analytical chemistry[1]It is about studying the composition, content, structure and morphology of substancesChemical informationIt is an important branch of chemistry.It is to identify which components are contained in the substance and what components the substance consists of, determine the relative content of various components, and study the molecular structure or crystal of the substance.The development history, analytical methods, application fields and error elimination of analytical chemistry are introduced.
1920s and 1930s[2]The content of analytical chemistry was greatly enriched by using the solution chemical equilibrium theory and kinetic theory in physical chemistry at that time, such as precipitation formation and coprecipitation phenomenon, indicator action principle, titration curve and end point error, catalytic reaction and induced reaction, buffer action principle, and made analytical chemistry move forward
The second important stage
Decades after 1940s[3]，the Second World WarBefore and after, the development of physics and electronics promoted the development of various instrumental analysis methods, and changed the situation that chemical analysis was the main form of classical analytical chemistry.
Atomic energy technologyWith the development of semiconductor technology, analytical chemistry is required to provide a variety of sensitive, accurate and fast analytical methods, such as semiconductor materials, some of which require a purity of more than 99.9999999%. Driven by the new situation, analytical chemistry has achieved rapid development.
The most remarkable feature is the wide application of various instrumental analysis methods and separation technologies.
The third important stage
Since the 1970s, the arrival of the information age marked by computer application has pushed analytical chemistry into the third reform period[4]。
becauselife sciencesWith the development of environmental science and new material science, the improvement of basic theory and testing means, modern analytical chemistry is fully possible to provide comprehensive information on composition, content, structure, distribution, morphology and so on for various substances, so that past problems such as micro analysis, thin-layer analysis, nondestructive analysis, instantaneous tracking, online monitoring and process control can be easily solved.
Analytical chemistry has widely absorbed the latest achievements of contemporary science and technology, and has become one of the most dynamic disciplines in the contemporary era.
qualitative analysis[5]: Identify which components are contained in the substance and what components the substance consists of.
Quantitative analysis: determine the relative content of various components.
Structural analysis: The study of the molecular structure or crystal of a substance.
Characteristics of analytical chemistry
1. Highlight the concept of "quantity" in analytical chemistry
For example, the measured data cannot be chosen at will;The data accuracy and deviation are related to the analysis method adopted.
2. Sample analysis is a process of obtaining information and reducing system uncertainty
3. Highly experimental
Emphasize hands-on ability, cultivate experimental operation skills, and improve the ability to analyze and solve practical problems.
4. Strong comprehensiveness
It involves chemistry, biology, electricity, optics, computer, etc., reflecting ability and quality.
Analytical chemists should have a strong sense of responsibility.
Scope of application
Analytical chemistry has extremely high practical value, has made important contributions to human material civilization, and is widely used inGeological survey、Mineral exploration, metallurgy, chemical industry, energy, agriculture, medicineClinical laboratory, environmental protectionCommodity inspection、Archaeological analysis、Forensic medicineCriminal investigation and identification.
Requirements for analytical methods
The analysis method should be simple, not only for field work (such asGeological survey, chemical prospectingenvironmental monitoring、Soil testingSimple and effective chemical analysis methods are needed, as is the routine indoor analysis.
Because the method is simple and the steps are few without losing the required accuracy and precision, which means saving time, manpower and costs.For example, when gold stores purchase gold jewelry, they draw a line on the touchstone (the scientific name is stripe), and then identify the fineness of gold from the color of the stripe.This fringe methodMineral identificationStill used in.
Of course, this method is not as good as fire assay orAtomic absorption spectrometryIt is accurate, but it has reached the goal of identifying gold articles.For another example, the urine sugar content of diabetics can beEnzyme test paperIt is simple and convenient for the patient to estimate the sugar content from the color change of the test paper.On the other hand, although atomic absorption spectrometry can also indirectly determine the sugar content in urine, it is not used because it is uneconomical.
Research
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1931 E. WessonBergerFor the proposed residue determination, only 10 micrograms of sample are takenUltramicroanalysis。The instruments used range from test tubes to advanced instruments (with automatic equipment attached)electronic computerProcedure control, recording and storage).Analytical chemistry is based on the basic theory and experimental technology of chemistry, and absorbs the knowledge of physics, biology, statistics, electronic computers, automation and other aspects to enrich its own content, so as to solve various analytical problems raised by science and technology.
Research questions
① What elements and/orGroup(qualitative analysis);
② Quantity of each component orSubstance purityHow (quantitative analysis);
③ In substanceatomHow they are linked to each other to form molecules and how they are arranged in space (structural and stereoanalysis).
Research object
fromSimple substanceTo complex mixtures and macromolecular compounds, fromInorganicTo organic matter, from low molecular weight tohigh polymerQuantity (e.g. 10Atomic mass unit）。The sample can be gaseous, liquid and solid.The sample weight can range from more than 100g to less than mg.
Analysis type
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The elements known by ancient people include carbon and sulfur as non-metallic elements, and copper, silver, gold, iron, lead, tin and mercury as metal elements.
Although the name of analytical chemistry originated fromR. BoyleBut its practice should be as old as chemical process.It is impossible to imagine the high development of ancient smelting, brewing and other technologies, and there is no simple means of identification, analysis, production process control, etc.The subsequent rise in the East and WestAlchemy、alchemyIt can be regarded as the precursor of analytical chemistry.
3000 BC，EgyptianKnown weighing techniques.The earliest instrument for analysisEqual arm balanceIt was recorded in the papyrus (1300 BC).The stone standard weights (about 2600 BC) kept by the Babylonian priests still exist.However, the equal arm balance was used for analysis, when it was used in the oven assay in the Middle Ages（Fire assayOne).
4th century BCIt is known that touchstones are used to identify the fineness of gold.
3rd century BC，ArchimedesIn solving the purity problem of the gold crown of Syracuse King Xilang II, the difference between the density of gold and silver was used, which was a pioneer of damage free analysis.
Around AD 60，Pliny the ElderApply the Chinese nutgall extract on the papyrus paper to detect the impurity iron (Ⅲ) in copper sulfate, which is the first one usedOrganic reagent, also the earliestTest paper。
1751，J. T. Eller von BrockhausenUse the same method to detect the iron content in the blood slag (after ashing).
Capacity analysis
In 1663,Boyle reported thatAcid-base indicator。But the real capacity analysis should be attributed to FranceJ. - L. Gai Lussac。
1824He published the determination of effective chlorine in bleaching powder, using sulfonated indigoindicator。Then he titrated plant ash with sulfuric acid and silver nitrate with sodium chloride.These three works representRedox titration、Acid-base titrationandPrecipitation titration。Complexometric titrationCreated fromJ. Von LibichHe titrated cyanide ion with silver (I).Another outstanding contributor to capacity analysis is GermanyK. F. MooreThe buret designed by him to hold strong alkali solution is still in use today.He recommended oxalic acid as the reference material for alkalimetry,Ammonium ferrous sulfate(also called Mohr salt) as the reference material for redox titration[6]。
Microanalysis
The earliest microanalysis wasChemical microscopyThat is, observe the crystal state, optical properties, particle size and spherical diameter of the sample or reactant under the microscope.
Mid 17th century, R. Hooke was engaged in the study of microscopy and published Microscopic Atlas in 1665.French pharmacist FA. In 1784, H. de Karozier used a microscope toChloroplatinateThe forms of potassium and sodium are different.
1747, German chemistA. S. MagrafIt was confirmed by microscope that sucrose and beet sugar were the same substance;
1756Examine platinum group metals with microscope.
1865, A. Halwish, Microscope in Toxicology.
1877, S.A. Boriki wrote "Analysis of Minerals and Rocks by Chemical/Microscopic Method", and used gas reagents (such as hydrogen fluoride, chlorine), fluosilicic acid and ammonium sulfide to interact with minerals and their slices.T. H. Berens is not only engaged in crystal inspection of inorganic substances, but also extends to organic crystals.
1891, O. Lyerman proposed thermal microscopy, that is to observe the changes of crystals when exposed to heat under a microscope.50. Kevler and his wife designed two microscope heating tables for the identification of drugs and organic compounds.Thermomicroscopy requires only one crystal.Later, it developed into an electron microscope with a resolution of 1 angstrom.
The earliest microanalyzer who does not use a microscope shouldGermany JW. De Bellina。He is engaged in wet microanalysis, pipe blowing and flame reaction, and has published《Microchemistry Experiment Technology》One book.The recognized founder of modern microanalysis isF. Amish。He designed and improved the micro chemical balance to make its sensitivity meet the requirements of micro chemical analysis, improved and proposed new operating methods to achieve the determination of milligram level inorganic samples, and confirmed that the accuracy of nanogram level sample determination is no less than milligram level determination.The founder of organic micro quantitative analysis isF. PregelHe once isolated a degradation product from bile, and its amount was not enough for a constant hydrocarbon analysis. After listening to the lecture on micro quantitative analysis made by Emehi in 1909 and visiting his laboratory, he decided to change the constant combustion method to the micro method (samples in milligrams), and achieved success;Published in 1917《Organic micro quantitative analysis》He won the Nobel Prize in Chemistry in 1923.
If the constant operation is not suitable for microanalysis, it needs to be improved.For example, constant filtration is to quantitatively transfer the precipitation into the filter paper cone or filter crucible.If this method is used for micro precipitation filtration, the substances adhered to the original beaker wall can no longer be ignored, so the method must be changed.Micro filtration uses filter rods to suck out mother liquor, leaving all precipitated in containers.The container can be a 25ml porcelain crucible, which can also be used as a weighing vessel;The sediment can also be washed in it, and then the washing solution can be sucked out with a filter rod.This can avoid sedimentation loss and simplify operation procedures.
inorganic compoundThe behavior on filter paper has attracted attention in the 19th century.German chemist FF. In 1850, Runge separated the dye mixture by dropping it on blotting paper.Earlier, he used filter paper or cloth pieces stained with starch and potassium iodide solution as bleachDrip test。He added yellow blood salt to the middle part of the paper soaked with iron (III) sulfate and copper (II) solution, and then added a second drop after each drop was inhaled, so as to obtain a beautiful pattern generated by himself.In 1861, CF. Schoenbein's capillary analysis, he dipped the filter paper strip into the water containing several kinds of inorganic salts, and the water carried "salts" up along the paper strip, with water rising the highest, and other ions separated into connected bands according to their "mobility".This is very similar to "paper chromatography".His students succeeded in "separating organic compounds on filter paper", which can clearly and completely separate "organic dyes".
Using filter paper or porcelain plate to detect inorganic and organic substances is Pregel's contribution.The method is simple and easy to operate with high selectivity and sensitivity. The drop test belongs to the scope of microanalysis.His two books, "Drip Test" and "Chemistry of Concentration, Selection and Sensitive Reaction", are required reading for analysts.Austria after 1921F. FaigerThe drop test method was systematically developed.
1960s, proposed by H. WeissRing furnace technology。Put the microgram sample in the center of the filter paper, then use the solvent to wash, and heat the outer edge of the filter paper to evaporate the solvent, so as to separate into several concentric rings.If the ions are colorless, sensitive color developing agent or fluorescent agent can be sprayed.Both detection and semi quantitative results can be obtained.
Chromatography
Chromatography, also known as chromatography, is basically a separation method[7]。
1906, RussiaМ. С. ZwittChlorophyll was separated by adding green leaf extract juice to the top of calcium carbonate precipitation column and then rinsing with pure solvent.The study was published in Germany《botany》Magazine, so it failed to attract people's attention.
1931It was only when R. Kuhn and E. Leder of Germany found this law again and showed its effectiveness that people could trace back to Zwitt's research and earlier related research from the literature, such as JT. Wezeng used soil column for separation;In 1893, L. Reed used a kaolin column to separate inorganic salts andOrganic salt。Four years later DT. Wear bleach to separate oil.
Gas adsorption chromatography began in the 1930s with P. Shufutan and A. Youken.In the 1940s, Germany Y. Hesse used gas adsorption to separate volatile organic acids.E. Glukoff of England also used the same principle to separate helium and neon in the air in 1946, and made it in 1951Gas chromatograph(SeeGas chromatography）。The successful development of the first modern gas chromatograph should be attributed to E. Kramer.
Gas distribution chromatography According to the principle of liquid-liquid distribution, AJ. P. Martin and R50. It was proposed by M. Singer in 1941.Because of the importance of this work, they won the 1952 Nobel Prize in Chemistry.M. J.E. Golay proposed to use long capillary string, which is another innovation.
The chromatography-mass spectrometry (GC-MS) method is one of the most effective analytical methods, which can separate and identify complex organic mixtures within a few hours by transferring the leaching fluid obtained by chromatography into the mass spectrometer.
Liquid chromatographyIt includes liquid-liquid and liquid-solid chromatography. The first state of the last two names represents mobile phase, and the second state represents stationary phase.stayatmospheric pressureThe flow rate of liquid chromatography is too low, so the pressure must be increased.The pioneer work in this field is PB. Hamilton was separated by high pressure liquid chromatography in 1960amino acid。
1963J.C. Giddens pointed out that the column efficiency of liquid chromatography should catch up with that of gas chromatography, so the filling particles of the former should be much smaller than those of the latter, so high pressure is required, and the pump used should have no pulse.
1966, R. Gentford and TH. High made of this pulse free pump.
1969J.J. Kirkland improved the filler to make it have the specified surface porosity, and then bonded the stationary phase (such as n-hexadecyl) on the carrier to make it resistant to heat and solvent decomposition.Carrier availablesilicon dioxide, bonding through Si-O-C or Si-C bond.
Thin layer chromatography
Thin layer chromatography uses thin layer silica gel instead of filter paper for chromatography.Since the silica gel particles are uniform and fine, the separation speed and degree are generally better than that of paper chromatography, and the separation of inorganic and organic substances is as effective as that of paper chromatography[8]。
Dutch biologist MW. In 1889, Beiyinke dropped a drop of mixed solution of hydrochloric acid and sulfuric acid in the middle of the animal glue thin layer. The hydrochloric acid diffused farther and formed another ring outside the sulfuric acid ring. Silver nitrate and barium chloride were successively used to show the existence of these two rings.
Nine years later, HP. DimensionEastmanThe same method was used to prove that there were two enzymes in the amylase of malt.
Until 1956Federal GermanyE. Starr improved the coating method and operation, and adopted measures such as fine particle (0.5~5 μ m) silica gel to make this method widely used.Quantitative thin layer chromatography started from JG. Kishner et al. (1954).They were the first to determine biphenyls in citrus and its processed products (seeThin layer chromatography)。
thermal analysis
Theophrastus, the Greek philosopher, once recorded the effects of various rocks, minerals and other substances when exposed to heat.France H. -50. Le Chatelier and WC. Roberts Austin is also calledDifferential thermal analysisThe ancestor of.
1960s, fineDifferential thermal analyzerAnd MJ. The differential scanning calorimetry proposed by O'Neill can measure the purity of compounds and other parameters, such as melting point and temperature of vitrification, polymerization, thermal degradation, oxidation, etc. (seethermal analysis）。
Early 20th century, proposedThermogravimetric methodIt is used to study the weight change of materials, such as steel and precipitation, when they are heated.Honda Kotaro created the first oneThermobalanceIt was originally only used to solve metallurgical problems.It is used in the analysis of C. Duval.He has studied the thermal behavior of more than 1000 kinds of precipitates.For example, calcium oxalate can be burned into calcium oxide at high temperature or calcium carbonate at about 550 ° C.As a weighing form, the latter is better, because it saves energy during burning, the conversion factor value is large (so the error is small), and calcium oxide is free from moisture absorption during weighing.
During electrolysis, copper (II) is reduced at the cathode and separated as a single substance (zero valence), and then weighed, which should be classified as the gravimetric method.At this time, electrons can be considered as precipitants.And lead (II)anodeOxidation toLead dioxideThe form is attached to the anode.In the 1860s, the former France was composed of German C. Luko and American JW. Gibbs independently proposed.
Organic reagent
Early 19th century, for inorganic gravimetric analysisOrganic reagentOnly oxalic acid and its ammonium salt and ammonium succinate are available.The former is used for separation of calcium and magnesium and determination of calcium.The latter is used to precipitate ferric iron to separate it from divalent metal ions.
1885, M.A. Ilinski and G.von Knowles proposed that 1-nitroso-2-naphthol is the precipitator of cobalt in the presence of nickel, and it is also the first chelating agent.as foranionIn the early 20th century, W. Miller proposed 4,4-benzidine as the precipitator of sulfate radical.
1950, ChinaLiang ShuquanOrganic reagents are used for gravimetric analysis to determine tungstate.
1950, M. Bush introduced 4,5-dihydro-1,4-diphenyl-3,5-phenylimino-1,2,4-triazacyclopentadiene (nitrate reagent for short) as nitrate precipitant.After 1975, it became a good precipitator of perrhenate.
1950, Л. A. Chugayev synthesized dimethylglyoxime and observed that it formed red precipitate with nickel (Ⅱ).Two years later, OE. ClothLongkeDimethylglyoxime reagent was applied to the determination of nickel in steel.Since then, new organic reagents with high sensitivity and selectivity have been emerging.ChinaZeng Yun'eWhen using this reagent,rare earth elementOfMolar absorptivityIt can be as high as 0.98~1.2 × 10 L/(Mocm).
colorimetryUse sunlight as the light source, and compare the color depth by visual inspection.The earliest record is WA. Lampardius determined iron and nickel in cobalt ore in glass measuring cylinder with standardReference solutionCompare with the sample solution.
1846, A. Jacqueline proposed thatAmmonia solutionDetermination of copper with blue.Then came TJ. Determination of iron (1852) by Heropos thiocyanate method;Determination of ammonia by Nessler method;Nitrate was determined by phenol disulfonic acid method (1864);hydrogen peroxideDetermination of titanium (1870) by HPLC;Methylene blueDetermination of hydrogen sulfide (1883);Determination of silicon dioxide by phosphosilicic acid method (1898).SpectrophotometerUse monochromatic light andPhotomultiplier tubeThe wavelength range is 220~1000 nm, which is wider than the visual range (400~700 nm).
Illuminate the suspension with light and observe it from the top. When the line of sight is at right angles to the light, it is calledSpecific fog method；If the line of sight and light are in a straight line, it is calledTurbidimetry。
1750sIn atomic weight measurement, G.J. Marder used visual inspection to measure the brightness of silver chloride suspension in the upper liquid.Then,J. - S. STAUse a standard suspension as the reference.
1894, USAT. W. RichardsThe first fogometer is designed.The specific fog method was originally used to observe the chlorine (or bromine) ion andSilver ionWhether the concentration reaches equivalent.This method is then used for quantitative determination with high sensitivity. It can determine 3 micrograms of phosphorus in one liter of water or 10 micrograms of acetone in one liter of water.
Molecular spectrum analysis
Infrared spectroscopy is a powerful means for organic chemists to identify unknown compounds.infrared spectrumIt was applied to gasoline knock research in the 1920s, and then used to identify natural andsynthetic rubberAnd unknown substances and impurities in other organic compounds.In the 1970s, on the basis of the vigorous development of electronic computers, the experimental technology of Fourier transform infrared spectroscopy (FTIR) entered the laboratory of modern chemists, becomingstructural analysisImportant tools.Far-infrared spectrum(200~10 cm) and microwave spectrum (10~0.1 cm) are spectroscopic methods for studying molecular rotation[9]。
Raman spectrum (seeRaman spectroscopyIt is another way to study molecular vibration.The signal of early Raman spectroscopy was too weak to be used, and its application in analytical chemistry was not promoted until laser was used as a monochromatic light source.Raman spectroscopy has been adoptedFourier transformation FT-Raman spectral analysis technology, confocal micro Raman spectral analysis technology, surface enhanced Raman effect analysis technology, etcMineral analysisAnd other fields play an important role.
1800, F.W. Herschel found infrared.The following year JW. Ritter found the ultraviolet region by silver chloride reduction.The following year, WH. Wollaston observed dark lines in the sunlight spectrum.
1815， J.vonFraunhoferAfter research, the hidden line is named Fraunhofer line.In the literature, sodium line is called D line, which is also stipulated by Fraunhofer.R. W. BunsenA gas lamp named Bunsen burner is invented. The flame of the lamp is nearly transparent and does not emit light, which is convenient for spectral research.
1859Bunsen and his colleagues physicistsG. R. KirchhoffStudy the characteristic emission and absorption spectra of each element in the flame, and point out thatFraunhofer lines yesatomic absorptionLine, because there are various elements in the sun's atmosphere.The instruments they used already have the elements of modern spectroscopes.They can be called the founders of emission spectrometry.
The analysis of inorganic substances in natural products and industrial products, such as rocks, minerals, ceramics, steel, alloys, mineral acids, caustic soda, etc., belongs to inorganic analysis;Petroleum, dyes, plastics, foodSynthetic drugsThe analysis of Chinese herbal medicine belongs to organic analysis.In short, where hydrocarbons and theirderivativeThe analysis of is organic analysis, while the analysis of other substances is inorganic analysis.However, some inorganic substances are sometimes mixedOrganic matterOrganic substances also contain inorganic substances.For example, river water and sea water contain organic matter, some manganese ore contains organic matter, coal contains ash, and oil containscomplex compoundMetal in form, inorganic filler in paper, etc.Such articles are used for both inorganic and organic analysis.
Other methods are equally effective for inorganic and organic substances, such asGas chromatographyIs one of them.Carbon monoxidecarbon dioxideHydrogen, nitrogen, oxygen, methane, ethylene, water gas, etc. can be separated one by one or grouped under selected conditions in the same column.orsat Gas analyzerThe same is true, but the principle of separation is different.
Trace analysis means that the sample contains very little.Generally, the sample with more content is the main component, and the sample with less content is the secondary component.E. B. Sandel believes that the content of 1%~0.01% is secondary.Some people think that 10%~0.01% is the secondary component.The content below one ten thousandth (0.01%) is called trace.The trend of trace analysis tends to determine lower and lower content, so ultra trace analysis appears, that is, the content is close to or lower than the general lower limit of trace.The name is only qualitative.See the following provisions for quantitative or more specific names:
Trace 10~10 μ g/g
Trace 10~10 μ g/g
Nano trace 10~10 μ g/g
Trace sand 10~10 μ g/g
Microgram/gram trace analysis has another meaning, that is, use the sample weighing of microanalysis to determineTrace element(e.g.<10 μ g/g).In order to distinguish from the preceding word, the latter word should be called micro sample trace analysis.
Modern analysis
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Analytical chemistry is the science that studies the composition of substances, includingchemical analysis、instrumental analysisTwo parts.Chemical analysis is the foundation, and instrumental analysis is the development direction in the new century.
analytical chemistry
chemical analysisIncluding titrimetric analysis and weighing analysis, which is based on thechemical propertyTo determine the composition and relative content of the substance.
Although most contemporary analytical methods are instrumental analysis, some instruments were originally designed to simplify the inconvenience of classical methods, and the basic principles still come from classical analysis.In addition, sample configuration and other pre-processing still need the assistance of classical analytical techniques.Here are some classical analysis methods:
Titrimetry
Gravimetric analysis
Inorganic qualitative analysis
instrumental analysis
Analysis instrument[10]：Contemporary analytical chemistry focuses on instrumental analysis. There are several categories of commonly used analytical instruments, includingAtomic and molecular spectrometer，Electrochemical analysis instrument，nuclear magnetic resonance，X-ray, andMass spectrometer。Analytical chemical methods other than instrumental analysis are collectively referred to asClassical analytical chemistry。
Analytical chemistry is an important branch of chemistry, which mainly studies the elements or groups in substances (qualitative analysis);What is the quantity or purity of each ingredient（quantitative analysis)；How atoms are linked into molecules, how they are arranged in space, and so on.
Instrument analysis classification table
Methods of instrumental analysis: It is used to determine the composition and relative content of substances according to their physical properties or physicochemical properties.Instrument analysis can be divided intoelectrochemistryAnalysis, optical analysischromatographic analysis And other analytical methods.As shown in the right figure.
Qualitative, quantitative, structural, morphological, energetic, dynamic and other comprehensive information
Notes on analysis method
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Ideal condition
① The selectivity is the highest, so it has specificity, that is, there is little interference, so that the separation steps can be reduced or omitted;
③ With the highest sensitivity, small or trace components can be verified and determined;
④ The determination range is the widest, and both large and trace amounts can be determined;
⑤ The most elements and species can be determined;
⑥ The method is simple, that is, the most easy to operate without high skill;
⑦ Economical, that is, it requires less expenses and greater benefits.However, it is impossible to combine all the advantages of one method. For example, in gravimetric analysis, if you want to improve the accuracy, you need to extend the analysis time (for example, use the heavy precipitation method to purify the precipitation).Because the chemical method is required to measure the atomic weight accurately to 1/100000, it takes the most time.
Separation and enrichment methods
Although there are many sensitive and selective (even specific) methods, if the concentration of the element to be measured is close to or lower than that of the methodLower limit of determinationEnrichment is still inevitable.There are many enrichment methods, such as sublimation, volatilizationdistillationFoam flotation (seeTrace enrichment）、adsorbent(withmolecular sieve, activated carbon, etc.), chromatographyCoprecipitation, co crystallizationAmalgamAction, selective dissolutionsolvent extraction、Ion exchangeEtc.
Before detection or determination, it is often necessary to make the substance to be tested (or detected) andInterfering substanceSeparate from each other.Important separation methods include distillation, solvent extraction, ion exchangeElectrodialysis, precipitationelectrophoresisAnd most of them are the same as the enrichment method.Enrichment can be considered as a separation method to increase the concentration.
Concealed function (seeConcealment and unmasking）Although it is not separation, its function makes the ion lose its normal properties, that is, the ion exists in the reaction system in another form.However, in analytical chemistry, the purpose of separation is to make interfering ions no longer interfere, so in a broad sense, concealment and its opposite effect should be included in the scope of separation.Concealment and unmasking have been used in analytical chemistry for a long time.Gravimetric analysis, photometry and polarography have been applied, especially in the drop test and complexometric titration.
Sampling and sample decomposition
The most important requirement for sampling is representativeness, that is, the samples to be analyzed must be representative of all.Sampling of homogeneous or easily mixed substances is not a problem, and gaseous and liquid samples belong to this category.Uneven solid materials, such as ore and coal, shall be sampled according to the specified procedures.Otherwise, the analysis results cannot represent the raw materials, which is a waste of human and material resources.Field ore sampling is mostly carried out by geologists.The obtained large samples are crushed and reduced to small samples by analysts according to certain procedures in the laboratory.On the other hand, pure samples synthesized by combustion analysis of organic elements have no such problem[11]。
Sample melting is the second step.Melting includes dissolution and melting, also called decomposition.Some samples can be dissolved in water, acid orMixed acid, alkali, andOrganic solventMedium.If the above method cannot be dissolved, the flux can be used instead.Fluxes can be divided into alkaline (such as sodium carbonate), acidic (such as potassium bisulfate), oxidizing (such as sodium peroxide) and reducing (such as sodium thiosulfate).If the composition to be analyzed is easy to volatilize or the melting temperature is high, and the crucible is severely corroded, sintering can be used instead, that is, the particle surface is partially melted.Smith methodMix and sinter the silicate rocks with ammonium chloride and calcium carbonate (1:8-12) to determine the content ofalkali metalThis is an example.Organic compounds and biological samples can be ashed by dry method or wet method.Dry ashing is heating to carbonization and gradually burning in the presence of sufficient oxygen, or oxidizing with atomic oxygen at a lower temperature (low-temperature ashing).Wet ashing utilizes oxidizing acids (e.gnitric acidPerchloric acid, concentrated sulfuric acid).Dry method and wet method have their own advantages and disadvantages, which shall be determined according to the sample.
systematic error
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Control experiment
Control test is an effective method to check whether there is systematic error in the analysis process.The standard sample or pure substance with known content is used for parallel determination in the same method under the same conditions, and the results are corrected according to the error between the analysis results and the known content, which can reduce the systematic error[12]。
For the newly established analytical method, it is generally required to compare with the classical method, measure the same sample, and compare the precision and accuracy of the measurement results to judge the feasibility of the established method.
Recovery test
When the standard sample cannot be obtained, the accuracy of the analytical method isRecovery testTo measure the results.The recovery test is to first measure the content of a component in the sample with the established method, then take several identical samples (n ≥ 5), add a proper amount of pure products of the component to be tested, and determine them under the same conditions
The closer the recovery is to 100%, the smaller the system error is, and the higher the method accuracy is.The low recovery rate may be caused by improper sample preparation, incomplete extraction or systematic error of the method itself;The higher recovery rate may be related to the poor selectivity of the method, impurity interference and other factors.Recovery test is often used in the analysis of trace components.
Blank test
Blank testIt is an analytical test conducted with the same methods, instruments and reagents as the test sample, but without adding the sample.The results obtained become blank values. The blank values can be deducted from the analysis results of the test to eliminate the errors caused by impurities introduced by reagents, solvents and test vessels.
Development History
Although the name of analytical chemistry originated from Boyle, its practical application isChemical processIts history is also ancient.The high development of ancient smelting, brewing and other technologies is closely related to identification, analysis, production process control and other means.Alchemy and alchemy, which have sprung up in the East and West, can be regarded as the precursor of analytical chemistry.
The development of ancient chemistry
By 3000 BC, the Egyptians had mastered some weighing techniques.The earliest analytical instrument was the equal arm balance, which was recorded in the papyrus scroll in 1300 BC.The stone standard weights (about 2600 BC) kept by the Babylonian priests still exist.However, the equal arm balance was used for chemical analysis, which began in the oven assay in the Middle Ages.
Elements recognized in ancient times, including carbon and sulfur for nonmetals and copper, silver, goldiron, leadtinAnd mercury.In the fourth century BC, touchstones were used to identify the fineness of gold. In the third century BC, Archimedes used the density difference between gold and silver when solving the purity problem of the gold crown of Syracuse King Xilang II, which was a pioneer of non-destructive analysis.
Around AD 60, Pliny the Elder painted the Chinese nutgall extract on papyrus to detect the impurity iron of copper sulfate, which was the earliest organic reagent and test paper.As late as 1751, Eller von Brockhausen used the same method to detect the iron content in blood slag (after ashing).
Fire assay is an ancient analytical method.As far back as the 13th century BC,BabylonThe king sent a letter to the Egyptian pharaohAmenphis IVIt said: "The gold sent by your majesty has been reduced in weight after being put into the furnace..." This shows that people have known more than 3000 years ago“true gold does not fear fire”This fact.Philip VI of France once stipulated the steps of gold inspection, in which he proposed tobalanceConstruction requirements and use methods of.
18th and 19th centuries
Swedish chemists in the 18th centuryBergmann It can be called the founder of inorganic qualitative and quantitative analysis.He first proposed that metal elements can be separated and weighed in other forms besides metal state, especially the insoluble form in waterGravimetric analysisThe origin of meso wet process.
German chemistClaptottIt not only improves the steps of weight analysis, but also designs a variety ofNonmetallic elementDetermination steps.He accurately measured the composition of nearly 200 minerals and various industrial products such as glass and nonferrous alloys.
Representatives of analytical chemistry in the 18th centuryBezelius。He introduced some new reagents and techniques, and used "ashless filter paper", "lowash contentFilter paper "and" washing bottle ".He is the first oneAtomic weightA chemist who measured more accurately.In addition to inorganic substances, he also measured the "percentage of elements in organic substances".He paid particular attention to the blowpipe analysis, that is, a few samples were placed in the "carbon block recess" and heated with "oxidation" or "reduction flame" to observe their changes, so as to obtain qualitative knowledge about the samples.This method has been used until the 19th century. It has the advantages of being fast and requiring few samples. It can also be used for field exploration and mineral resources prospecting.
One of the outstanding figures in analytical chemistry in the 19th century wasFrazeniusHe founded an analysis instituteChemistrySchool (this school still exists today);And founded in 1862GermanHe has been the editor in chief of the magazine Analytical Chemistry.He wrote《qualitative analysis》、《quantitative analysis》The two books are compiled into various languages, includingPublished in the late Qing DynastyChinese translation of, named《Chemical examination》And《Chemical calculation》。He revised the "cationic hydrogen sulfide system" of qualitative analysis to five groups of, and also noted that "pH value is a key factor formetal sulfide Precipitation.stayCapacity analysisHe proposed to useTitration of ferric iron with tin dichlorideUntil the yellow disappears.
1663BoyleReported usingPlant pigmentAs an acid-base indicator, it is a pioneer in volumetric analysis.But the real capacity analysis should be attributed to Guy Lussac of France.In 1824, he published "Determination of effective chlorine in bleaching powder", using "sulfonated indigo" as an indicator.Then he titrated "plant ash" with sulfuric acid, and usedsodium chlorideTitration of "silver nitrate." These three works represent respectively redox titration, acid-base titration and precipitation titration.Complexometric titration method originated fromLiebig He titrated cyanide ion with silver.
Another outstanding contributor to capacity analysis is GermanyMohrThe "buret that can hold strong alkali solution" designed by him is still in use today.He recommendedoxalateAlkalimetricReference materialAmmonium ferrous sulfate (also called Mohr salt) is used as the reference material for redox titration.
The earliest "microanalysis" is "chemical microscopy", that is, to observe the "crystalline state", "optical properties", "particle size" and "spherical diameter" of samples or reactants under a microscope.Mid 17th centuryHookeHe was engaged in the research of microscopy and published Microscopic Atlas in 1665.In 1784, French pharmacist De Karozier used a microscope toChloroplatinic acidThe form of salt is different from potassium and sodium.GermanyIn 1747, the chemist Margraf confirmed that sucrose and beet sugar were the same substance with a microscope;Examined by microscope in 1756Platinum group metals。In 1891, Lehrman proposed thermomicroscopy, that is to observe the changes of crystals when exposed to heat under a microscope.KovlerAnd his wife designed two kinds of microscope heating tables to facilitate the research of drugs andOrganic compoundIdentification of.Later, it developed into an electron microscope with a resolution of 1 angstrom.
The earliest microanalyst who does not use a microscope should follow GermanyDe Bellina。He is engaged in "wet microanalysis", as well as pipe blowing and flame reaction, and has published the book "Experimental Technology of Microchemistry".The founder of modern microanalysis isamici , he designed and improved microChemical balanceTo make its sensitivity meet the requirements of micro chemical analysis;The new operation method was improved and proposed to realize the determination of milligram level inorganic samples, and it was confirmed that the accuracy of nanogram level sample determination was no less than milligram level determination.
The founder of organic micro quantitative analysis isPregelHe once isolated a degradation from bileproductThe amount is not enough for a constant hydrocarbon analysis.After listening to Emich's lecture on micro quantitative analysis in 1909 and visiting his laboratory, he decided to change the constant combustion method to the micro method (samples in milligrams) and achieved success;In 1917, he published Organic Microquantitative Analysis, and in 1923, he was awardedNobel Prize in Chemistry。
German chemistLongaIn 1850, the dye mixture was dropped on the blotting paper to separate it. Earlier, he used filter paper or cloth pieces dyed with starch and potassium iodide solution to make a drip test of bleaching solution.He added "yellow blood salt" to the middle part of the paper soaked with iron sulfate and copper solution, and then added a second drop after each drop was inhaled, so as to obtain a beautiful pattern generated by himself.In 1861, Shernbein's capillary analysis appeared. He dipped the filter paper strip into the water "containing several kinds of inorganic salts". The water carrying "salts" rose along the paper strip, with water rising the highest. Other ions were separated into connected bands according to their mobility.This is very similar to paper chromatography.His students have successfully studied the separation of organic compounds on filter paper, which can be clearly and completely separatedOrganic dye。
In the 1960s,weiss Ring furnace technology is proposed.Put the microgram sample into the filter paper, then wash it with solvent, then heat it on the outside of the filter paper to evaporate the solvent, and then separate it into several concentric rings.If the ion is colorless, sensitive color developer or fluorescent agent can be sprayed to detect and obtainSemiquantitativeresult.
Development overview
Fire assay is a well tested analytical method.As far back as the 13th century BC, the king of Babylon sent a letterEgyptian PharaohAmenphis IV said: "The gold sent by your majesty will lose weight after it is put into the furnace..." This shows that more than 3000 years ago people knew the fact that "true gold is not afraid of fire".In the 14th century, in Europe, the law stipulated that the pot assay was a means to test gold.HungaryKing Charles I once ordered every mining city to establish a fire assay laboratory.King of FrancePhilip VI once stipulated the steps of gold inspection, in which he also proposed the structural requirements and use methods of the balance used. For example, the balance should not be placed in a place exposed to wind or cold, and the user's breathing should not affect the balance weighing.
The book "Fire Art" published in 1540 has detailed the method of making baking bowls and blowing ashes.Soon afterwards, fire assay was extended to the analysis of some base metals, especially copper and lead ores.GermanyG. AgricolaIn the seventh chapter of his masterpiece Kunyu Gezhi, the fire assay is systematically described.This method, also called dry method, is applicable to metals that can be precipitated from samples in granular or button form, but not to nonmetals.
Qualitative and quantitative analysis Swedish chemistT. O. BergmanIt can be called the founder of inorganic qualitative and quantitative analysis.He first proposed that metal elements can be separated and weighed in other forms besides metal state, especially in the form that is insoluble in waterGravimetric analysisThe origin of meso wet process.At that time, there was no atomic weight and no molecular formula of compounds.His conversion factor was obtained directly from experiments.
German chemistM. H. ClaptoteNot only the steps of gravimetric analysis are improved, but also the steps of determining various non-metallic elements are designed.He accurately measured the composition of nearly 200 minerals and various industrial products such as glass and nonferrous alloys.
Representatives of analytical chemistry in the 18th centuryJ. J. Bezelius。He introduced some new reagents (such as hydrofluoric acid for decomposition of silicate rocks and determination of silica) and some new techniques, and used ashless filter paper, low ash filter paper and washing bottles.He was the first chemist to measure the atomic weight more accurately.In addition to inorganic substances, he also measured the percentage of elements in organic substances.He attached particular importance to the analysis of pipe blowing.Blow pipe analysis can be considered as the miniaturization of metallurgical operation, that is, a few samples are placed in the carbon block recess and heated with oxidation or reduction flame to observe its changes, so as to obtain qualitative knowledge about the samples.This method was used until the 19th century. It has the advantages of being fast, requiring few samples, and can also be used for field exploration and mineral resources prospecting.
One of the outstanding figures in analytical chemistry in the 19th century was CR. Frazenius, who founded an analytical chemistry school, still exists today;In 1862, he founded the German magazine Analytical Chemistry, and his descendants have continued to serve as the chief editor until now.His two books, Qualitative Analysis and Quantitative Analysis, were translated into many languages, including the Chinese version published in the late Qing Dynasty, which were respectively named Chemistry Textual Research and Chemistry Mathematics.He revised the cationic hydrogen sulfide system for qualitative analysis into five groups, and also noted the impact of pH on the precipitation of metal sulfide.stayCapacity analysisHe proposed to titrate ferric iron with tin dichloride until the yellow disappears.
Determine the content of pollutants in the air, such as NO2, SO2, CO, which not only affect the human respiratory tract, but also cause acid rain.Cadmium smoke will cause renal function decline, and excessive inhalation will lead to headache, dizziness, vomiting, chest pain and death.
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Doping test.
（5） , Criminal investigation
The content of trace elements in each person's hair is different, and the site can be judged by measurement
