utilizeRadionuclideAnd various methods for in vitro analysis (mainly quantitative analysis) of various elements or compounds by nuclear radiation, collectively referred to as radiometric analysis.[1]The main methods are: radiometric analysis, radiochemical analysis, activity analysis, excited X-ray fluorescence analysis, Mossbauer resonance spectrum, positron annihilation method, nuclear magnetic resonance method, etc.
RadionuclideAdvantages for analysis: ① the tested object can be identified in the complex system according to the type and energy of the ray, which can greatly simplify the purification and separation of the sample in most cases; ②adoptRadioactivity measurementThe detection limit is usually three to six orders of magnitude smaller than that of general physical and chemical methods.
One of the earliest radioassays used was the nuclide dilution method.Its basic principle is that after the marker and non marker with the same structure are mixed, they behave the same in the process of separation and purification. The dilution multiple of the marker can be calculated from the reduction multiple of the specific radioactivity. As long as the amount of either of them is known, the amount of the other can be calculated according to the change of the specific radioactivity.The sensitivity of nuclide dilution method is not very high, but the dilution method derived from it to calculate the overall metabolic library and the back dilution method to calculate the content of markers are still widely used.
Another radiometric analysis technology developed from nuclide dilution method is competitionRadioassay。It uses the same marker structure as the tested substance, and its working principle is to make the two competitively combine with the specific binding reagent.The more the measured substance, the less the marker in the combination, and the quantity of the measured substance can be determined according to the radioactivity of the combination.This method has wide application, high sensitivity and simple operation, and has become the most widely used radiometric analysis method.
The structure of the markers used in other radiometric analysis technologies is different from that of the tested object. Their working principle is to combine the markers with the tested object, and finally calculate the quantity of the tested object according to the radioactivity of the complex.The binding reaction belongs to the general chemical reaction, which is called nuclide derivative analysis, and the antigen antibody reactionImmunoradiometric assay。The same principle is also used to analyze hormone receptors and the specificity of hormones in plasmaBinding protein。holdRadionuclideThere are two kinds of radioassay combined with enzyme reaction.One is to measure the activity of enzymes by the rate at which labeled substrates are converted into labeled products, which is called enzyme radioassay.The other is to use enzymes and markers as tools to quantify certain substances to be measured, which is called radioenzymatic analysis.
Activation analysisIt is to bombard the measured sample with neutrons or charged particles to make some elements radioactive, then judge the element type according to the nature of the emitted ray, and calculate the amount of the element according to the quantity of the ray.
With the development of the basic theory of nuclear physics and nuclear technology, in vitro radiometric analysis is also adding new content.For example, the Mossbauer effect can be used to measure the changes in the chemical state and electronic configuration of iron atoms in iron containing macromolecules in the life process, and the perturbation angle correlation method can be used to study the changes in the configuration of liquid biological macromolecules when diseases occur.
The development of radiological analysis technology is causing profound changes in medical laboratory and biochemical technology.On the one hand, some old techniques are being replaced by radiometric analysis techniques, for example, many hormone determinations are now mostly usedRadioimmunoassay；On the other hand, many previously undetectable trace substances are gradually getting reliable determination methods, such as various rare elements, cyclic nucleotidesprostaglandin、HypothalamusHormone, etc.[2]
brief history
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At the beginning of the 20th century, with the discovery of natural radioactivity, we began to explore the use of natural radionuclides in analytical chemistry to simplify operations and improve the sensitivity of analysis.In 1912, G. Hervey et al. first used radioactive lead (210Pb) as an indicator to determine the solubility of lead chromate.In 1925, R. Ellenburger used radioactive lead (212Pb) as an indicator to analyze natural lead by precipitation method.In 1932, Hervey et alGraniteBefore analyzing the sample, add radioactive lead of known specific activity to the sample solution, and analyze the lead by isotope dilution method, and obtain satisfactory results.All of these areRadioactive indicatorstayanalytical chemistryThe application in provides conditions.Subsequently, it is also widely used in extraction, precipitation, adsorption, titration, evaporation and other analytical operations.In 1934, F. Jorio Curie and I. Jorio Curie discovered artificial radioactivity, and E. Fermi and others proposed that almost all elements can induce radioactivity under the action of thermal neutrons.In 1936, Hervey and H. Levy successfully analyzed impurities such as dysprosium in yttrium oxide and europium in gadolinium oxide by (n, γ) nuclear reaction for the first time, opening up a new field of activation analysis.Then, in 1938, GT. Sieberg et al. carried out the charged particle activation analysis for the first time.With the establishment of reactors and various accelerators, the continuous improvement of multi-channel spectrometers and the popularization and application of microprocessors, activation analysis has been developed by leaps and bounds.Since the 1950s, microanalysis techniques (i.eNuclear analysis technology）。Some of them study the microstructure of matter through the interaction between positrons and matterpositron annihilation Technology, nuclear recoil free gamma ray resonance absorption -- Mossbauer effect -- application, as well as ion beam backscattering analysis, nuclear reaction analysis, channel effect application and particle excitation developed in the 1970sX-ray fluorescence analysisEtc.Radioanalytical chemistryDue to its advantages of high sensitivity, small sampling volume and non destruction of samples, it has been paid attention to and developed rapidly.
Analytical method
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Methods commonly used in radioanalytical chemistry can be divided into two categories: ① methods using radioisotopes as indicators, such as radioanalytical method, radiochemical analysis, isotope dilution method, etc.; ②Methods such as activation analysis, particle excited X-ray fluorescence analysis, Mossbauer spectrumNuclear magnetic resonance spectrum, positron annihilation andsynchrotron radiationEtc.
Radioassay
Using radionuclidesRadiolabeled compoundAn analytical method used as an indicator to determine the content of non radioactive samples to be measured by measuring their radioactivity.Used in capacity analysisRadioassayIt is called radioactive titration.
Radiochemical analysis
It is a technology to determine the amount of radioactive substances contained in the sample by measuring radioactivity after separating and purifying the sample with appropriate methods.For example, the potassium content is determined by measuring the radioactivity of natural radionuclide potassium 40 (half life is 1.28 × 109 years, and the abundance is 0.111%).Isotope dilution method is used to mix the radioactive isotope or labeled compound with known specific activity and the same as the substance to be measured with the sample evenly, separate and purify part of it, and measure its specific activity.Calculate the content of the substance to be measured according to the change of specific activity before and after mixing, that is, isotope dilution multiple.(SeeIsotope dilution method, sub stoichiometric analysis)
activation analysis
After the stable nuclides in the sample to be tested are converted into radionuclides by nuclear reactionNuclear reaction cross section、Particle flux, ray energy, half-life and radioactivity to determine the content of the substance to be measured.Can be divided intoneutron activation analysis、Charged particle activation analysisAnd photon activation analysis.As a highly sensitive nuclear analysis technology, activation analysis is widely used in the analysis of biological samples and trace materials in high-purity materials, as well as in environmental science, archaeology, forensic science and other fields.
Excited X-ray fluorescence analysis
When α, β, γ or X rays act on the sample, due to Coulomb scattering, orbital electrons absorb part of its kinetic energy, making the atom excited.When the excited state returns to the ground state, the characteristic X-ray is emitted, and the type and content of elements are analyzed according to the energy and intensity of the characteristic X-ray.Its sensitivity is very high and it is widely used.
Mossbauer resonance spectrum
Namely, nuclear gamma ray resonance spectrum without recoil.Because of its high resolution, it can also measure the small changes in the electronic state outside the nucleus, so it can get the chemical shift, the binding state inside the molecule andIntermolecular interactionInformation of extranuclear electrons.It has been used in the analysis of physical and chemical states of iron, tin, europium, thulium, tantalum, etc.(SeeMossbauer spectroscopy）
Positron annihilation method
A positron is the antiparticle of an electron.This method uses positron annihilation lifetime to study the microstructure of materials, such as metal defects and phase transitions of various materials, as well as free electrons and solvated electrons in solutions.
Nuclear magnetic resonance method
The molecular structure of samples, especially the molecular structure of organic compounds, is determined by the NMR spectral characteristics such as chemical migration, coupling constant, multiplicity, width and intensity of absorption peak and temperature effect.
characteristic
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Compared with general analytical chemistry, radioanalytical chemistry has the following characteristics: based on the measurement of radioactivity or characteristic radiation, the analytical sensitivity is high (generally up to 1ppm), the accuracy is high, the analysis speed is fast, the method is simple and reliable, the sampling volume is small, and sometimes the sample structure can not be damaged.
Each analysis method has its own characteristics and the most suitable analysis range.Isotope dilution methodThere should be a radioactive standard with known specific activity,Sub stoichiometryThere is no such need;neutron activation analysisGenerally, it is suitable for the analysis of medium and heavy elements and some light elements, and can analyze thick samples;Charged particle activation analysisAnd backscattering analysis are mainly used for surface analysis, in which charged particle activation analysis is particularly suitable for light element analysis, while backscattering analysis is more sensitive to medium and heavy elements,X-ray fluorescence analysisIt has good resolution and detection sensitivity.Generally, appropriate analysis methods are selected according to sample conditions and analysis requirements.No analytical method is comprehensive and appropriate, and sometimes it is necessary to select a combination of several methods to obtain satisfactory results.
Application of immunoradiometric analysis
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Immunoradiometric analysisIt is a derivative technology of radioimmunoassay. It was first proposed by Miles and Hales in 1968 for the determination of insulin in raw plasma.It is a more sensitive technique to label excess antibody instead of antigen in reaction system.Because immunoradiometric analysis needs to consume a lot of antibodies and antibodies must be solidified, PcAb cannot meet this requirement and cannot be popularized.
McAb has high specificity,Hybridoma technologyA large number of McAbs are provided. Due to the maturing of solid phase technology in recent years, McAb is adsorbed or coupled with solid phase carrier. On the other handone hundred and twenty-fiveI Conduct McAb marking.When measuring a certain Ag, solid phase antibody and labeled antibody are added to form a sandwich complex of AgAb * Ag, and its radioactivity is measured. The amount of Ag is proportional to the measured radioactivity.So McAb came out asImmunoradiometric analysisThe development of technology provides conditions.
In recent years, with the expanded application of McAb, there has been a new development of so-called immune engineering or double determinant immunoradiometric analysis, that is, using aAntigenic determinantMcAb is used as a marker, then the solid phase MCAb - Ⅰ, tested antigen andone hundred and twenty-fiveThe sensitivity and specificity of I labeled McAb - Ⅱ will be further improved when they form the so-called two site or three site immunoradiometric assay.For example, hCG double site immunoassay can accurately determinebiological activityThe content of intact hCG is of great significance in rapid pregnancy test and early diagnosis of choriocarcinoma.[3]
