Flame photometer is an analytical instrument based on emission spectrometry. It uses flame as the excitation light source, and uses a photoelectric detection system to measure the radiation intensity emitted by the excited elements when they return from the excited state to the ground state. It judges the element category and content according to its characteristic spectrum and light wave intensity.It includes gas and flame combustion part, optical partPhotoelectric converterAnd test record.The temperature of the flame is relatively low, so only a few elements can be excited, and the spectrum obtained is relatively simple, with less P disturbance.Flame photometryIt is especially suitable for the determination of alkali metal and alkaline earth metal elements that are easily excited.[1]
Flame photometryYes PressRoman goldThe formula is used for quantitative analysis, that is, I=the b-power of aXc, where I is the intensity of the spectral line, c is the content of the element to be measured, and a is the evaporationExcitation conditionRelevant constants;B is the self absorption coefficient, because the flame is used as the excitation light source, its temperature can be kept stable by controlling the flow of air and gas, and because the liquid sample is used, the sample composition has less influence, so a is a relatively stable constant in each measurement, generally because the sample concentration is low, self absorption can be ignored, so I=λ c, and can be usedRelative strengthAnd the measurement method of.
Conduct flamePhotometric analysisUse the liquid to be measuredAtomizerTurn it into a sol and introduce it into the flame. The element to be measured is generated by thermal dissociationGround state atom, excited in the flame to produce spectrumMonochromatorDecompose intoMonochromatic lightThen measured by the photoelectric system, because the temperature of the flame is relatively low, only a few elements can be excited, and the spectrum obtained is relatively simple with less interference,Flame photometryEspecially suitable for those easy to be excitedalkali metalandalkaline-earth metalDetermination of
In order to stabilize the flame and eliminate the interference of some elements during the determination, it is often necessary to add“Buffer”For example, the simultaneous existence of K, Ca and Mg has an impact on the determination. If these three elements are mixed into a saturated solution as a "buffer", when added to a certain amount in the test solution, the impact is a single constant value, which can be used as background deduction. When measuring sodium, the presence of a large amount of HCO32 can make the result low, and can be removed by heating after acidification of the test solution with hydrochloric acid
Application examples
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1) Sodium detection:
1a) Detection of sodium content in raw pine oil;1b) Detect exchangeable sodium content in soil;1c) Test fuel（crude oil, gasoline, diesel);1d) Test the sodium content in the glass sample;1e) Detection of sodium content in straw and forage;
2) Detection of sodium and potassium:
2a) Detection of sodium and potassium content in silicate, inorganic ore and metal ore;2b) Detect the content of sodium and potassium in fruit juice;
3) Detection of potassium:
3a) Detection of potassium content in fertilizers;3b) Detection of potassium content in plant samples;3c) Detect available potassium content in soil;3d) Detect the potassium content in the resin mixture;3e) Detect the potassium content in the glass sample;
4) Lithium detection:
4a) Test the lithium content in lubricating oil and grease;
5) Calcium detection:
5a) Detection of calcium content in beer;5b) Detection of calcium content in biological liquid;5c) Evaluate the calcium content in milk;5d) The simplest flame photometric measurement of calcium content;5e) Detection of calcium content in fruit juice;5f) Detection of calcium content in biscuits and hard bread;
6) Barium detection:
6a) The simplest flame photometric measurement of barium content;
7) Detection of base metal:
7a) Detection of alkali metal content in cement
8) Sulfate detection:
8a) The simplest flame photometric measurement of sulfate;
influence factor
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Lifting amount
The amount of lifting affects the sensitivity.Too high or too low a lift will causeAtomizerThe atomization is unstable.The range of instrument lifting capacity of each manufacturer is different and has a certain range of variation.The methods to increase the lifting capacity are: (1) increase the flow of auxiliary gas.This increases the negative pressure to increase the lifting capacity.(2) Shorten the length of the injection tube.Shortening the length of the injection tube reduces the resistance of the tube and increases the flow rate of the test solution.On the contrary, if you want to reduce the lifting amount, you can reduce the flow of auxiliary gas or lengthen the length of sample injection tube.
Analytical line
Of each elementAnalytical lineThere are many, usuallyResonance lineIt has the highest sensitivity and is often used as an analytical line, but when measuring samples with higher concentrations, it is necessary to choose thisSensitive line。 For example, a=589.0nm is used as the analytical line for sodium determination, and 330.0nm is used as the analytical line for higher concentrations.
Burner position
adjustburnerHeight and fore and aft position, so thatHollow cathode lampBeam passingfree electronIn the flame zone with maximum concentration, the sensitivity is the highest and the stability is the best.If high sensitivity is not required, such as when measuring high concentration test solution, the sensitivity can be reduced by rotating the burner angle to facilitate detection.
flame
Flame type and state play an important role in sensitivity, and different flames should be selected according to the characteristics of the measured elements.Flames are divided into air by type -- hydrogen flame, air--acetyleneFlamenitric oxide--Acetylene flame.Air hydrogen flameflame temperature Low, used to determine elements easy to atomize in the flame, such as arsenic, selenium, etc;The air acetylene flame belongs to the medium temperature flame, which is difficult to measuredissociationSuch as magnesium, calcium, copper, zinc, lead, manganese, etc;Nitric oxide -- acetylene flame is a high temperature flame, which is used to determine elements in the flame that are difficult to dissociate, such as vanadium, aluminum, etc.The flame can be divided into lean flame, stoichiometric flame and rich flame according to the state.Lean flame refers to the flame when excessive oxidant is used. Because a large amount of cold oxidant takes away the heat in the flame, the flame temperature is low, and because the oxidant is sufficient, the combustion is complete, and the flame has an oxidizing atmosphere, this flame is suitable forAlkali metal elementDetermination of.The stoichiometric flame is the flame burning at the ratio of fuel and oxidant calculated according to the stoichiometric relationship. It is characterized by high temperature, less interference, stability and low backgroundalkali metalAnd elements that are easy to form refractory oxides. Most common elements use this flame.Rich flame is a flame that uses excessive fuel. Due to incomplete combustion, the flame has a strongReducing atmosphereTherefore, this flame hasReducibility, applicable to the determination of elements that are easy to form refractory oxides, such as molybdenumrare earth elementEtc.
slit
When the measured element has no adjacent interference line, such as potassium, sodium, etc., a large slit can be used.When the measured element has adjacent interference lines, such as calcium, iron, magnesium, etc., a smaller slit can be used.The above factors affecting sensitivity are unity of opposites.In the specific testing work, the testing personnel should consider several factors as a whole, and adjust several factors according to the conditions of the instrument and the tested sample to achieve the best working condition.
difference
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The flame photometer uses the principle of atomic emission to atomize the corresponding substances (solid is prepared into a solution, such as dissolving with acid. The liquid is at high temperature, and the gas is excited under the condition of discharge). The excited electrons are highenergy level, instability willtransitionreturnground state, different atomsElectronic energy levelDifferent, light waves of different wavelengths will be emitted during the transition. By analyzing the light waves, we can know what the atoms are.Similarly, the intensity of light waves can be analyzed to determine the content of the atom.For example, FPT-640 flame photometer (generally equipped with potassium and sodium detector) is used to analyze potassium and sodium in blood, as well as in silicic acid industry.Ultraviolet visible spectrophotometerIt is based on the absorption principle. The ultraviolet region (200-400) is generally used to analyze organic substances. Some specific functional groups will have absorption (molecular absorption). It is often used to measure the content of preservatives. Generally, the maximum absorption of wavelength is used. However, when there are multiple substances absorbing, it is often used to scan a single sample completely, then measure a composite sample, and take multiple points for calculation,You can know the content of different substances (this is a master's thesis of a teacher);The visible area (400-760) is generally used to analyze ions, just like the generalSpectrophotometerSame as 721 type.
1）flame temperature : If the temperature is too low, the sensitivity will decrease; if the temperature is too highalkali metalSerious ionization, impact
Flame (about 1900 ℃) is more suitable and convenient
-Ratio of fuel gas to auxiliary fuel gas: keep appropriate
-Sample solution suction amount: if it is too large, the flame temperature will drop
2）gas pressure : The gas pressure shall be kept constant during measurement.
3）Sprayer: The sprayer is not clean, which may cause poor atomization of the test solution. The test solution must be clear during the determination, and the sprayer must be cleaned with water or ethanol at any time.
4) Liquid level height: the change of liquid level height will cause the change of element concentration after excitation, and the test height shall be kept consistent during measurement.
1) Ionization and self absorption of elements can lead to bending of calibration curve and narrowing of linear range.For example, the self absorption of potassium is serious at high concentration, which makes the calibration curve curve to the abscissa direction;At low concentrationsionizationIncrease, radiation increases, and the correction curve bends to the ordinate direction.
2) Coexistence in the sampleion pairDetermination has influence, such asalkali metalThe spectral lines are enhanced when they coexist, which leads to higher results.
3) The physical properties of the sample shall be consistent withstandard solution The composition of is consistent
