Atomic resonance line source lamps and spectrophotometers for use with such lamps

The present invention is directed to a lamp assembly for use in atomic absorption spectrometers in which an atomic element hollow cathode lamp assembly has a lamp formed by a hollow cathode electrode and an anode electrode within a sealed envelope. A base structure is attached to the envelope, and located within the base structure is a resistor network consisting of four resistors connected to a common lead and having four plug terminals protruding from the base structure. Two further plug terminals also protruding from the base structure are connected respectively to the cathode and anode electrodes to provide a connecting structure for connecting these electrodes to a lamp power supply. The five plug terminals protruding from the base structure and connected respectively to the resistors and the common lead provide a further connecting structure of the resistor network to a measurement circuit in an atomic absorption spectrophotometer. The resistor network represents the atomic element of the lamp by virtue of two of the resistors, and further, represents a lamp operating current by virtue of the other two resistors. All of the plug terminals are arranged in a conventional octal plug configuration with a boss on the base structure for insuring correct electrical connection.

Referring now to FIGS. 1 and 2, a single atomic element hollow cathode lamp 
assembly HCL has a lamp formed by a hollow cathode electrode CA and an 
anode electrode AN within a sealed envelope SE. A base BA is attached to 
the envelope SE, and located within the base BA is a resistor network RN 
consisting of four resistors R1, R2, R3 and R4 connected to a common lead 
EL. Two plug terminals p6 and p7 protruding from the base BA and connected 
respectively to the electrodes CA and AN provide connecting means for 
connecting these electrodes to lamp power supply means LPS (see FIG. 4). 
Five plug terminals P1 to P5 protruding from the base BA and connected 
respectively to the resistors R1 to R4 and the lead EL provide further 
connecting means for including the resistor network in measurement circuit 
means MCM (see FIGS. 3 and 4) in an atomic absorption spectrophotometer. 
The resistor network is representative of the atomic element of the lamp 
by virtue of the resistors R1 and R2 and is furthermore representative of 
a lamp operating current by virtue of the resistors R3 and R4. As shown in 
FIG. 2, the terminals P1 to P7 are arranged in a conventional octal plug 
configuration with a boss BA1 on the base BA for ensuring correct 
electrical connection. 
When in the operative position in a spectrophotometer, the lamp assemblY 
HCL will be located in the optical path thereof and electrical connection 
from the terminals P1 to P7 to a fixed socket SK in the spectrophotometer 
will be made via a connecting lead CL with socket and plug connectors. 
Instead of being located within the base BA the resistor network RN could 
possibly be located within the connecting lead CL, and in this case the 
lead CL can be cx;nsidered as forming part of the lamp assembly with 
appropriate parts of the lead CL providing part of the connecting means 
for the electrodes and providing the whole of the further connecting means 
for the network. Another possibility would be to locate the network RN 
inside the sealed envelope SE. Both these possible variations from the 
arrangement shown in FIGS. 1 and 2 indicate that it is not necessary for 
the lamp to be provided with a separately identifiable base. 
Referring now to FIG. 3, the resistor network RN is shown together with 
measurement circuit means MCM and a microprocessor .mu.P in a 
spectrophotometer. The measurement circuit means MCM includes a 
multiplexer MPX and an analogue-to-digital converter ADC respectively 
controlled by and connected to the microprocessor .mu.P via a bus BS, and 
a resistor R5 connected to a voltaqe source +V. By means of the 
multiplexer MPX the resistors R1 to R4 are connected in turn in series 
with the resistor R5 and the common lead EL and hence the voltage across 
each of the resistors R1 to R4 in turn is applied to the 
analoque-to-diqital converter ADC. The ohmic values of the two resistors 
R1 and R2 together represent the atomic element of the single atomic 
element hollow cathode lamp assembly incorporating the network; 
conveniently one of these two resistors represents the tens value and the 
other resistor represents the units value of the atomic number of the 
atomic element. The ohmic values of the two resistors R3 and R4 together 
represent a lamp operating current; conveniently the maximum operating 
current for the electrodes of the lamp assembly incorporating the network. 
The microprocessor .mu.P is conditioned to identify the atomic element 
responsive to measurement of the resistor network by the measurement 
circuit means MCM, that is to say the two successive digital outputs of 
the converter ADC responsive to the resistors R1 and R2. The lamp current 
information derived by the measurement circuit means MCM from the resistor 
network, that is to say the two successive digital outputs of the 
converter ADC responsive to the resistors R3 and R4, is used by the 
microprocessor .mu.P together with other lamp current information, as will 
be described in detail with reference to FIGS. 4 and 5, to control the 
lamp power supply means LPS connected to the electrodes of the respective 
hollow cathode lamp. 
It will be appreciated that although the resistive network as described is 
inexpensive and convenient the electrical network incorporated in the 
hollow cathode lamp assembly as described above to represent the atomic 
element and the maximum lamp operating current could be other than 
resistive. With suitably adapted measurement circuit means, the network 
could for example be capacitive or it could provide a binary 
representation by using connections which are open or short circuit or by 
using diodes. 
The single atomic element hollow cathode lamp provided with an electrical 
network as described above with reference to FIGS. 1 and 2 is one example 
of a lamp assembly according to the invention. Other lamps for producing 
resonance line radiation characteristic of one or more atomic elements 
when operated by lamp power supply means may he provided with similar 
networks to form atomic absorption spectrophotometer source lamp 
assemblies according to the invention. One such other lamp is an 
electrodeless discharge lamp. In this case an electrical network may be 
similarly provided in an assembly with the lamp to enable the single 
atomic element for which the lamp emits resonance line radiation to be 
identified in the spectrophotometer. Electrodeless discharge lamps are 
usually provided with an auxiliary power supply external to the 
spectrophotometer. The network in the lamp assembly in this case could 
also represent a particular value of electrical power which is identified 
in the spectrophotometer and used to control the auxiliary power supply. 
Another such lamp is a multiple atomic element hollow cathode lamp. In 
this case also an electrical network may be provided in an assembly with 
the lamp to enable all the atomic elements for which the lamp emits 
resonance line radiation to be identified in the spectrophotometer. 
Multiple atomic element hollow cathode lamps conventionally emit resonance 
line radiation for particular combination of two, three or four atomic 
elements, and the network could represent these atomic elements 
individually or it could represent the particular combination. The network 
could also represent a maximum lamp current in a manner similar to that 
described above for a single atomic element hollow cathode lamp. 
Referring now to FIG. 4, there is shown an atomic absorption 
spectrophotometer holding four single atomic element hollow cathode lamp 
assemblies HCL1 to HCL4 each in accordance with the lamp assembly HCL 
described above with reference to FIGS. 1 and 2 and each connected to 
measurement circuit means MCM and a microprocessor .mu.P essentially as 
described above with reference to FIG. 3. The four lamp assemblies HCL1 to 
HCL4 are held in a turret TU operated by turret control means TUC to 
position a selected one of the four lamp assemblies HCL1 to HCL4 at a time 
in the optical path of the spectrotometer. FIG. 4 shows the lamp assembly 
HCL1 in the optical path. Radiation emitted by the lamp assembly HCL1 
passes from the respective cathode CA1 through an atomiser AT which may be 
of the conventional flame type or electrothermal furnace type. Samples to 
be analysed by the spectrophotometer are fed into the atomiser AT from an 
automatic sampler AS operated by automatic sampler control means ASC and 
the atomiser is operated by atomiser control means ATC. Having passed 
through the atomiser AT, the radiation passes through a monochromator MN. 
The wavelength of the radiation passed by the monochromator MN is selected 
by wavelength control means MWC and the bandpass, that is to say the slit 
width, of the monochromator MN is selected by slit control means MSC. A 
photomultiplier tube detector DET provides an electrical voltage signal 
whose amplitude is proportional to the intensity of radiation emerging 
from the monochromator MN, and a logarithmic converter LG provides an 
amplified voltage signal proportional to the logarithm of the output of 
the detector DET. The concentration of the atomic element in respect of 
which the samples presented to the atomiser AT are analysed is essentially 
proportional to the output signal of the logarithmic converter LG. 
The two electrodes of each of the lamp assemblies HCL1 to HCL4 are 
connected to the lamp power supply means LPS with only the hollow cathode 
electrodes CA1 etc being schematically shown in the Figure with a single 
connection in each case. The resistor networks RN1 to RN4 of the 
respective lamp assemblies HCL1 to HCL4 with each network having four 
respective resistors R1 to R4 as shown in FIGS. 1 and 3, are connected to 
a multiplexer MPX1. For simplicity of illustration onlY one connection is 
shown from each of the networks RN1 to RN4 to the multiplexer MPX1 
although there is an individual connection from each of the sixteen 
resistors therein to the multiplexer MPX1. Each of these sixteen network 
resistors is connected in turn in series with the resistor R5 to the 
voltage source +V via the multiplexer MPX1 controlled by latch circuit 
means LH. The voltage across each of the sixteen network resistors is 
connected in turn to the analogue-to-digital converter ADC via a further 
multiplexer MPX2 which is also controlled by the latch circuit means LH. 
The multiplexers MPX1 and MPX2, the resistor R5, the voltage source +V, 
the latch circuit means LH and the analogue-to-digital converter ADC form 
the measurement circuit means MCM to which the networks RN1 and RN4 are 
connected. The output signal of the logarithmic converter LG is also 
connected to the analogue-to-digital converter ADC via the multiplexer 
MPX2. In operation of the spectrophotometer the networks RN1 to RN4 are 
measured by the measurement circuit means MCM as soon as the lamp 
assemblies HCL1 to HCL4 are connected thereto. Thereafter this measurement 
is repeated as a background check routine which is interrupted when it is 
necessary for another analogue signal produced by the spectrophotometer, 
for example the output of the logarithmic converter LG, to be applied to 
the analogue-to-digital converter ADC via the multiplexer MPX2. The 
background check routine can be used, for example, to provide an error 
signal if a lamp is not present in a required position. 
A microcomputer MCP includes the microprocessor .mu.P, a volatile 
read-write memory RAM for temporarily holding data for processing by the 
microprocessor .mu.P, and a read-only memory ROM holding program 
information for conditioning the operation of the microprocessor .mu.P. 
The bus BS connects the microprocessor .mu.P to the read-write memory RAM, 
to the read-only memory ROM, to the analogue-to-digital converter ADC, to 
the latch circuit means LH, to the lamp power supply LPS, to the turret 
control means TUC, to the automatic sampler control means ASC, to the 
atomiser control means ATC, to the slit control means MSC and to the 
wavelength control means MWC. 
In addition to holding program information the read-only memory ROM also 
holds atomic element related information, including in particular 
wavelength information, at a location therein associated with the 
respective atomic element of each of a plurality of single atomic element 
hollow cathode lamp assemblies with which the spectrophotometer may be 
used. There may be in excess of sixty such single atomic element hollow 
cathode lamp assemblies but at any one time only one or some of these lamp 
assemblies, for example the four lamp assemblies HCL1 to HCL4, will be 
located in the spectrophotometer with their networks connected to the 
measurement circuit means MCM. The microprocessor .mu.P is conditioned to 
identify the atomic element of the one or more lamp assemblies whose 
networks are connected to the measurement circuit means MCM responsive to 
measurement of the respective network thereby. In the case of the four 
lamp assemblies HCL1 to HCL4 shown in FIG. 4 this identification is 
responsive to the output of the analogue-to-digital converter ADC in 
respect of the voltages measured successively across the resistors R1 and 
R2 of the respective networks RN1 to RN4 of the lamp assemblies. The 
microprocessor .mu.P is further conditioned to apply to the wavelength 
control means MWC wavelength information derived from the read-only memory 
ROM for that one of the one or more lamp assemblies whose atomic elements 
are identified and the lamp of which furthermore is present in the optical 
path of the monochromator. The turret TU and turret control means TUC 
include means which enable the microprocessor .mu.P to identify the lamp 
present in the optical path of the monochromator. 
The read-only memory ROM also holds lamp current information. The 
microprocessor .mu.P is conditioned to control the lamp power supply means 
LPS using this lamp current information for the one or more lamp 
assemblies whose atomic elements are identified via the measurement 
circuit means MCM. It is advantageous for the microprocessor .mu.P to use 
the maximum lamp current information derived from the networks RN1 to RN4 
via the measurement circuit means MCM together with the lamp current 
information derived from the read-only memory ROM to control the lamp 
power supply means LPS. If the networks RNl to RN4 did not contain the 
resistors R3 and R4 representative of the maximum lamp operating current 
of the respective lamp assemblies, then the lamp current information in 
the read-only memory ROM could be held at locations therein associated 
with the respective atomic element of each of the plurality of hollow 
cathode lamp assemblies with which the spectrophotometer may be used and 
could entirely define the operating current for the respective lamps. 
For an analysis consisting of the operation of the spectrophotometer to 
analyse one or more samples in respect of the single atomic element of one 
of the plurality of hollow cathode lamp assemblies for which information 
is stored in the read only memory ROM, both atomic element related 
information and sample related information are needed. Automatic operation 
of the spectrophotometer is facilated by both types of information being 
brought together to form an information set which is continuously stored 
for at least the duration of that analysis in a non volatile read-write 
memory NVM. The microprocessor .mu.P is connected by the bus BS to the 
memory NVM and is conditioned to use that information set to control that 
analysis 
The atomic element related information for each information set in the 
memory NVM is derivable from the read-only memory ROM and transferred 
thereto by the microprocessor .mu.P upon identification of the atomic 
element of the respective lamp assembly. This atomic element related 
information will include the wavelength information already mentioned 
together with slit width information for application to the slit control 
means MSC. In the case where the atomiser AT is of the flame type, the 
atomic element related information derivable from the read-only memory ROM 
will include information identifying fuel type and fuel rate for 
application to the atomiser control means ATC and may also include 
measurement time information. The time for which the output signal of the 
detector DET, received via the logarithmic converter LG, multiplexer MPX2 
and analogue-to-digital converter ADC, is averaged by the microprocessor 
.mu.P for noise reduction of that signal is determined by the measurement 
time. In the case where the atomiser AT is of the electrothermal furnace 
type, the atomic element related information will again include wavelength 
information and slit width information, it will furthermore include 
furnace heating cycle information for application to the atomiser control 
means ATC, and it may include measurement time information relevant to 
determining peak height and peak area results from the output signal of 
the detector DET. 
The sample related information for each information set in the memory NVM 
may be entered into an appropriate location therein by the user of the 
spectrophotometer via a keypad KPD connected by the bus BS to the 
microprocessor .mu.P. This sample related information will include the 
number of standard concentration samples to be held in the automatic 
sampler AS and information identifying the concentration of those standard 
samples. The feature of background correction, which is well known and 
therefore not otherwise mentioned in this specification, will normally be 
provided for use in the spectrophotometer and the sample related 
information will in this case also indicate whether or not background 
correction is to be used in a particular analysis. The atomic element 
related information may also include an overriding instruction to switch 
off background correction for atomic elements for which the wavelength of 
radiation to be passed by the monochromator is above a certain value. 
The results of an analysis of one or more samples in respect of a single 
atomic element are temporarily stored in the volatile read-write memory 
RAM of the microcomputer MCP and eventually outputted to a suitable 
recorder, for example a printer PRI shown connected by the bus BS to the 
microprocessor .mu.P, and possibly also to a display (not shown). 
It is convenient to mention here that the automatic sampler AS will be of a 
type specifically appropriate for use either with a flame type atomiser AT 
or an electrothermal furnace type atomiser AT as the case may be. 
Furthermore the automatic sampler control means ASC will normally partly 
be specific to and located in the particular automatic sampler AS and 
partly be permanently associated with the microprocessor .mu.P and located 
in the main body of the spectrophotometer. It is well known for atomic 
absorption spectrophotometers to be primarily provided with one type of 
atomiser and to be adaptable for use with the other type of atomiser as an 
accessory. For example it is known to have an atomic absorption 
spectrophotometer which is primarily for use in the flame mode but 
adaptable for use in the electrothermal mode; and in this case the 
atomiser control means ATC for the electrothermal furnace will normally be 
provided as an accessory with that furnace rather than being located in 
the main body of the instrument and permanently associated with the 
microprocessor .mu.P. Appropriate sensors (not shown) will be provided so 
that the type of atomiser AT and automatic sampler AS are identified to 
the microprocessor .mu.P for appropriate operation. In the case mentioned 
where the atomiser control means ATC is provided as an accessory part of 
the spectrophotometer it can have its own non-volatile read-write memory 
to hold a plurality of sets of furnace heat cycle information, and this 
information which has been mentioned above as being derivable from the 
read-only memory ROM may instead remain in the non-volatile read-write 
memory of the electrothermal furnace atomiser control means ATC which may 
then be considered as part of the non-volatile read-write memory NVM 
holding the total information set for an analysis. 
The non-volatile read-write memory NVM has the capacity to store a 
plurality of information sets as described above. Thus an analysis 
sequence consisting of the operation of the spectrophotometer to analyse 
one or more samples held in the automatic sampler AS in respect to each of 
a set of atomic elements in turn is controlled by the microprocessor .mu.P 
being conditioned to use each of the plurality of information sets in 
turn, one information set for each atomic element of the set of elements. 
The plurality of information sets will be continously stored in the 
read-write memory NVM for at least the duration of the analysis sequence. 
For example, the memory NVM will have the capacity to store at least four 
information sets, one for each of the four single atomic element hollow 
cathode lamp assemblies HCL1 to HCL4 shown in FIG. 4. With the use of four 
such lamp assemblies, the atomic element related information in each 
information set is derivable from the read-only memory ROM. The 
spectrophotometer may additionally be able to use lamps other than the 
lamp assemblies according to the invention which have networks identifying 
the respective atomic element. For example in each of the four turret lamp 
locations there may be accommodated a conventional single atomic element 
hollow cathode lamp. In this case the user of the spectrophotometer may 
simply provide, via the key pad KPD, information to the microprocessor 
.mu.P identifying the atomic element of each lamp and in response thereto 
the microprocessor .mu.P can derive all the necessary atomic element 
related information from the read-only memory ROM and transfer it for use 
into the non-volatile memory NVM. In a more precise reproduction of the 
function of any one of the resistor networks RN1 to RN4, the user could 
also provide information via the key pad KPD corresponding to the lamp 
current information of those networks. As another example, conventional 
electrodeless discharge lamps may beaccommodated in each of the four 
turret lamp locations. In this case again the user will provide via the 
key pad KPD information identifyinq the respective atomic element of the 
lamp, and additionally the user will have to provide information for an 
auxiliary power supply for operating electrodeless discharge lamps. As 
another example, multiple atomic element hollow cathode lamps may be used. 
These lamps may be conventional, in which case the user will provide via 
the keypad KPD information identifying the lamp as a multiple element 
lamp, information identifying the atomic elements of the lamp and lamp 
current information. A possible modification is that the multiple atomic 
element hollow cathode lamp may be provided with a resistor network, to be 
measured by the measurement circuit means MCM, by which it will provide 
lamp current information and information identifying it as a multielement 
lamp. The user will then provide information via the keypad KPD 
identifying the atomic elements of the lamp and the microprocessor .mu.P 
will be conditioned to derive atomic element related information from the 
read only memory ROM and transfer it to a separate information set in the 
non-volatile read-write memory NVM for each of those atomic elements. 
In addition to the ability to use lamps other than the lamp assemblies 
according to the invention, the spectrophotometer may be provided with a 
manual override facility such that even when a lamp assembly having a 
network according to the invention is present the user will be able to 
enter, via the keypad KPD, atomic element related information into an 
information set in the non-volatile read-write memory NVM which is 
different to the information which would otherwise be derived from the 
read-only mesory ROM. 
An external computer (not shown) may be connected via a suitable interface 
circuit to the bus BS. One use of an external computer can be to further 
facilitate automatic operation of the spectrophotometer by augmenting the 
function of the non-volatile read-write memory NVM. For example once an 
information set consisting of atomic element related information and 
sample related information as described above has been entered into the 
non-volatile memory NVM for a particular analysis, that information set 
may be transferred to the external computer for recall at any later date 
for use in repetition of the same analysis even though the capacity of the 
non-volatile memory NVM may have been fully used for different analyses in 
the meantime. 
It will be appreciated that in the above description of an atomic 
absorption spectrophotometer with respect to FIG. 4, only those features 
of such a spectrophotometer have been mentioned which are relevant to the 
invention and there are other features which conventionally are present or 
may be present. For example, the lamp power supply is normally modulated 
and the signal from the detector DET is correspondingly demodulated prior 
to processing by the logarithmic converter LG. Also the detector DET will 
be subject to gain control which may be automatic. Also double beam 
operation, that is the provision of a reference optical path which 
bypasses the atomiser and the use of the signal derived via this reference 
path to provide baseline correction which counteracts instrumental drift, 
particularly of the hollow cathode lamp output and the detector output, is 
a well known optional feature of atomic absorption spectrophotometers. In 
the case of the spectrophotometer described above with reference to FIG. 4 
which is capable of automatic operation for a long period of time, double 
beam operation will be particularly advantageous and very likely 
incorporated. 
Referring now to FIG. 5, there is shown a flow chart of an operation of the 
spectrophotometer shown in FIG. 4. 
In operation 1 "Switch On" the user switches on the electrical supplies to 
the spectrophotometer. In operation 2 "Initialise", the user ensures that 
the four single atomic element hollow cathode lamp assemblies HCL1 to HCL4 
are loaded by being located in the turret TU and electrically connected, 
and that four corresponding information sets are located in the 
non-volatile read-write memory NVM. There will be only one loading 
position for the lamps which will coincide with the position in which a 
lamp is located on the optical axis of the spectrophotometer, that is to 
say the position of the lamp assembly HCL1 as shown in FIG. 4. As each 
lamp assembly is loaded in turn the microprocessor .mu.P can transfer the 
relevant atomic element related information for the respective information 
set from the read-only memory ROM into an appropriate location in the 
non-volatile memory NVM responsive to measurement of the respective one of 
the lamp assembly networks RN1 to RN4 by the measurement circuit means 
MCM. At the time that each lamp is in the loading position the user can 
enter the relevant sample related information for the respective 
information set into the memory NVM via the key pad KPD and the 
microprocessor .mu.P. It may be that the operation of the 
spectrophotometer is to be a repeat, for a new set of samples in the 
automatic sampler AS, of an immediately preceding analysis sequence for a 
different set of samples in respect of the atomic elements of the same 
lamp assemblies HCL1 to HCL4. If this is the case, the lamp assemblies 
will already be loaded and the corresponding information sets will be 
present in the non-volatile memory NVM prior to "Switch On" and the 
"Initialise" operation 2 will not need to be performed by the user. In 
operation 3 "Power to Lamps" the user switches on the lamp power supply 
means LPS to each lamp in turn and responsive to this action for each lamp 
in turn the appropriate lamp current information is derived from the 
non-volatile memory NVM by the microprocessor .mu.P and applied to the 
lamp current supply means LPS. In the case where the atomiser AT is of the 
flame type an operation (not shown) after either operation 2 or 3 and 
involving action by the user is required to ignite the flame of the 
atomiser AT. In operation 4 "Start Automatic Sampler" the user initialises 
the operation of the automatic sampler AS, and responsive to this 
operation appropriate information is entered from the automatic sampler 
control means ASC into the read-write memory RAM after which the operation 
of the spectrophotometer can be entirely automatic under control of the 
microprocessor .mu.P without further intervention by the user. 
Responsive to operation 4, the microprocessor .mu.P performs operation 5 
"Set N=1". N represents a turret couznt. The turret count N determines 
which one of the four lamp assemblies HCL1 to HCL4 should be in the 
optical path for the duration of a run of the automatic sampler AS, that 
is to say an analysis of the samples therein for one atomic element, and 
it also determines which information set in the non-volatile memory NVM 
will be used by the microprocessor .mu.P during that analysis. The turret 
count N is held in the read-write memory RAM for the duration of each 
analysis. Responsive to operation 5, the microprocessor .mu.P performs 
operation 6 "Set Lamp Turret to N". In this operation the turret TU is 
driven to position N (At this stage N=1 corresponding to say the lamp 
assembly HCL1) by the turret control means TUC. Responsive to operation 6, 
the microprocessor .mu.P controls operation 7 "Set Slits" in which the 
monochromator MN slit width is set by the slit control means MSC using 
slit width information from the information set in the non-volatile memory 
NVM, and then the microprocessor .mu.P controls operation 8 "Set 
Wavelength" in which the monochromator MN wavelength is set by the 
wavelength control means MWC using wavelength information from the 
information set in the non-volatile memory NVM. As is conventional, the 
gain of the detector DET will be automatically adjusted in conjunction 
with setting the monochromator wavelength. Also responsive to operation 6 
the microprocessor .mu.P will transfer measurement time information from 
the non-volatile memory NVM to the volatile read-write memory RAM for use 
by the microprocessor .mu.P during subsequent maasurements of the samples 
for the one atomic element. 
Following operation 8, the microprocessor .mu.P controls operation 9 
"Measure Blank". In this operation, under control of the automatic sampler 
control means ASC, the automatic sampler AS provides a sample to the 
atomiser AT having nominally zero concentration of the one atomic element 
for which the set of samples are to be analysed. This sample is atomised 
by the atomiser AT under control of the atomiser control means ATC, and 
the output signal of the detector DET is passed via the logarithmic 
converter LG and the multiplexer MPX2 and analogue-to-digital converter 
ADC of the measurement circuit means MCM to the microprocessor .mu.P and 
the result is stored in the read-write memory RAM as a baseline 
measurement representing zero concentration of the atomic element for the 
duration of the analysis of the set of samples for that atomic element. In 
the case where the atomiser AT is of the flame type, the microprocessor 
.mu.P will apply fuel type and fuel rate information from the non-volatile 
memory NVM to the atomiser control means ATC for the atomisation of this 
and all subsequent samples in the analysis for the particular atomic 
element. In the case where the atomiser AT is of the electrothermal 
furnace type, the microprocessor .mu.P will apply furnace heating cycle 
information from the non-volatile memory NVM to the atomiser control means 
ATC for the atomisation of this and all subsequent samples in the analysis 
for the particular atomic element. Following operation 9, the 
microprocessor .mu.P controls operation 10 "Measure Standards". In this 
operation, a predetermined number of standard, i.e. known concentration 
samples, which number is present in the relevant information set in the 
non-volatile memory NVM, are provided in turn by the automatic sampler AS 
to the atomiser AT. In each case the detector DET output signal is fed via 
the measurement circuit means MCM to the microprocessor .mu.P and an 
absorbance result is calculated by comparison with the baseline 
measurement in the read-write memory RAM and then stored in the read-write 
memory RAM. Following operation 10, the microprocessor .mu.P performs 
operation 11 "Calibration". In this operation the microprocessor .mu.P 
derives the known concentration values of the standard samples from the 
relevant information set in the non-volatile memory NVM and uses these 
concentration values together with the absorbance results for the standard 
samples, which have been stored in the read-write memory RAM in operation 
10, to calculate a set of calibration coefficients which are then stored 
in the read-write memory RAM for the duration of the analysis for the one 
atomic element. These calibration coefficients enable the functions 
conventionally known as scale expansion and curvature correction to be 
applied to subsequent sample measurements. 
Following operation 11, the microprocessor .mu.P controls operation 12 
"Measure Sample, Calculate and Store Concentration". In this operation, a 
sample from the set of samples which is to be analysed in respect of the 
single atomic element is provided by the automatic sampler AS to the 
atomiser AT. The absorbance result for that sample derived from the output 
signal of the detector DET is applied to the read-write memory RAM, the 
calibration coefficients in the read-write memory RAM are applied to the 
absorbance result to produce a concentration result, and the concentration 
result is stored in the read-write memory RAM. Following operation 12, the 
microprocessor .mu.P controls operation 13 "Automatic Sampler End?". In 
this operation the automatic sampler control means ASC senses whether or 
not the automatic sampler AS has reached the end of its run and does not 
have a further sample to be measured. If the answer is "No", operation 12 
is repeated for the next sample. When operation 12 has been performed for 
all the samples and their respective concentration results stored in the 
read-write memory RAM, the next operation 13 will produce the answer "yes" 
and the microprocessor .mu.P will proceed to operation 14 "N=Limit?". In 
this operation the turret count N is checked to determine whether or not 
it corresponds to the number of turret positions, for example four turret 
positions as shown in FIG. 4. For the first analysis N=1 as set by 
operation 5, and so operation 14 produces the answer "No" in response to 
which the microprocessor .mu.P performs operation 15 "N=N+1" in which it 
increments the value of the turret count N. Responsive to operation 15, 
the microprocessor .mu.P performs operation 6 in which the turret TU is 
driven to the next position to bring the next lamp assembly HCL2 into the 
optical path of the spectrophotometer and operations 7 to 13 are repeated 
to provide another set of concentration results in the read-write memory 
RAM for the same set of samples in the autosampler AS in respect of the 
single atomic element of the next lamp assembly HCL2. When eventually 
operation 14 produces the answer "Yes" the microprocessor .mu.P performs 
operation 16 "Print Formated Results and Stop". In this operation the 
concentration results of all the samples of the set of samples in the 
automatic sampler AS in respect of the atomic elements of all the single 
atomic element lamp assemblies HCL1 to HCL4 in the turret TU are extracted 
from the read-write memory RAM in formated form and printed by the printer 
PRI and the spectrophotometer is then stopped, that is to say most of the 
electrical supplies are switched off and a dormant condition is set. An 
analysis sequence for a new set of samples will then require the user to 
start the whole sequence of operations from operation 1.