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Mastering the correct usage method of the Sherrwood flame photometer is the core to ensure accurate data
Date: 2025-11-10Read: 0
The Sherrwood flame photometer is a classic analytical instrument based on the principle of atomic emission spectroscopy, specifically designed for rapid determination of alkali metals (such as sodium and potassium) and some alkaline earth metals (such as lithium and calcium) in samples. It is widely used in clinical testing, agricultural soil analysis, food testing, and industrial water quality monitoring. Its operation may seem simple, but if the steps are not standardized, it can easily lead to reading drift, decreased sensitivity, cross contamination, and even abnormal combustion. Mastering the scientific and rigorous use of the Sherrwood flame photometer is the core of ensuring accurate data and equipment safety.
1、 Preparation before use: calibration first, solution compliance
Check whether the pressure of gas (usually liquefied petroleum gas or propane) and auxiliary gas (compressed air) is stable (gas 0.05-0.1MPa, air 0.2-0.3MPa), ensuring that the flame is in a light blue cone shape;
Prepare standard series solutions (such as 0, 2, 4, 6, 8mmol/L Na/K) using deionized water (conductivity ≤ 1 μ S/cm) to avoid interference from impurities;
Start up and preheat for 15-30 minutes to stabilize the temperature of the optical system and flame chamber;
Rinse the injection tube with blank solution (deionized water) and zero it.
2、 Standard curve establishment: standardize operations to avoid pollution
Inhale standard solution in descending order of concentration, and clean the pipeline with blank solution for more than 30 seconds after measuring each concentration to prevent residual cross contamination;
Repeat the measurement of each concentration 2-3 times, take the average and draw a calibration curve. The correlation coefficient R should be ≥ 0.999;
If the sample matrix is complex (such as serum or fertilizer extract), it is recommended to use the "standard addition method" or dilute it to a linear range.
3、 Key points of sample testing
The sample needs to be clarified and free of particles. If necessary, centrifuge or filter (0.45 μ m filter membrane) to prevent clogging of the atomizer;
Before inhaling the sample, equilibrate the system with blank liquid;
After the reading stabilizes, record the result. If there is a large fluctuation, check whether the flame is jumping and whether the injection capillary is leaking;
After testing high concentration samples, rinse with blank solution for a long time (≥ 1 minute) to protect the atomization system.
4、 Special precautions
When measuring sodium and potassium simultaneously: pay attention to whether the filter switching is in place, and some models need to be manually replaced to avoid channel crosstalk;
High salt samples: prone to salt accumulation in the combustion head. During testing, dilute acid (such as 1% HNO) cleaning can be temporarily stopped;
Flame abnormality (yellow flame, backfire, flameout): Immediately turn off the gas, check for gas path blockage, proportional imbalance, or waste liquid pipe water seal failure.