Autosampler Maintenance Tips

**Information collect from internet

The autosampler is another high-frequency maintenance module that requires extra attention among the four basic modules of modern high-performance liquid chromatography systems. With the development of modern liquid chromatography, liquid chromatography instrumentation has also developed more and more sophisticated, in which the autosampler has also become more and more complex and precise equipment.

When the components in the autosampler show aging, wear and tear, leakage and other problems, it may become the root cause of some chromatographic problems.

Common failures of autosamplers and aspects that require attention to maintenance are: wear of the sringe, wear of the sringe holder, wear of the rotor gasket, clogging or leakage of the dosing ring, improper installation of the needle holder and connector, connector, leakage of the metering pump, etc. These aspects then correspond to the production of a series of chromatographic problems, such as ghost peaks, residuals, delays, high system pressures, leakage of liquids, and poor reproducibility of repeat sample response.

Needles, needle holders

Poor sealing between the needle and the header can lead to leakage, cross-contamination, and anomalies reflected in the chromatogram as ghost peaks or poor reproducibility of quantitative analysis. The header and needle should be considered as one “functional” part and must be replaced at the same time if there is a problem. A damaged needle may further damage the header, and if only the header is replaced, the new header will immediately be damaged by the old needle and vice versa. If the needle and seat are clogged, it is important to identify the source of the clogging. Certain other components upstream (e.g., sample vial caps or orifice sealing membranes, deteriorated plunger rods or fittings) may generate debris that can clog the needle and seat. When clogging occurs, try backflushing the needle seat capillary.

Needles are recommended to be maintained and replaced annually, or should be replaced in time when the needle is bent, burred, blunted, worn, leaking or clogged, or when certain upstream components release debris, which needs to be replaced and drained, or else it will lead to leakage or leakage of liquid, which will further lead to residual samples or cross-contamination, and the occurrence of a secondary injection effect after the injection of the sample, which will ultimately manifest itself on chromatograms as ghost peaks, reproducibility, and reproducibility of quantitative analyses Insufficient and other anomalies.

Needle holders are likewise recommended to be replaced annually for maintenance, or if the needle holder becomes worn, leaking or clogged. If salt crystals are found on the header, it is possible that the header is leaking. The header capillary is the first fine diameter line that the sample passes through in the liquid chromatography system, so if the sample contains solid particles, the header is likely to become clogged.

Injection valve

The injection valve, which is often referred to as the six-way valve (below left), is a very important part of the autosampler in all components, if the use of improper maintenance, there will often be clogging, leakage of liquid abnormalities.

The size specifications of the fittings and capillary lines that are connected to the injection valve are critical; if they are not properly sized, or if they are not accessed properly, they can lead to leaks, or cause additional dead volume to increase, producing poor peak shapes (as shown above, right).

Worn rotor gaskets in the feed valve are a frequent cause of chromatographic problems.

The rotor gasket will be worn over time or damaged by particles, resulting in a secondary injection effect in the injector, and the sample may also be residual in the injection valve, cross-contamination, etc., which is manifested in the chromatogram as residual peaks in the blank injection, or the sample band broadening makes the chromatographic peaks appear to be broadened, bifurcated, and other anomalies. Under normal circumstances, the rotor gasket should be maintained and replaced annually, or should be replaced if it is worn out, clogged, or leaking at the intersection.

Metering pump

The metering pump of the autosampler will determine the accuracy of the sample volume. Like the injection valve, the gasket in the metering pump (part #2 in the figure below) is a wear and tear part that needs to be replaced and maintained. In addition, deterioration of the plunger rod (part #7 in the figure below) can also lead to inaccurate injection volumes and poor peak area reproducibility. (The gasket material of the inlet valve and metering pump may be different for different brands of instruments, and the lab technician should ensure that the correct solvent and/or pH conditions are selected for the different materials. (Instrument manufacturers often provide kits containing all consumable parts of the autosampler module in a single package).

Timely replacement of the metering pump sealing washer: The replacement of this position of the sealing washer should be noted that, unlike the pump, the user must first enter the instrument's diagnostic and maintenance interface, the metering pump within the plunger rod retracted before disassembling the metering pump, otherwise the plunger rod is in the position of compression when disassembling the installation of the installation of the time will be troublesome. Metering pumps are used very infrequently, almost negligible, but the sealing washer will be worn, the use of three or five years of instruments will sometimes be found in this position leakage, but the frequency of this problem is very low.

!!!Common breakdown

1.Unstable baseline and increased ghost peaks

Phenomenon: Fig1 a and Fig1 b are the same standard analyzed. Fig1 a has unstable baseline and increased ghost peaks, while Fig1 b has stable baseline and normal spectrum.

Fig1 a is an unstable baseline with increased ghost peaks.Fig1 b is the normal spectrum, and it is also the spectrum after cleaning.

Cause: After eliminating pump, mobile phase and detector problems, this phenomenon indicates that the injection system is contaminated.

Solution: Replace the cleaning solution of the original autosampler with 5% aqueous perchloric acid solution, draw about 100mL with a syringe, fill the sample bottle with the above cleaning solution, replace the column with a plastic damping tube, with the waste liquid connected to the outlet of the damping tube and not connected to the detector. Turn on the pump and set a regular flow rate. Set up the autosampling program with an injection volume of 200 μL and an analysis time of 1 minute for 20 consecutive times.

After the end of the cleaning solution is replaced by pure water, the sample bottle is filled with pure water, according to the same operation as above, (taking into account the large amount of injection and the number of repetitions, prepare 5 sample bottles filled with the appropriate amount of liquid, put them into the sample tray, set up an automatic sampling program, and each bottle is pumped continuously for 4 times, and the 5 sample bottles are pumped for a total of 20 times, so as to avoid sucking the empty).

Note: 5% perchloric acid aqueous solution can effectively remove the dirt in the system, if there is no perchloric acid, can be used in methanol, purified water, large injection volume of multiple cleaning, can also play the same effect.

2.Sudden drop in pump pressure to 0 or very small

Phenomenon: During a continuous analysis of samples, the system was normal at the beginning of the analysis, but when analyzing the eighth sample, I suddenly found that the pump pressure dropped to 0.3Mpa, while the normal pump pressure was 5.5Mpa. I smelled methanol in the injector (the methanol content in the mobile phase was very large). Opened the door of the injector, found that the tube under the drain valve had liquid dripping out with methanol odor, stopped the system, pressed shift+9 and found that the inlet and rinse ports were very salty.

Cause: The inlet port is blocked, the mobile phase cannot enter the column and leaks out, resulting in a drop in pump pressure.

Solution: According to the autosampler routine maintenance

3.Poor sample reproducibility

Causes:1) Metering pump not allowed;

2) Six-position valve is worn.

Solution:

(1)Metering pump suction accuracy judgment. In the sample bottle filled with a sufficient amount of pure water, wipe clean the outside of the water, weighing with an analytical balance, record the reading W1, put into the sample tray, set up the sampling program, the sample volume of 100 μL, ten consecutively, after the end of the filter paper to wipe dry the surface of the sample bottle of water, placed on the balance weighing, get a reading of W2, W1-W2 should be the value of the value of the 1mL of pure water at the corresponding temperature of the mass. If the difference is not significant, the metering pump is not a problem. If there is a problem with the metering pump, it is possible that the metering pump plunger rod or sealing ring problem.

(2)six-position valve wear. According to the autosampler manual, remove the six-position valve, observe whether the three ports have wear and tear, if the wear is serious, then replace the new six-position valve, according to the operation of the book, assembled, debugging, reproducibility can be good.

4.Clogged needle holders

Many people have encountered the problem of clogging the needle seat, sometimes accidentally used a hard plastic bottle cap or bottle cap on the feed pad reused many times, the feed needle needle down, will be the cap or bottle pad debris sucked into the needle hole, the needle fell to the needle seat up after the mobile phase through the 100ul dosing ring flow through the needle seat, debris was brought to the needle seat inlet, resulting in clogging of the needle seat, the system pressure This results in clogging of the syringe, high system pressure, or leakage of the syringe.

Ultra-clean bench found that after the problem, enter the instrument diagnostic interface, the needle up, away from the needle seat, remove the front cover of the autosampler module, remove the needle seat to connect the screws of the six-way valve, and force the needle seat to remove the needle seat, the needle seat inverted to the liquid-phase pump, the flow rate is set to 5 ml/min pressurized, the general clogging can be immediately rinsed down, if the rinsing down to the needle can not be placed in the ultrasonic ultrasound instrument, and then connect to the pump to flush, or simply extend the pipeline while connecting to the pump to flush and sonicate. Then connect the pump to flush, or simply extend the pipeline, while connecting the pump to flush the ultrasound, once I even used the pump to flush the ultrasound while using the gas phase manual injection needle core to poke the inlet of the needle to finally get out the inside of the clogging, and then back to the installation of all OK.

5.Mechanical failures

Problems on the mechanical arm of the autosampler, carefully observe the movement of the sampler's mechanical arm at work, mainly including lateral and longitudinal, these movements rely on belts, gears and screws to complete. Autosampler mechanical failure is mainly caused by dust in the air, dust in the air adsorbed on the belt, screw and gears, increasing the friction, and when serious, directly leading to the intended action can not be completed, and even the instrument power on the autosampler self-test can not be passed, there is a problem that can be turned off the instrument, with a clean nonwoven cloth does not fall off the fibers to wipe the screws, belts and gears and other transmissions, rubbing can not be The place can use hand to pull the belt, and then wipe, experienced instrument shell can be disassembled to wipe.

Note: Never wipe lubricant on the screw, because the lubricant itself will aggravate the adsorption of dust. After wiping restart the instrument to try, many times the problem can be solved. As for the more complicated problems such as inaccurate positioning of the robot arm or inability to grasp the vials, it is best to have a specialized engineer come to your home to do the maintenance.

The maintenance and troubleshooting of the autosampler is an accumulation of experience. The components of HPLC are interconnected, if one component is faulty or contaminated, blocked, it may affect the components behind it, and at the same time, you have to check whether the components in front of it are faulty. For example, if the baseline is unstable, check whether the detector is contaminated, check whether there is any problem with the mobile phase, whether the injector is dirty, whether the column is contaminated, whether the column is not stabilized well, whether the ambient temperature is stable and so on. So sometimes it is more difficult to check the problem than to repair the machine. This requires us to accumulate more experience in the work, more observation, more brains. This is the only way to familiarize with your machine and use it better.