The appearance of pocket colorimeters solved the problem of spectroscopic qualitative and quantitative testing of trace samples. Based on this feature, this type of instrument is widely used in biological, medical, and other fields where the sample volume is sparse and expensive.
The unique feature of the micro-volume colorimeter is that it requires very little test sample volume, with the ability to measure samples down to 0.3 μL in existing instruments, saving very rare and expensive sample volumes. The detection wavelength ranges from 200 to 1 000 nm, and most instruments are set with fixed-point test wavelengths of 230 nm, 260 nm, and 280 nm, which are convenient for DNA, RNA and protein testing. The tungsten and deuterium lamps are replaced by xenon lamps with stable luminescence and no preheating as light sources, which have a longer life and greater light intensity. The instruments with slightly higher precision use inductively coupled array detectors, whose spectral range, quantum efficiency, signal-to-noise ratio and other indicators are much higher than those of photodiode arrays.
Compared with an ordinary pocket colorimeter, the completion time of the portable colorimeter is greatly shortened, and the procedure of cleaning the cuvettes is omitted. Just wipe with lens tissue. The detection functions that this type of instrument can achieve are as follows: ordinary colorimeter detection, DNA/RNA concentration detection, protein concentration detection, etc.
Analysis of Calibration Method for Pocket Colorimeter
Calibration with standard substance of filter liquid
This method can refer to JJG 178-2007 for calibration of some items. The main key technical indicators of the instrument such as wavelength accuracy, wavelength repeatability, absorbance accuracy, and stray light can be listed as calibration items. For the calibration of wavelength accuracy and wavelength repeatability, the existing iron oxide wavelength solution standard material can be used. The standard solution has more than 10 sharp and clear absorption peaks in the wavelength range of 240-650 nm. The accuracy of absorbance can use the method given in JJG178-2007 to prepare a certain concentration of potassium dichromate perchloric acid solution or potassium dichromate sulfuric acid solution, and use a high-precision UV-visible photometer to determine the value at 235 nm, Absorbance values at 257 nm, 313 nm, 350 nm. Secondly, pay attention to the matching of the ambient temperature during calibration and the temperature during fixed value. Stray light characteristics can use 10 g/L according to the requirements of JG 178-2007. Sodium iodide solution and 50 g/L sodium nitrite were used to detect the transmittance or absorbance of the instrument at 220 nm and 340 nm, respectively. The above calibration methods and items are based on the measurement principle of the pocket colorimeter, combined with the technical parameters given by the manufacturer, the user can use the calibration results to have a comprehensive evaluation of the calibrated instrument. In addition, if you want to know more about the baseline flatness and baseline noise of the instrument, you can also refer to JG178-2007 to develop a calibration method.

Calibration was performed with concentration standard substance
The method is based on the direct determination of the content of nucleic acid and protein substances by pocket colorimeter and uses DNA reference material, RNA reference material, or protein reference material to determine the difference between the measured value of the reference material and the market value as the indicator of the instrument. The value error is used to evaluate the metrological characteristics of the instrument. This type of instrument is preset with the fixed-point wavelength test function, and the relationship between the absorbance value and the concentration value is preset. The maximum absorption wavelengths of nucleic acids and proteins are 260 nm and 280 nm. In order to judge the purity of nucleic acids or proteins, A230 nm is added to indicate some contaminants such as carbohydrates, phenols, peptides, etc. in the sample, and A320 nm is used to indicate the sample. turbidity and other interfering factors. Calibrating this type of instrument with a concentration standard material can also incorporate the repeatability of the measured value and the linearity of the instrument into the calibration project. Of course, the evaluation of the linearity of the instrument requires the use of a series of standard solutions of different concentrations.
Based on the above analysis, the first calibration method can carry out calibration work on the basis of a little refinement, and it is relatively easy to use for the majority of metrology workers, and the reference material is cheap and easy to obtain. Although the latter calibration method can give the advantages and disadvantages of measurement characteristics such as the indication error and linearity of the measurement results of the pocket colorimeter, how to select the reference material in the actual calibration process, only a single reference material is still nucleic acid and protein. Commonly used, because the two are quantitatively measured at different absorption wavelengths, and the accuracy of the concentration measurement at different wavelengths is examined. In addition, the stability, economy and easy availability of DNA or RNA reference materials and protein paper reference materials need to be considered, and the requirements for storage conditions should not be too high, especially for some DNA content reference materials. It is convenient for measurement staff to perform on-site calibration. Therefore, on the basis of JJG178-2007, a series of standard solutions are developed to calibrate the measurement characteristics of such instruments such as wavelength accuracy, absorbance accuracy, stray light, etc. Through the calibration results, the technical indicators of the instrument can be objectively and comprehensively evaluated. Provides more comprehensive data for the user to understand the instrument.
