Atomic Absorption Instrument Training

1. Atomic Absorption Instrument Training

2. Daily Maintenance and Care

• Working Environment Requirements: Atomic absorption instruments are precision equipment, so the working environment must be dust-proof and moisture-proof. The temperature should be stable between 15-30°C; if the humidity exceeds 70%, an air conditioner (for dehumidification) or a dehumidifier should be equipped. Good ventilation is required to expel waste gas in a timely manner. The waste liquid bucket should be cleaned regularly to prevent instrument corrosion.
• Power Supply Requirements: Graphite furnace analysis uses electric heating, so stable and reliable power supply must be ensured. The host, graphite furnace, and other equipment should be connected to different power quadrants separately. The graphite furnace power supply should be equipped with an air switch, and the instrument should be grounded independently, with the grounding resistance less than the specified value.
• Gas Source Requirements: High-purity gases must be used for acetylene and argon. Impure acetylene will interfere with experiments, while argon protects the graphite tube and sample atomization. Nitrous oxide is used in the analysis of high-temperature elements. There are strict regulations for the use, transportation, and storage of acetylene: the distance between the gas cylinder and open flames must be more than 10 meters; acetylene cylinders should not be stored together with oxidizing gases; pressure reducing valves must be verified and calibrated; attention should be paid to the outlet pressure and internal cylinder pressure; and leak detection must be performed when replacing gas cylinders.
• Air Compressor Maintenance: For oil-free air compressors, drain water under pressure after use; if there is a secondary gas-liquid separator, observe the moisture condensation. For oil-lubricated air compressors, pay attention to replacing and replenishing lubricating oil to prevent oil from entering the pipeline.
• Water Circuit Inspection: Graphite furnace analysis is equipped with a cooling circulating water system, which functions to quickly cool the graphite furnace to room temperature. Pure water or distilled water should be used in the water tank, which should be cleaned every six months. The water temperature is set to 20°C to prevent fogging on the quartz window.
• Light Source Inspection: Element lamps have a service life; preheat them for half an hour before use, and set the lamp current appropriately (excessive current will reduce the lamp life and analysis sensitivity). The element lamp should be free of external damage; handle it gently without touching the quartz window, and clean it with alcohol-soaked degreased cotton. The quality of the lamp can be judged by absorbance, peak-seeking wavelength, luminous intensity, detector negative high voltage, etc. Multi-element lamps are not suitable for 990 and A3 instruments, and it is recommended to purchase them from formal manufacturers.
• Precautions for Nebulizer Use: The nebulizer affects the stability, reliability of measurement data, and detection limit. The impact bead must have high smoothness; when adjusting, pay attention to the front-back distance and avoid touching it. The front end of the capillary sampling tube is prone to blockage; use the back-blowing method to clear blockages, and do not use metal wires for glass nebulizers. After measurement, clean the nebulizer by aspirating and spraying distilled water. The temperature in the workroom should not be lower than 10°C; if there are bubbles in the sample, tap with fingers or remove them with a syringe.
• Precautions for Graphite Tube Use: Do not touch the graphite tube with hands; use tweezers to hold it. The graphite tubes used for 990 and A3 instruments are universal for high, medium, and low temperatures; samples requiring extremely high temperatures need special coatings. Graphite cones should be cleaned in a timely manner to avoid crystallization, and severely damaged ones should be replaced promptly. Pre-burn the graphite tube to clean it before use; ensure the sampler needle is in the correct position during installation. The resistance of graphite tubes may vary between batches, so the heating program can be optimized.
• Precautions for Burner Use: Clean the burner head regularly (using ultrasonic cleaning); if crystallization is severe, replace it with a new one or have it disassembled and cleaned by engineers. Ensure proper installation of the burner head, and clean the system after analyzing high-content samples.
• Regular Maintenance Items: Drain water from the air compressor before shutting down; clean the system after using organic reagents, and check the waste gas pipe. Regularly clean the lamp window, liquid droplets on the sample tray, and ventilation equipment, and pay attention to rainproofing and dustproofing. For graphite furnace analysis, pay attention to adjusting the atomization temperature and sampler needle position; regularly check the cylinder pressure, burner head, nebulizer, cooling circulating water, and indoor dust removal.

3. Emergency Handling

• Power Failure Handling: If a power failure occurs during a flame experiment, the instrument will automatically close the fuel gas and oxidant valves to extinguish the flame. Close the main cylinder valve; after power supply is restored, re-run the self-inspection, turn on the gas cylinder, and resume the experiment.
• Water Cutoff Handling: If water supply is cut off during graphite furnace analysis, the graphite furnace will stop heating. Develop the habit of touching the furnace body to check the cooling status before sampling.
• Acetylene Leakage Handling: If acetylene leakage is smelled or an alarm is heard, check for the leak point and eliminate the hidden danger before using the equipment again.
• Backfire Handling: Backfire occurs when the fuel gas supply efficiency is lower than the combustion speed, causing the flame to burn inside the atomization chamber. The atomization chamber is equipped with an explosion-proof membrane and an explosion-proof valve. If there is an open flame during backfire, extinguish it first, then reinstall the explosion-proof valve or membrane before reuse.

4. Simple Fault Diagnosis and Maintenance

• COM Port Occupation: This may be caused by damage to the computer’s communication port; when replacing with a new computer, the port number needs to be changed. It may also be due to damage to the serial communication cable or the host power not being turned on. For issues with electronic components, engineers are required to troubleshoot.
• Wavelength Self-Inspection Failure: Possible causes include no lamp in the working lamp position or the lamp not being lit, the far-infrared device being blocked by light (e.g., the graphite tube not being removed), or the atomizer blocking light during flame absorption.
• Peak-Seeking Showing Insufficient Energy: This may be because the element set in the software does not match the element of the installed lamp, or the element lamp is aged (resulting in unstable luminescence or insufficient intensity).
• Abnormal Ignition:
  • No Response When Ignition Button is Pressed: Possible causes include insufficient air compressor pressure, the water seal float switch not floating, improper installation of the burner head, the emergency flameout switch being activated, strong light irradiating the flame detector or detector damage, the detector optical cable falling off or being in the wrong position, or excessive lamp current setting.
  • Auxiliary Flame Normal but Burner Head Flame Failing to Ignite: Possible causes include incorrect flow settings for fuel gas and oxidant, or the flame detector not detecting the auxiliary flame.
• Excessive Noise: May be caused by substandard environmental conditions, power supply issues, faulty lamps, interference from surrounding magnetic fields or high-power equipment, or deformed workbenches (which also affect noise levels).
• Unstable Combustion: May be caused by issues with the air compressor, outlet pressure of fuel gas and oxidant, blocked burner head, excessive exhaust volume, or wind/accumulated water in the surrounding area.
• Poor Flame Reproducibility: May be caused by excessively high concentration of the tested sample, incomplete sample pretreatment, position deviation of manual or automatic sampling, or aged graphite tubes.
• Low Test Sensitivity: For flame methods, this is related to the light source, fuel gas ratio, and standard sample preparation; for graphite furnace methods, it is related to the graphite tube, heating conditions, and procedures.
• Poor Standard Curve Linearity: May be caused by light source fluctuations, aged element lamps, excessively wide slits, spectral bandwidth effects on alkali metal elements, or excessively high sample concentration.

5. Interactive Q&A

• Hydride Generator: Its detection limit is at the same level as that of the graphite furnace. Clean the system before and after use; adjust the light spot position to pass through the center of the quartz absorption tube. Avoid introducing high-concentration samples, as related components may need to be replaced after high-concentration sample introduction.
• Cesium Determination: Cesium is more difficult to determine than other elements; refer to the analysis manual of Yangtze Auto and the cesium determination manual for requirements.
• Sodium Determination: If the absorbance of pure water is high, spectral interference and flame self-absorption effects may be the causes (this will be the focus of the next course). Generally, the background correction function is not enabled for flame absorption.
• Flame Atomizer: The disassembly method was not covered in this course.
• Insignificant Absorbance Change of Gradient Solutions: May be due to insufficient sensitivity, which is related to the nebulization efficiency of the nebulizer (this will be covered in subsequent courses).
• Easily Damaged Iron Lamps: Iron element lamps may have a shortened service life due to the special influence of certain elements. Judge the quality of the lamp by luminescence stability, peak-seeking wavelength, luminous intensity, and negative high voltage.
• High Negative High Voltage When Arsenic Lamp is Installed: Arsenic is a special element, so the negative high voltage may be high in the extremely short or extremely long wavelength range of the instrument. For other elements, high negative high voltage may indicate a faulty lamp.