DE2045134A1 - Atomic fluorescence spectrometer - Google Patents

Description

H12 P1O D

HEWIETT-PACEAED COMPANY Palo Alto / California, USA

Atomic fluorescence spectrometer

Priority: September 12, 1969; UNITED STATES; Ser ₀ NOo 857 360

Starting point of the invention;

The present invention relates generally to an apparatus for the Atomic fluorescence spectroscopy (A.IV.S.), as used e.g. in chemical investigations, to determine the concentration of a to determine a certain element in a sample. In a nutshell, becomes thermal in a typical A.F.S "system of a sample Energy supplied to convert this into atomic vapor, the has a considerable number of free atoms that ■ are in their G-round energy states. From a source of light has wavelengths which are characteristic of a selected atomic species in the sample, radiation energy is transmitted through the sample, which is in the form of an atomic vapor, is conducted to bring the selected atoms to higher energy levels. Then the excited atoms return to the ground state and give off their energy in the form of emitted radiation. The emitted radiation is detected by a detector, the output of which is an indication of the concentration of the selected atomic species in the sample. The detector is arranged so that it only picks up radiation from the Sample is emitted, and no radiation from the light source receives "

109Ö12 / U32

20 4 513a

All of the radiation emitted by the selected atomic species includes both the desired fluorescent radiation emitted by the light source is caused, and an undesirable thermal radiation, which is based on the thermal energy "the is used to produce atomic vapor. The background radiation "based on a thermal excitation" is from The fluorescence radiation is distinguished by modulating the light of the light source and synchronously only the Detects radiation generated by the modulated light source. The resulting usable signal received from the Detector is obtained, indicates the fluorescence radiation and is equal to the difference between the total radiation and the thermal radiation ,,

So that the detector is selective and as sensitive as possible to the Fluorescent radiation responds, the thermal radiation that is received by the detector should be opposite to the Fluorescence radiation can be kept as small as possible. This has been attempted to achieve by using a filter or has placed a monochromator between the vapor of the sample and the detector to only select a narrow band of wavelengths passing around a resonance line of the selected type of elements and around other spectral lines to block, which are emitted by the steam of the sample «,

By using a filter or a monaural generator Numerous significant difficulties arise at the detector entrance. The monochromator must be ζ "Β. a high resolution possess, if not, the insensitivity to examination should be reduced. From the fact that the monochromator or filter operates at one wavelength, other disadvantages arise. The sensitivity of the examination is caused by the thermal radiation in the optical bandpass

109812/1532 original in *

2,5134

of the monochromator are also limited by certain Elements such as copper, nickel, and iron produce a variety of spectral lines; however, only one of these is possible Lines through the monochromator and is detected by the detector, further reducing sensitivity results. Furthermore, each element that to determine the use of a monochromator, that responds to a particular wavelength. Therefore, if a sample is to be examined for several elements, the monochromator can be exchanged for each element to be determined. The use of multiple monochromators is both costly and time consuming. Furthermore, in an A.IVS system, in which the sample is consumed, If it is converted into atomic vapor, the examination of a small amount of the sample for several elements is only possible when there is an elaborate system that allows rapid switching from one monochromator to another can be made. Such a system is economical impracticable

Summary of the invention:

The present invention relates to an atomic fluorescence spectrometer which does not require filters or monochromators between the sample vapor and the detector. In the illustrated embodiment of the invention, a sample to be investigated is excited by energy from z _o B "of a high frequency power source to the sample in the atomic vapor to convert the free atoms of a selected, to be examined element contained by a light source generates a radiation beam having spectral lines characteristic of the selected element, and this beam is radiated into the sample vapor to excite the atoms of the selected element. Falls on a detector

• - 4 -

109812/1532 originally inspected.

2 O Ä 5 1 3

both fluorescent radiation from the particular atoms excited by the light beam and thermal radiation Radiation from all atoms of the sample caused by the excitation energy have been generated.

The desired output from the detector is: Output signal that of the fluorescence radiation of the sample vapor is equivalent to. An essential feature of the present invention "is that the fluorescence radiation directly from the sample vapor can be detected without inserting a filter or monochromator here needs, whereby not just one but all resonance lines of the fluorescence radiation to the desired output signal can contribute. The fluorescence radiation is not overshadowed by the thermal radiation, since the latter is essential is decreased. This is achieved by the fact that the excitation energy, which is used to vaporize the sample, is pulsed and that the detector is operated synchronously, so that the fluorescence radiation is detected only during the time intervals between the energy pulses. While at each of these time intervals the thermal radiation of the sample falls rapidly to a very low value in relation to it the fluorescent radiation generated by the action of the light beam, whereby it is achieved that the detector output signal is mainly based on the desired fluorescence radiation generated by the light beam, with which the free atoms are irradiated, and that only a small proportion of thermal radiation is present.

Fluorescent radiation is differentiated from thermal radiation in that the light from the light source is chopped or, is chopped, and that the radiation is determined, which emitted synchronously with the chopper from the sample vapor will. The frequency of the chopper is lower than that

- 5 -10 9817/1 ^ 32

_0RIQ . _l

_M AL

2 O 4,513

Frequency with which the thermal energy is pulsed so that several pulse signals are generated at the output of the detector during each chopper period which correspond to the radiation from the sample vapor between the excitation pulses Z _{0, for} example, from the high-frequency energy source. Two different detector output signals are generated which correspond to the radiation from the sample vapor, depending on whether a beam is radiated from the light source or not. These two signals are separately averaged and the difference between these signals is formed to produce an output signal indicative of the concentration of the selected element in the sample.

As noted above, a feature of the present invention is that the fluorescent radiation is detected without the need for filters or monochromators be used by the selected spectral lines to the Detector arrive, and instead the entire spectrum of radiation from the sample is determined. This results in a high examination sensitivity especially for elements »the generate radiation that is distributed over several spectral lines. In addition, an examination of a sample on several elements by simply switching from one light source to another. No filters or monochromators need to be changed or be exchanged when different elements are to be determined. There can be multiple items in a short amount of time can only be determined by the fact that quickly between different Light sources is switched. An analysis of several elements can therefore be carried out if only a small amount of sample is available.

In the following the invention will be described in more detail with reference to one in the Drawing illustrated preferred embodiment explained will. Show in the drawing?

ORIGINAL INSPECTED »

1098 12/1 B 32 * " ⁶ ~

2 O 4 S Ί 3 - 6 -

Pig «1 a combined schematic representation in the form of a Block diagram of a preferred embodiment of the present invention,

2a-e are graphs showing various waveforms used in the operation of the present invention Invention occur, and

FIGS. 3a-c show diagrams of spectral lines in which the radiation is shown which is emitted by a sample to be examined will.

Description of a preferred embodiment t

1 shows a chamber 11 which can receive a sample of a substance which is to be examined with regard to the concentration of one or more selected elements contained in this sample. Through a sample introduction device 13, the sample is introduced into the chamber 11 in such a form that it can be dissociated into free atoms. If the sample consists of a gas, the sample introduction device can consist of a simple economy valve in order to introduce a continuous flow of gas into the chamber under a required pressure nebulize, the sample can optionally be mixed with a carrier gas, and to introduce the sample in a suspension into the chamber. Solid samples may be applied directly to the inner walls of the test chamber itself, and then sputtering are vaporized by z "B _s" The chamber 11 is a vacuum pump 15 at a low and constant pressure which is typically in the range of 1-10 mmHg, maintained .

ORIGIHAL

- 7 -109812/1632

; * 204513a

The working process is improved by the low pressure in the chamber, which will be described below should «■

Energy from a high voltage source 17 is supplied via a controlled switch 19 to a winding 20 which is wound around the chamber 11 to create an electric field in the chamber and thereby to excite the sample so that a large number of molecules of the sample in be steam or a plasma of free atoms is dissociated, the state in their basic energy are "the RF energy, .by which the sample is excited to dissociate them, can at a selected frequency within a wide frequency range radiated, which, for example, _o in of the order of 10-2500 MHz. Although only a single coil 20 is shown in the drawing to deliver radio frequency energy to the plasma in chamber 11, other means using normal capacitive or inductive coupling techniques may be used. Z, B ₀ , if the high-frequency excitation source is in the microwave range, the sample chamber can be arranged in a resonance cavity «

Other devices can also be used to excite the sample into a plasma of free atoms. For example, _0, the power source 17 are replaced by a high-voltage DC discharge circuit, and the coil 20 may be replaced by two discharge electrodes which are arranged inside the sample chamber. 11

Several electrodeless metal vapor discharge lamps 21, 23, are aligned with each other so that each of these lamps has a Radiation beam generated on a common, in the Sample chamber 11 leading beam path lies ", each of these lam-

- 8 - 1 0 9 8 1 ? / 1 6 3 2 ORiGiMAL INSPECTED

2 ü 4 b 1 3 4.

pen consists of a small glass ampoule in which a small amount of the "special element or composition, which contains this element is enclosed together with an inert gas «. The one contained in each lamp Element is chosen to correspond to an element in the sample plasma that is to be examined. So if in If three different elements are to be found in the sample, the three lamps 21, 23, 25 each contain a different one of these three elements. One type of metal halide lamp that can be used in the present invention is "1st described in U.S. Patent 3,319,119

The discharge lamps are fed with energy in a similar way, like the sample chamber 11. In detail, the three lamps 21, 23, 25 are each provided with coils 27, 29, 31 and switches 33, 35, 37 coupled to the high-frequency source 17. The switches 33> 35, 37 are operated to deliver radio frequency energy to the ampoules in any selected sequence. The switches 33, 35, 37, like the switch 19, are indicated in dashed lines to indicate that they are in be designed in any suitable way so that they are suitable for the particular frequency and the voltage level of the energy supplied by the energy source 17. If, for example, energy in the microwave range is generated by the energy source 17, then these switches can be made from microwave waveguide circulators exist"

By the high frequency energy from the energy source 17, the gas in a selected ampoule is ionized and there are the atoms of the element contained therein are excited, so that light is emitted with wavelengths such as those has characteristic spectrum of the element. The beam emitted by the selected discharge lamp with the characteristic Radiation is through a window part at the end

- 9 109817 / 1P32 _..-. _v .. - =

_ 9 ■ -

The beam radiated into the sample chamber 11 from the chamber 11 can be strengthened in the sample chamber by the fact that window parts and two mirrors 39, 4-1 can be provided to reflect the radiation into the sample chamber as shown «. The one from the discharge lamps Radiated beam with the characteristic radiation is selected by the corresponding type of atoms of the Element in the sample plasma is absorbed, causing the atoms to move from their G-round energy levels to higher energy levels will. Many of the excited atoms then return to their basic energy state and emit in random Directions again radiation. This phenomenon is known as atomic fluorescence

The sample plasma emits in addition to the characteristic Wavelength of the selected type of atoms that are excited by the light source, including radiation at a Number of wavelengths «This is due to the fact that by the high frequency excitation energy from the energy source 17, through which dissociates the sample, likewise randomly all atoms in the sample chamber at energy levels above the G-round energy level be stimulated. At the arbitrary distribution of the atoms that have been excited in this way, fall the atoms subsequently down to lower energy levels and emit energy in a variety of wavelengths. The energy that is given off randomly by all atoms is called thermal radiation and this is just like which emits fluorescence radiation in all directions. Thermal radiation is undesirable because it reduces the sensitivity of the examination and adversely affects examination selectivity. This radiation is related to the However, as will be described below, fluorescence radiation is kept as small as possible.

- 10 109817/1532 ORlGJNALiNSPECTED

Both the fluorescent radiation are arranged between the sample chamber and the detector, the total radiation received from the sample, that is, as the thermal radiation is supplied irradiated through a window part on the side of the sample chamber 11 to a detector 43 ₀ Suitable light collecting lens elements (not shown). The windows on the side and ends of the chamber are made of a material that is transparent to the characteristic radiation of all of the elements to be examined in the sample. For most of the elements, stained glass windows suffice; however, certain elements require windows made of quartz, sapphire, lithium fluoride or other materials. The window material must withstand the plasma temperatures that are generated in the sample chambers, and typically at 1000 ⁰ G or higher.

The plasma in the sample chamber is kept at a low pressure, which is lower than atmospheric pressure, by the vacuum pump 15 is to increase the yield of fluorescence radiation and the broadening of the pressure-induced Decrease spectral lines. On the other hand, this reduces the overall sensitivity of the examination and the selectivity of the System improved »Due to the low pressure plasma, one also obtains a radiation permeability in the far ultraviolet range of the spectrum, reducing the investigation area to a greater number of elements, including some Non-metals, can be expanded.

The radiation received from the sample is sent directly to the detector 43 given There is no need to insert filters or monochromators between the sample chamber 11 and the detector 43 so that the detector can see the entire radiation spectrum extending over a wide range of wavelengths receives. The detector preferably comprises one or more photomultiplier, which are chosen so that they have a spectral

- 11 1098 12/1 532 ofüCtfJAL inspected

Have Anspreehempfindlichkeit, the ₀ example of wave-lengths in the size of 8000 from the infrared region to the far ultraviolet region, Z - 1000 S ranges. The detector 43 is arranged in such a way that it only picks up radiation which is emitted by the plasma and does not receive any direct radiation from the discharge lamps 21, 23, 25.

That from. the detector 43 obtained signal is amplified by an amplifier 45 and then either via a first controlled switch 47 and a second controlled switch 49 to a first or second _0, the signal averaging circuit 51 or 53 _o supplied. As will be explained further below, the output signal from the signal averaging circuit 51 corresponds to the radiation from the sample, which is largely based on fluorescence radiation and has a small proportion of thermal radiation; while the output signal of the signal averaging circuit 53, only the thermal background radiation corresponds to "The background signal is subtracted by a subtraction circuit 55, to generate from the output signal of the averaging circuit 51 to a signal that is _o proportional only the fluorescent radiation The output signal from the subtracter circuit 55 is converted by circuit 57 to a signal proportional to the concentration of a particular selected element in the sample. Circuit 57 is basically a logarithmic puncture generator; however, additional complex conversion functions can be provided to expand the range of elemental concentrations that can be detected. Additional means, indicated by line 58, can be used to couple logarithmic circuit 57 to the switch in a feedback circuit to control the switching speed at which the radio frequency energy is applied to the sample chamber, thus controlling a Prevent overexcitation of the plasma ₀

109817/1532

inspected

204513 /,

The sample is supplied from the high-frequency energy source 17 with excitation energy in pulses which occur with a predetermined repetition frequency, Z ₀ B ₀ 500 Hz. This is accomplished by opening and closing switch 19 periodically under the control of a timer circuit or clock 59. During a portion of each clock period, radio frequency energy is applied to the sample to excite the atoms of the sample. During a subsequent portion of the same clock period, the radio frequency energy is turned off on the sample plasma, causing the thermal radiation from the atoms in the sample to fall off rapidly. There is a period of time after this drop, typically 1-10 msec, during which the atoms in the sample are still in their dissociated form. During this time, the sample can be illuminated with light by one of the discharge lamps, which has the characteristic spectrum of the selected atomic type, and only the free atoms of this atomic type can absorb light. As already described above, the atoms that absorb the light then emit it again, which generates fluorescence radiation.

The detector output is only gated open by the energy source 17 during the time periods between the excitation pulses, whereby most of the undesired effects caused by the thermal background radiation are switched off. Specifically, the switch 47 is closed to pass the output signal obtained from the detector for a predetermined period of time during each period when the high frequency switch 19 is opened. The two switches ^ 9, 47 are synchronized by the clock

- 13 109817 / 1S32

2Ö45134

actuated. After the initial drop in thermal radiation, the switch 47 is closed by the actuation of a monostable third delay multivibrator 61. Most of the output from switch 47 is due to fluorescent radiation from the plasma; however, there is also a small proportion of thermal radiation. As already explained above, the portion of the fluorescence radiation signal is based on the excitation of the sample vapor by the light beam from one of the discharge tubes 21, 23, 25, while the portion of the thermal radiation signal is based on the residual effects of the high-frequency excitation energy. These two components are distinguished from each other in that the light beam is modulated or periodically interrupted with the aid of a mechanical chopper wheel 63 which is rotated about an axis 65 which runs parallel to the plane of the figure by suitable drive devices (not shown). The chopper wheel 63 comprises suitable segments, so that the light beam having a predetermined frequency on the order of, for _o example, 50 Hz, wirdo interrupted The controlled switch 49 is operated in synchronism with the chopper, as indicated by the drawn in broken line arrow between these both directions , so that when the chopper 63 is in such a position that light can fall into the plasma, the detector signal is passed to the signal averaging circuit 51 and that if the light beam cannot fall into the plasma, the Detector signal is passed to the signal averaging circuit 53. Consequently, the signal averaging circuit 51 generates an output signal corresponding to the total plasma radiation, while the signal averaging circuit 53 generates an output signal corresponding to the thermal background emission radiation. As already mentioned above, the desired signal consists of the difference between the outputs of the signal averaging circuits 51 and 53, and this difference is determined by the subtraction circuit.

- 14 1098T271532 ■ originally inspected

204513 /,

tion 55 received

Although a mechanical chopper is used in the embodiment shown in FIG. 1, it should nevertheless be easily understood that other devices can also be used to modulate the light from the light source. Z ₀ as the light sources may even by timed circuits, through the selected switch of the switch 33 »35, 37 may be actuated, or another switch (not shown ^ which is connected in series with the excitation circuit for a lamp periodically In this case, the controlled switch 49 would be operated in synchronism with the timer circuits that operate the lamp switches

Overall operation of the system shown in FIG. 1 can begin on can be best understood with reference to the diagrams in FIGS. Fig. 2a shows the average value of the high frequency energy pulses at the output of the controlled switch 19 be generated. These pulses begin at intervals of 2 msec, corresponding to the clock speed of 500 Hz. In this figure, the width of use of each pulse corresponds to half a period of the timer frequency; it can, however shorter usage widths can also be selected. Fig. 2b shows the mean output signal from the detector 43, which is based on the all radiation from the sample plasma is based. The radiation is maximal during the high frequency excitation pulses. While the time intervals between the excitation pulses depends on the radiation emitted by the sample vapor depends on whether the light beam is radiated into the plasma or blocked. In the absence of the light beam, the sample radiation falls rapidly to a low value corresponding to the thermal emission radiation, which is indicated by the part 67 of the waveform the Figo 2b is shown. When the light beam arrives

- 15 -

109812/1532 original er

is emitted, the result is a sample radiation which is indicated by the waveform part 69 shown in dashed lines; and as shown in the drawing, the emitted radiation largely corresponds to the fluorescent radiation of the selected type of atoms and this radiation is larger and falls off at a slower rate than the radiation in the absence of the ray of light "

As can be seen from Fig. 2c, the switch 47 is closed only during a predetermined time interval between the high frequency energy pulses. The pulses shown in this figure correspond to the output pulses of the monostable delay multivibrator 61. Each pulse is delayed so that it begins after a predetermined time interval t, after the end of the high frequency excitation energy pulse. The signals transmitted while switch 47 is closed are shown in Hg ₀ 2d ₀ It can be seen that the detector output signals which are transmitted are such. Signals correspond to that occur after the thermal radiation has dropped slightly _o

Figo 2e represents the output of the switch 47 in a somewhat larger time scale. When the light beam is turned off, so that it does not fall into the sample chamber 11 d _e ho when it is locked by the chopper wheel 63, so a plurality of output signal pulses 67 are generated, since the chopper wheel interrupts the light beam at a speed or "frequency that is less than the speed at which the high-frequency energy is pulsed." A plurality of signal pulses 69 are transmitted from the detector. Since the switch 49 is operated synchronously with the chopper 63, the signal pulses 67 are the signal averaging circuit 53 and the signal pulses 69 the

- 16 -

109817/1532

^ AL SWSPSCTED

2 O 4 5 ">. 3 7 _t - 16 -

Signal averaging circuit 51 supplied »If the averaged values of these signal pulses have been subtracted from one another, then is the one caused by the thermal background emission radiation Effect turned off.

As has already been noted above, in the embodiment of an atomic fluorescence spectrometer shown in FIG. 1, no filter or monochromator elements are required which have to be inserted between the sample chamber 11 and the detector 43. For this reason, the above described disadvantages associated with the use of filtering devices accounted _o Despite these disadvantages, when a filter or a monochromator is used in the inventive system, werdenο further increased assay sensitivity

The advantages of the present invention can be better understood from the graphical representations of Figures 3a-c. FIG. 3a shows the spectral distribution of the radiation from the sample chamber 11 in the system of FIG. ₀ 1 when the plasma is generated, ie ₀ when the plasma is created by a pulse from the high-frequency energy source 17. The intensity I of the spectral peaks is shown arbitrarily in units up to 400. The particular element to be detected has certain characteristic spectral fluorescence peaks, which are denoted by E. The other spectral lines represent the non-fluorescent transitions of the selected element as well as other types of atoms in the sample chamber. When the plasma is generated, the spectral lines correspond essentially to the thermal radiation based on the high frequency excitation. The radiation from the light source is characteristic of the selected element and contributes to the generation of the "E" peaks. These peaks fluctuate in their

- 17 -

original ■; ■: ·.: s-ücted 109817/1532

204513 /;

intensity depending on the speed with which the light is Light source is chopped or chopped.

3b and 3c show the spectrum of the radiation from the sample when the generation of the plasma is switched off, d _o ho during the time intervals between the excitation pulses from the radio frequency energy source 17. The wavelength range shown in these two figures is the same as that in FIG the pig. 3a; however, the light intensity I is shown on a scale which corresponds to a sensitivity 100 times greater than the scale in Pig. 3a. In the pig. 3b and 3c show sample radiation when the light is switched on or switched off, ie when the light beam is blocked or interrupted or when the light beam is incident on the plasma. As can be seen from Figure 3b, the total radiation from the sample is very small when both the plasma is not excited and the light is switched off. If, however, as shown in FIG. 3c, the light is switched on, only the selected atoms are excited by the radiation of the light, as a result of which the precisely defined spectral peaks are generated. Since the excitation of the plasma is switched off at this time, the thermal background emission radiation from the sample is very low compared to the characteristic radiation of the selected element. As already described above, the detector 43 is gated open during the times during which the Generation of the plasma is switched off “The whole in the graphs of the Pig. The spectrum of the radiation shown in FIGS. 3b and 3c is applied directly to the detector 43, so that all characteristic spectral lines contribute to the usable output signal. Furthermore, as already described above, the fluorescence radiation, which is based on the action of the light source, is separated from the low proportion of thermal radiation in that the averaged

■ '. - 18 10 9 812/1532 ORIGINAL

2 ΰ 4 5 ι 3 /,

Values of the two different output signals generated by the detector are subtracted from one another. Since the thermal radiation is kept at a low value and since the entire radiation spectrum is applied to the detector, the examination sensitivity is very high without the use of filters can be changed, that is _, "by the fact that the discharge tubes are optionally switched on in order to put them into operation one after the other"

ORIGINAL INSPECTED - 19 ~

109812/1532

Claims (1)

2 O 4 5 Ί 3 Pa t ent ans ρ rühe to) atomic fluorescence spectrometer with a device for Taking a sample and converting that sample into a vapor that contains free atoms of a selected type of atoms in the sample contains; with a light source for generating a radiation beam for irradiating the sample vapor, wherein the radiation beam has spectral lines that are characteristic is for the selected type of atoms; and with a device for determining the radiation emitted by the Atoms of the sample vapor is emitted, characterized by one in the absorbing the sample and converting means (11) contained source for generation pulses of energy to periodically excite the sample at a first predetermined frequency; by a circuit arrangement (59,61,47), which is coupled to the locking device (43) and to the source for generating the energy pulses is synchronized to an output signal accordingly of the radiation to be generated by the sample due to the excitation of the sample by the radiation beam during the Periods between the pulses emitted by the source for generating the energy pulses, the output signal being forms an indication of the selected type of atoms in that sample. 2ο device according to claim 1, wherein the circuit arrangement is characterized by a facility (63) in order to modulate the radiation beam, which with irradiating the sample with a second predetermined frequency lower than the first frequency; by a first scanning device (47) associated with the source for generating the energy pulse is synchronized to the output - 20 - 109817/1532 "*", nal iKSFeciBJ ZöÄb'i 3 /, - 20 - the locking device (43) only during the time intervals to key in between the energy pulses; by a second scanning device (49) connected to the modulation device (63) is synchronized in order to pass the output of the detection device alternately to a first and a second averaging device (51,53), in order to thereby transmit the radiation which from the sample vapor emitted in the absence and presence of the radiation beam, to average separately; and by means (55) for producing the difference between the output signals from the first and second Averaging device for generating the output signal that is indicative of the type of atoms selected. 3. Apparatus according to claim 2, characterized in that the first and the second Auftasteinrichtung (47, 49) in series between the locking device (43) and the first and second signal averaging devices (51,53) are switched. 4. Apparatus according to claim 2 or 3, characterized by a device (61) with the first Auftasteinrichtung (47) is connected to delay the gating of the locking device until a predetermined Time interval has passed after the end of each energy pulse. 5. Device according to one of claims 2-4, characterized in that a function generator (57) is provided in order to convert the signal received from the device (55) forming the difference into a signal, which is directly proportional to the concentration of the selected type of atoms in that sample. !1 - 109817/1632 AS 204513 /, 6o device according to A _n demanding 5, characterized in that a feedback and the source (17,19) is open ken n ζ calibration η et (58) between the puncture generator (57) provided for generating the power pulses to the pulse train of energy pulses to control to prevent overexcitation of the sample vapor. 7 «A device according to any of claims 2-6, characterized by means (45), to enhance the given from the detection means to the first and second averaging means output signals _β 8 <, device according to one of claims 1-7, characterized characterized in that the receiving the sample and converting means a chamber (11) having a first window part for irradiating the radiation beam and has a second window part, which is arranged outside the beam path dTesas radiation beam in order to emit radiation, which has been emitted from the sample vapor to pass to the detection device, and a device (13) contains to introduce the sample into this chamber and that. the source (17) a device for generating the energy pulses (20) for generating an electric field in the chamber to generate a plasma in the chamber and in this way the sample dissociates into free atoms. 9c device according to claim 8, characterized in that g e k e η η ζ ei without t that a device (15) is provided, to create a vacuum in the chamber. 10. Apparatus according to claim 8 or 9, characterized in that the means for generating an electric field a high frequency energy source (17) - 22 - 109817/1532 owginal ιι «« ηβ 2 0 4 513 / ₊ which is coupled to the chamber (11) » 11. Device according to one of claims 1-10, dadureh. characterized in that the source for generating the energy pulses comprises a gate circuit (19) which is shown in Series connected between the radio frequency energy source (17) and the chamber (11) and at the first predetermined frequency can be operated » 12 "Device according to one of claims 1-11, dadureh characterized in that the light source comprises a plurality of vapor discharge lamps (21,23 »25) through which radiation beams can be generated that have spectral lines that are characteristic of different types of atoms, and in that the tubes are arranged so that the radiation from each tube is directed to that receiving and converting the sample Facility is directed, and that facilities (33 »35.37) are provided around the various vapor discharge tubes to be put into operation consecutively » ORIGINAL INSPECTED Blank page