Flame photometer
Flame photometer is based on the emission spectrum of an analytical instrument. Including: gas and flame burning part, optical part, photoelectric converter and test recording part. The process is sprayed into the flame atomized by the atomizer to stimulate luminescence, measured by the detector after the separation of emission intensity, which is proportional to the content of the test element in the sample. Such as: the salt placed in the flame photometer, the flame is yellow, which is due to the outer salt of sodium atoms in the electron absorption of flame heat, and transition to the excited level, and then by the excited level returned to normal When the electron will release the energy. The characterization of this energy emits the spectral line ring color spectrum that is characteristic of sodium atoms. The use of the heat of the flame to make a element of the atomic excitation light, and use the instrument to detect the strength of its spectral energy, and then determine the level of a substance in the material, such instruments called the flame photometer. Today, the more advanced flame photometer at the same time multi-element simultaneous analysis and testing, integrated air compressor built-in design, and with software records.
working principle
Flame photometric method according to the Roman formula for quantitative analysis, that I = aXc the b-th power, where I is the intensity of the line, c is the content of the element to be tested, d is the element to be tested with the evaporation, the excitation conditions B is a self-priming coefficient. Since the flame is used as an excitation light source, its temperature can be kept stable by controlling the flow of air and gas. Since the influence of the liquid sample and the sample component is small, A determination of a times is a more stable constant, generally due to the lower concentration of the sample, self-absorption can be neglected, so I = λc, and the relative strength of the measurement method can be used for analysis.
For flame photometric analysis, the test solution with a nebulizer into a sol into the flame, the element to be detected due to thermal dissociation to generate ground state atoms, the flame is excited to produce a spectrum, the monochromator is decomposed into monochromatic After light through the photoelectric system measurement, due to the relatively low humidity of the flame, it can only stimulate a few elements, and the resulting spectrum is relatively simple, less interference, flame photometric method is particularly suitable for the more easily excited alkali and alkaline earth metal determination .
In the determination of the flame in order to stabilize and eliminate some of the elements of the interference, often in the determination of the solution by adding "buffer", such as K, Ca, Mg exist at the same time on the determination of the impact, if these three elements dubbed saturated solution "Buffer" in the test solution is added to a certain amount, the impact is a single constant value, can be used as background subtraction, sodium measurement, the presence of a large number of HCO32- can result in low acid hydrochloric acid test solution can be used After heating to remove.
Application examples
1) sodium detection:
1 a) detection of sodium content in raw pine oil; 1 b) detection of sodium content in soil; 1 c) detection of sodium content in fuel oil (crude oil, gasoline, diesel) Detection of straw, forage sodium content;
2) Detection of sodium and potassium:
2a) Detection of sodium and potassium in silicate, mineral and metal mines; 2b) Detection of sodium and potassium in fruit juices;
3) potassium detection:
3a) detecting the potassium content in the fertilizer; 3b) detecting the potassium content in the plant sample; 3c) detecting the available potassium content in the soil; 3d) detecting the potassium content in the resin mixture; 3e) detecting the potassium content in the glass sample;
4) Lithium detection:
4a) testing of lubricating oil, grease in the lithium content;
5) Detection of calcium:
5a) Detection of calcium in beer; 5b) Determination of calcium in biological fluids; 5c) Assessment of calcium in milk; 5d) Simplest flame photometric measurement of calcium content; 5e) Detection of calcium in fruit juice; Detection of cookies, hard bread in the calcium content;
6) Barium detection:
6a) Simplest flame photometry of barium content;
7) Detection of base metal:
7a) Detection of alkali metal content in cement
8) Sulfate test:
8a) Simplest flame photometry of sulphate;
Influencing factors
Lamp current
Flame Atomic Absorption Spectrophotometer use mostly hollow light source cathode lamp, hollow cathode lamp operating parameters only one lamp current. Lamp current determines the size of the lamp radiation intensity. Increase the lamp current within a certain range can increase the radiation intensity, while lamp stability and signal to noise ratio also increased, but the instrument sensitivity decreased. If the lamp current is too large, it will cause the lamp itself to self-eclipse phenomenon and shorten the lamp life; will discharge is not normal, so that the lamp radiation intensity instability. Conversely, reducing lamp current within a certain range can reduce radiant intensity, improve instrument sensitivity, but reduce lamp stability and signal-to-noise ratio. If the lamp current is too low, will make the lamp radiation intensity weakened, leading to a serious decline in stability and signal to noise ratio can not be used. Therefore, the specific test work, such as the measured sample concentration is high, then the use of a larger lamp current, in order to obtain better stability; such as the measured sample concentration is low, then ensure the stability to meet the requirements of the premise, the use of Lower lamp current for better sensitivity.
Nebulizer role is to test fluid atomization. It is an important part of atomic absorption spectrophotometer, its performance on the determination of sensitivity, precision and chemical interference have a significant impact. The more stable the nebulizer spray, the more uniform the droplet, the higher the atomization efficiency, the higher the corresponding sensitivity, the better the precision and the less chemical interference. Atomizer adjustment is currently achieved by manually adjusting the relative position of the impinging ball and capillary. Detector should be adjusted to the atomizer atomization small and uniform, it is best to drop evenly in the impact of the ball around the distribution, if it can not be achieved, the impact of the ball to the center of the droplet can also be symmetrical distribution.
Increase the amount
Increase the size of the sensitivity level. Excessive or low lift will atomize the atomizer unstable. Each manufacturer's equipment to enhance the range of different, each have a certain range of changes. Increase the amount of increase measures are: (1) increase the gas flow to help increase. This increases the negative pressure to increase the amount of lift. (2) shorten the inlet tube length. Shorten the length of the inlet tube so that the tube resistance is reduced, so that the test fluid flow increases. Conversely, if you want to reduce the amount of lift, you can reduce the amount of co-combustion gas flow or increase the length of the injection tube.
Analysis line
There are many analysis lines for each element. Usually the resonance line has the highest sensitivity and is often used as the analysis line. However, the sensitivity line should be selected when measuring higher concentration samples. For example, sodium is measured as a = 589.0 nm for the analysis line and 330.0 nm for the higher concentration as the analysis line.
Burner position
Adjust the burner height and front and rear position so that the beam from the hollow cathode lamp passes through the maximum flame area of ​​free electron concentration where the sensitivity is highest and the stability is best. If you do not need high sensitivity, such as the determination of high concentrations of test solution, you can rotate the burner angle to reduce the sensitivity in order to facilitate the detection.
The type and status of the flame play an important role in the sensitivity. Different flames should be selected according to the characteristics of the tested element. The current flame by type has air - hydrogen flame, air - acetylene flame, nitric oxide - acetylene flame. Air - hydrogen flame flame temperature is low, used in the determination of flame easily atomized elements such as arsenic, selenium, etc .; air - acetylene flame flame temperature is used to determine the more difficult to dissociate the flame elements such as magnesium, calcium , Copper, zinc, lead, manganese, etc .; nitric oxide - acetylene flame is a high temperature flame, used in the determination of the flame is difficult to dissociate elements such as vanadium, aluminum and so on. Flames according to the state points poor flame, stoichiometric flame, rich flame. Flames of leanness refer to the flames when excess oxidant is used. This is due to the large amount of cold oxidant that removes the heat from the flame, which is lower in temperature and fully oxidizes, burns completely and has an oxidizing atmosphere, Determination of alkali metals. Stoichiometric flame is a stoichiometric combustion of fuel and oxidant ratio flame, it has the characteristics of high temperature, less interference, stability, low background, with the exception of alkali metals and easy to form refractory oxide elements, the most common elements Commonly used in this flame. The rich flame is the flame that uses excess fuel. Since the combustion is not complete and the flame has a strong reducing atmosphere, the flame is reducible and suitable for the determination of elements that are more likely to form refractory oxides such as molybdenum, rare earth elements, etc. .
When the measured element without adjacent interference lines, such as potassium, sodium, etc., can use a larger slit. When the measured element has a nearby interference line, such as calcium, iron, magnesium, etc., can be used smaller slit. The above factors affect the sensitivity of opposites. In the specific testing, inspectors should consider several factors, according to the instrument and the sample under test to adjust several factors in order to achieve the best working condition.
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