First, note:
1. Avoid running microwave power transmissions without any sample or microwave absorbers. Even though the protection conversion of overloaded microwave energy has been designed in the CEM microwave system, absolute long-term no-load microwaves may still cause aging and damage to the magnetron and the sensor. Attempting to test the performance of a temperature and pressure sensor by applying microwave power under no-load conditions is wrong because air is a non-condensed matter and does not absorb microwaves.
2. The following samples are not suitable for use in microwave digestion vessels. It is forbidden to operate the following materials in the microwave system at will (according to CEM company , explosives ( TNT , nitrocellulose, etc.) propellant (肼, perchlorate, etc.) perchlorate · Glycol (ethylene glycol, propylene glycol, etc.) aviation fuel ( JP-1, etc.) pyrophoric chemicals , lacquer, ether (solder - ethylene glycol phenyl ether, etc.) acrolein (acetone, methyl ethyl ketone) Ethylene (butane, hexane, etc.) two-component mixture of acetylene compounds (nitric acid and phenol, nitric acid and triethylamine, nitric acid and acetone, etc.) glycerin nitrate, nitroglycerin or other organic nitrates
Second, the operation steps:
1. After starting the machine and before each running method, press the “P/T†button to check whether the temperature and pressure indication is normal: temperature T<50C. Press the "1" key to check the method before running the method. There must be a "CONTROL" display under "°C".
2 , the sample: digestion of the sample in a closed container, may be potentially dangerous, so in the early stage of the experiment for unknown samples should be identified by color and olfactory characteristics of the sample, whether it is flammable, volatile, and strictly control the sample size. According to the following guidelines: digestion of organic samples should be limited to ≤ 0.5 g / container, inorganic samples should be limited to ≤ 1.0 g / container.Precautions:
1 Unfamiliar sample sample size should be strictly limited to: within 0.5 grams.
2 The sample weight should be as consistent as possible.
3 In the same batch of reactions, different types of reaction tanks may not be mixed at the same time or samples of different natures may be mixed and digested.
4 Do not allow the sample to adhere to the wall of the container when loading . If it is adhered, rinse it into the solution with solvent or deionized water.
3. Adding acid: The amount of solvent in the lining of the capacity of 55 ml is 5 ml of acid (5 ml < total volume of solution < 20 ml).
Precautions:
1 Different reagent systems cannot be used simultaneously in the same batch of reactions (the same acid or solvent must be used in the same batch).
2 Solvent selection: HNO3 , HF and HCl are common acids during digestion . H2SO4 and H3PO4 will produce high temperature. When used, there should be strict temperature control. H3ClO4 is very dangerous in confined containers and is forbidden to use.
4 , container installation:
1 Make sure that each can has a pressure spring and tighten the lid of each can.
â‘¡ ensure that each lined tanks have been installed shell protective cover, protective cover while ensuring a dry state.
5 , load method load method or edit / create method edit / creative method - user directory USER Directory - selection method (or new method) - select sample type (Organic) - select control mode ( RAMP TO TEMPERATURE ) - - setting reaction process - named method according next-- - MEMO fill test (can be omitted) - return to the initial screen by the end of the next (this time both New method CURRENT mETHOD initial interface being displayed). Note: ( 1 ) Press “1†to check the method before running the method . “CONTROL†must be displayed under “°C†. And internationally published literature materials):
( 2 ) The CEM instrument can automatically adjust the power output, but should pay attention to the matching relationship between the power platform and the number of containers when setting the method: 6-25 cans ( 600W ), more than 25 cans ( 1200W ), and try to minimize power. in principle.
6 , placed:
1 The number of jars is more than 6 per experiment .
2 When using 6-16 cans, first discharge them in the inner ring and place them as evenly as possible.
3 When using 17-24 cans, it can be placed evenly on the outer ring.
4 When using 25-32 cans, place half of the cans evenly on the inner ring and the other half evenly on the outer ring. 5 When using 33-40 cans, fill the inner ring first, and place the rest evenly on the outer ring.
7 , press the star / pause button to start the digestion process
8. If abnormality is found during the digestion process, press the star/pause button to pause the program. Press the star/pause button again to continue.
Press the stop button to stop the digestion.
9. After the digestion process is completed, the instrument automatically enters the cooling process.
10 , container exhaust operation steps: the screen indicates that the temperature is lower than 80 ° C (as As , Hg and other elements need to be reduced to 60 ° C ), remove the digestion tank in the fume hood slowly open the cover to release the remaining pressure, then all spin Open the lid.
11 , and finally carry out related follow-up operations, including acid, transfer, constant volume and so on.
12 , Shutdown: Wait 15 minutes after the end of the reaction and then shut down.
Note: The switch is at least one minute apart.
Appendix 1 Control Mode Selection:
1, Standard Control standard temperature / pressure control: the target set temperature and pressure values, the fastest machines excited reaction, and reaches at the set control target value. Note: This mode is generally for CEM service personnel.
2 , Ramp to Temperature proportional temperature / time control: according to the set target temperature value, by changing the microwave emission power, the reaction temperature is reached and controlled at the set target temperature value. Note: This mode helps chemistry lab personnel to clearly understand the real-time reaction of chemical reactions, find the critical point of reaction and the optimal reaction conditions. This mode is widely used and is more suitable for digestion of unfamiliar samples. The above temperature is the critical decomposition temperature of the sample.
Low sugar / starch / carbohydrate: 140 ° C , protein: 145 ° C - 150 ° C , polysaccharide: 150 ° C , lipid / fat > 160 ° C -165 ° C ,
3 , Ramp to Pressure proportional pressure / time control: According to the set target pressure value, by changing the microwave emission power, the reaction is uniformly boosted and controlled to the set target pressure value. At the same time, the temperature sensing displays the corresponding temperature rise curve in real time. Note: This mode is suitable for the digestion of familiar samples and must be available with a pressure sensor.
4 , Power / Time proportional power / time control: Because this mode can not change the power value and time, the most primitive control method, not suitable for closed response. It is mainly suitable for specific methods and power tests using non-closed containers such as beakers. Closed reactions without temperature and pressure control may have serious consequences.
Appendix 2 : General principles for method content editing:
Digestion is generally recommended to use two-step digestion:
2 . The temperature of the digestion is determined by the rate of temperature rise: the first step is controlled within 20 ° C / min , and the second step is within 10 ° C / min . The heating time should be > (target temperature - temperature before temperature rise ) / heating rate
3 . The pressure is the default value and does not need to be modified.
note:
1 . If the sample is not digested (or extracted) after being digested (or extracted) by the recommended procedure, the original procedure should be adjusted as appropriate before the next experiment (appropriately increase the final retention time or increase the final temperature).
2 . In order to extend the life of the can, it should be done
(1) Samples that can be digested at low temperature do not need high temperature digestion
(2) The heating rate cannot be too high
(3) The holding time at high temperature should not be too long
Appendix 3 : Precautions when analyzing the machine
1. As / Hg (atomic fluorescence spectrometry): Digestion necessarily all measured Hg, As, not only to the whole digestion acid must rush to near dryness, and the same volume hydrochloric acid pH range (reducing agent must thiourea / Vc reducing joint ).
2. For heavy metals such as Pb , Cd and Cr , if the graphite furnace is tested, the conditions must be optimized:
( 1 ) The digestion solution first catches the acid, and roughly reaches 0.5-1mL according to the volume of the constant volume.
(2) Graphite furnace according to manufacturers recommendations and experiences with Matrix modifiers, such as Pb recommended matrix modifier concentration 10mg / mL of (NH4) H2PO4, sometimes combined with that concentration of 1mg / mL of Mg (NO3) 2, better
( 3 ) Conditions must be optimized, such as ashing temperature and atomization temperature.
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