 
rinse fluid may be delivered through the metering probe toward the intake 
end 12. However, during the intake stroke thereof, fluid may be withdrawn 
from either container 16 or container 17. In addition, during a brief 
intake stroke following each intake of liquid, a small volumn of air is 
drawn into the inlet end 12 of the metering probe. 
As best seen in FIGS. 2 to 4, the metering probe 10 is supported by a 
suitable mounting 66 which permits rotation of the probe about a vertical 
axis. The mounting member 66 is, in turn, mounted for rotation between two 
extreme positions by an adjusting or servo motor 70 about an axis 68, 
perpendicular to the vertical axis. Servo motor 70 is controlled by the 
central control unit 84. FIG. 4 shows the metering probe 10 in solid line 
in a first extreme position in which the capillary tip 71 is in the rinse 
fluid container 14, and in a second extreme position indicated by a broken 
line 10' wherein the capillary tip 71 is in the sample introduction 
opening 18 of the graphite tube assembly 20 of the atomic absorption 
spectrometer. 
As best seen in FIGS. 2 and 3, the apparatus employs a carousel-type sample 
platter consisting of a turntable 52 mounted on a base plate 54 for 
rotation about a vertical axis 56. The turntable carries a ring of sample 
containers 16 concentric with its axis of rotation. The base plate 54 is 
eccentrically pivotable, as indicated by arrow 82, about an axis 58 
between a fixed stop member 60 and a variable stop means, by a motor 64 
(FIG. 4) controlled by the central control unit 84. The variable stop 
means is illustrated in the form of a ratchet wheel 62 mounted on a shaft 
63, which is supported by brackets 61 and 61' depending from the main 
frame or supporting structure 55 beneath the base plate 54. The ratchet 
wheel 62 coacts with a pawl 65 mounted towards the periphery of the base 
plate 54. In the embodiment illustrated in FIGS. 5 and 6, ratchet wheel 62 
has stop faces 64 and 64', which are separated from each other by teeth 66 
and 66'. These elements are so arranged that when the base plate 54 is 
pivoted anticlockwise (as viewed in FIGS. 2 and 3) toward the ratchet 
wheel 62, the pawl 65 engages one of the teeth 66 or 66' to thereby rotate 
the ratchet wheel 62 clockwise about its axis 63 until the successive, 
respective, stop face 64 or 64' engages the bottom side of the base plate 
54. FIG. 5 shows the base plate 54 in engagement with the stop face 64, 
after the pawl 65 has acted upon the tooth 66, corresponding to the 
pivotal movement of the base plate about its axis 58 through a large 
angle. At this time the base plate is in its position, as shown in FIG. 3. 
FIG. 6 shows the base plate 54 in engagement with the stop face 64', after 
the pawl 65 has acted upon the tooth 66', corresponding to the pivotal 
movement of the base plate about its axis 58 through a small angle. When 
the ratchet wheel is in its position as shown in FIG. 6, the base plate 54 
is in a position intermediate those shown in FIGS. 2 and 3, whereby the 
capillary tip 71 of the probe 10 can be dipped into the liquid additive 
container 17. 
As best seen in FIGS. 2 and 3, the base plate 54, in addition to carrying 
the rotatable table 52, also carries the rinse fluid container 14 and the 
liquid additive container 17. These containers are so positioned that the 
liquid additive container is interposed between the rinse fluid container 
and the rotatable table 52. When the base plate 54 is in engagement with 
the fixed stop member 60, as shown in FIG. 2, the rinse fluid container 14 
is positioned underneath the capillary tip 71 of the probe 10 so that the 
tip may be dipped into the container 14 by pivoting the probe 10 about its 
horizontal axis. When the base plate is positioned as shown in FIG. 3, it 
is in engagement with the stop face 64 of the ratchet wheel 62. This 
corresponds to the positional relationship shown in FIG. 5 and, at this 
time, the capillary tip 71 of the probe 10 is positioned above one sample 
container 16 so that the tip may be dipped into the container by pivoting 
the probe about its horizontal axis. 
Still referring to FIGS. 2 and 3, the rotatable table 52 is provided with 
teeth or serrations 72 about its periphery, which are adapted to receive a 
stop latch 76 that interlocks in such a manner as to prevent anticlockwise 
rotation of the table 52 during the time when the base plate 54 is 
pivoting clockwise. On the opposite side of the table 52 there is provided 
a second stop latch 74, which is mounted for engagement with the 
serrations 72. This stop latch is controlled by linkage 74' that engages a 
cam wheel 67 mounted on the shaft 63 (FIG. 4). The control curve on the 
cam wheel 67 is formed so that the stop latch 74 engages a serration 72 on 
the table only after both measuring cycles, corresponding to each sample, 
have been completed. As a result, upon the completion of both measuring 
cycles, when the base plate 54 pivots towards the variable stop, the 
rotatable table 52 is advanced one step to place the next succeeding 
sample in operative position. 
Reverting to FIG. 1, the rinse fluid vessel 14 is designed as an overflow 
type vessel, having an inner chamber 47 and an outer annular chamber 48, 
with a drain duct 46 leading to a collector vessel 50 for the used rinse 
fluid. The dimensions of the inner chamber 47 are so selected that when 
the capillary tip 71 of the probe is dipped therein, and at full stroke of 
the stepping motor pump 24, the inlet end 12 of the metering probe will be 
completely rinsed with the rinsing fluid. As a result, when the probe is 
at the rinse station, rinse liquid ejected through the probe tip fills the 
inner chamber 47 and overflows into the outer chamber 48 from which it 
flows to the waste container 50. This accomplishes the rinsing of both the 
interior and exterior of the probe, so that after completion of this 
operation no significant contamination occurs when the capillary tip is 
later immersed. 
The liquid additive container 17 is in the form of a pneumatic trough-like 
vessel so that small amounts of liquid additive will always be able to 
flow from the interior of the container if liquid additive is removed from 
the withdrawal portion by means of the capillary tip 71 of the probe. 
Still referring to FIG. 1, the rinse fluid pump 24 has, for example, a 
complete stroke of about 2 ml. and the second pump 36 has a stroke of 
about 50 .mu.l. The controlled stepping motor 36' is selected so as to 
have 5000 steps which correspond to one stroke or a volume of about 50 
.mu.l of the pump 36. The number of steps is adjusted by the central 
control unit 84 in such a way that during a measuring cycle 20 .mu.l 
(equal to 2000 steps) of sample liquid will be aspirated, 10 .mu.l (equal 
to 1000 steps) of liquid additive will be aspirated, and 5 .mu.l (equal to 
500 steps) of air will be aspirated after each intake of liquid. 
It will be appreciated that the control of the pumps 24, 36, the motors 64, 
70 and other elements which require synchronized control, is effected by 
the central control unit 84. The stroke of the rinse fluid pump 24 is 
preset; the number of steps of the stepping motor 36' for the pump 36 is 
adjustable at and stored in the central control unit and thus may be 
called from same by a data processor 85 for evaluation of the measuring 
signals. In one form the data processor includes a microcomputer in which 
the control program, including the number of steps of the stepping motor 
36', is stored. As pointed out hereinbefore, in the form of the invention 
presently being described, each complete cycle of operation includes two 
measuring cycles. In the first measuring cycle, only the sample is 
analyzed, and in the second measuring cycle the sample plus the liquid 
additive is analyzed. For simplicity, only the second measuring cycle will 
be described in detail, because the first measuring cycle is similar 
thereto, but with the omission of the steps concerning the addition of the 
liquid additive. Thus, briefly, in the first measuring cycle rinse fluid 
pump 24 is actuated to fill the entire system including the metering probe 
with rinse fluid. The capillary tip 71 is dipped into the rinse fluid 
vessel 14 and rinse fluid is expelled, thereby cleaning the interior and 
exterior thereof. Thereafter, the capillary tip is dipped into the sample 
vessel 16, and a partial intake stroke of the pump 36 aspirates a 
preselected quantity of sample liquid. The capillary tip is then removed 
from the sample vessel and a further partial intake stroke of the pump 36 
aspirates a small preselected quantity of air into the capillary tip. 
Thereafter, the tip is again dipped into the rinse fluid vessel 14 to 
decontaminate the exterior thereof before being positioned over the sample 
introduction opening 18 in the graphite tube assembly of the atomic 
absorption spectrometer. The timing diagram of FIG. 8 illustrates the 
correlation of the various elements of the system during the second 
measuring cycle. Referring in particular to FIG. 8, arbitrarily, the 
condition of the apparatus at the starting point or time of zero seconds, 
is assumed to be that point in time at which the capillary tip 71 of the 
metering probe 10 is positioned above the sample introduction opening 18 
of the graphite tube assembly 20. In this position the inlet end 12 of the 
metering probe 10 is filled with a measured quantity of liquid. After a 
starting pulse originating from the control device of the atomic 
absorption spectrometer, the probe 10 is pivoted about its horizontal axis 
to such a degree that the capillary tip 71 dips into the sample 
introduction opening 18. This position is shown in FIG. 4 by the broken 
lines 10' and in FIG. 8 it is indicated at 86 by the initial slight return 
pivot of the metering probe 10. One second thereafter the stepping motor 
36' is actuated 3000 steps to move the pump 36 in the direction of 
delivery to thereby expell 20 .mu.l of sample and 10 .mu.l of air 
(indicated at 88, FIG. 8). In this manner a measured quantity of liquid is 
transferred to the atomic absorption spectrometer for analysis. 
Five seconds after the liquid has been delivered to the atomic absorption 
spectrometer, the metering probe 10 is pivoted back from the sample 
introduction opening 18 (indicated at 90, FIG. 8) and moved azimuthally 
(at 92) until the capillary tip 71 is positioned above the base plate 54 
where the probe 10 is pivoted (at 94) to its lowest horizontal position to 
dip the capillary tip 71 into the inner chamber 47 of the rinse fluid 
container 14. At this point in time the entire apparatus is in its 
position as shown in FIG. 2. Thence, the rinse fluid pump 24 is actuated 
in the direction of discharge (at 96), whereby about 2 ml. of rinse fluid 
is delivered through the capillary tip 71 into the inner chamber 47 and 
overflows therefrom to thereby fill the capillary tip and inner chamber 47 
with pure fresh rinse fluid. Then, the rinse fluid pump 24 takes a brief 
intake stroke (at 98), with the check valve 32 in its closed position. 
During this interval of time, as indicated in FIG. 8 at 100, the metering 
probe pivots slightly about its horizontal axis 68 so that the capillary 
tip 71 is relocated above the rinse fluid container 14. It will be 
appreciated that at this particular point in time the entire metering 
probe as well as the pumps 24 and 36 are filled with rinse fluid. 
Next, in the sequence of operation, the stepping motor 36' takes 500 steps 
to effect a partial intake stroke of the pump 36 to aspirate 5 .mu.l of 
air into the capillary tip 71, as indicated at 102 in FIG. 8. 
Simultaneously therewith the drive motor 64 is energized so that the base 
plate 54 pivots anticlockwise about axis 58, i.e., away from the fixed 
stop member 60 (at 104, FIG. 8). The ratchet pawl 65 at the periphery of 
the base plate 54 engages a tooth 66 of the ratchet wheel 62 to rotate 
same until a face 64 abuts the bottom side of the base plate. At this time 
the base plate is at its position as illustrated in FIG. 3, wherein the 
capillary tip 71 is again located above a sample container 16 mounted on 
the rotatable table 52. Because the shaft 63 rotates with the ratchet 
wheel 62, the cam 67 will also rotate to bring the pawl 74 into engagement 
with a serration 72 on the rotatable table 52 at the end of said movement, 
but without advancing the table at this time, as indicated at 106 in FIG. 
8. 
After about 12 seconds, total elapsed time, the metering probe is again 
pivoted by the adjusting motor 70 to its lowest horizontal position, as 
indicated at 108 in FIG. 8, wherein the capillary tip 71 is immersed in 
sample container 16. Thereafter, the stepping motor 36' drives the pump 36 
to aspirate 20 .mu.l. of sample liquid into the capillary tip 71, as 
indicated at 110 in in FIG. 8. Then, the capillary tip is lifted from the 
sample container by energizing the adjusting motor 70, as indicated at 
112, and the base plate 54 is again returned to its engaged position with 
the fixed stop member 60, by means of the drive motor 64, as indicated at 
114, while the stop latch or pawl 74 remains in engagement with the 
serration 75, as indicated at 116. During this movement of the base plate, 
the stepping motor 36' drives the pump 36 to aspirate 5 .mu.l of air into 
the capillary tip 71, as indicated at 118. After the base plate 54 has 
reached its final position at the fixed stop member 60, the adjusting 
motor 70 is briefly energized to immerse (at 120) and withdraw (at 122) 
the capillary tip 71 in the inner chamber 47, which is filled with rinse 
fluid at this time. As a result the capillary tip is decontaminated and 
any sample material adhering to the exterior thereof is removed. At this 
stage of the operation, about 22 seconds have elapsed from the start of 
the measuring cycle being described. 
Next, in the sequence of operations, the base plate 54 is again pivoted 
(indicated at 124, FIG. 8) in an anticlockwise direction by the 
energization of the drive motor 64 so that the pawl 65 mounted on the base 
plate 54 acts on the tooth 66' of the ratchet wheel 62 to rotate same, 
with its shaft 63, until the bottom side of the base plate 54 engages the 
stop face 64' (FIG. 6). During this time the stop latch or pawl 74 is 
maintained in engagement with the serration 72 by the cam wheel 67 and its 
associated linkage 74', so that, with the anticlockwise rotation of the 
base plate 54, the rotatable table 52 is advanced in a clockwise 
direction. At the termination of the movement of the base plate 54, when 
its bottom side abuts the stop face 64' of the ratchet wheel 62 (FIG. 6), 
the rotatable table will have been advanced one step to thereby position 
the next subsequent sample container 16 in its operative position. Also, 
at the termination of this movement, the cam wheel 67, which rotates 
together with the ratchet wheel 62, has been rotated so that the pawl 74 
is disengaged from the serration 72 on the rotatable table 62, as 
indicated at 126 in FIG. 8. The capillary tip 71 is at this time located 
above the liquid additive container 17 so that pivotal movement (at 128) 
of the metering probe to its lowest horizontal position by means of the 
adjusting motor 70 dips the tip into the withdrawal portion of the liquid 
additive container 17. At this point in time 25 seconds have elapsed from 
the initiation of the cycle being described. 
As a next step, the stepping motor 36' is again actuated to effect a 
partial intake stroke of the pump 36 so that the capillary tip 71 
aspirates 10 .mu.l. of liquid additive, as indicated at 130 in FIG. 8. 
Subsequently, the adjusting motor 70 is actuated and the capillary tip is 
lifted from the container 17 (at 132). 
After a further partial intake stroke of the pump 36 for aspirating 5 
.mu.1. of air into the capillary tip (134, FIG. 8), the base plate 54 is 
moved to its position (136) wherein it is in engagement with the fixed 
stop member 60 by means of the drive motor 64. At this instant of time the 
capillary tip 71 is back again in the position as shown in FIG. 2 and, in 
the same manner as before, the adjusting motor 70 is briefly energized to 
immerse (138) the tip in the inner chamber 47, which is filled with rinse 
fluid to decontaminate it by removing any liquid additive adhering to the 
exterior thereof. 
After immersion in the rinse fluid container 14, the metering probe 10 is 
pivoted by means of the adjusting motor 70 to its opposite end position 
(140, FIG. 8), while simultaneously it is pivoted azimuthally (142) until 
the capillary tip 71 is positioned above the sample introduction opening 
18 in the graphite tube assembly 20 of the atomic absorption spectrometer. 
This completes the timing diagram of FIG. 8. At this point in time the 
system is in position for pivoting the probe 10 about is horizontal axis 
to dip the capillary tip 71 into the sample introduction opening 18 and 
introduce a measured quantity of liquid sample, liquid additive and air 
into the atomic absorption spectrometer for analysis, thereby completing 
the second measuring cycle, as well as completing the complete cycle of 
operation. The apparatus is now ready to commence the first measuring 
cycle of a new complete cycle of operation. 
In the foregoing example, the invention was described in its simplest form, 
wherein the first measuring signal of the sample, only, was obtained in 
the first measuring cycle, and the second measuring signal was obtained of 
the sample after the addition of 10 .mu.1. of liquid additive in the 
second measuring cycle. The sample liquid may, for instance, be urine of 
which the quantity of lead contained therein is to be determined, and the 
liquid additive is lead nitrate in water (C.sub.A = 250 mg/1). 
In the case described above, the quantity of the component to be determined 
in the sample is determined according to the general relation 
EQU M.sub.P = S.sub.1 .times. e 
from the signal measured S.sub.1 obtained for the sample, only, in the 
first measuring cycle; e represents a calibration factor for the 
particular sample liquid. Generally, this calibration factor is: 
##EQU1## 
wherein M.sub.m and M.sub.n are the amounts of the component in question 
yielding measured signals S.sub.m and S.sub.n. In the present specific 
case M.sub.m = M.sub.P + M.sub.A , i.e. it is the sum of the amount of 
M.sub.P of the component to be determined in the sample P and of the 
amount of M.sub.A added with the liquid additive A, and M.sub.n = 
M.sub.P. Then, S.sub.2 is the signal measured in the secondary measuring 
cycle. 
This results in: 
##EQU2## 
for evaluation of the measured signals S.sub.1 and S.sub.2 as obtained 
from one sample of liquid; with M.sub.P = C.sub.P .times. V.sub.P and 
M.sub.A = C.sub.A .times. v.sub.a the respectively selected units of 
concentration are (mg. per 1.): 
##EQU3## 
This formula is preprogrammed in the data processor 85, wherein C.sub.A is 
a constant, and V.sub.A and V.sub.P, respectively, are the number of steps 
of the stepping motor 36', which are either stored in or may be called-up 
from the central control unit. 
The apparatus as described above may be readily adapted to a measuring 
method in which the addition of the liquid additive will afffect the 
measuring signal. In that case a solvent container 144, FIGS. 2 and 3, 
will be mounted on the base plate 54 in addition to the raise fluid 
container 14 and liquid additive container 17 which, like the liquid 
additive container 17, is designed as a pneumatic trough. The container 
144 contains the same pure solvent as employed in the liquid additive. The 
measured signal S.sub.1 in the first measuring cycle will then not be 
taken of the measuring sample P alone, but of a sample to which there has 
been added a volume of solvent identical to the volume V.sub.A of the 
liquid additive added in the secondary measuring cycle. In this 
embodiment, the ratchet wheel 62, as seen in FIG. 7, includes an 
additional stop face 64" and an additional tooth 66", which are designed 
to position the base plate 54 so that the solvent container 144 is below 
the metering probe 10 during an appropriate portion of the first measuring 
cycle. The cam wheel 67, mounted on the shaft 63 together with the ratchet 
wheel 62, is designed so that the rotatable table 52 will advance only 
with the second anticlockwise pivotal movement of the base plate during 
the secondary measuring cycle. 
The time sequence of operation is programmed in a manner similar to that 
described hereinbefore, and the number of steps of the stepping motor 36' 
is adjusted by the central control unit or stored in the microcomputer. 
Evaluation of the measuring signals is, as follows: 
##EQU4## 
with V.sub.L = V.sub.A. 
The apparatus, for use in combination with an atomic absorption 
spectrometer, has been described, wherein the signal measured is 
determined by the respective quantitities of sample. However, this 
apparatus may readily be employed in combination with an optical 
absorption system, wherein the signal measured is dependent on the 
concentration of the component to be determined. In the simplest case, the 
procedure follows the modification last discussed hereinbefore, with the 
extinctions being measured, respectively; the evaluation formula being as 
follows: 
##EQU5## 
For convenience, V.sub.A and V.sub.P and V.sub.L are selected to be equal, 
so that: 
##EQU6## 
In measuring methods off this kind, the general formula for the 
calibration factor is: 
##EQU7## 
It will be appreciated that the apparatus may be further modified by making 
corresponding changes in the time sequence program, by making 
corresponding changes in the design of the ratchet wheel 62 and the cam 
member 67 and by making corresponding changes in the evaluation formula in 
such a way as to perform a number of calibrating measurements with one 
sample in either a quantity dependent or a concentration dependent 
measuring method. When employing such a method, the ratchet wheel 62 and 
the cam wheel 67 coact in such a way as to advance the rotatable table 
only after the last measuring cycle has been performed with one particular 
liquid sample. 
Thus, an improved automatic sample preparation apparatus and method for 
making successive measurements with an analyzer has been shown. Although 
specific embodiments have been illustrated and described, it will be 
obvious to those skilled in the art that various modifications may be made 
without departing from the spirit of the invention, which is intended to 
be limited solely by the appended claims.