Atomic absorption spectroscopic analytic apparatus

A sample injector (32) with an upwardly opened sample receiving hole is connected to an atomizer (36) of a flame type atomizing means and on a burner chamber (7) a flameless type atomizing means is mounted ahead of a burner head (9). For distribution of the sample by an auto-sampler (40) it is so arranged that the nozzle is movable to the sample bottle of the auto-sampler (40) and the sample injector (32) or a sample injection hole (30) of the atomizing means placed at the measuring position. This arrangement enables injection of the sample into the atomizing means of either type by means of a common auto-sampler, this facilitating switching between the flame system and the flameless system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an atomic absorption spectrophotometer 
and, more particularly, to an atomic absorption spectrophotometer with an 
arrangement for flame system-flameless system switching in the atomizing 
means. 
2. Prior Art 
As atomizing method in atomic absorption spectroscopic analysis there are 
known two alternatives of flame system in which atomizing is done by 
burning a sample in a burner and flameless system in which atomizing is 
done by flowing a high-amperage current through a graphite tube of an 
electric furnace. In order to enable switching of these two atomizing 
systems with a single atomic absorption spectro-photometer, Hidehisa 
Nishigaki, one of the present inventors, already proposed an atomic 
absorption spectro-photometer provided with switchable atomizing means of 
each system (See Japanese Laid-open Patent Publication No. 61-286737.) 
The flame system with its low sensitivity is suited for analysis of samples 
high in concentration, while the flameless system with its high 
sensitivity is recommended for analysis of samples low in concentration. 
These two systems are different in sampling method. In the flame system 
the sample solution is sucked via tube into an atomizer. In the atomizer 
the sample solution is mixed with a fuel gas and a combustion improving 
gas, the mixture is led from a burner chamber to a burner head and there 
it is atomized in a flame. Since the sample is sucked into the burner 
chamber continuously, the quantity of the sample is required to be quite 
large. Meanwhile, in the flameless system a trace amount of the sample 
(several tens .mu.l) is injected into a sample inlet tube made of graphite 
and the graphite tube is then heated to atomize the sample. 
As measurement is made by the flame system, it sometimes occurs that the 
sensitivity attainable is insufficient depending on the sample's 
concentration. And, should it be the case, it is necessary to do another 
measurement by the flameless system. During measurement by the flameless 
system, it also occurs that the sample's concentration is so high that the 
limits represented by the analytical curve are exceeded. Should it be the 
case, it is necessary to do re-measurement with the sample diluted 
properly or do it later by the flame system. 
When measurement is taken with the flame system and the flameless system 
being switched, immediate re-measurement with the same sample is 
infeasible even by switching the atomizing method in case of an atomic 
absorption spectrophotometer provided with atomizing means of the flame 
system and the flameless system for the sampling method is different for 
each type of atomizing means. 
With the atomic absorption spectrophotometer, too, adoption of an 
auto-sampler for automatic injection of a sample is conceivable. It is, 
however, infeasible to use a common auto-sampler for both systems if a 
suction type of sampling method is adopted for the flame system and a 
sampling method in which a trace amount of sample is dripped is adopted 
for the flameless system. 
SUMMARY OF THE INVENTION 
It is a principal object of the present invention relating to an atomic 
absorption spectrophotometer provided with two atomizing means of flame 
and flameless systems respectively to make switching between the flame 
system and the flameless system still more easy by making feasible 
injection of the sample into either atomizing means by the use of a common 
auto-sampler. 
According to the present invention, the flame type atomizing means and the 
flameless type atomizing means are made switchable and the latter is 
disposed ahead of the burner head of the flame type atomizing means (i.e. 
on the side the operator is positioned) to facilitate use thereof, and at 
the same time make a common auto-sampler made usable in both atomizing 
means. For that a sample injector having an upwardly opening sample 
receiver for injection of the sample into the atomizing means of the flame 
system is connected to the atomizer and the auto-sampler is so disposed to 
enable injection of the sample into both of the sample injector of the 
flame system and the sample injection hole of the flameless system. 
If it should be the case that the sample's concentration is too low and 
determination is infeasible during automatic analysis by the flame system 
by using an auto-sampler, the auto-sampler is used for injection of the 
sample into the graphite tube of the flameless system with the flameless 
type atomizing means moved to the measuring position for high sensitivity 
analysis. 
Inversely, should it be the case that the sample's concentration is found 
too high during measurement by the flameless system, the atomizing means 
of the flame system is moved to the measuring position for the sample to 
be injected into the atomizing means of the flame system. 
According to the present invention, the atomizing means of the flame system 
and of the flameless system can be switched as necessary and, if the 
sample to be measured next is low in concentration switching is done to 
the flameless system and vice versa and moreover a common auto-sampler can 
be used for efficient measurement of samples in a wide range of 
concentration. 
The foregoing and other objects, features, aspects and advantages of the 
present invention will be become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a schematic plan view showing an embodiment of the invention and 
FIG. 2 is a schematic view showing the flame type atomizing means of the 
same embodiment. 
It is assumed that, as shown in FIG. 1, the flame type atomizing means is 
placed at the measuring position. That is, the flame type atomizing means 
is so positioned that an optical axis 46 passes through the flame in a 
burner head 9. A sample injector 32 is connected via a flexible tube 34 of 
polytetrafluoroethylene to an atomizer 36 of a burner chamber 7 of the 
flame type atomizing means. The position of the sample injector 32 is 
fixed and the tube 34 has its length enough so that the fixed sample 
injector 32 need not be moved even when the burner chamber 7 is moved 
upward in FIG. 1 as the flameless type atomizing means is moved to the 
measuring position. The sample injector 32 is for microsampling and is 
funnel-shaped with its sample receiver opening upward. 
The flameless type atomizing means is installed ahead of the burner head 9 
on the burner chamber 7 (The operator stands below in FIG. 1 and the 
operator's side is called "ahead"). A numeral 22 denotes an electric 
furnace of the flameless type atomizing means comprising a graphite tube, 
being energized to be heated, and holds holding it on both sides. The 
graphite tube has therein a sample injection hole 30. 
An auto-sampler 40 is equipped near both atomizing means, there is disposed 
an arm 42 with a nozzle attached at its tip for sucking and discharging 
the sample into the sample injector 32 or the sample injection hole 30 to 
properly distribute the sample put on the auto-sampler 40, and the nozzle 
attached to the arm 42 is moved as it swings between the sample containers 
on the auto-sampler 40, the sample injector 32 and the sample injection 
hole 30. As the flameless type atomizing means is placed at the measuring 
position, the sample injection hole 30 moves to a predetermined position 
on the optical axis 46. 
There is provided a drive means 44 for automatically and selectively 
placing the flame type atomizing means and the flameless type atomizing 
means at the predetermined position on the optical axis 46. The drive 
means 44 comprises a moving mechanism for moving both linked atomizing 
means in vertical and longitudinal directions respectively and a pulse 
motor as driver. 
Since, as shown in FIG. 1, the flameless type atomizing unit is placed 
ahead of the burner head 9, there is no risk of the burner head 9 
obstructing the graphite tube changing work, the positioning precision of 
the sample injection hole 30 in the graphite tube and, moreover, the 
graphite tube can be set safely for immediately starting flameless type 
measurement even when the burner head 9 is quite hot just after completion 
of flame type measurement. The burner head 9 is still hot even more than 
30 minutes after completion of measurement and there is a risk of 
suffering a burn if it is touched by bare hand. Thus, by placing the 
flameless type atomizing means ahead of the burner head 9, the flame type 
and the flameless type measurement can be done freely, securely and 
safely. Another merit of this arrangement is that safe sampling is ensured 
for there is no risk of the arm 42 moving above flame when an auto-sampler 
is used. 
When a low-concentration sample has arrived during measurement by the flame 
system as shown in FIG. 1, switching to the flameless type measurement is 
feasible by moving the linked atomizing means upward as seen in the figure 
so that the optical axis passes through the flameless type atomizing means 
and then injecting the sample by the nozzle of the arm 42 through the 
sample injecting hole 30 of the flameless type atomizing means. Inversely, 
when, for example, a high-concentration sample has arrived during 
measurement by the flameless system, switching to the flame type 
measurement is feasible by moving the linked atomizing means downward as 
seen in the figure so that the optical axis passes through the flame and 
then injecting the sample by the nozzle of the arm 42 from the 
auto-sampler 40 into the sample injector 32 of the flame type atomizing 
means. 
In this embodiment the sample can be injected into the atomizing means at 
the measuring position no matter whether it is of the flame type or the 
flameless type. 
FIG. 3 shows a second embodiment. 
In this embodiment it is so arranged that the sample injector 32 moves with 
the burner chamber 7 and the sample can be injected into the atomizing 
means of both flame type and flameless type when the former is at the 
measuring position. When the flameless type atomizing means is at the 
measuring position, the sample cannot be injected into the atomizing means 
of either type. 
In the embodiment of FIG. 3 sample injection is feasible with the flame 
type atomizing means placed at the measuring position, when the flame type 
atomizing means is used for measurement but when flameless type atomizing 
means is used, the sample is injected with the flameless type atomizing 
means once moved off the optical axis 46 as shown in FIG. 3 and then the 
flameless type atomizing means is returned to the predetermined position 
on the optical axis 46 to be used for measurement. 
FIGS. 4 and 5 show an example in which switching of the types of atomizing 
means is done manually, not automatically. The embodiment of FIGS. 4 and 5 
is already proposed by Nishigaki, one of the present inventors, and is 
described in Japanese Laid-Open Patent Publication No. 61-286737. FIG. 4 
is a perspective view of the atomizing means and FIG. 5 is another 
perspective view of the same with flameless type atomizing means removed. 
A support bed 1 is made up of a holding frame 2 and a movable plate 3 set 
therein to be freely slidable in the longitudinal direction (X-direction). 
A front member 2a of the holding frame 2 has set therethrough 
longitudinally a female screw 4 in which an adjusting screw 5 has screwed, 
and the inner end of the adjusting screw 5 is in contact with the front 
edge 3a of the movable plate 3 to be freely rotatable. Hence, the movable 
plate 3 set in the holding frame has its position adjustable along the 
side members thereof by rotating the adjusting screw 5. 
The flame type atomizing means 6 is made up of the burner head 9 connected 
to the rear end portion of the burner chamber 7 via a cylinder 8. The 
burner head 9 has its extent of rotation about its axis finely adjustable 
with respect to the cylinder 8 and a screw 10 is provided for preventing 
rotation of the cylinder 8 after fine adjustment. At the top center of the 
burner chamber 7 there is provided a shaft-receiving hole 11 and along the 
front edge of the top side two screw receiver accommodating tapped holes 
12a, 12b are provided. Near the rear end of one lateral side there is 
provided a dial holding piece 13 projecting sideways, and in the underside 
of the burner chamber projecting downward is a rotary shaft and inside 
this rotary shaft 14 there is formed a female screw opening downward (not 
shown). 
About the center of the movable plate 3 the height adjusting screw 15 is 
provided freely rotatable about the perpendicular axis. Near the rear edge 
of the movable plate 3 a rotation stopper 16 is provided erect and in the 
upper portion thereof a notch 16a corresponding to the crosssection of the 
burner chamber 7. A male screw 15a of the height adjusting screw 15 is 
coupled with the female screw of the rotary shaft 14 with the rear end 
portion of the burner chamber 7 of the atomizing means 6 fitted in the 
notch 16a of the rotation stopper. When the height adjusting screw 15 is 
rotated in this condition, the rotation of the atomizing means 6 is 
prevented by the rotation stopper 16 and with the direction of the flame 
29 through which the optical flux passes kept substantially transverse 
(Y-direction), it is feasible to adjust the height of the atomizing means 
6 by lifting or lowering it along Z-direction. In order to accurately set 
the direction in which the optical flux passes the flame 29 transversely 
(Y-direction), the screw 10 may be loosened for adjustment to be made by 
rotating the burner head 9 about the cylinder 8 and, after adjustment, the 
screw 10 may be retightened. Rotation of the height adjusting screw 15 may 
be stopped by tightening the screw 17 for stopping the rotary shaft 14 
after due adjustment of the height of the atomizing means 6. 
Meanwhile, a flameless type of atomizing means 20 has its casing 21 so 
formed that a plate 21a placed on top of it and a front wall 21b has an 
inverted L crosssection and there are mounted electric furnaces 22 with 
graphite tubes et cetera housed therein on the plate 21a. In the front 
wall 21b of the casing 21 there is formed a notch 23 larger in size than 
the crosssectional shape of the burner chamber 7. About the center of the 
underside of the top late 21a there is provided a rotary shaft (not shown) 
corresponding to the shaft receiving hole 11 and a piece for adjusting the 
extent of rotation is projected forward from about the center in the upper 
portion of the notch 23. 
When the atomizing means 20 is to be attached to the other atomizing means 
6, screw receivers 25a, 25b are screwed into the tapped holes 12a, 12b in 
the topside of the burner chamber 7 and then fine adjusting screws 26a, 
26b are screwed into the screw receivers 25a, 25b respectively. Now the 
casing 21 is set astraddle of the burner chamber 7 with the burner chamber 
7 fitting in the notch 23, the rotary shaft (not shown) projecting 
downward from the underside of the top plate 21a is set in the shaft 
receiving hole 11 formed in the topside of the burner chamber 7 to be 
freely rotatable and the forward end of a projected piece 24 for adjusting 
the extent of rotation is positioned between the fine adjusting screws 
26a, 26b. The direction in which the optical flux passes through the 
electric furnaces 22 is then set to be substantially transverse 
(Y-direction). In this case, the direction of the electric furnace can be 
made accurately transverse (Y-direction) by rotating the casing 21 with 
the rotary shaft (not shown) projecting downward from the underside of the 
top plate 21a as fulcrum by means of the fine adjusting screws 26a 26b, 
i.e. by turning these screws with a projecting piece 24 for fine adjusting 
the extent of rotation therebetween. 
For the flame type measurement it is necessary to match the optical axis of 
the light source with that of the flame 29, while for flameless type of 
measurement it is necessary to match the optical axis of the light source 
with that of the electric furnace 22. For switching from the flame type 
measurement to the flameless type measurement, therefore, it is required 
to shift the optical axis of the electric furnace 22 to the position of 
the optical axis of the light source. For that, it is essential to move 
back the movable plate 3 by the necessary extent by means of the front and 
rear adjusting screw 5 and then also rotate the height adjusting screw 15 
for lifting by the necessary extent. Switching from the flameless type 
measurement to the flame type measurement also can be carried out by a 
contrary proceeding with same manner as the above proceeding. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention as defined by the appended claims, 
they should be construed as included therein.