Judgment and inspection of common faults of the ho

Judgment and inspection of common faults of hydrogen system

FID (hydrogen detector) has high sensitivity, small dead volume, fast response and wide linear range. It can be effectively combined with capillary column, and has become the most widely used detector for microanalysis of organic substances at present. The FID detection system is mainly composed of detector, detection circuit (amplifier) and gas circuit. When a fault occurs or the analysis spectrum is abnormal, we should first judge which part of the problem is

fid system common abnormal conditions are: 1. Unable to ignite - the problem mainly lies in the gas circuit or detector; 2. The base flow is very large - the problem mainly lies in the gas path or detector; 3. The noise is very loud at this time - there may be problems with the gas circuit, detector and circuit; 4. The sensitivity is significantly reduced - it is possible that the gas path, detector and circuit are abnormal; 5. No peak - it is possible that the gas path, detector and circuit are abnormal; 6. Abnormal chromatographic peak shape? The sampler, gas circuit and detector are the main inspection objects; 7. The baseline drift is serious - both the gas path and the detector are possible; 8. Sometimes there is a signal, sometimes there is no signal

-- the problem mainly lies in the circuit

I. check the gas circuit: check whether the flow of H2 (hydrogen), N2 (nitrogen) and air (air) is normal. Too small air flow and serious air leakage of the nozzle will cause a large explosion sound and fail to ignite; Too little hydrogen and too much nitrogen make ignition difficult and easy to shut down; Nozzle leakage and chromatographic column leakage will not only make ignition difficult, but also lead to reduced sensitivity and even no peak; The flow ratio of hydrogen and nitrogen will significantly affect the sensitivity; Too much hydrogen flow will also cause noise; Unclean gas path system, including sampler pollution, detector pollution or insufficient aging of chromatographic column, will cause base flow, large noise and baseline drift. Please pay attention to the size of the basic current during ignition: before ignition, the baseline position of the amplifier should be adjusted at or near the zero position of the recorder as far as possible. Without rotating the zero adjustment potentiometer, the distance of the recording pen from the zero position after ignition can indicate the size of the basic current, which can be determined by changing the range of the recorder or the attenuation multiple of the amplifier. Generally speaking, when H2 gas is adjusted back to the normal working value after ignition, the basic current deviation is less than 1mV, indicating that the system is very clean, If the base current is less than 10mV, it can generally be used. If the base current is greater than dozens of MV, it indicates that the system is seriously polluted. At this time, the noise and drift are large, and the stability time of the instrument is also long. A simple way to check which part is polluted is to continuously, Bi directionally and proportionally control the flow or pressure of the hydraulic system, which will raise the working temperature of a part separately. If the base flow is significantly larger, the part will be seriously polluted. The blockage and leakage in the gas path (including the sampler) often leads to abnormal peaks; The normal peak shape will be destroyed if the liner in the injector is not flattened

II. Check the detector: check whether the nozzle leaks, which will affect ignition, sensitivity, peak shape and baseline drift; Check whether the position of the image pair between the polarizer and the nozzle is correct: the nozzle mouth is higher than the plane of the polarizer circle, and the sensitivity decreases significantly. This is often caused by the column tube jacking up the quartz nozzle when installing the chromatographic column tube. If the image counter nozzle mouth is lower than the plane of the polarizer circle or the polarizer collides with the nozzle, the noise will increase; Check whether the collector insulation is good. If the collector insulation is poor, the noise will be great, the baseline will be unstable, and the drift will be serious; Poor contact or disconnection of the collector ion current signal line will cause no peak; If there is no oil flowing out of the oil return pipe and the detector is polluted, the change of base flow can be determined by heating up. The way to remove pollution is to disassemble and wash parts and components and carry out high-temperature aging

III. check the circuit: when the instrument is not ignited and the collector plug is unplugged, it can judge and check whether the amplifier is normal by walking the baseline. Generally, the noise should be less than 5 when walking the baseline of the amplifier цν， Drift should be less than 10 цν/zero point five ч。 If possible, you can input a micro electric precision high current to the amplifier, that is, connect an Ω high resistance in series with a battery to the input end of the amplifier (Collector ion line plug end), and the other end of the battery is grounded. The amplifier gain is in Ω gear, and the output should be about 100mV. If the amplifier gain is in Ω gear, the output should be about 10mV, which indicates that the amplifier works normally. In the absence of high resistance, it is used to touch the input end of the amplifier, A large signal should appear at the end, which is the simplest way to roughly judge whether the amplifier is normal. If the above inspection is not normal, the circuit should be further checked. The false welding and faulty welding of the wiring of the high resistance switching relay and the zc310j integrated operational amplifier often cause the amplifier to malfunction. You can use a small soldering iron to heat and weld each spot weld one by one to judge and check; The circuit (mainly high resistance) in the shielded iron box of the amplifier will be seriously affected by moisture, resulting in increased noise; The core wire of collector ion signal wire is thin and easy to break, which often leads to signal blocking and no peak; The polarization pole to ground voltage (polarization voltage) is generally 220v-230v (some products are designed to be 250v-300v). If the high-voltage regulator that gives the polarization voltage is damaged, the FID polarization voltage will be abnormal, resulting in no peak or chromatographic peak deformity. Use a multimeter to measure the DC voltage of the polarization pole to ground to check whether the polarization voltage is normal. Sometimes, the noise will also come from the high-voltage zener diode that gives the polarization voltage. The judgment method is to remove the V polarization point voltage and see whether the noise is eliminated or reduced. In addition to replacing the high-voltage zener diode, connect a 300K Ω resistor in series on the 230V polarization voltage, and then connect a 0.33 polarization pole to the ground ц F/400v capacitor can also effectively filter out the noise from the high-voltage zener diode. If the amplifier has an output, but zeroing does not work, the problem must be in the zeroing potentiometer or the corresponding connecting line