Atomic fluorescence solution configuration
The preparation of the atomic fluorescence standard solution is a dilution process, and the high-concentration standard solution to be purchased is diluted to the required concentration as required, and becomes a concentration sequence, and the measured atomic fluorescence value is linearly determined.
Therefore, the preparation of the solution will directly affect the accuracy of the verification results. Since the measurement conditions of arsenic and antimony are basically the same, the two elements can be simultaneously determined. Therefore, the JJG939-2009 “Atomic Fluorescence Spectrometer” verification procedure requires the preparation of a mixed standard solution of two elements. The preparation reagents and solution preparation methods provided in JJG939-2009 are relatively simple. The following is a summary discussion on the preparation, storage and precautions of the standard solution for atomic fluorescence photometer verification.
1. Reagents and their properties for atomic fluorescence spectrophotometry
1. Hydrochloric acid: excellent grade pure (GR)
Concentrated hydrochloric acid is a colorless or slightly yellow volatile liquid with a pungent odor. It is miscible with water and soluble in lye. The operation should be carried out in a fume hood.
2. Potassium borohydride (borohydride)
The purity is not less than 95%. White to off-white fine crystalline powder or lump, which is highly hygroscopic and therefore needs to be stored together with a desiccant. Soluble in water, liquid ammonia, insoluble in ether, benzene, hydrocarbons, stable in nature, strong in reducibility, and its solution is mainly used as a reducing agent. Because the potassium borohydride solution is easily decomposed by light, the solution needs to be stored in a brown bottle in the dark.
3. Potassium hydroxide (sodium hydroxide)
Analytically pure (AR) is used to protect potassium borohydride. It is a white crystal at room temperature, it is water-absorbing and highly corrosive; it is easily soluble in water and emits a lot of heat.
4. Thiourea: Analytically pure (AR)
White bright bitter crystal, soluble in cold water, ethanol, slightly soluble in ether, solubility in water at 20 ° C is 137g / L. It is toxic and can be absorbed by contact with the skin. Therefore, avoid contact with the skin when formulating the solution.
5. Secondary deionized water
Refers to the water obtained by sub-boiling distillation of deionized water, which is generally used in physicochemical or analytical tests. Among them, the water prepared by the ion exchange method is called deionized water, and the deionized water is not water without ions, but water obtained by ion exchange without disturbing ions and having a neutral pH (interfering ions generally refer to calcium, Magnesium, carbonate, sulfate, etc., but the organic matter normally contained in deionized water cannot be removed). Deionized water is different from distilled water. The distillation method can only remove non-volatile substances in water, and can not remove the gas dissolved in water. The purity of distilled water is generally not as good as that of deionized water. The deionized water has lower conductivity than distilled water. Under normal circumstances, ordinary quantitative analysis of distilled water can be used, instrument water is generally selected according to the results of the magnitude of water, the minimum standard is deionized water, here because the result is relatively high in magnitude, so the use of secondary deionized water.
6. Standard solution
Standard stock solution of arsenic (GBW08611, 1000μg/mL, U=1μg/mL, k=2, China Measurement Science Research Institute), 锑 (GBW (E) 080545, 100μg/mL, U=1%, k=2).
2. Equipment required for reagent preparation for atomic fluorescence photometer verification
1. Balance: The maximum weight is 200g or 500g, and the division value is not more than 0.1g.
2. Glass measuring tools (Grade A): 100mL, 200mL, 1000mL capacity bottles; 100mL, 500mL beakers; 1mL, 5mL, 10mL, 20mL pipettes or pipettes; glass rods.
3. Other experimental instruments.
Third, the atomic fluorescence photometer verification reagent preparation, preservation and precautions
1. The principle of action of reagents for atomic fluorescence photometer verification
JJG939-2009 stipulates that a standard solution of arsenic and antimony should be prepared. The key to the determination of arsenic and antimony is the reduction of As(V) and Sb(V) to hydrides. As(V) and Sb(V) react with potassium borohydride for a longer period of time, and As(III) and Sb(III) are more likely to form a hydride. The pretreatment should reduce the pentavalent arsenic and antimony to trivalent, so it is necessary to add thiourea and ascorbic acid for prereduction. JJG939-2009 stipulates that 100g/L thiourea aqueous solution should be added when formulating standard solution. Ascorbic acid is not mentioned because the function of ascorbic acid is to make the solution more stable and promote reduction. The role of thiourea is reduction and Cu2+Co3+, The Ni2+ plasma acts as a masking effect, and the reduction effect of thiourea and ascorbic acid together is better. According to the requirements of JJG939-2009, the standard solution prepared needs to be used now, and the addition of ascorbic acid has no effect.
During the analysis, the potassium borohydride solution was added simultaneously under acidic conditions, and the following reaction occurred:
E is a hydride element (arsenic, antimony), and m may or may not be equal to n.
After the formed hydride is atomized, it is excited by the light energy of the source to transition to a higher energy level, and radiates atomic fluorescence while returning to a lower energy level.
It should be noted that potassium borohydride is a strong reducing agent, which is easily decomposed under neutral and acidic conditions, reacts with oxygen and carbon dioxide in water or air, and is easily decomposed by light. The addition of potassium hydroxide to the solution allows it to be present more stably, and maintaining it at a low temperature slows its decomposition. At the same time, potassium hydroxide easily reacts with silicon in the glass to form sodium silicate, so the prepared solution is stored in a plastic bottle to maintain the effective concentration of the solution. If it is used now, it will have little effect on glassware.
2. Preparation of reagents for atomic fluorescence photometer verification
(1) Preparation of 100g/L thiourea solution
Take the preparation of a 100 mL solution as an example. Weigh 10g thiourea (white crystalline solid, put it in a small beaker and weigh it by differential method) on the analytical balance, dissolve it with a small amount of secondary deionized water, gently stir the glass rod, if the dissolution is not complete, please use a suitable water bath. Heat, but not too high. The dissolved thiourea solution was transferred to a 100 mL volumetric flask using a glass rod to volume. In the preparation of the thiourea solution, ascorbic acid may be added or not.
(2) Preparation of 100 ng/mL standard storage solution of arsenic and antimony
The step-by-step dilution method can reduce errors and improve accuracy. Therefore, when diluting the arsenic and antimony standard solutions, it is diluted in two steps to obtain a standard stock solution. Pipette 1 mL of arsenic standard solution and 10 mL of hydrazine standard solution into a 100 mL volumetric flask with a pipette or pipette, and dilute to volume with secondary deionized water to prepare 10 μg/mL arsenic and bismuth standard intermediate solution. Then, 1 mL of the prepared 10 μg/mL arsenic and bismuth standard intermediate solution was taken in a 100 mL volumetric flask, and the volume was adjusted with secondary deionized water.
(3) Preparation of standard mixed solution of arsenic and antimony
Pipette 100 ng/mL arsenic and bismuth standard stock solutions 0 mL, 1.0 mL, 5.0 mL, 10.0 mL, 20.0 mL in a 100 mL volumetric flask, and add 100 mL/L thiourea solution 20 mL, respectively. 10 mL of hydrochloric acid was diluted to the mark with secondary deionized water.
(4) Preparation of 5% hydrochloric acid solution
Take 50 mL of concentrated hydrochloric acid in a measuring cylinder, dilute with about 200 mL of secondary deionized water, then transfer to a 1000 mL volumetric flask and dilute with secondary deionized water.
(5) Preparation of potassium borohydride solution
The concentration of potassium borohydride is determined by the concentration of the element to be measured. The concentration of the carrier liquid acid is determined by the concentration of potassium borohydride, and the final waste liquid is acidic. In the daily test, the preparation of 1.5% potassium borohydride solution basically meets the verification requirements. The specific preparation method is as follows: 15 g of potassium borohydride is weighed and dissolved in 200 mL of secondary deionized water previously added with 5 g of potassium hydroxide on an electronic balance, stirred until dissolved, and transferred to a 1000 mL volumetric flask by a glass rod for drainage, and then used twice. Dilute the deionized water to the mark.
3. Precautions in solution preparation
(1) The glass measuring tool used in the preparation of the solution is based on the analysis side.
The method is different for cleaning. Glassware for the determination of trace elements, first brushed with a brush, rinse off the soluble matter with water and brush off the dust adhering to the surface, then immerse the dropper, pipette, small test tube in a 10% nitric acid solution for more than 8 hours. Then rinse with pure water. When the washed glassware is set down, the water should flow out of the vessel wall without water drops. At this point, the glassware was washed 3 times with a small amount of pure water, and the impurities brought by the tap water were washed away and drained naturally.
(2) The unit of the solution to be carefully formulated is the mass concentration or the volume concentration.
(3) After the solid reagent is dissolved in the beaker, it is drained into the volumetric flask with a glass rod, and the beaker and the glass rod are washed several times with the secondary deionized water, and the washing water is also poured into the volumetric flask. The beaker and the volumetric flask are at least cleaned. 3 to 4 times.
(4) When the volume is set, first dilute with deionized water to dilute to about 3/4 volume, then shake the volumetric flask several times (do not shake it) for preliminary mixing. Then add the secondary deionized water to the near mark and add it a little bit to make the concave surface of the solution tangent to the volumetric line of the volumetric flask. Then use a glass stopper to refill the volumetric flask back and forth several times to mix the solution well.
(5) When using a pipette or a pipette to measure the reagent, it must be rinsed 2 to 3 times with the desired solution.
(6) When the solution is aspirated, the lower mouth of the pipette or pipette should not be too shallow or too deep to be inserted into the solution to be taken. If it is too shallow, it will cause suction, and the solution will be sucked into the earball to stain the solution. Deeply, it will stick too much solution outside the tube.
(7) In order to reduce the measurement error, the pipette should use the top scale as the starting point each time, and release the required volume downwards instead of how much volume is taken. Except for the blow-off pipette, a small amount of solution remaining at the end of the pipette can not be forced to flow out by external force.
(8) Before using the volumetric flask, test the leak, that is, put tap water in the bottle near the marking line, cover the plug, hold the stopper by hand, and stand the volumetric flask to observe whether there is water seepage in the bottle mouth. If it does not leak, After erecting the bottle, turn the stopper about 180° and then stand up again.
(9) Do not use the volumetric flask to store the prepared solution for a long time. If the prepared solution needs to be stored for a long time, it should be transferred to a clean grinding reagent bottle.
(10) When the volumetric bottle is not used for a long time, it should be washed. Put the stopper on the paper pad to prevent the stopper from opening after a long time.
(11) The concentration of the reducing agent is determined by the sample, and the concentration of the carrier liquid is determined by the concentration of the reducing agent, and finally the waste liquid is acidic. If it is not acidic, potassium borohydride will precipitate at the lowest point of the pipeline and then clog.
(12) Food should not be placed in the laboratory to avoid cross-infection.
(13) If you are suspicious of the concentration of potassium borohydride solution and carrier fluid, you can use pH test paper to test it. If the waste liquid is acidic, it will meet the experimental requirements; if the waste liquid is alkaline, the potassium borohydride solution The concentration is too high.
(14) The standard stock solution can also be prepared with 5% hydrochloric acid, the solution properties will be more stable and can be stored for a long time.
4. Preservation of solution for atomic fluorescence
In addition to the standard stock solution can be stored for 6 months at 0 ~ 5 ° C, other solutions are best used now.
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