SU851257A1

SU851257A1 - Chromatographic detector

Info

Publication number: SU851257A1
Application number: SU782599710A
Authority: SU
Inventors: Виталий Константинович Новик; Исай Абрамович Клейнман; Владимир Михайлович Пошеманский; Андрей Генрихович Сегалла; Валерий Евгеньевич Шепелев; Михаил Сергеевич Чупахин
Original assignee: Предприятие П/Я А-7815
Priority date: 1978-03-31
Filing date: 1978-03-31
Publication date: 1981-07-30

Description

(54) ХРОМАТОГРАФИЧЕСКИЙ ДЕТЕКТОР(54) CHROMATOGRAPHIC DETECTOR

Изобретение относитс к устройствам дл хроматографического детектировани вецеств и может быть -испол зовано при анализе примесей в веществах высокой степени чистоты, загр зненности воздушной среды и т.п. Известно значительное количество разнообразных устройств дл детектировани веществ в хроматографии. Наиболее распространенным типом детекторов , примен 1 4ых в хрс ла тог рафии, вл ютс катарокетры, содержащие нагреваемую электрическим током мета лическую нить (или термистор), по изменению сопротивлени (с измеиени температуры) которой суд т об измене иии теплопроводности, а следовательно , состава омывающей чувствительный элемент смеси 1.. Однако такие датчики, будучи пара метрическими (т.е. требующими источников питани ), обладают малой разре шающей способностью. В пересчете на изменение э емпературы, происход щее вследствие изменени .теплопроводност газа, чувствительность нити составл ет . Этот предел обусловлен как недостаточной чувствительностью измерит.ельннх приборов, так и в основном, собственными тепловыми щумами нити, возникающими при ее нагревании. Кроме того, эти детекторы позвол ют измерить лишь концентрацию (или поток) выход щего из хроматографической колонки вещества, в то времен как в р де случаев возникает необходимость получать и производную во времени от указанных параметров. Применение генераторных чувствительных элементов, позвол ющих значительно упростить преобразование скорость изменени концентрации полезный сигнал- и непосредственно регистрировать скорость изменени концентраций (потока) вещества, т.е. дифференцирующих датчиков, позвол ет значительно расширить возможности хроматографического метода. Известен также хроматографический детектор, включающий корпус, в котором расположен пироэлектрический чувствительный элемент с нагревателем , омывае№1й потоком анализируемой смеси, и систему регистрации электрического сигнала с чувствительного элемента. Пироэлектрический чувствительный элемент в указанном детекторе выполнен в виде полого цилиндра с радиально направленным вектором пол ризации. По своей наружной поверхности чувствительный элемент имеет непосредственный контакт с внутревней полостью корпуса, а нагреватель в виде металлической спирали расположен соосно чувствительному э екеату с зазором, по которому пропускаетс анализируема смесь. Влагодар The invention relates to devices for chromatographic detection of constituents and can be used in the analysis of impurities in substances of high purity, air pollution, and the like. A significant number of various devices for the detection of substances in chromatography are known. The most common type of detectors, used in the 4th phase of lagarography, are cataroquets containing a metal filament (or thermistor) heated by an electric current, by varying the resistance (from a temperature change) of which the variation of thermal conductivity and, therefore, composition washing the sensitive element of mixture 1 .. However, such sensors, being parametric (i.e. requiring power sources), have a low resolution. In terms of the change in temperature resulting from the change in the thermal conductivity of the gas, the sensitivity of the filament is. This limit is due both to the inadequate sensitivity of the measuring instruments, and mainly to their own thermal threads of the thread, which arise when it is heated. In addition, these detectors can measure only the concentration (or flux) of the substance leaving the chromatographic column, while in a number of cases it is necessary to obtain and time derivative of the specified parameters. The use of generator sensitive elements, which makes it possible to significantly simplify the conversion, the rate of change of concentration, the useful signal, and directly record the rate of change of concentration (flow) of a substance, i.e. differentiating sensors, allows you to significantly expand the possibilities of the chromatographic method. Also known chromatographic detector, comprising a housing in which there is a pyroelectric sensitive element with a heater, washing No. 1 stream of the analyzed mixture, and a system for recording an electrical signal from the sensitive element. The pyroelectric sensitive element in the specified detector is made in the form of a hollow cylinder with a radially directed polarization vector. On its outer surface, the sensing element has direct contact with the inner cavity of the housing, and the heater in the form of a metal spiral is located coaxially sensitive to the ekeat with a gap through which the analyzed mixture is passed. Moisture

{Использованию пироэлектрического чувствительного элемента шлеетс возможность непосредственно регвстрировать производную величину концентрации во времени. Температура нагревател на несколько гргшусов превышает температуру чувствительного элемента и корпуса детектора. Таким образе, в известном детект фе пироэлектрический чувствительньЕй элемент оказываетс noMetqettHUM в неоднородное тепловое поле и, вл сь стоком тепла, имеет два тепловых контакта с протекающим веществом и с корпусом детектора, выполн ющим в даннс 4 случае функции холодильника. При этом подразумеваетс , что между холодильником и чувствительным элементом существует надежный тепловой конгакт, осуществление которого представл ет собой сложнуютехническую задачу, особенно если учитывать, что температура детектора в процессе анализа должна мен тьс 2}.{The use of a pyroelectric sensing element makes it possible to directly register the derived concentration value over time. The temperature of the heater is several degrees higher than the temperature of the sensing element and the detector body. Thus, in the well-known detector, the pyroelectric sensitive element is noMetqettHUM in a non-uniform thermal field and, being a heat sink, has two thermal contacts with the leaky substance and with the detector body, which in this case performs the function of a refrigerator. In this case, it is implied that between the cooler and the sensitive element there is a reliable thermal conict, the implementation of which is a complex technical task, especially considering that the temperature of the detector during the analysis must change 2}.

Однако отклонение величины теплового сопротивлени контакта от нул (вследствие различи термических коэффициентов расширени ) вызывает паразитный электрический сигнал, эквивалентный полезному, св занному с изменением тегглопроводйости анализируемого вещества. При этом,если изменение теплопровЬдности анализируемой смеси в процессе измерений дает полезный сигнал детектора 510 мВ, то отклонение от нул величины контактного сопротивлени может привести к возникновению паразитно ,го сигнала (1-5)10 мВ. Таким образом , снижаетс надежность Детектировани и, кроме того, не достигаетс предлагаема порогова чувствительность пироэлектрического датчика (10 - 2 10 об.%).However, the deviation of the thermal resistance of the contact from zero (due to the difference in thermal expansion coefficients) causes a parasitic electrical signal, equivalent to a beneficial, associated with a change in the teglopludate of the analyte. At the same time, if the change in the thermal conductivity of the analyzed mixture during the measurement gives a useful detector signal of 510 mV, then a deviation from zero of the contact resistance value can lead to the appearance of a parasitic signal (1–5) 10 mV. Thus, the reliability of the Detection is reduced and, moreover, the proposed threshold sensitivity of the pyroelectric sensor is not achieved (10 - 2 10 vol.%).

Цель изобретени - повышение надежности и пороговой чувствительност детектировани .. The purpose of the invention is to increase the reliability and threshold sensitivity of detection.

Указанна цель достигаетс тем, что пироэлектрический чувствительный элемент помегцен соосно корпусу детектора с зазором, а нагреватель выполнен в виде источника электромагнитного излучени (или источника частиц 5-квантов, нейтронов, электронов и т.п.) и расположен в корпусе детектора или вне его. Источник электромагнитного излучени выполнен в виде высокочастотного нагревател охватывающего корпус детектора, причем его ось проходит через центр чувствительного элемента и сечениеThis goal is achieved by the fact that the pyroelectric sensitive element is coaxially aligned with the detector case with a gap, and the heater is made as an electromagnetic radiation source (or a source of 5-quantum particles, neutrons, electrons, etc.) and is located inside or outside the detector case. The source of electromagnetic radiation is made in the form of a high-frequency heater enclosing the detector case, and its axis passes through the center of the sensing element and the cross section

сердечника равно размеру в плане чувствительного элемента.core equal to the size in terms of the sensing element.

Кроме того, пироэлектрический чувствительный элемент выполнен из части пироэлектрического кристалла, остальные части которого служат дл креплени и теплоизол ции, или в ,виде двух идентичных последовательно обтекаемых, анализируемой смесью вклюг ченных дифференциально элементов, один из снабжен нагревателем.In addition, the pyroelectric sensing element is made of a part of a pyroelectric crystal, the remaining parts of which are used for mounting and thermal insulation, or in the form of two identical sequentially streamlined, analyzed by a mixture of differentially included elements, one of which is equipped with a heater.

OO

Детектор выполнен в виде двух идентичных камер, снабженных дифференциально включёнными нагрева ьоаии пироэлектрическими чувствительными : элементами, о е 1ваемыми в одной из The detector is made in the form of two identical chambers, equipped with differentially switched on heating by pyroelectric sensitive elements:

5 камер а ализируетлой смесью, а в другой - газом-носителем, причем в кажд й иэ камер пироэлектрический чувствительный элемент выполнен в виде двух идентичных псЬледователько установлеимых по ходу газа эл&лентов, один из которых снабжен нагревателем и обе пары элементов включены в дифференциальную схему.5 chambers with a mixture of lasers, and another with a carrier gas, in each chamber of the chambers the pyroelectric sensing element is made in the form of two identical transparently installed gaseous electrons, one of which is equipped with a heater and both pairs of elements are included in the differential circuit .

При этом благодар лучистому наг5 реву температура пироэлектрического чувствительного элемента становитс на 0,5-1,5 градуса выше температуры корпуса детектора с анализируемого вещества, омывающего его по всей поверхности. Таким образом, сам пи0 роэлектрик становитс источником однородного теплового пол . В зависимости от теплопроводности сладайющего чувствительный элемент .вещества мен етс интенсивность теплообмена пироэлектрика с корпусом детектора и, следовательно, температура пироэлектрика, что вызывает перрток, пропорциональный при соответствующем нагрузочном сопротивлении ско At the same time, due to the radiant heating, the temperature of the pyroelectric sensing element becomes 0.5-1.5 degrees higher than the temperature of the detector body with the analyte washing it over the entire surface. Thus, the pyroelectric itself becomes a source of a uniform thermal field. Depending on the thermal conductivity of the sensing element of the substance, the intensity of heat exchange between the pyroelectric and the detector body and, consequently, the temperature of the pyroelectric, which causes a percussion proportional to the corresponding load resistance

0 рости изменени температур и фик сиру.емый с помощью систекол регистрации электрического сигнгша.0 increase in temperature and fixed with the help of sistekol registration of electrical signals.

В детекторе теплообмен между пироэлектрическим чувствительный элементом и корпусом детектора осзОДествл 5 етс только за счет теплорроводности анализируемой смеси. Это исключает возможные нерегул рные источники паразитного теплообмена (например вследствие малой разности температур In the detector, the heat exchange between the pyroelectric sensing element and the detector detector case is only due to the thermal conductivity of the analyzed mixture. This eliminates possible irregular sources of parasitic heat exchange (for example, due to a small temperature difference

0 между пироэ.лектриком и стенками детек тора радиационным теплообменсм между ними можно пренебречь). В этом случае порогова чувствительность определ етс исключительно фундамен- 0 between the pyroelectric and the detector walls, the radiative heat transfer between them can be neglected). In this case, the threshold sensitivity is determined solely by the foundation

5 тальными источниками тепловых и электрических шумов. Исключение нерегул рных источников теплообмена позвол ет повыситьСтабильность тепловых . параметров детектора и, следовательно , надежность измерений. , 5 tual sources of thermal and electrical noise. The exclusion of irregular heat exchange sources allows to increase the thermal stability. detector parameters and, therefore, measurement reliability. ,

Claims

About if in a known detector the total noise is equivalent, then in the proposed one it does not exceed (3-6). Accordingly, the minimum detectable concentration (Threshold sensitivity) for a known detector is .10 vol.%, And for the proposed detector 10 -2 -2-10 vol.%. Fig 1-7 shows the proposed detector. Pyroelectric sensitive element 1 is located in the case with the thief. The heater 2 as a radiation source is located in the housing or outside it; Depending on the type of heater used, as well as the cxeNfti attachment and activation of the Pyroele T1 sensor, the details of the structure can be measured. So when used as a high-frequency heater, it can be made, for example, as an indogctor, conjugated with; detector housing with the exterior or embedded in the housing (Figs 2 and 3). In both cases, the heater is executed as a release of the toroid 3 in this way, the axis of the toroid passes through the center of the electrode 4 of the pyroelectric sensing element, and the core of the core is equal to the size of the electrode, which ensures uniform heating of the sensitive element. If a source of visible or infrared radiation is used as a heater, then just like in the pre-case, it can be located as a detector detector, as well. In the latter case, the radiation is not sensitive to the tecto case. It is located directly in the direction of the polar axis of the pyroelectric sensing element and has a cross section {a section of the sensing gel electrode. e.: In / particular, with optical fibers to mate, the second end of each of which is located near the source of radiation, which can be located {| arbitrarily include: the detector housing. Obviously, for a warm-up warmer, the sensor {South element radiation must be the same and the intensity of both the field facets of the pyroelecric,. Radiation sources can, as is well known, be located in the detector housing, in this case FIG. 4) the sources of the hot-spot are marked in the special tubes 6y adjacent to the high of the conductor |} m, for example, the sapphire crystal to eliminate the irregularity of the flow of the mixture being analyzed in the detector. As sources in this case can be used, for example, miniature LEDs. Application as a particle source heater, for example; 5-quantoV | allows the use of a hull design that is basically the same as | ; azania in FIG. 4. However (in this case, the tubes must be made of lead in order to focus the radiation directly onto the pyroelectric sensing element. The threshold sensitivity and accuracy of detection significantly depend on the thermal resistance between the pyroelectric sensing element and the detector body. Therefore, the gain of the sensitive element and the transmission of an electrical signal to the recording system must be carried out in such a way as to minimize the thermal conductivity of the elements This is achieved under the condition that, for example, the sensitive element is suspended on thin non-expandable wires of any dielectric material (Fig. 5), two of which must be metallized and soldered (or welded) to opposite pyroelectric electrodes. The second ends of the filaments are fixed in the plugs 8 provided in the detector case and made of any heat-insulating electrically insulating material (for example, fluoroplastic). Electro contacts 9 must be provided in traffic jams, to which metallic threads are connected, 11 (a sensitive element with a recording system. Another variant of the invention may be, for example, the following. Since it is known that only the polarized part of the segment has the pyroelectric effect electric crystal (or ceramic), the pyroelectric element can be made of complex shape (Fig. 6). In this case, the legs, two of which are metallized to remove from the electrodes, are not inserted in the cork 8. The change in temperature of the analog & CMF mixture in known catarometers is perceived as a useful signal. In order to increase the reliability of detection and decrease the error caused by temperature fluctuations of the analyzed mixture, it is proposed to use two identical included differential sensitive elements. arranged in series in one chamber (fig. 7), one of which is exposed to the heater, and the other is not exposed. It should be borne in mind that there may be two pyroelectric elements that are independent of each other. It is also possible to use one element with two spatially separated polarized areas (Fig. 7). Differential inclusion of pyroelectric sensitive elements can be carried out using a two-chamber detector, in this case a carrier substance is passed through one of the chambers, and a carrier mixture is passed through the other analyte. Another variant of the two-chamber detector is possible in which the analyzed mixture passes through both chambers, but in one of them the sensitive element is not exposed to the heater. A two-chamber detector is also possible, in each of the chambers of which there are two successively installed along the gas path (one pair is analyzed by the mixture, or the carrier of the other pair is separate) the electrical sensitivity sensors, one of which is exposed to the generator. A difference signal is taken from each and the difference of these signals is recorded. The detector operates as follows, Example 1. The pyroelectric sensing element is heated by means of infrared radiation sources (aB LEDs) with a total capacitance of 2.5 watts. The sensitive element is made of the PTS-19 PTS-19 cell-ceramic ceramics, it has a single area, the resistance at room temperature is 5–10 ° Ω and is suspended on quartz threads. The signal is recorded by an electrometric amplifier BK2-16 recorded on a KSP-4 recording recorder. Input resistance of the electrometer Yu Ohm. RF-helium with a feed rate of 35 cmVmin is used as a carrier gas, and a chromatographic column with a diameter of 3 mm polyethylene glycol on celite 545 is used. A sample with a propane concentration of 0.05% is introduced. The signal of the pyroelectric sensing element is 87 + 0.5 mV per operating scale, which corresponds to the threshold sensitivity.%. The introduction of a sample with a propane concentration of 0.1% under the same conditions causes a signal of 173 + 1.0 mV. Example 2. Unlike Example 1, the pyro sensor is heated using a high-frequency (RF) generator (the rest of the test conditions are the same as in Example 1). The signal of the pyroelectric sensor is 82.5 V, 5 mV, which corresponds to a threshold sensitivity of 4.5-10 vol.%. Froze The conditions of the experiment are the same as in Example 1. A sample is introduced with a heptane concentration of 0/05%. The pyroelectric sensor signal is 62.5 + 0.4 mV. Thus, the proposed detector has a higher threshold sensitivity (as compared with the known tlO-4 2 ".%). In addition, it is distinguished by high reliability of determining low concentrations of impurities in the analyzed substance, which allows for the analysis of impurities in wadest, high purity vales, without their prior concentration. Claim 1. Chromatographic detector, including an enclosure, in which a pyroelectric sensing element with a heater is located, washes-. the flow of the analyzed mixture, and the electrical signal detection system from the sensing element, characterized in that, in order to increase the threshold sensitivity and reliability of detection, the pyroelectric sensing element is placed coaxially with the detector case with a gap, and the heater is made in the form of an electromagnetic radiation source and is located in the housing detector or outside it.

2. Detector POP.1, characterized in that the source of electromagnetic radiation is made in the form of an RF heater encompassing the detector case, with its axis passing through the center of the sensing element and the core section equal to the size in terms of the sensing element.

3. The detector according to claim 1, characterized in that the source of electromagnetic radiation is implemented in the form of a high-frequency open toroid heater located in the detector housing, and its axis passes through the center of the sensing element and the core section is equal to the size in terms of the sensing element.

4. The detector according to claim 1, 6 tons of l and h y and so that the pyroelectric sensitive element is made of part of the pyroelectric cryotall (or ceramics), the remaining parts of which are used for fastening and thermal insulation.

5. The detector according to claim 1, denounced by the fact that the pyroelectric sensing element is made in the form of two identical sequentially streamlined analyte (differential connected elements, one of which is equipped with a heater.

6. A detector according to Claim 1, characterized in that it is made in the form of two identical chambers, equipped with differentially activated heated pyroelectric sensing elements, bathed in one of the chambers with an antisense mixture, and in the other - with a carrier gas.

7. The detector according to claim 6, which differs) w and with the fact that in each of the cars the pyroelectric sensitive tement is made in the form of two elements identical in series to the gas flow, one of which is equipped with a heater and about. The elements of the elements are included in the differential scheme .

Sources of information taken into account in the examination

1. Brazhnikov V.V. Differential detectors for gas chromatography. M., 1974, p. 14-25.

2. Authors certificate of the USSR 405069, cl. G 01 N 31/08, 1975 (prototype).

////// //,