GB2141222A - Atomic absorption spectrophotometer - Google Patents

Abstract

An atomic absorption spectrophotometer uses hollow cathode lamp assemblies (HCL1-HCL4) encoded by means of recesses and/or projections. The code represents one or more atomic elements corresponding to their resonant line(s). The presence or absence of the projections and/or recesses is read by corresponding code readers (CCR1-CCR4) feeding a microcomputer (MCP), which includes a microprocessor ( mu P) a read-only memory (ROM) and a read-write memory (RAM) to identify the elements. The read only memory (ROM) contains wavelength information at a location associated with each element, by means of which the microprocessor causes the correct operating current to be supplied by the lamp power supply (LPS) and causes the monochromator (MN) to be driven to the appropriate wavelength by the monochromator wavelength control (MWC). The projections and/or recesses may be formed in the lamp base or in a separate card attached to the lamp and inserted into a card reader. <IMAGE>

Description

SPECIFICATION Atomic absorption spectrophotometer The invention relates to an atomic absorption spectrophotometer including a source lamp for producing resonance line radiation characteristic of one or more atomic elements, a monochromatorfor passing radiation of a selected wavelength characteristic of one or more atomic elements, wavelength control means responsive to wavelength information applied thereto for setting the monochromator to said selected wavelength, a microprocessor, a memory holding wavelength information at a location therein associated with each of the respective one or more atomic elements of a plurality of said lamps, and means for enabling the microprocessor to identify the one or more atomic elements of said source lamp wherein the microprocessor is arranged to apply to said wavelength control means wavelength information derived from said memory for an atomic element which is so identified.

A spectrophotometer as set forth in the preceding paragraph is described in U.K. Patent Application No. 8133968 (PHB 32832). The spectrophotometer described in that application uses a source lamp which includes an electrical network of resistors housed in the base of the lamp and comprises a measurement circuit to identify from the value of the resistors the particular wavelengths the lamp will emit i.e. the particular atomic elements of which the line radiation is characteristic.

It is an object of the invention to provide an atomic absorption spectrophotometer having an alternative means of identifying the atomic elements of the lamp.

The invention provides an atomic absorption spectrophotometer as set forth in the opening paragraph characterised in that the source lamp is encoded by means of projections and/or recesses formed therein or on a body attached thereto, the code being representative of said one or more atomic elements, and that the spectrophotometer further includes sensors arranged to apply electrical signals to the microprocessor dependent on the pattern of projections and/or recesses to enable the microprocessor to identify the one or more atomic elements.

In a first construction the source lamp may have attached thereto a card bearing the projections and/or recesses, the sensors being provided within a body having a slot into which the card may be inserted to enable the code to be read. The card may be a punched card bearing a plurality of apertures and the sensors comprise a light source and a plurality of light detectors. The sensors may comprise a regular array of light emitting diodes arranged opposite a similar array of photodiodes, the punched card being arranged to be positoned between the two arrays.

In an alternative construction the source lamp may be provided with a base encoded by means of a plurality of projections, sensors being provided to detect the presence or absence of a projection at a given location on the base. The sensors may comprise the combination of a light emitting diode and a photodiode adjacent each given location. Alternativelythe sensors may comprise spring biassed members arranged to engage with the projections and/or recesses and to operate one or more switches dependent on their engagement.

The spectrophotometer may further comprise a lamp turretfor holding a plurality of source lamps and sensors may be provided for each lamp position on the turret.

The invention further provides a spectrophotometer in which the projections and/or recesses are further representative of the lamp operating current the spectrophotometer including lamp power supply means and the memory holding lamp current information, the microprocessor being conditioned to control said lamp power supply means using, together with said lamp current information from the memory, further lamp current information derived from the sensors.

An analysis consisting of the operation of the spectrophotometerto analyse one or more samples in respect of an atomic element of a said lamp assembly may be controlled by the microprocessor being conditioned to use an information set continuously stored in a read-write memory for at least the duration of that analysis, the information set having atomic element related information, including said wavelength information, derivable from the read-only memory for that atomic element, together with sample related information derivable from elsewhere for said one or more samples.

The spectrophotometer may have holding means for holding more than one source lamp at a time with optical code readers being provided for each of the source lamps so held, the outputs of the optical code readers being connected to said microprocessor, and positioning means for positioning one lamp at a time of the lamp assemblies so held in the optical path of the monochromator, and in which an analysis sequence consisting of the operation of the spectrophotometer to analyse said one or more samples in respect of each of a set of atomic elements in turn, wherein the source lamp for each atomic element of the set is part of a said lamp assembly, is controlled by the microprocessor being conditioned to control said holding and positioning means to position a said lamp emitting radiation characteristic of each atomic element of said set of elements in turn in the optical path of the monochromator and by the microprocessor being conditioned use each of a plurality of said information sets in turn, one information set for each atomic element of said set of elements, the plurality of information sets being continuously stored in the read-write memory for at least the duration of said analysis sequence.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which; Figure 1 shows schematically a side elevation and an end elevation of a first embodiment of a resonance line source lamp in the form of a hollow cathode lamp assembly for use in a spectrophotometer according to the invention, Figure 2 is a perspective view of a second embodiment of a resonance line source lamp in the form of a hollow cathode lamp assembly for use in a spectrophotometer according to the invention, Figure 3 shows the hollow cathode lamp assembly of Figure 2 together with a card reader, Figure 4 shows a cross-sectional view on line A-A of the card reader shown in Figure 3.

Figure5showsthe hollow cathode lamp assembly of Figure 1 in combination with mechanical sensors, Figure 6shows schematically a side elevation and an end elevation of a third embodiment of a resonance line source lamp in the form of a hollow cathode lamp assembly for use in a spectrophotometer according to the invention, Figure 7 shows the hollow cathode lamp assembly of Figure 6 in combination with a sensor, Figure 8 shows a lamp turret carrying four of the lamps shown in Figure 2 and four card readers, Figure 9 shows in block schematic form an atomic absorption spectrophotometer using four lamp assemblies, and Figure 10 is a flow chart of an operation of the spectrophotometer shown in Figure 9.

As shown in Figure 1 a resonance line source lamp in the form of a single element hollow cathode lamp assembly HCL comprises 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 carries two terminal pins P1 and P2 to which the anode AN and cathode CA are connected and which project from the base BA. These terminal pins provide connecting means for a lamp power supply means LPS (see Figure 9) to the anode AN and cathode CA.

The base BA has a plurality of recesses RE formed around its periphery, the presence or absence of recesses at particular locations around the periphery of the base forming a digital code. The digital code is representative of the atomic element of the lamp and may also represent the current required by the lamp HCL from the lamp power supply means LPS.

Sensors are arranged to read the code on the base BA and produce an electrical output dependent on the code which output is fed to a microprocessor FP in the spectrophotometer (see Figure 9).

Figure 2 shows an alternative lamp assembly comprising a hollow cathode lamp HCL having a card CC attached thereto by a string ST which passes through a hole in a lug LU on the base BA of the lamp HCL. The card CC has a plurality of cut-outs RE along one edge which form a digital code which code represents the atomic element of the lamp and may further represent the lamp operating current.

An alternative form of coding of the card CC is to form an array of apertures (punched holes), the presence or absence of an aperture at a particular position on the card forming a digital code, which digital code is representative of the atomic element ofthe lamp and may further represent the lamp operating current. Typically the apertures are circu larbuttheymaytake otherforms, for example square or rectangular. The card CC may be replaced by a body having a different form, such as a bar or a rod, the body being provided with the recesses and/or projections.

Figure 3 shows the hollow cathode lamp HCL with the card CC attached thereto by the string ST inserted into a slot CCS in a card reader CCR. A cross sectional view on line A-A of the card reader CCR is shown in Figure 4. The card reader CCR comprises a housing CCH having a slot CCS in one wall thereof through which the card CC is inserted. Within the housing CCH an array of light emitting diodes LED is arranged opposite a corresponding array of photodiodes PHD. When the card CC is fully inserted in the slot CCS it intercepts the path between the two arrays and hence the presence or absence of apertures in the card at particular locations can be detected by detecting whether or not a particular photodiode is illuminated. Cables CRC1 and CRC2 feed signals to the light emitting diode array LED and from the photodiode array PHD respectively.Instead of having an array of light emitting diodes it would be equally possible to provide a single diffuse source of light which the card CC interrupts. Alternatively the sensors for the holes in the card CC may be mechanical fingers or pneumatic sensors.

Figure 5 shows the hollow cathode lamp HCL of Figure 1 together with a mechanical sensor arrangement for detecting the presence of recesses in the base. The lamp HCL is assembled against a base plate BP by any convenient means and an arrangement comprising a plurality of regularly spaced spring loaded fingers SLF is also mounted in a fixed position relative to the base plate BP so that when the lamp HCL is assembled on the base plate the fingers engage the lamp base BA and either enter a recess or are depressed against a restoring spring force to operate associated micro switches MS.

The lamp shown in Figure 6 is similar to that shown in Figure 1 the only difference being the way in which the code is formed on the base BA. As shown in Figure 6 the code is formed by a series of projections PR on the base BA of the lamp HCL. The presence or absence of a projection at particular positions around the periphery of the lamp base forming a digital code which is representative of the atomic element of the lamp and may also represent the operating current required by the lamp HCL from the lamp power supply means LPS.The projections PR on the lamp base BA may be detected by mechanical sensors such as the spring loaded fingers SLF shown in Figure 5 or, as shown in Figure 7, may be detected by arranging a plurality of housings PRH, each containing a light emitting diode and a photodiode, at regular intervals around the base BA so that the projections PR, when present, intercept the optical path between the light emitting and photodiodes.

Figure 8 shows a turret TU in the form of a turntable which carries four source lamps HCL1 to HCL4 and four code readers CCR1 to CCR4. The lamps HCL1 to HCL4 are of thetype shown in Figure 2 and the code readers CCR1 to CCR4 each have a slot CCS1 to CCS4 into which the encoded cards CC1 to CC4 are inserted. This arrangement has the advantage that the presence of a card can be continuously monitored and that the type of lamp inserted can also therefore be continuously monitored. Even without the continuous monitoring of the optical code it can be readily detected when a lamp is removed from a lamp socket by monitoring the current from the lamp supply means LPS since when the lamp is removed the current supplied to that socket will fall to zero.

While the lamp assemblies described with reference to Figures 1 to 7 have been single atomic element hollow cathode lamps other lamps for producing resonance line radiation characteristic of one or more atomic elements could equally be used.

Such lamps include multi-element hollow cathode lamps and electrodeless discharge lamps.

Referring now to Figure 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 Figure 2 and each connected to a code reader CCR1 to CCR4 whose outputs are connected to a microprocessor SLOP. 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 spectrophotometer. Figure 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 electro-thermal furnace type. Samples to be analysed by the spectrophotometer are fed into the atomiser ATfrom 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 photomultipliertube 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 is 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, only the hollow cathode electrodes CA1 etc being schematically shown in the Figure with a single connection in each case. In operation of the spectrophotometer the code readers CCR1 to CCR4 the code on the cards CC1 to CC4 attached to the lamps HCL1 to HCL4 as soon as the cards are inserted. Thereafter this measurement is repeated as a background check routine which is interrupted when it is necessary fox an analogue signal produced by the spectrophotometer, for example the output ofthe logarithmic converter LG, to be applied to the microprocessor via the analogueto-digital converter ADC. 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 IlP, a volatile read-write memory RAM for temporarily holding data for processing by the microprocessor Prop, and a memory ROM holding program information for conditioning the operation of the microprocessor pP. The memory ROM is conveniently a read only memory. The bus BS connects the microprocessor ZIP 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 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 assemblies HCL1 to HCL4, will be located in the spectrophotometer with their cards inserted in the code readers CCR. The microprocessor ;iP is conditioned to identify the atomic element of the one or some lamp assemblies.In the case of the four lamp assemblies HCL1 to HCL4 shown in Figure 4 this identification is responsive to the output of the code readers CCR1 to CCR4 which are interrogated in turn by the microprocessor via the latch circuit means LH. The microprocessor ijP 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 some of the 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 IlP to identify the lamp present in the optical path of the monochromator.

The read-only memory ROM also holds lamp current information. The microprocessor FP is conditioned to control the lamp power supply means LPS using this lamp current information for the one or some lamp assemblies whose atomic elements are identified via the code readers CCR. It is advantageous for the microprocessor pLP to use the maximum lamp current information derived from the code via the code readers CCR together with the lamp current information derived from the read-only memory ROM to control the lamp power supply means LPS. If the code did not contain elements 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 facilitated 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 FP 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 FP upon identification of the atomic element of the respective lamp assembly. This atomic element related information will include the wavelength information already 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 and analogue-to-digital converter ADC, is averaged by the microprocessor sLP for noise reduction of that signal is determined by the measurement time. In the case where the atomiser AT is of the electro-thermal 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 FP. 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 to the microprocessor pP, 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 atomiserAT or an electro-thermal 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 FP 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 electro-thermal mode; and in this case the atomiser control means ATC for the electro-thermal furnace will normally be provided as an accessory with thatfurnace rather than being located in the main body of the instrument and permanently associated with the microprocessor FP. Appropriate sensors (not shown) will be provided so that the type of atomiser AT and automatic sampler AS are identified to the microprocessor pP 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 electro-thermal furnace atomiser control means ATC which may then be considered as part of the non-volatile read-write memory NVM holding the total information sensor 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 of each of a set of atomic elements in turn is controlled by the microprocessor FP 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 continuously 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 HCL2 shown in Figure 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 described with reference to Figures 1 to 7 which are coded to identify 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 keypad KPD, information to the microprocessor FP identifying the atomic element of each lamp and in response thereto the microprocessor FP can derive all the necessary atomic element related information from the readonly memory ROM and transfer it for use into the non-volatile memory NVM. As another example, conventional electrodeless discharge lamps may be accommodated in each of the fourturret lamp locations. In this case again the user will provide the keypad information identifying the respective atomic element of the lamp, and additionally the user will have to provide information for an auxiliary power supply for operating electrodelessdischarge 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 an encoded card, to be read by the code reader CCR, by which it will provide lamp current information and information identifying it as a multi-element lamp.The user will then provide information via the keypad KPD identifying the atomic elements of the lamp and the microprocessor SLP 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.

The spectrophotometer may be provided with a manual override facility such that 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 whch would otherwise be derived from the read-only memory 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 Figure 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 Figure 9 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 Figure 10, there is shown a flow chart of an operation of the spectrophotometer shown in Figure 9.

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 Figure 4. As each lamp assembly is loaded in turn the microprocessor FP 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 the identification of the respective one of the lamp assembly codes by the microprocessor from the code read by the code readers CC1 to CC4.At the time that each lamp is in the loading position the user can enterthe relevant sample related information for the respective information set into the memory NVM via the keypad KPD and the microprocessor vP. 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 IlP 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 auto matic under control the microprocessor iP without further intervention by the user.

Responsive to operation 4, the microprocessor FP performs operation 5"SetN=1". N represents a turret count. 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 P during that analysis. The turret count N is held in the read-write memory RAM forthe duration of each analysis. Responsive to operation 5, the microprocessor pP 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 aP 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 wP 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 FP will transfer measurement time information from the non-volatile memory NVM to the volatile read-write memory RAM for use by the microprocessor FP during subsequent measurements of the samples for the one atomic element.

Following operation 8, the microprocessor AP 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 analogue-to-digital converter ADC to the microprocessor pbP and the result is stored in the read-write memory RAM as a baseline measurement representing zero concentration of the atomic elementforthe 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 microp rocessor 41P 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 electro-thermal furnace type, the microprocessor AP 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 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 nonvolatile 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 analogue to digital converterADC to the microprocessor FP 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 iP performs operation 11 "Calibration".In this operation the microprocessor FP derives the known concentration values of the standard samples from the relevant information set in the non-volatile memory NVM and uses these concentrations 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 FP 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 readwrite memory RAM. Following operation 12, the microprocessor FP 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 FP will pro ceed 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 Figure 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 FP performs operation 15 "N=N+1" in which it increments the value of the turret count N. Responsive to operation 15, the microprocessor pP 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 auto-sampler AS in respect of the single atomic element of the next lamp assembly HCL2. When eventually operation 14 produces the answer "Yes" the microprocessor AP 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 the 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.

Claims (13)

1. An atomic absorption spectrophotometer including a source lamp for producing resonance line radiation characteristic of one or more atomic elements, a monochromatorfor passing radiation of a selected wavelength characteristic of one or more atomic elements, wavelength control means responsive to wavelength information applied thereto for setting the monoch romator to said selected wavelength, a microprocessor, a memory holding wavelength information at a location therein associated with each of the respective one or more atomic elements of a plurality of said lamps, and means for enabling the microprocessor to identify the one or more atomic elements of said source lamp wherein the microprocessor is arranged to apply to said wavelength control means wavelength information derived from said memory for an atomic element which is so identified, characterised in that the source lamp is encoded by means of projections and/or recesses formed therein or on a body attached thereto and that the spectrophotometer includes sensors arranged to apply electrical signals to the microprocessor dependent on the pattern of projections and/or recesses on the source lamp to enable the microprocessor to identify the one or more atomic elements.

2. A spectrophotometer as claimed in Claim 1 in which the source lamp may have attached thereto a card bearing the projections and/or recesses, the sensors being provided within a body having a slot into which the card may be inserted to enable the code to be read.

3. A spectrophotometer as claimed in Claim 2 in which the card may be a punched card bearing a plurality of apertures and the sensors comprise a light source and a plurality of light detectors.

4. A spectrophotometer as claimed in Claim 3 in which the sensors may comprise a regular array of light emitting diodes arranged opposite a similar array of photodiodes, the punched card being arranged to be positioned between the two arrays.

5. A spectrophotometer as claimed in Claim 1 in which the source lamp may be provided with a base encoded by means of a plurality of projections, sensors being provided to detect the presence or absence of a projection at a given location on the base.

6. A spectrophotometer as claimed in Claim 5 in which the sensors may comprise the combination of a light emitting diode and a photodiode adjacent each given location.

7. A spectrophotometer as claimed in any of Claims 1,2 or 5 in which the sensors may comprise spring biassed members arranged to engage with the projections and/or recesses and to operate one or more switches dependent on their engagement.

8. A spectrophotometer as claimed in any preceding claim comprising a lamp turret for holding a plurality of source lamps in which sensors are provided for each lamp position on the turret.

9. A spectrophotometer as claimed in any preceding claim in which the code is further representative of the lamp operating current the spectrophotometer including lamp power supply means and the memory holding lamp current information, the microprocessor being conditioned to control said lamp power supply means using, together with said lamp current information from the memory, further lamp current information derived from the sensors.

10. A spectrophotometer as claimed in any preceding claim in which the memory is a read-only memory.

11. A spectrophotometer as claimed in Claim 10 when dependent on Claim 1, in which an analysis consisting of the operation of the spectrophotometer to analyse one or more samples in respect of an atomic element of a said lamp assembly is controlled by the microprocessor being conditioned to use an information set continuously stored in a readwrite memory for at least the duration of that analysis, and in which said information set has atomic element related information, including said wavelength information, derivable from the readonly memory for that atomic element, together with sample related information derivable from elsewhere for said one or more samples.

12. Aspectrophotometeras claimed in Claim 11, in which the spectrophotometer has holding means for holding more than one source lamp at a time with sensors being provided for each of the source lamps so held, the outputs of the sensors being connected to said microprocessor, and positioning means for positioning one lamp at a time of the lamp assemblies so held in the optical path of the monochromator, and in which an analysis sequence consisting of the operation of the spectrophotometer to analyse said one or more samples in respect of each of a set of atomic elements in turn, wherein the source lamp for each atomic element of the set is part of a said lamp assembly, is controlled by the microprocessorbeing conditioned to control said holding and positioning means to position a said lamp emitting radiation characteristic of each atomic element of said set of elements in turn in the optical path of the monochromator and by the microprocessor being conditioned use each of a plurality of said information sets in turn, one information set for each atomic element of said set of elements, the plurality of information sets being continuously stored in the read-write memory for at least the duration of said analysis sequence.

13. An atomic absorption spectrophotometer substantially as described herein with reference to the accompanying drawings.