US2706928A - Spectrophotometric apparatus - Google Patents

Description

April 26, 1955 R. LEE ETAL sPEcTRoPHoToMETRIc APPARATUS Filed Jan. 6, 1951 /NvENToRS N O Y Em R L .mo LM W mnh/mu pmu..

SPECTRPHOTOMETRIC APPARATUS Royal Lee, Elm Grove, and William A. Hanson, Fox

Point, Wis., assignors to Lee Foundation for Nutritional Research, Milwaukee, Wis., a corporation of Wisconsin Application .anuary 6, 1951, Serial No. 204,808

2 Claims. (Cl. 38-1) The present invention relates to apparatus adapted for use in emission spectroscopy.

An object of the invention is to provide an improved spectrophotometric apparatus of the emission type including means for integrating or averaging a selected spectral intensity over a short period to determine the concentration of an element in a sample under investigation.

Another object is to provide spectrophotometric apparatus including means for expeditiously making a graphic record of the spectral intensity.

Still another object is to provide a spectrophotometric apparatus which includes an improved form of llametype radiation source.

The invention further consists in the several features hereinafter described and claimed.

In the accompanying drawing,

Fig. l is a diagrammatic view of a spectrophotometric apparatus arranged in accordance with the invention, and

Fig. 2 is a sectional detail view of an emission device for the apparatus, taken generally on the line 2-2 of Fig. l.

In the drawing, 19 designates generally a radiation source or emission device, hereinafter more fully described, in which a sample substance is to be burned. The light emitted by the ilame in which the sample substance is burned is passed into a suitable light filter or monochromator 11, preferably adjustable, and including the usual collimator 12. The segregated light leaving the monochromator is incident on a photo-sensitive device 13, such as a photo-emissive vacuum photo-tube, which in some instances may be an electron multiplier tube. The photo-sensitive device is electrically connected to a suitable amplifier 14, such as of the D.C. type, the output tube of which is connected to integrating means here shown to comprise a condenser 16 which is discharged selectively through a ballistic galvanometer 17 or a stylus-actuating coil 1S of a recorder 19. The recorder may be of any suitable type and is here shown to carry a moving tape or strip 20 cooperating with a recording stylus 21. The throw of the galvanometer, or the area under the curve 22 scribed on the record strip 20 to one side of a longitudinal base line Z2', is a measure of the relative intensity of the segregated light, and hence a measure of the concentration of the element present in the sample.

The radiation source or emission device 10 comprises a vertical heat-resisting tube 23, such as' of quartz, transparent to the radiation under investigation. The tube 23 is mounted on a base plate 24 having an insulating pillar 25 on which is pivotally mounted a cover plate 26 for the upper end of the tube, thus forming a combustion chamber 27 within the tube. The base plate and cover plate, of metal or heat-resisting insulation, have respective sets of perforations 28 and 29 at the ends of the quartz tube. An inlet fitting 30 is secured to the bottom of the perforated base plate 24 and is connected to a conK duit 31 for supplying oxygen to the combustion chamber, the conduit having a control valve 32 with one or more valve members 33, such as of the push-button type. The emission device is provided with ignition means, here shown to be of the spark type. The base plate and cover plate form opposed high-voltage ignition electrodes and are preferably provided with projections 34 and 35 forming electrode tips. The electrodes are connected to the secondary winding of an induction coil or transformer 36, the primary of which is connected to a supply circuit 37 2,705,923 Patented Apr. 26, 1955 through a switch 38. The switch is closed as by means of a manually operable plunger 39 which also actuates a lever 40 engaging one of the valve members 33 of the oxygen control valve, so as to open the control valve in advance of the closing of the switch 38. ln some instances a reflector 41 is mounted behind the quartz tube 23.

The sample to be investigated, such as a small predetermined quantity of blood or other biological material, is deposited and dried on a carrier 42 of combustible material. The carrier preferably comprises a predetermined quantity of ashiess and spectroscopically pure cotton or filter paper, which is placed in the combustion chamber 27. The combustible carrier is here shown to be in the form of a sheet which extends longitudinally in the quartz tube. It may be desired, for example, to determine the calcium content of the blood sample with respect to a standard, as hereinafter described. Oxygen is admitted to the combustion chamber, and the sample carrier is ignited by passing an electric discharge between the electrodes. The burning period is relatively short, preferably not more than about lone second. In some instances, the carrier may be impregnated with a suitable oxidizing material, such as potassium chlorate. However, it will be necessary to avoid interference with the segregated radiation of the sample. The carrier should be spectroscopically pure, at least with respect to the region of the characteristic radiation of the sample.

The monochromator is adjusted to pass a desired narrow band of the spectrum, such as a band containing one or both of the spectral lines 3833.7A and 3968.5A in the case of calcium. In some cases, two more monochromators may be used to pass different spectral lines, the light therefrom preferably being incident on the same photocell.

The segregated light incident on the photocell 13 is amplied by the D.C. amplifier 14 which has a suitably regulated plate supply circuit 43 with positive and negative terminals and with an on-off switch 44. The output tube 15 has a load resistor 45 connected to the positive terminal of the plate supply. One terminal of the integrating condenser 16 is connected to the anode of a diode or rectifier 46 the cathode of which is connected to the plate or anode of the output tube. The other terminal of the condenser is connected to a point of positive potential on the plate supply which is approximately equal to the potential of the output tube anode under quiescent conditions. By way of example, the plate supply is here shown to have a tapped voltage dividing resistor 47 for providing various points of different potential.

The condenser terminals are connected by a pair of conductors 48 to a switch 49, such as of the slide or wiping type, which automatically short-circuits the condenser at a moment immediately preceding the ignition of the sample carrier, so as to insure removal of any charge on the condenser. The switch 49 is here shown to be operable by the plunger 39 which actuates the oxygen valve 32 and the ignition switch 38. lf desired, another switch 49 may be provided for short-circuiting the condenser independently of the switch 49.

The integrating condenser 16 is also connected by a pair of conductors 50 and 51 to the ballistic galvanometer 17, the conductor 5E) including a discharge switch S2 and a selector switch 53. The capacity of the integrating condenser is so selected that it will not ll during the maximum time cycle, such as 30 seconds. The throw of the galvanometer is a measure of the concentration of the element under investigation, and may be compared with the throw produced by the combustion of one or more standards.

The condenser is further connected by a pair of conductors' 54 and 55 to the stylus-actuating coil 18 of the tape recorder 19. The conductor 54 is connected to the conductor 5t) at a point between the switches 52 and 53, and has a selector switch 56. The conductor 5S forms a branch of the conductor 51.

The recorder tape or strip 20 is pulled at a suitable constant speed, as by an electric motor 57 driving one of a pair of feed rolls 58 and 59 between which the tape is engaged. The stylus 21 resting on the tape will draw thereon the straight longitudinal base line 22 in the synapses absence of an actuating impulse. The recorder motor 57 is connected to supply conductors 6d one ot' which includes a switch 6i and in some instances a second seriesconnected switch 62. The switch 61 is actuated simultaneousiy with the condenser-d'ischarging switch 52, as by a connecting link 63. However, the switch 61 closes before the switch 52 so as to start the record tape in motion shortly before the switch 52 closes. The switch 62 is arranged to energize the motor independently of the switch 61.

The area under the sample curve 22, which represents an integral of the spectral intensity with respect to time, can be measured, as by square-counting, or by a planimeter orotherwise. so that this area may be compared with one or more reference areas corresponding to known blood calcium concentrations. Another method of procedure consists in comparing the sample curve with a standard curve 1.22 drawn from a base line 122 on a sheetV 12. The sheet may be transparent or translucent so as to permit superimposition on the sample curve. The standard curve 122 is obtained in the same manner as the sample curve.

In the use of the apparatus, assuming that a tape record is to be made, the selector switch 55 is closed and the elector switch 53 is open. The cover 26 of the emission device 1t) is opened and the impregnated sample carrier 42 is placed in the combustion chamber 27, The monochromator is adjusted to pass the selected spectral line or lines of the sample substance. The plunger 39 is then depressed for a part of its stroke, opening the oxygen valve 32 to till the combustion chamber with oxygen, and also closing the switch 49 to short-circuit the integrating condenser 16. The plunger is then depressed further to close the ignition switch 3S, whereupon a spark will pass through the combustion. chamber and initiate combustion of the sample carrier. lt desired, the plunger may be partially released to discontinue the sparking as soon as combustion starts, but the oxygen valve should remain open sutiiciently long to effect complete combustion of the sample carrier. It is also necessary to remove thev short-circuit on the condenser before ignition occurs. The combustion period is relatively short, on the order of one second. The segregated light impulse incident on the photo-sensitive device is amplified by the D.C. amplilier 1.4, producing a voltage change on the load resistor 4S, which results in charging of the condenser 16 through the diode 46 to an extent depending on the spectral intensity and the period of combustion. The diode 46 prevents discharge of the condenser through the load resistor and the output tube. The motor switch 61 is then closed to start the recording tape in motion, and immediately thereafter the switch 52 is closed to discharge the condenser through the stylus-actuating coil of the recorder, thus scribing the curve 22 on the record tape, as hereinbefore described. As soon as the record curve is completed the switches 52 and 61 are opened. The curve 22 is then compared with reference areas or curves to determine the concentration of the element in the sample, as hereinbefore explained.

When the ballistic galvanometer is to be used as the indicator, the procedure is the same except that the switch 56 is open and the switch 53 is closed, the throw of the galvanometer then being a measure of the concentration of the element in the sample.

The size or weight of the combustible carrier sheets is not critical, provided that the element under investigation is dissipated in the flame before the end of the combustion period.

What we claim as new and desire to secure by Letters Patent is:

l. ln a spectrophotometric apparatus, a radiation source to which is subjected for a limited period a substance containing an element whose concentration is to be determined, whereby to excite said element, means for segregating from the radiation of the source a portion therent characteristic of the element, electronic means including a photocell and amplifier therefor for integrating in terms of an electrical charge the intensity of the segregated light over the excitation period, said amplifier having an output circuit including an integrating condenser for storing the charge, and ballistic indicating means for translating said electrical charge into a visual indication.

2. In a spectrophotometric apparatus, a radiation source adapted to excite for a limited period an element contained in a sample, means for segregating from the radiation of the source a portion thereof characteristic ot the element, a photo-sensitive device on which the segregated light is incident and of a type producing an electrical impulse proportional to light intensity, an electronic amplier for amplifying the electrical impulse and having an output circuit containing a load resistor the voltage across which varies with the electrical impulse, an integrating condenser' in said output circuit normally at zero potential diiierence and adapted to be charged by variation of voltage acrossl the resistor, a rectiiier in series with the condenser for permitting ow of charging current into said condenser but preventing back flow, and current-actuated visual indicating means having a circuit connection with said condenser, said circuit connection being open during the condenser-charging period and being closed to discharge the charged condenser into said indicating means.

References Cited in the tile of this patent UNTED STATES PATENTS 1,894,132 Stone Ian. 10, 1933 2,282,643 Cutting May 12, 1942 2,324,899 Arthur July 20, 1943 2,344,719 Nusbaum et al Mar. 2l, 1944 2,346,512 Schribner et al. Apr. 11, 1944 2,390,816 Suits Dec. 11, 1945 2,391,225 Clark Dec. 18, 1945 2,420,077 Hasler et al May 6, 1947 2,436,104 Fisher et al. Feb. 17, 1948 2,509,649 Norman May 30, 1950 2,517,121 Liston Aug. 1, 1950 2,527,122 Heigl et al. Oct. 24, 1950 2,577,814 Saunderson et al Dec. 1l, 1951 2,577,815 Saunderson et al Dec. 11, 1951 2,597,001 latte May 20, 1952 OTHER REFERENCES Gibb, Optical Methods of Chemical Analysis, first edition, published by McGraw-Hill Book Co., New York City, 1942, page 8.

Claims (1)

1. IN A SPECTROPHOTOMETRIC APPARATUS, A RADIATION SOURCE TO WHICH IS SUBJECTED FOR A LIMITED PERIOD A SUBSTANCE CONTAINING AN ELEMENT WHOSE CONCENTRATION IS TO BE DETERMINED, WHEREBY TO EXCITE SAID ELEMENT, MEANS FOR SEGREGATING FROM THE RADIATION OF THE SOURCE A PORTION THEREOF CHARACTERISTIC OF THE ELEMENT, ELECTRONIC MEANS INCLUDING A PHOTOCELL AND AMPLIFIER THEREFOR FOR INTERGRAT-

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