Frequently Asked Questions About QuEChERS Products in Experiments
Q1: Is Hawach’s QueChers product mainly used in food?
A: Yes, the method is currently mainly used in the food field. QuEChERS was originally a method for extracting multiple pesticide residues in fruits and vegetables, but now it has been used in more and more fields (eg, veterinary drugs, polycyclic aromatic hydrocarbons, and antibiotics, etc.) to detect more and more different samples. (such as plasma, meat, and soil). However, compared with the pesticide detection methods in agricultural products, the latter methods have not been extensively verified.
Q2: Can you give us a rough comparison of the use of conventional SPE and QuEChERS products, the cost of each sample is listed, probably estimated on the line.
A: The cost of these two methods is relatively difficult. It is affected by factors such as the specific test items, whether the samples need to be concentrated, and whether you use QuEChERS products. There is a statistic that should explain this problem. Nearly 40% of the 130 to 150 participating laboratories in Europe in 2009 used the QuEChERS method to detect pesticide residues. For private laboratories, QuEChERS adoption rates are as high as nearly 70% due to their increased cost. The high throughput and organic solvent savings of the samples brought by the QuEChERS method are also the reason why this method has received wide attention in foreign laboratories. Lethony has done a statistic in Europe. The traditional purification method requires approximately 500 mL of organic solvent (Luke method), while the QuEChERS method requires only 10 mL or 15 mL.
Q3: If the pesticide is volatile, then when we use this kind of pesticide, will it be evaporated into the air at a slightly higher temperature?
A: Volatileness is not strong enough to volatilize at room temperature. It is only because of the exothermic reaction of anhydrous magnesium sulfate with water, which can cause loss of these pesticides.
Q4: Previously, activated carbon was used to remove the pigment, and the sample had a large loss. Because in normal experiments, it is often necessary to deal with pigments (generally to remove pigments), can I use it as a filler to make pillars or SPE cartridges to remove pigments? Is it still selective for water-soluble and fat-soluble pigments?
A: Hawach can provide finished products of graphitized carbon black SPE columns.
Q5: Freezing and degreasing: The extract or the purified sample is placed in the refrigerator for more than 1 hour (or frozen overnight). Adsorption of reversed-phase adsorbent: C18E or C8 adsorbent is added to the extract to remove fat. Can the above two methods of degreasing be used together or separately? What are the advantages and disadvantages of each?
A: The decreasing effect of the frozen degreasing and C18E adsorbents is equivalent, but it takes longer to use the degreasing and freezing, which is fatal to increasing the sample throughput. At the same time, other non-polar interferences can be removed by using the C18E adsorbent. Of course, the cost of using C18E degreasing will be a little higher.
Q6: What is the difference between the QuEChERS purification technology and the homogenizer after pumping through the suction filter bottle, and then purifying the sample by rotary evaporator and nitrogen blowing treatment? Can QuEChERS purification technology reduce steps and increase efficiency?
A: Use these steps to evenly “paste the filter with a suction filter and then purify the sample by rotary evaporator and nitrogen blowing treatment” to pre-process the sample. First, these steps have no purification function, and are all steps of extraction and concentration. Second, these steps can be very cumbersome. The use of rotary steaming and nitrogen blowing is very time consuming and laborious, and is very disadvantageous for improving sample throughput. The QuEChERS method step is very simple, using the matrix-dispersive solid-phase extraction technique and the high sensitivity of the mass spectrometer to eliminate the sample concentration step (not absolute); and in view of the compatibility of acetonitrile and some instruments, solvent conversion is generally not required. Conventional pretreatment methods use a large amount of solvent to extract the target compound, and then spend a lot of time to concentrate. These are well avoided in the QuEChERS method. The sample used in the QuEChERS method: the extraction solvent ratio is usually 1:1. The relationship (data validation, for high-humidity samples, the majority of pesticides used in this ratio can be guaranteed), which reduces the step of sample concentration.
Q7: What kind of material is used for the extraction of the centrifuge tube? Does the centrifuge tube of the polypropylene purchased by itself have an effect on the extraction, such as adsorption of pesticides?
A: At present, the commercial QuEChERS kits are all made of polypropylene centrifuge tubes. There is no data showing that the polypropylene centrifuge tubes will adsorb pesticides, but it is better to use screw-type centrifuge tubes, so that the sealing performance will be better.
Q8: In the process of the first step of extraction, after adding the filler, it will release heat, and the temperature of the centrifuge tube is still quite high. Will it affect the recovery rate of the pesticide? Some pesticides appear to be sensitive to temperature.
A: The exotherm of anhydrous magnesium sulfate and water does increase the temperature of the centrifuge tube. Generally, it has been added to the salting out package after it has been extracted. After the addition, it is required to understand the violent oscillation, so that the heat can be dissipated; In the sample pulverization, dry ice is added, or the sample is pulverized and placed in a refrigerator overnight to be cooled, and then the loss can be reduced.
Q9: After purging the nitrogen, do you want to blow it dry? Or do you want to stay a little?
A: If you directly enter the LC-MS analysis after purification, you can use no solvent conversion; when the solvent is converted, the nitrogen is blown to near dryness, then a small amount of solvent to be converted is added, and then nitrogen is blown to near dry to constant volume.
Q10: Is it necessary to filter with 0.45 μm or 0.22μm filter after purification? If it is used, is there any adsorption on the pesticide? Is it not harmful to the column?
A: This question depends on personal thoughts. The membrane will definitely have a little protection for the column. We have been using the membrane, and there is no obvious absorption of the pesticide on the membrane.
Q11: If it is a sample with less water content, such as tea, I am now weighing 3.75g of tea and adding 11.25g of water to make the water content high. Is this reasonable?
A: For dry samples, especially tea-based matrices, I generally take the reduction of sample weight and water soaking. We have been doing this.
Q12: Is the graphitized carbon black powdery or granulated? Which type of effect is better when the sample is pretreated (especially to remove the pigment)?
A: At present, the graphitized carbon we use is fine particles with a particle size between 120 and 400 mesh. In pre-treatment, if matrix-dispersed solid phase extraction is used, the fine-grain effect of the particles should be better. In the case of conventional SPE, the particles are too fine to cause too much back pressure, which usually results in the sample not passing. At present, the average particle size is between 120-400 mesh.
Q13: During the sample pulverization process, it is mentioned that dry ice can be added to prevent the loss of volatile pesticides. Will the dry ice sublimate into a gas, will it take away the components to be analyzed? Can it be changed into an ice bath?
A: First of all, dry ice biochemicals will not take away pesticides. If pesticides are so volatile, then we do not need to test these pesticides. Volatile pesticides say that his boiling point is relatively low, and dry ice sublimation should reduce the environment and sample temperature to protect such pesticides without volatilizing them. As for whether to use the ice water bath, it is ok. The purpose of adding dry ice is to reduce the temperature of the sample to protect the volatile pesticides. The ice water bath can also achieve this purpose. However, the ice water bath does not seem to operate very well, because it needs to be oscillated immediately after adding the salting out package (in case of local overheating, and the violent and legitimate is also beneficial to the heat dissipation). At this time, the heat release will be particularly high, and the temperature will rise very much. High, no device can oscillate while still allowing ice water bath. If there are no conditions, the sample can be refrigerated to ensure that the temperature of the sample before analysis is as low as possible.
Q14: Hawach has a finished product of graphitized carbon black SPE column. After the column has been used for a long time, will it be blocked because of the adsorption of pigment? If it is blocked, can it be removed by removing the adsorbed pigment? Can only be replaced?
A: Graphitized carbon black column is a one-time use. After use, his adsorption is saturated. Once used again, there is no function of removing pigment.