HAWACH To Talk About The 30 FAQs About HPLC Column (Chapter 3)

Q11: What are the reasons for retention time drift?
There are two different situations for retention time which does not reproduce: retention time drift and retention time fluctuation. The former means that the retention time only changes in one direction, while the latter means that there is no fixed fluctuation in retention time. Separating these two situations is often helpful in finding the cause of the problem.

For example, retention time drift is often caused by HPLC column aging, which is unlikely to cause irregular fluctuations in retention time. In fact, most of the reasons for the retention time drift are column aging of different mechanisms, such as loss of stationary phase (for example, through hydrolysis), HPLC column contamination (caused by the sample or mobile phase), etc.

Several common reasons for retention time drift are as follows:

1. HPLC Chromatographic column equilibrium
If we observe retention time drift, we should first consider whether the HPLC column has been completely equilibrated with the mobile phase. Usually, 10-20 column volumes of mobile phase are required for equilibration, but if a small number of additives (such as ion-pair reagents) are added to the mobile phase, it takes a considerable amount of time to equilibrate the HPLC column.

Mobile phase contamination may also be one of the reasons. A small number of contaminants dissolved in the mobile phase may slowly accumulate on the HPLC column, causing drift in retention time.

2. The stability of the stationary phase
The stability of the stationary phase is limited, even if it is used within the recommended pH range, the stationary phase will slowly hydrolyze. For example, the silica gel matrix has good hydrolytic stability at pH 4.

The rate of hydrolysis depends on the type of mobile phase and the ligand. Bifunctional ligands and trifunctional ligands are more stable than monofunctional ligands; long-chain bonds are more stable than short-chain bonds; alkyl bonds are more stable than cyano bonds. Cleaning the column frequently will also accelerate the hydrolysis of the HPLC column stationary phase. Other silica-based bonded phases can also undergo hydrolysis in aqueous solutions, such as amino bonding.

3. HPLC Chromatographic column pollution
Another common cause of retention time drift is column contamination. HPLC chromatographic column is a very effective adsorption filter, which can filter and adsorb any substance carried by the mobile phase. Sources of contamination can be the mobile phase itself, the mobile phase container, connecting tubes, pumps, injectors and instrument seals, and samples. The source of pollution can usually be determined through experiments.

If there is a strong component remaining on the HPLC column in the sample, it may be a potential source of retention time drift. These roots are usually the sample matrix. A simple way to avoid column contamination is to prevent it from happening. A strong solvent under the given chromatographic conditions is usually used, but not all contaminants can be dissolved in the mobile phase. Using guard columns is a very effective method. Backflushing the column is only a last resort.

4. Composition of the mobile phase
The slow change in mobile phase composition is also a common cause of retention time drift. For example, the volatilization of volatile components in the mobile phase is equal to the circulating flow.

5. Hydrophobic collapse
When a reversed-phase packing HPLC column with a small pore size and good end-group sealing uses nearly 100% water as the mobile phase, sometimes a sudden loss of separation occurs and the retention of the analyte is significantly reduced or not retained at all. This is called hydrophobic collapse.

This phenomenon is caused by the mobile phase not infiltrating the surface of the stationary phase. The salvage method is to infiltrate the stationary phase with a mobile phase containing a large number of organic components and then balance it with a mobile phase with high water content.

This phenomenon can also occur with long-term column storage. The use of reversed-phase HPLC columns with embedded polar groups (such as Waters SymmetryShield RP HPLC columns) or non-end-sealed HPLC columns (such as Waters Resolve HPLC columns) can also avoid collapse.

Q12: Why are there shoulders or forks?
①The sample volume is too large: use the mobile phase to prepare the sample, the total sample volume is less than 15% of the first peak;
②Sample solvent is too strong: use a weak sample solvent;
③The HPLC column collapses or forms a short-circuit channel: replace the HPLC chromatographic column, using weaker corrosive conditions;
④The sintered stainless steel in the HPLC column fails: replace the sintered stainless steel, add an online filter, and filter the sample;
⑤The injector is damaged: replace the injector rotor.

Q13: Why is there a ghost peak?
①Residual peaks of the injection valve: clean the valve with a strong solvent after each use to improve the cleaning of the valve and the sample;
②Unknown in the sample: processing the sample;
③The column is not equilibrated: re-equilibrate the HPLC column, using the mobile phase as the sample solvent (especially ion pair chromatography);
④Trifluoroacetic acid (TFA) oxidation: freshly prepared every day, with antioxidants;
⑤Water pollution (reverse phase): check the water quality by changing the equilibrium time, and use HPLC grade water.

Q14: Why is there peak tailing?
①Column overload: reduce the sample volume, increase the column diameter and use a higher capacity stationary phase;
②Peak interference: clean the sample and adjust the mobile phase;
③The role of silicon hydroxyl group-add triethylamine: passivate the HPLC column with alkali, increase the concentration of buffer or salt, lower the PH value of the mobile phase, and purify the sample;
④The sintered stainless steel in the HPLC column fails: replace the sintered stainless steel, add an online filter, and filter the sample;
⑤The column collapses or forms a short-circuit channel: replace the HPLC chromatographic column, using weaker corrosive conditions;
⑥The dead volume or the volume outside the column is too large: the connection point is reduced to very low. Make appropriate adjustments to all the connection points, and use the connection pipe with a thin inner diameter as much as possible;
⑦Decreased column efficiency: replace columns with lower corrosion conditions and use protective columns.

HAWACH To Talk About The 30 FAQs About HPLC Column (Chapter 3)

Description, Principle And Use Of SPE Cartridge

The SPE cartridge is a sample pretreatment device developed from the chromatography cartridge for extraction, separation, and concentration. It is mainly used in sample pretreatment of target compounds in various food, agricultural and livestock products, environmental samples, and biological samples.

Reuse of SPE cartridge
It is mainly used in sample pretreatment of target compounds in various food, agricultural and livestock products, environmental samples and biological samples.

Before choosing, you must first understand this knowledge:

1. Selection of cartridge pressure for solid phase extraction
The cartridge pressure can be divided into a reduced pressure, pressurized, and normal pressure. The reduced pressure cartridge can reduce the amount of stationary phase silica gel used. The disadvantages are: a large amount of air passing through the silica gel will volatilize the solvent (sometimes there is condensation outside the SPE cartridge); it may cause the loss of easily decomposable substances; the use of air pumps will extend the extraction time through the cartridge and increase noise. SPE cartridge pressurization is a better way to use, especially suitable for the separation of easily decomposable samples.

The pressurization can increase the flow rate of the eluent and reduce the product collection time. The disadvantages are: reduce the number of trays in the cartridge; if the pressure is too high, the solvent flow rate is too fast and the separation effect is reduced, so cartridge pressurization is used in the separation of ordinary organic compounds. More applicable. When other conditions are the same, the atmospheric cartridge has high efficiency but time-consuming, such as the separation of natural compounds.

Size selection of SPE cartridge
The ideal type of SPE cartridge should be larger in inner diameter and length. As the cartridge length increases, the corresponding number of trays is higher, the cartridge inner diameter is larger, and the origin of the sample after injection is smaller (reflected on the cartridge, the sample layer is thinner), and the resolution becomes larger. The disadvantage is that the use of an extraction cartridge with a larger inner diameter requires more silica gel and solvent, which increases the cost of the experiment.

The ratio of diameter to length of commonly used extraction cartridges is generally 1:5 to 1:10, and the amount of stationary phase silica gel is 30 to 40 times that of the sample. The shorter the extraction cartridge has a smaller inner diameter, the corresponding number of plates is lower, and the origin of the sample after injection is larger (reflected on the cartridge, the sample layer is thicker, and the sample layer is less than 0.5 cm in the SPE cartridge. It is easier to separate completely), and the degree of separation becomes smaller.

If the separation of the required components and impurities is large (the required component separation R>1), use an extraction cartridge with less silica gel and a smaller inner diameter (for example, use a 2cm×20cm cartridge for a 200 mg sample); if The required group and impurity separation are small (required component separation R<1), the inner diameter of the extraction cartridge can be enlarged, and the eluent with smaller polarity can also be used.

Principle and use
The solid phase extractor uses a solid adsorbent to adsorb the target compound in the liquid sample, separate it from the sample matrix and interfering compounds, and then use the eluent for elution or heat desorption to achieve the purpose of separating and enriching the target compound. Compared with liquid-liquid extraction, solid-phase extraction has many advantages: solid-phase extraction does not require a large number of immiscible solvents, and no emulsification occurs during the treatment process.

It uses a highly selective adsorbent (stationary phase), It can significantly reduce the amount of solvent, simplify the sample processing process, and reduce the cost. Generally speaking, the time required for solid-phase extraction is 1/2 of liquid-liquid extraction, and the cost is 1/5 of liquid-liquid extraction. The disadvantage is that the recovery rate and precision of the target compound are lower than that of liquid-liquid extraction. The mode and principle of solid phase extraction. Solid phase extraction is essentially a liquid chromatography separation.

Its main separation mode is the same as that of liquid chromatography and can be divided into normal phase (the polarity of the adsorbent is greater than the polarity of the eluent), reverse phase (the polarity of the adsorbent is less than that of the eluent), ion exchange and adsorption. The adsorbent used in solid phase extraction is also the same as the stationary phase commonly used in liquid chromatography but differs in particle size. The adsorbents used in normal-phase solid phase extraction are all polar, used to extract (retain) polar substances.

How the target compound remains on the adsorbent during normal phase extraction depends on the interaction between the polar functional groups of the target compound and the polar functional groups on the surface of the adsorbent, including hydrogen bonds, π-π bond interactions, and dipoles. -Dipole interaction and dipole-induced dipole interaction and other polarity-polarity interactions. Normal phase solid phase extraction can adsorb polar compounds from non-polar solvent samples.

The adsorbents used in reversed-phase solid-phase extraction are usually non-polar or weakly polar, and the extracted target compounds are usually medium-polar to non-polar compounds. The effect between the target compound and the adsorbent is hydrophobic interaction, mainly non-polar-non-polar interaction, van der Waals force, or dispersion force. The adsorbent used in ion exchange solid phase extraction is a charged ion exchange resin, the target compound to be extracted is a charged compound, and the interaction between the target compound and the adsorbent is electrostatic attraction.

Description, Principle And Use Of SPE Cartridge

Characteristics Of Several Commonly Used Filter Membranes

1. Nylon
Features: Good temperature resistance, can withstand 121 ℃ saturated steam hot-press sterilization for 30min, the maximum working temperature is 60 ℃, good chemical stability, can withstand dilute acid, dilute alkalies, alcohols, esters, oils, hydrocarbons Various organic and inorganic compounds such as halogenated hydrocarbons and organic oxides.
Uses: Electronics, microelectronics, semiconductor industry water filtration, tissue culture medium filtration. Chemical liquid filtration, beverage filtration, high-purity chemical products filtration. Filtration of aqueous solution and organic mobile phase.

2. Polyvinylidene fluoride film (PVDF)
Features: Membrane filter can not tolerate acetone, DMSO, THF, DMF, dichloromethane, chloroform, and so on.
Uses: Hydrophobic polyvinylidene fluoride membrane is mainly used for gas and steam filtration, high-temperature liquid filtration;
Hydrophilic polyvinylidene fluoride membranes are mainly used for purification and filtration of sterilization filtration solvents and chemical raw materials such as tissue culture media and additives, aseptic treatment of reagents, and filtration of high-temperature liquids.

3. Mixed cellulose ester (MCE)
Features: relatively uniform pore size, high porosity, no medium shedding, thin texture, low resistance, fast filtration speed, minimal adsorption, low-cost price, but not resistant to organic solutions and strong acid and alkali solutions.
Uses: The pharmaceutical industry requires hot-pressed sterilized water injections to filter out particles from large infusions.
For the sterilization of heat-sensitive drugs (insulin ATP, coenzyme A, and other biochemical preparations), use a 0.45-micron filter (or 0.2)
Analysis and determination of particles and oil-insoluble substances in solution, and determination of water pollution index.
It is used in scientific research departments such as somatic cell hybridization and mitochondrial complementation prediction heterosis research.

4. Polypropylene (PPM)
Features: No adhesives, stable chemical properties, flexibility, not easy to break, high-temperature resistance, can withstand high-pressure sterilization. Poisonous and tasteless, acid and alkali resistant.
Uses: It is suitable for making various coarse and fine filters and folding filter elements.
It is suitable for the filter membrane of plate and frame filter press in beverage, medicine, and other industries.
It is suitable for the support and pretreatment of the reverse osmosis membrane and ultrafiltration membrane.
Polypropylene membrane is non-toxic, and can be widely used in medicine, chemical industry, food, beverage, and other fields; it is hydrophobic, and it is particularly good for gas filtration.

5. Polyethersulfone (PES)
Features: The microporous filter membrane made of ether sulfone is a hydrophilic filter membrane. It has the characteristics of a high flow rate, low dissolution, and good strength. It does not adsorb proteins and extracts and pollutes the sample.
Uses: low protein adsorption and high drug compatibility, specially designed for biochemical, inspection, pharmaceutical, and sterilization filtration devices.

6. Polytetrafluoroethylene (PTFE)
Features: The most extensive chemical compatibility, can withstand DMF, DMSO, dichloromethane, THF, chloroform, and other strong solvents.
Application: Filtration of all organic solutions, especially strong solvents that other filter membranes cannot tolerate.

Characteristics Of Several Commonly Used Filter Membranes

No Ready-made Fruit in God’s Hand

Three guys finally got the God through trials and errors. They were eager to ask God for help. Right after the God asked what they want, the first man claim a big courtyard, the second a farmstead, and the third a bar of gold. God promised them. At last, the first man was given a pile of bricks, the second a bag of seed.

Introduction Of The Performance Characteristics Of Syringe Filter

The syringe filter is suitable for the filtration of a small number of samples in the laboratory. It has low adsorption to the sample, thus ensuring the maximum recovery of small or high-value samples. The filter shell is made of polypropylene and is welded by ultrasonic waves without sticking. Mixture, so it will not contaminate the sample.

The advantages of syringe filter:

1. Faster flow rate

The larger surface area of the filter increases the flow rate and the amount of filtration, and also makes the filtrate easier, because it reduces the pressure required to empty the syringe.

2. Higher operating pressure

The maximum shell pressure of the filter is 10.5bar (150psig), which means you can filter faster than before.

3. Reliable performance

Syringe filters are manufactured in a controlled environment and automated process. During the assembly process, the operator's hands never touch the filter.

main feature:

1. Syringe filter, individually packaged aseptically
2. Perform UV absorption test. HPLC analysis of 1 mL of acetonitrile and 1 mL of water filtered by this device showed that there was no absorption peak at 214 nm and 254 nm with an intensity greater than 0.004 AUFS (after the head-on amount of the column).
3. Syringe filter is a fast, convenient and reliable sterilization filter tool used routinely in the laboratory.
4. A variety of filter membranes of different materials and a variety of pore sizes.

With the continuous advancement of technology, the application scope of syringe filter is gradually wider, including:

1. Ambient air, waste gas, water quality analysis;
2. Drug testing, medical research, life science research;
3. Microelectronics semiconductor, chemical industry, cement/mineral analysis;
4. Inspection and analysis of raw materials, finished products and semi-finished products of food, beverages and medicines;
5. Education and commercial research and development laboratory water and organic phase solution filtration and teaching, quality inspection, quality control; chromatography, mass spectrometry sample preparation, etc.

Syringe filter is ideal for liquid clarification and sterilization filtration.

Filter sterilization is the fastest way to remove bacteria from liquids and has minimal effect on solution composition. The syringe filterseries is used to provide different pore size ranges, and has the characteristics of high flow rate and low adsorption. The effective filtration area is fine, and it is the syringe filter product with the largest filtration volume and the fastest filtration speed among the high-quality filters on the market.

The filter can be sterilized by ethylene oxide (EO) or gamma irradiation, while supporting Luer connection and hose connection, allowing users to easily complete various configurations. Key advantages include: high throughput; low adsorption; no PVC; 100% integrity testing; bidirectional filtration.

Syringe filter: reliable removal of particles from liquids and gases

Prior to sample analysis, removing incompatible particles from the sample by filtration will significantly extend the life of the column. Prior to column chromatography, syringe filter filtration was the simplest and fastest method for filtering small volumes of solution. Compatible with various aqueous solutions, solvents and chemical reagents.

Compared with similar competitive products, the filtration speed is high and the purity is high, which is very suitable for standard analysis operation. The use of uncoated natural hydrophobic PTFE membrane is not only suitable for gas filtration applications, but also for the clarification and filtration of corrosive solutions without leaching. The use of PES membrane and PP shell has higher chemical compatibility with the use of. Our key advantages include: extremely low adsorption; extensive chemical compatibility; and very few extractables or extracts.

The syringe filter is suitable for water system and various organic solvents, resistant to all solvents, low solubility, breathable and impermeable to water, large air flux, high particle rejection rate, good temperature resistance, resistance to strong acids, alkalis, organic solvents and oxidants, Aging resistance, non-stickiness, non-flammability and non-toxicity, biocompatibility and other characteristics are widely used in chemical, environmental protection, electronics, food, energy and other fields.

Introduction Of The Performance Characteristics Of Syringe Filter

Hawach To Talk About The Modified QuEChER With Extraction

Based on the introduction of the traditional QuEChERS method, HAWACH combined with the research status of different types of sample pretreatment technology in recent years briefly described the research and application of the improved QuEChERS method in pesticides multi-residue detection from extraction and purification. Hopefully, it can provide a reference for the detection of different types of substrates.

1. Optimize the extraction process
The extraction process uses an extraction solvent to extract the target substance in the matrix through liquid-liquid, liquid-solid, and other methods, and at the same time, the organic phase is separated from the aqueous phase with salt.

Choose different solvents and salts according to different characteristics of the matrix and pesticides to be tested to achieve the best extraction effect. There are two main aspects of its optimization: (1) extraction solvent, (2) buffer salt, and the salting-out process.

1.1 Selection and application of extraction solvents
The extraction solvent should not only satisfy the best extraction effect of the target compound, reduce its degradation loss, but also extract the interferences in the matrix as little as possible. Therefore, in the face of complex sample matrices, researchers used different extraction solvents to obtain better extraction results.

Stöckelhuber et al. used gas chromatography-tandem mass spectrometry to determine the residues of 9 pesticides commonly used in grapes in arthropods and gastropods in the soil under the vines using gas chromatography-tandem mass spectrometry. Comparing the extraction effects of acetonitrile and ethyl acetate, it was found that the peak area of the acetonitrile extract was much smaller than that of ethyl acetate.

Considering the toxicity of acetonitrile, ethyl acetate was selected as the extraction solvent, with PSA and anhydrous magnesium sulfate purification, the recovery rate of the 9 pesticide residues was 84% ~ 110%, the relative standard deviation was less than 18%, and the detection limit was 0.02 ~ 0.20 mg/kg (mass fraction).

When Maestroni et al. used gas chromatography-tandem mass spectrometry to determine 59 pesticide residues in grape leaves, acidified ethyl acetate was used as the extraction solvent, which has a good extraction effect for small and medium polar pesticide projects, and can greatly reduce co-extraction of interfering substances. However, this extraction solvent will have a very low recovery rate for more polar substances and is not suitable for the determination of pesticide residues with high polarity.

1.2 Selection and application of buffer salt and salting-out process
The buffered salt can ensure the stability of the target component to be tested which is sensitive to pH. The function of salting out is to promote the separation of the organic phase from the aqueous phase and the distribution of the analyte in the organic phase.

Faraji et al. found that the use of salt packs with sodium bicarbonate had the best extraction effect when detecting acetamiprid, imidacloprid, spirotetramat, and their metabolites in figs. The presence of sodium bicarbonate has little effect on the recovery rate of spirotetramat and its metabolites, but it can significantly increase the recovery rate of acetamiprid, imidacloprid, and their metabolites. This is because acetamiprid, imidacloprid, and their metabolites are alkaline compounds, and sodium bicarbonate can reduce their ionization.

Hawach To Talk About The Modified QuEChER With Extraction

200rmp Press-Button Lifting, Water Bath Rotary Evaporator

The rotary evaporator is a popular and ideal scientific research equipment in the chemical industry, medicine, food, environmental protection, universities and so on. This

 

industrial rotary evaporator

 

series is most economic products, the lifting way all adopt manual lifting, with very smooth up and down adjustment.

The

 

rotovap for sale

 

at Hawach is stable and durable. The design of a

 

laboratory rotary evaporator

 

follows the principle of efficiency, practicality, and economy, all for the sake of customers, the best choice to buy rotovap.

Features for RE200-W series industrial rotary evaporators

1. The rotating speed can reach 200rmp/min;
2. Temperature can reach 90-100°C for water bath;
3. Effective dual-flux coil condenser of laboratory rotary evaporator increases the evaporation process;
4. Integral bath with a safety handle which is safe and easy to clean;
5. Button-press lifting can be used to adjust the position of rotary bottle in the bath;
6. Seal ring of PTFE spring composite with the high vacuum;
7. Rotating bottle of 2L, 5L rotovap for sale;
8. The vacuum gauge is equipped as a reference to adjust accordingly.

3 different display of laboratory rotary evaporators can choose with the following details:

D1 for digital panel displaying temperature;
D2 for digital panel displaying temperature and rotating speed;
D3 for LCD displaying D1 for digital panel displaying temperature speed.

200rmp Press-Button Lifting, Water Bath Rotary Evaporator

The potential of cannabis as a therapeutic agent in the treatment of various diseases is one of the characteristics that make it highly valuable. With the significant advances in medical research and research, as more and more people learn and see the role of cannabis in the treatment of a variety of diseases, the value of cannabis in the medical community has played an important role.

Studies have shown that one of the brain disorders that cannabis can play an important role in chronic traumatic encephalopathy (CTE).

CTE, a medical disease of the brain, was first described by Dr. Harrison Martland in 1928 as “fist drunk syndrome”. For many reasons, until recently, CTE research has not made much progress.

In fact, CTE mainly troubles individuals with persistent or repetitive brain injury. This situation is common among victims of domestic abuse, military personnel, athletes (especially contact sports), boxers, etc.

In individuals with CTE, clumps of protein “Tau” from slowly in the body. As time passes, they will spread throughout the brain structure, thereby killing cells in the brain, but the symptoms of CTE will not show immediately Studies have shown that in most cases, some symptoms begin to appear in their 20s.

The research on the effects of cannabis on CTE patients has been carried out for quite a long time. According to the current signs, the effects of cannabis on CTE patients are the same but different. Because everyone has a unique endocannabinoid system, the degree of interaction and response to cannabinoids varies greatly. However, despite this variability, facts have shown that cannabis can help manage CTE by reducing post-traumatic convulsions or seizures, reducing anxiety levels, and reducing motor injury.

Studies conducted in 2014 also showed that cannabis can also help in the treatment of head trauma resulting in excessive production of extracellular glutamate (a toxic substance). According to recent research results, CBD can help prevent the toxicity of glutamate by reducing the toxicity of hydrogen peroxide in the CNS, that is, cannabis can play a role in the treatment of apoptosis, neuroinflammation and cerebrovascular failure.

Although all the information about CTE and cannabis has been discovered, there are still many unknown places. Chronic traumatic encephalopathy (CTE) is a unique brain disease. Although we have not yet reached a curable stage, the possibility of cure can be greatly increased through cannabis.

Cannabis VS Chronic Traumatic Encephalopathy

Which flower do you like best?

Introduction To Flash Column Chromatography

Flash column chromatography is a fast and usually easy method to separate complex mixtures. The principle of flash column chromatography and thin-layer chromatography is the same, but it can be used for the separation of preparative substances.

Because we use compressed air to push the solvent through the column, it is called flash column chromatography. This not only makes the separation effect better but also shortens the column passing time.

Preparation and operation of flash column chromatography:
1) Determine the weight of the dry, solvent-free mixture be separated.
2) Use thin layer chromatography to select the solvent system so that the Rf value is between 0.2 and 0.3, but if the mixture is complex, this may not be realistic. In more complicated situations, gradient elution may be required.
Simply put, the polarity of the solvent is continuously increased during purification and elution. This technique is described in more detail later. However, in TLC analysis, you must determine which solvent system will make the different spots within the range of 0.2 to 0.3.
3) Determine the method used to apply the sample to the column. You have three choices: net sample method, solution method, or silica gel adsorption method.

Net sample method:
If the sample is a non-sticky oil, it is easiest to use the net sample method. You can use a long dropper filter to introduce liquid into the column and then rinse with a predetermined solvent system to wash all the components into the column.

Solution method:
The clean sample method may sometimes cause the separation column to break. Therefore, for liquids and solids, the more common method is to dissolve the sample in a solvent and then add the solution to the separation column. The most ideal state is that all components of the mixture have an Rf of 0 in the solvent system (usually pentane or hexane).

This is difficult to achieve in most cases, so choose a solvent that only moves one compound in the mixture, or you can simply use the eluent of your choice. Remember: the latter two options are risky for more difficult separations and purifications.

Silica gel adsorption method:
The last technique is to deposit (adsorb) compounds onto silica gel, which is useful for some liquids and all solids. Note: Silica gel is acidic, so this step will destroy some acid-sensitive compounds. They usually need to be regenerated on the silica gel column.

First, dissolve the mixture in dichloromethane in a round-bottom flask and add silica gel (the mass of silica gel is about twice the mass of the compound). The solution was concentrated on a rotary evaporator. Note: Silica gel is a very fine powder and can be easily drawn into the rotary evaporator.

Use glass wool to plug the connector or the pump’s protective device to prevent solids from being drawn into the pump. Quick rotation can also avoid this problem. When the solids are substantially dry (when most solids fall off the wall of the container, indicating that the solids have dried), remove the flask from the rotary evaporator and use a vacuum pump to exhaust the solvent (assuming there are no volatile substances in the mixture).

Note: Plug the vacuum pump connector with glass wool, otherwise you may find silica gel (and your compound) enter the vacuum tube and deposit there. Once it is completely dry (no more bubbles in the solid), remove the flask from the vacuum system and scrape the solid off the wall with a clean spatula. Now, you can simply use a powder funnel to add this part of the solid to the top of the separation column, and then rinse with eluent (1.5mL each time).

Introduction To Flash Column Chromatography

Remember These Tips To Increase Your Pipettor Service Life

The precision instruments are the foundation of research and quality control labs all over the world. Pipettors are an essential tool for life science research. The piston achieves liquid suction and discharges through the telescopic movement of the spring.

Under the push of the piston, part of the air is discharged, and the liquid is sucked using atmospheric pressure, and then the air is discharged by the piston. When using a pipettor, operate with the elasticity of the spring to control the pipetting speed and force. Here, HAWACH discusses 15 tips to lengthen the pipettor service life.

1. When sucking liquid, be sure to release thumb slowly and steadily. Never let go suddenly, to prevent the solution from being drawn too fast and rushing into the pipettor to corrode the plunger and cause air leakage.

2. In order to obtain higher accuracy, the tip needs to draw the sample solution in advance, and then formally pipettor, because when the serum protein solution or organic solvent is drawn, a layer of “liquid membrane” will remain on the inner wall of the tip, causing too small discharge volume and produces errors.

3. Liquids with large concentration and viscosity will produce errors. To eliminate the error, the compensation amount can be determined by experiment. The compensation amount can be set by changing the reading with the adjusting knob.

4. Use the analytical balance to weigh the weight of the pure water and calculate it to correct the liquid picker. 1ml of distilled water weighs 0.9982g at 20℃.

5. It is undesirable to impact repeatedly the pipettor to tighten it. The long-term operation will loosen the internal parts and damage the pipettor.

6. Do not pipettor when the pipettor is not equipped with a pipettor tip.

7. When setting the range, please note that the set range is within the range of the pipettor, do not turn the button out of the range, otherwise, it will jam the mechanical device and damage the pipettor. The number is clearly in the display window and rotate to the desired range.

8. Pipettors are strictly forbidden to absorb highly volatile and highly corrosive liquids (such as concentrated acid, concentrated alkali, organic matter, etc.).

9. Do not use a large range of pipettors to remove small volumes of liquid, so as not to affect the accuracy. At the same time, if you need to remove a large amount of liquid outside the range, please use a transfer pipettor.

10. If not in use, adjust the range of the pipettor to the maximum scale to keep the spring in a relaxed state to protect the spring.

11. It is best to clean the pipettor regularly, use soapy water or 60% isopropyl alcohol, then use distilled water to clean, and dry naturally.

12. Before high-temperature disinfection, make sure that the pipettor can adapt to high temperatures.

13. Calibration can be performed in the environment of 20℃~ 25℃ by repeating the weighing of distilled water several times.

14. Check if there is any liquid leakage during use. After absorbing the liquid, hang it vertically and let it stand for a few seconds to see if the liquid level drops. If the liquid leaks, the reasons are: (1) whether the tip matches; (2) whether the spring piston is normal; (3) if it is a volatile liquid (as is the case with many organic solvents), it may be a problem of saturated vapor pressure. Aspirate the liquid several times before pipetting.

15. After the use of pipettor, hang it vertically on the pipettor holder, but be careful not to drop it. When there is liquid in the pipettor tip, do not place the pipettor horizontally or upside down to prevent the backflow of liquid from corroding the piston spring.

Remember These Tips To Increase Your Pipettor Service Life

HAWACH To Talk About The Modified QuEChERS With Purification Optimization

Optimize the purification process
PSA, GCB, C18, and other adsorbents have their own advantages and disadvantages. PSA is alkaline because it contains 2 amine groups, which will affect the recovery rate of acid pesticides such as folpet, bacteriostatic, and GCB will adsorb flat structural compounds and reduce the recovery rate of pesticides such as hexachlorobenzene and thiabendazole. C18 will adsorb some pesticides such as diazinon and tebuconazole, reducing its recovery rate.

In order to improve the recovery rate of these susceptible pesticides, the researchers tested the combination of these three adsorbents in different proportions, and also tried a variety of different materials, and achieved satisfactory results. The purification optimization includes adjusting the content of PSA, GCB, C18, and other adsorbents according to different substrates and using other adsorbent materials to purify the substrate.

1. Adjust the content of adsorbent and other experimental conditions
The researchers used statistical software to examine the influencing factors such as solvent volume, buffer salt, and the content of various adsorbents from a theoretical point of view and obtained variables that have a greater correlation with the results, and then used the optimization software to fit a curve to calculate the best solution.

Manav et al. used Plackett-Burman experimental design (PBD) to screen for variables such as acetonitrile volume, formic acid content, sodium chloride, anhydrous sodium sulfate, sodium acetate, diatomaceous earth, anhydrous magnesium sulfate, and quality of C18. The Behnken design (BBD) method is optimized to determine the best combination of extraction and purification effects.

The results showed that when measuring 25 pesticide residues in dairy products, the sampling volume was 10g, 10 ml of acetonitrile (containing 1% formic acid) was added, and extracted with 5.7g of sodium chloride, 6g of anhydrous sodium sulfate, and 4.2g of sodium acetate. After shaking and centrifugation, take 7 ml of supernatant and purify with 0.5 g of diatomaceous earth, 300mg of anhydrous magnesium sulfate, and 150mg of C18, and use GC-MS to obtain satisfactory results.

Viera et al. used a full factorial design to screen: 3g samples were extracted with 10 ml acetonitrile containing 5% formic acid, separated with 1.5g sodium chloride, 4g anhydrous magnesium sulfate, and 2ml were taken after shaking centrifugation. The purification of 300 mg anhydrous magnesium sulfate, 50 mg C18, and 10 mg GCB in the clear solution can obtain good results and meet EU requirements.

2. Use new materials as adsorbents
The purification process plays a very critical role in the QuEChERS method, so a large number of researchers are constantly exploring new materials as adsorbents. Some reported materials include Z-Sep, chitosan, magnetic nanoparticles (MNPs, graphene) Oxides tri-Bua-rGO, fluorinated adsorbents, phenolic resin-based activated carbon fibers (ACFs), etc. These materials have achieved good results as adsorbents in the purification process.

Moreno-González et al. determined the pesticide residues in various edible oils. In the case of using acetonitrile as the extraction solvent, the purification effect of the combination of Z-Sep Plus and C18 + PSA was compared. It was found that the former can significantly reduce the matrix effect, which is Z-Sep Plus is better at removing lipids than C18 and PSA.

The selection and use of new materials not only obtain better experimental results but also enriches the reserve of QuEChERS adsorbent materials, which provides a basis for the expansion of its scope of use and enables it to have a wider application range.

HAWACH To Talk About The Modified QuEChERS With Purification Optimization

Use Of Membranes And Laboratory Solvent Filters

The sterile microporous filter membrane is mainly composed of a filter container, a support basket, and a filter bag. The principle is that when a bag filter is used to filter liquid, the liquid enters from the side inlet of the filter and is supported by the basket.

The filter bag is flushed into the filter bag above the filter bag. The liquid penetrating the filter bag is along the metal support mesh basket wall. The liquid outlet at the bottom of the sterile needle filter is excluded, and the filtered particulate impurities are trapped in the filter bag to complete the filtration process.

Laboratory solvent filter devices are mainly used for liquid chromatography mobile phase filtration, particulate matter analysis, and microbial contamination detection.

They are standing equipment in chemical laboratories. Borate glass or 316L sanitary stainless steel is selected as the material, which can filter various aqueous solutions, organic substances and corrosive liquids in the analysis, and can be autoclaved at 121°C for disinfection.

Laboratory solvent filter application range: It can be used for liquid filtration in scientific research, chemical analysis, instrument analysis, health inspection, pharmaceutical industry and agricultural machinery, automobiles, construction institutions, etc., to detect and remove particles and bacteria in the liquid filter.

For example sterility test, medium sterilization, and filtration, cleanliness of medium and small power internal combustion engines, jet fuel and solid particle pollution of the hydraulic system, etc., such as the use of lattice filter membrane, also suitable for hydraulic oil, high-purity reagents and water quality Such as the counting method.

 

How to use laboratory solvent filter
1. Remove the sealing ring before using the new filter, and then soak it with 10% sodium hydroxide to saponify the oil stain, and then wash it repeatedly with clean water several times until it is completely clean.

2. The filter used for aseptic operation should be sterilized.

3. Put the filter membrane lightly on the cleaned filter bottom filter plate, then cover the filter barrel and tighten the bolts.

4. Insulation preheating, before adding the liquid to be filtered, only low temperature preheating, preheating temperature ≤ 36 °, due to the inherent factors of metal heat transfer and uneven heating, the measured point of the temperature control probe is in the temperature control box The thermometer will show between 36°-58°.

5. When the preheating temperature reaches the condition that the required filtered liquid does not condense, add the liquid to be filtered, then adjust the temperature to the desired degree in the temperature control box. When the selected temperature is reached, the heating system will automatically cut off the power.

6. When the preheating and heating are completed, seal the upper cover of the road junction, open the pressurized intake valve, and gradually pressurize from 0.05Mpa—0.1Mpa—0.2Mpa—0.3Mpa, at this time the liquid is discharged from the lower port of the filter.

7. When pressurized to 0.3Mpa, no liquid is discharged from the lower port of the filter. At this time, the filter membrane is clogged or the accuracy of the filter membrane is too high. It is necessary to adjust the filtration accuracy of the filter membrane.

8. After the filtration is completed, first close the pressurizing valve to make the pressure display of the filter pressure gauge return to 0, and then open the filter cartridge to take out the material. It is strictly forbidden to open the pouring port and the filter cartridge when the filter is under pressure, so as not to occur Human injury.

9. When the filter is not under pressure, open the upper filter cartridge to see the solids on the filter membrane, remove the solids, and complete the filtration cycle.

10. After each experiment, please clean and reserve the laboratory solvent filter.

Use Of Membranes And Laboratory Solvent Filters