The following are the key influencing factors and detailed explanations of the multifunctional dairy analyzer:
1、 Characteristics of the sample itself
1. Homogenization degree
Insufficient homogenization of milk samples can lead to layering, resulting in uneven fat distribution, which directly affects the accuracy of infrared fat measurement or ultrasonic oscillation viscosity measurement. It is recommended to perform standardized homogenization treatment immediately after sampling.
2. Temperature control
Most dairy ingredients, such as fat melting and protein denaturation, are temperature sensitive. If the sample temperature deviates from the set value by ± 1 ℃, it may cause a deviation of more than 5% in protein determination by turbidity method. A Peltier temperature control module is required to maintain a detection environment of 37 ℃± 0.5 ℃.
3. Microbial contamination
After storing fresh milk for more than 4 hours, the acidic substances produced by bacterial metabolism will change the pH value, causing the conductivity method to fail to measure salt content. It is recommended to complete the testing within 2 hours after sampling, or add harmless preservatives for preservation.
2、 Instrument hardware performance
1. Cross sensitivity of sensors
Near infrared spectrometers are susceptible to moisture interference (water peaks cover multiple wavelengths), and multiple regression algorithms need to be used to eliminate background noise. The optical path length error of the flow colorimetric cell should be less than 0.1mm, otherwise the difference in absorbance can reach 8%.
2. Cleanliness of flow system
Residual milk stains blocking the circulation pool can cause pressure fluctuations and shift the ultrasonic resonance frequency. After daily testing, it is necessary to use alkaline cleaning solution and ultrasonic vibration for double cleaning, and disassemble the valve body for deep maintenance every week.
3. Light source stability
After more than 500 hours of use, the brightness of the LED light source will decrease by more than 3%, and a built-in reference channel is required for real-time calibration. Equipment using pulsed xenon lamp light source with a flash life of more than 10 ^ 6 times is more suitable for high-frequency detection.
3、 Environmental operating conditions
1. Temperature and humidity fluctuations
For every 1 ℃ change in ambient temperature, the reading of the density refractometer drifts by about 0.0002g/cm ³. Require the laboratory to install air conditioning to maintain a temperature of 25 ℃± 2 ℃ and a relative humidity of less than 70% to prevent condensation on optical lenses.
2. Electromagnetic interference suppression
Equipment such as compressors driven by frequency converters can generate electromagnetic pulses that interfere with the conductivity electrode signal. The instrument should be well grounded (grounding resistance<4 Ω), and filter capacitors should be installed in critical circuits.
3. Vibration protection
The unbalanced torque of the centrifugal sampling system can cause a deviation in the angle of light scattering. The instrument needs to be fixed on a shock-absorbing platform and kept away from large equipment operation areas.
4、 Operation and maintenance standards
1. Calibration traceability management
Use standard milk powder (GBW (E) series) for multi-point calibration every month, and send it to the metrology institute for statutory verification every year. After replacing the spare parts, gain correction must be performed again.
2. Precise control of injection volume
The automatic pipette needs to be regularly calibrated, and the sample volume error should be less than 1%. When manually pouring, it is necessary to slowly inject along the pipe wall to avoid the generation of bubbles.
3. Timely replacement of consumables
Blockage of the filter membrane will cause the back pressure to rise to the warning value. At this time, the 0.45 μ m hydrophilic filter membrane should be replaced in a timely manner. Electrode aging manifests as prolonged response time and needs to be replaced periodically according to the instructions.
5、 Data processing algorithm
1. Multi parameter compensation mechanism
Advanced instruments use partial least squares (PLS) to establish mathematical models between various components, which can automatically correct the influence of color quenching effects on the fluorescence based determination of vitamin B2.
2. Outlier elimination strategy
Set the 3 σ principle to automatically filter outlier data, but manual review is required for special samples such as colostrum. The historical database should store no less than 10 sets of parallel sample spectra for traceability.
The accuracy of a multifunctional dairy analyzer depends on multiple aspects such as sample preparation, instrument performance, environmental control, operating procedures, and data processing. In practical applications, it is necessary to establish a standardized operating procedure (SOP), conduct regular performance validation, and optimize according to the specific characteristics of the testing items in order to obtain reliable testing results.