When the system fails, you can tentatively change some states and change one parameter at a time. For example, to limit the problem of spectral peak de-dimensionality, the mobile phase can be changed sequentially, the guard column can be changed, and the analytical column can be changed. Do some simple changes and maybe solve the problem.
2. Secondary comparison rules
The fault has been identified before the hands-on maintenance, or the solution to the fault has been determined. In other words, the solution has been found before the hands-on. For example, during the injection process, the peak value of the internal standard is found to be low, and the repeating injection can be repeated to see how reproducible, if it is accidentally low, whether the bubble is in the quantitative tube. This rule can be used to examine the situation after a system change. After changing the flow backwards, the standard can be fed twice before the formal injection to check the stability of the retention time and the stability of the chromatographic peak. If there are extra peaks in the gradient elution, you can elute once with the no-load gradient (is there really a problem?), use this rule to avoid unnecessary changes and determine corrective actions as soon as possible.
3. Replacement rules
It is a good way to find faulty parts by replacing the suspicious parts with good ones. If you suspect that the detector is causing noise, switch to a good performance detector. If the fault is eliminated, there is a problem with the replaced detector. The scale of this rule application is large and small, from changing the entire part to replacing the integrated blocks on the printed circuit board.
4. Change back to the rules
This rule is used in conjunction with the replacement rule. After the good parts have replaced the suspicious parts, the situation has not been improved and the original parts should be replaced. The maintenance cost of this is small, and it prevents the used parts from being accumulated. This rule only applies to a single fault. The principle of exchange back does not apply to the following situations:
(1) The new part is damaged when removed (eg pump seal washer);
(2) The price of the parts is low (such as the column lining filter);
(3) The risk of damage if the original parts are reinstalled;
(4) Parts that are replaced regularly.
5. Reference condition rules
There are usually two reference conditions: 1 standard reference condition; 2 test reference condition.
Standard reference conditions, also known as standard test conditions, are conditions that are easily verifiable from one system to another, from one laboratory to another. The data measured with this condition helps identify problems between actual tests and systems. If the system pressure rises under certain test conditions, the pressure is normal under standard conditions. This indicates that system anomalies are caused by changes in the laboratory. The table below lists the standard test conditions for enabling a new column, and the system can also be used to check the condition of the system during use.
Mobile phase methanol/water (volume ratio = 70/30)
Column C18
Reverse flow rate 1mL/min
Detector UV254nm
Sample uracil (for t0)
Phenol, acetophenone, nitrobenzene, anisole, toluene
Mobile phase n-hexane/isopropanol (volume ratio = 75/25)
Chromatide
Polar bonded phase flow rate 1mL/min
Detector UV254nm Sample nitrobenzene, benzyl alcohol, 2,4-dinitrotoluene, p-nitrobenzyl alcohol
Mobile phase n-hexane/dichloromethane/isopropanolamine (volume ratio = 95/4/1)
Column silica gel
Normal phase flow rate 1mL/min
Detector UV254nm
Sample 2-phenyl-2-propanol, methyl benzyl alcohol, cinnamyl alcohol
The test reference conditions are used to check the daily operation of the normal system. It is convenient to choose zui to verify this condition. Two calibration chromatograms can be printed daily for comparison to check for changes in retention time, peak width, system pressure, and more. The slope of the peak, the number of column plates, and other parameters were found to vary from the original chromatogram, indicating that the system may have problems during operation. Of course, the problem does not take into account the actual analysis procedure, and it is not clear at first glance by looking up the standard reference chromatogram.
6. Recording rules
This rule is often overlooked. It should be recorded after each maintenance and troubleshooting. For example, it is time consuming and laborious to analyze a problem systematically for a particular failure of the system because it is not recorded. From the long-term point of view, the specific faults that occur in the system are also extremely important for future operations. Each instrument should be provided with a maintenance record, including date, fault location, phenomenon, cause, solution and result. It is also important to note that the parts that have been tried or replaced must be marked.
Good maintenance records have the following benefits:
(1) Let all operators know what has happened and pay attention during the operation;
(2) Help the operator to describe the fault phenomenon;
(3) When the fault occurs again, the problem can be solved as soon as possible according to the information.
7. Forecasting rules
Personnel with maintenance practices and maintenance habits should be able to predict system failures, and spend more time on maintenance. The system will reimburse the failures and eliminate chain damage. For example, if you do not pay attention to maintenance, the pump's sealing gasket is broken, causing leakage of the mobile phase, which will corrode the pump and other components. Being good at maintenance saves time and money, not the instrument controls the operator. For example, when the work starts or ends at work every day, it is found that the lamp life causes a baseline drift to replace the lamp. If the lights are all broken, they need to be shut down, and the damage may be higher than the cost of one lamp.
8. Buffer rules
This rule reminds you to wash the buffer in the system when you stop. Residues of the buffer in the system can cause wear, corrosion and blockage. In addition, physiological buffers are highly susceptible to bacteria and mold. The ideal rinse is a mobile phase of the same composition without buffer. Do not store pure water in the system to prevent growth of bacteria. 10% organic solvent or 0.02~0.05% sodium azide can be added to water. Flush in the laboratory as follows: rinse with pure water for 30~60min (1mL/min) and then rinse with methanol for 30min and then shut down. Never use organic solvents to rinse as soon as it is turned on, otherwise the inorganic salts will precipitate in the system, causing undesirable consequences.
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