Abstract: Due to the rapid development of modern science and technology, the tasks faced by ion chromatographs have far exceeded the scope of traditional qualitative and quantitative analysis. Due to the development of science and technology, the field of human ion chromatography analysis and detection has been greatly expanded: from constant analysis to trace, trace, and ultra trace analysis.
In the analysis of samples of aerospace power materials, for the daily analysis of some inorganic anions, inorganic cations, organic acids, etc., in the past, volumetric methods, gravimetric methods, and spectrophotometric methods were often used to determine the required measurement items. These methods affect the accuracy and precision of the measured samples due to the strict operation procedures, tedious and time-consuming, complex interference factors, and poor repeatability. In the past ten years or so, the analysis and application of inorganic anions, inorganic cations, organic acids, etc. using ion chromatography at home and abroad have developed very fast. The author introduced a high-grade imported DX600 ion chromatograph from Dionex Corporation of the United States, and played a very important role in the application of actual work.
Over the past few years, the use of DX600 ion chromatograph for the analysis and application of inorganic anions and cations, organic acids in space power materials has made certain progress. The new generation of advanced ion chromatograph technology replaces the classic chemical analysis method, making the detection method faster, more accurate and precise, better sensitivity, reproducibility and reproducibility are also very satisfying, thus improving the ion The reliability of the chromatograph test data. The test results confirmed that the ion chromatograph has the advantages of high sensitivity, excellent analysis accuracy, less interference, very simple analysis operation, good selectivity and reproducibility.
The important function, separation technology and method of an ion chromatograph
1. The important role of ion chromatography in scientific and technological production
Before the 1980s, ion chromatographs were limited to ion-exchange separation and conductivity detection to analyze simple inorganic anions and cations, and have now developed into a variety of separation methods and detection methods. Ion chromatographic analysis has changed the situation of using traditional chemical analysis methods to measure inorganic anions and inorganic cations, and achieved the purpose of rapid determination of multiple ions. It is an important role in the analysis of inorganic anions, inorganic cations, organic acids and other analytical fields. Sensitive analysis method. It has occupied an extremely important position in the field of analytical chemistry. A few days ago, ion chromatograph is widely used in various fields and has been used as a routine analysis method in laboratory instruments.
2. DX-600 ion chromatography separation technology
The DX-600 ion chromatograph is mainly composed of four parts: active phase transportation system, separation system, detection system and data processing system. The flow chart of its component structure is shown in the figure.
(1) Ion chromatography active phase transport system: including liquid storage tank, gradient elution, high-pressure infusion pump device, etc., basically similar to the infusion system of high performance liquid chromatography.
(2) Sampling system for ion chromatography: There are three main types of sampling: pneumatic, manual and automatic sampling.
(3) Ion chromatography separation system: The separation system is the core and foundation of ion chromatography. The ion chromatography column is the "heart" of the ion chromatograph, which requires high column efficiency, good selectivity, and fast analysis speed. Ion chromatography is a kind of liquid-solid chromatography, which is a kind of high-performance liquid chromatography. However, column packing and separation mechanism have their own characteristics. The research of ion chromatography column is also a hot topic in the field of ion chromatography. The particle size of ion chromatography column packing is generally between 5 and 25 μm, which is slightly larger than that of high performance liquid chromatography, so its pressure is smaller than that of high performance liquid chromatography, generally monodisperse, and spherical.
(4) Suppression system of ion chromatography: For suppression type (dual column type) ion chromatography system, suppression system is an extremely important part, and it is also the most important feature of ion chromatography different from high performance liquid chromatography.
(5) Ion chromatography detection system: Conductance detection is the most commonly used method in ion chromatography detection. Due to the influence of the equivalent capacitance in the conductance cell, the relationship between the voltage and current applied to the conductance cell is non-linear, which makes it very difficult to measure the conductance value. In addition, the background conductivity value in the active phase is very high, and the correct measurement of the signal of the component to be measured from the larger background value is also an important issue in conductivity detection.
(6) Data processing system of ion chromatography: ion chromatography generally has low column efficiency. Compared with gas chromatography and high performance liquid chromatography, ion chromatography generally has low resolution, and it does not require high data collection speed, so Can be used in other types of data processing systems can also be used in ion chromatography. Moreover, in conventional ion analysis, the peak shape of the chromatographic peak is ideal, and the peak height quantitative analysis method can be used for analysis. The main data processing system is: recorder, automatic integrator, data workstation. The DX-600 ion chromatography data workstation provides PeakNet software, which can process multiple chromatograph information at the same time, and can control the pump, detector, automatic sampler and other systems of ion chromatography.
3. Analysis content of DX-600 ion chromatograph
(1) Instrument analysis content: The common anions separated and measured by ion chromatograph are its specialty. A needle sample is injected, and the measurement results of 7 common ions can be obtained within about 20 minutes, which is beyond the reach of other analytical methods. of.
(2) Common ions often detected are: anions: F-, Cl-, Br-, NO-2, HPO-24, NO-3, SO-24, formic acid, acetic acid, oxalic acid, etc .; cations: Li Na, NH 4, K, Ca 2, Mg 2, Cu 2, Zn 2, Fe 2, Fe 3, etc.
(3) Compared with AAS and ICP methods, ion chromatography method: the ion chromatography method used for the determination of cations has not shown superiority compared with atomic absorption spectroscopy (AAS) and plasma emission spectroscopy (ICP).
The main technical performance of two ion chromatograph
1. System characteristics of DX-600 ion chromatograph
All components have a front output panel. The menu-type interface is easy to learn and visualize the operation; the front panel is displayed in large characters and the contrast is adjustable, which can clearly display the operating status of the instrument; the screen is rich in information, you can quickly get the information and help you need; through the control panel or a A computer can monitor the system in real time; program the method and control the input and output through the module or software, and provide convenient operation; the components that can be randomly superimposed and connected to form a compact, streamlined appearance; key chromatographic data The real-time update can provide continuous diagnostic feedback information; the perfect user and service diagnostic system can provide real-time information on the operation of the instrument through two methods: front panel and software control; automatic routine calibration from the front panel saves time, Convenient; the front-pull fixed template design panel that is easy to detect and maintain can withstand corrosive liquids and gases; the infusion pump and detector can accommodate 100 program methods, and the program is not easy to lose in the event of a sudden power failure; The power supply can be switched automatically within the range of commonly used input voltage (90 ～ 265V), simplifying the instrument Installation; leak detection and maintenance devices can quickly find the instrument's liquid leakage failure.
2. Technical performance of DX-600 ion chromatography
(1) Basic principles of ion chromatography
Ion chromatography is a type of high performance liquid chromatography, so it is also called high performance ion chromatography (HPIC) or modern ion chromatography. The principle of separation is based on the dissociable ions on the ion exchange resin and the solute ions with the same charge in the active phase The reversible exchange performed and the difference in analyte solute affinity to the exchanger are separated. Suitable for separation of hydrophilic anions and cations. It is different from traditional ion exchange chromatography column chromatography mainly because the resin has a high degree of cross-linking and a low exchange capacity, the injection volume is very small, and the eluent is usually transferred online by the plunger pump. Continuous conductivity detection.
(2) Difference of ion chromatography separation column
The ion exchange resin is acid and alkali resistant, can be used in any pH range, is easily regenerated, and has a long service life. The disadvantage is poor mechanical strength, easy to swell, and easy to be polluted by organic matter. The separation column used in the DX-600 ion chromatograph is characterized by high column efficiency, fast exchange balance, and high mechanical strength. The disadvantage is that it is not resistant to acids and alkalis and should only be used in the pH range of 2-9.
3. Detection method of DX-600 ion chromatography
With the widespread application of ion chromatography, the detection technology of ion chromatography has evolved from a single chemically suppressed conductivity method to include electrochemical, photochemical, and other analytical instruments.
(1) Suppression conductivity detection method
Suppression type conductivity technology consists of the original suppression column technology, and has gone through the stage of continuous regenerable fiber tube and micro-membrane suppressor. The latest suppression technology uses electrolytic suppression method, so that the suppression conductivity detection can be performed automatically without the use of traditional regeneration liquid. Through conductivity suppression, the background conductivity value can be very low, and the detection sensitivity can reach a very high level. Suppression conductivity detection method is always the most ideal method.
(2) Ultraviolet absorption photometry
Anions with strong UV absorption at 195-220nm can be directly UV-absorbed by the eluent with weak UV absorption, and their selectivity and sensitivity are very high. It enables nitrate, nitrite and other ions to be detected to μg / L. Indirect UV detection is used for analysis that does not have UV-absorbing ions. The eluent has strong UV absorption and the detection signal is negative. Aromatic organic acids and phthalates and sulfobenzoates are mostly used in anionic eluents. The cation is a Cu2 or Ce3 solution with ultraviolet absorption as the eluent.
Application of Tri-ion Chromatograph in Space Power Material Analysis
Due to the rapid development of modern science and technology, the tasks faced by ion chromatographs have far exceeded the scope of traditional qualitative and quantitative analysis. Due to the development of science and technology, the field of human ion chromatography analysis and detection has been greatly expanded: from constant analysis to trace, trace, and ultra trace analysis.
1. Analysis of standard reagents
Ion chromatography is often used in the analysis of inorganic anions, inorganic cations, organic acids, etc. in space power materials. Including the determination of additives and impurities control by various intermediate products and final products. The determination of various anions in solution has good accuracy and precision. Very good results have been achieved in this way.
The standard solution of inorganic acid anions was measured six times in a row, and the relative standard deviation and detection limit of each ion were determined. (From a series of mixed standard samples) to obtain the linear correlation coefficient of each component to be tested, as shown in Table 1.
2. Analysis of high purity water
Determination of Na in high-purity water by ion chromatography is easy to operate, sensitive and fast. According to the above chromatographic conditions, the series of standard working solutions were analyzed, and the linear return equation was calculated based on the peak area, and the linear correlation coefficient r = 0.9998. This method was used to measure Na in high-purity water for 8 consecutive times, and the average value was 0.88 μg · L-1. See Table 2.
A known amount of chlorine (Cl-) standard solution was added to the cadmium nitrate solution sample, and the average value was 0.211 μg · L-1, and the meter recovery test was conducted under the experimental conditions. The uniform value recovery rate of this method is 95.3%, which shows that the measurement results are correct and reliable. See Table 3.
3. Analysis of cations
The analysis of alkali metals and alkaline earth metals has been widely used in ion chromatography. Use sulfuric acid or methanesulfonic acid as the eluent, anion exchange analysis, conductivity detection, analysis and detection can be completed in a single injection of 15min. When performing cation analysis, the accuracy, precision, and reproducibility of the test data are very good. According to the mixed standard samples of different concentrations of sodium, potassium, magnesium, and calcium, the standard deviation and relative standard deviation meet the requirements of laboratory quality control. . See Table 4.
From Table 4, the relative standard deviations are: sodium 0.7% to 1.3%, potassium 0.4% to 0.8%, magnesium 0.6% to 0.9%, and calcium 0.4% to 0.5%. Obviously superior to chemical analysis methods.
4. Comparability comparison
Using different analytical methods with comparability, the same standard (calcium carbonate) sample is analyzed, and the obtained measurement results are compared with each other, and the accuracy of the measurement is compared according to their conformity. Using this comparative experimental method is an effective way to analyze quality control methods. The comparison between the measured values ​​of ion chromatography and EDTA titration is now listed. See Table 5.
It can be seen that there is no significant difference in the amount of calcium carbonate measured by the above two methods, which can be regarded as an equivalent method. However, the analysis by ion chromatography is superior to the chemical analysis, and the determination is more convenient.
Four conclusions
The analysis and application of ion chromatograph on space power materials has been developed rapidly. This reflects a future development direction of ion chromatography. In the research and application of space power supply material analysis and product quality control, the instrument provides a large number of reliable analysis and testing data, and has achieved obvious results and economic benefits. DX-600 ion chromatograph is an indispensable modern analytical instrument for analyzing space power materials. It is believed that it will continue to play its unique role in the future analysis and testing field.
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