The analysis methods of second-hand high-resolution mass spectrometers mainly revolve around their core functions, including sample preparation, instrument operation, data acquisition and processing, etc. At the same time, optimization should be carried out based on their high-resolution characteristics. The following are specific analysis methods:
1、 Sample preparation
Sample state adaptation: Choose the appropriate processing method based on whether the sample is solid, liquid, or gas. For example, if the purity of a liquid sample is low, impurities need to be removed through filtration, extraction, concentration, etc; If the solid sample is thermally stable, it can be ground into powder and dissolved. Insoluble solids may require derivatization or direct solid injection technology; Gas samples are usually injected directly through gas sampling valves or enriched through adsorption desorption devices.
Solvent selection: Choose a solvent compatible with the ionization source, such as polar solvents commonly used for ESI sources and non-polar solvents commonly used for EI sources, to avoid solvent reaction with the sample or the generation of interfering ions.
Biological sample processing: For biological samples such as blood and urine, it is necessary to remove interference from large molecules such as proteins, such as precipitation and centrifugal filtration.
2、 Instrument operation
Power on preheating: Start the machine in the order specified in the instrument manual. Usually, turn on the vacuum pump and power supply first, and then turn on the host and workstation software to ensure that the vacuum system reaches the working vacuum level and the components such as the ion source and mass analyzer are stable. The preheating time is usually 30 minutes to 2 hours.
Ionization source parameter settings:
Ionization method selection: Select the ionization method based on the sample type, such as EI, ESI, MALDI, etc.
Parameter adjustment: Set ion source temperature, ionization voltage, gas flow rate (such as ESI sheath gas, auxiliary gas), etc. For example, the EI source is set with electron energy (usually 70eV) and ion source temperature (150-300 ℃); The ESI source is set with spray voltage (3-5kV), capillary temperature (200-350 ℃) and atomizing gas pressure.
Quality analyzer parameter settings:
Scanning range: Set the scanning range (m/z range, such as 50-1000).
Scanning speed and resolution: Choose according to requirements, with high resolution for qualitative analysis and fast scanning for quantitative analysis. High resolution mass spectrometers can provide m/z peaks up to 4-5 decimal places, which helps identify compounds with higher certainty and confidence.
Parameter settings for combined equipment: If combined with chromatography (such as GC-MS/LC-MS), chromatographic conditions (such as column temperature, flow rate, and mobile phase ratio) need to be set synchronously to ensure that chromatographic separation matches mass spectrometry detection.
3、 Data collection and processing
Injection method:
Chromatography injection: The sample is first separated by gas chromatography (GC) or liquid chromatography (LC), and then enters mass spectrometry through an interface, suitable for complex mixtures (such as food and environmental samples).
Automatic sampling: Batch samples can be sequentially injected through an automatic sampler to improve efficiency and reduce human error.
Data collection: Activate the "collection" function of the workstation software, and the instrument automatically scans the sample ions for mass to charge ratio, generating real-time mass spectra (with m/z on the horizontal axis and ion intensity on the vertical axis). For quantitative analysis, it is necessary to first collect the mass spectrometry signal of the standard sample, establish a standard curve (the relationship between ion strength and concentration), and then analyze the unknown sample.
Data processing:
Qualitative analysis: Determine the type of compound by comparing characteristic ion peaks (such as molecular ion peaks and fragment ion peaks) with standard spectral libraries (such as NIST libraries); High resolution mass spectrometry can directly provide accurate molecular weight and assist in structural identification.
Quantitative analysis: Select characteristic ions of the target compound (such as parent ion daughter ion pairs, suitable for triple quadrupole mass spectrometry), and calculate the sample concentration based on the standard curve.
Result validation: Export the analysis results (such as mass spectra and concentration reports) for result validation (such as excluding false positives and confirming peak purity).
4、 Special considerations for high-resolution mass spectrometers
Resolution optimization: The core advantage of high-resolution mass spectrometers lies in their high resolution, so it is necessary to fully utilize this characteristic in the analysis process. For example, when distinguishing compounds with similar mass, high-resolution mass spectrometers can provide more accurate mass measurements, thereby accurately identifying compounds.
Sensitivity and signal-to-noise ratio: High resolution mass spectrometers typically have high sensitivity, but attention should still be paid to signal-to-noise ratio when analyzing low concentration samples. The signal-to-noise ratio can be improved by optimizing instrument parameters (such as ion source temperature, ionization voltage, etc.) and sample processing (such as concentration, purification, etc.).
Maintenance and Calibration: Second hand high-resolution mass spectrometers may experience performance degradation due to prolonged use, therefore regular maintenance and calibration are necessary. For example, cleaning the injection system, replacing aging components, calibrating mass to charge ratio accuracy, etc.