How to judge the performance of the trace element analysis instrument

At present, trace element detection instruments popular in the market are graphite furnace atomic absorption and electrochemical apparatus. The spectrophotometric method used in many applications in the analysis cannot meet the requirements of sensitivity, and can only be used for high-level biochemical analysis and constant analysis. Atomic Absorption has higher precision and detection speed, should be the first, but due to more complex equipment, high prices, long return on investment, supporting a variety of carrier gas and other factors, generally more equipment in the top three units, and counties Most grades and below choose electrochemistry analysis instruments.

There are many kinds of trace element analysis instruments (microelement detectors), each with a specific market. There is a way to use the camera to shine on the nails and use televisions to look at the texture and color to detect trace elements. This is purely flickering. This kind of instrument cannot enter the hospital. Most of them are deceived in pharmacies or mobile booths.

No matter what the principle instrument is, it must meet the most basic requirements of the analytical instrument before it can be used for actual detection.

The main indicators of the instrument are the following:

1. Repeatability: Repeatedly measuring the same sample or measuring the error of multiple samples with the same content, generally expressed by the coefficient of variation, the smaller the better, this indicator is mainly the credibility of the expression instrument, precision and stability.

2. Lower detection limit: It refers to the lowest limit of the detectable content. Generally speaking, it uses triple noise as the standard. Generally, it uses low-contamination and high-sensitivity elements such as electrochemical detection with cadmium ions and atomic absorption with copper ions. This indicator indicates the sensitivity of the instrument.

3. Correlation coefficient: The regression coefficient for different concentrations of elements and linear equations, the maximum is 1, at least 0.99 or more.

4. Calibration curve deviation: The difference between a known amount and a certain point of the standard curve is smaller, the better, generally less than 10%.

Note: The 3 and 4 items express the accuracy of the instrument

Different types of analytical instruments have their merits and weaknesses, and any type of instrument cannot support the world. The advantages and disadvantages are relative. For example: Atomic Absorption detects metal cadmium with high sensitivity, while lead measurement sensitivity is extremely low. Electrochemical analysis instruments are not as fast as atomic absorption, but traditional atomic absorption requires a specific elemental lamp for each element and cannot be combined.

Electrochemical analysis instruments use electrodes as sensors, especially solid electrodes cannot be used stably for a long time, and a certain number of samples need to be re-treated such as mercury-plated film (referred to as lead, cadmium, etc.), but the measured lead can be quantified from 0.1 micrograms. Detection, this is atomic absorption can not be done anyway.

Atomic absorption assays are fast and accurate. However, it cannot be used for the detection of anions and organic substances. In addition, the use of high cost, high environmental requirements, in the grassroots unit users to promote the application of a certain degree of difficulty.

Electrochemical instruments use metallic mercury as a working electrode, which is suspected of polluting the environment, but can be used for analysis of cations, anions, organics, etc. The purchase, maintenance and operation costs are low, and the investment return rate is high and it is easy to promote. There are many national standards and industry standards that use electrochemical polarography and dissolution methods. Therefore, high-end users use atomic absorption, and users at the county level and below use more electrochemical instruments.

How to determine the performance of an instrument?

The average user has few points because of lack of professional knowledge, but he can grasp a few points. First of all, look at whether or not the instrument is stable. This is the most basic requirement of the instrument. It is the basis of analysis and inspection. If this indicator is not good, the others will not be able to talk about it. It is purely flickering. If the same sample, the results obtained by the test are fluctuating, showing a large difference, which indicates that the instrument has a problem. When the content of the measured substance is high, the stability of the measurement is generally good, but this does not indicate the problem, because the purchase of such instruments are used for trace element detection, rather than for high-level detection. Because it is a trace, the elemental peak obtained is not high, which is a test of the true performance of the instrument. For high content assays, the coefficient of variation can reach 1%, but it is good for low levels up to 5%. If you look at the actual measurement of the instrument, some manufacturers do not allow the operator to conveniently superpose the curve and do not set the procedure for obtaining the coefficient of variation in order to avoid the observation of repeatability. This is because the performance of the instrument is not good enough to be seen by others. The problem, in essence, is that the performance of the instrument is not closed, and producers are evading this issue. Actually, the variation coefficient of some manufacturers' instruments is between 10% and 20%. The error greatly exceeds the relevant regulations. The reliability of the results thus obtained is low, and the coefficient of variation of our company's products is controlled below 5%. At a glance.

Electrochemical polarographic analysis uses extremely small electrodes (mercury finger electrodes), and the sensitivity is related to the specific surface area of ​​the electrodes. The area has a large signal-to-noise ratio (referring to the ratio of signal to noise), high sensitivity, and strong anti-interference ability. Since the area of ​​the drop electrode depends on the volume, if it is large, it must be controlled without falling. Therefore, the surface area of ​​the electrode is severely constrained. This determines the noise and repetitiveness of the instrument made by the conventional electrode, which is currently used by all. Electrode-like apparatus is a common problem. Only my company's products solve this problem through the use of a series of technologies such as the use of a static mercury electrode. In this area of ​​technology is better than any of the same instruments, which can be confirmed by on-site comparisons. Another type of electrochemical instrument evades this type of problem. Solid electrodes are used to measure all elements, and mercury electrodes are used to attack instruments that use polarographic methods from an environmental perspective. In fact, in the test, mercury works in a closed environment and does not come in contact with the atmosphere. Just like the sphygmomanometer, the current standard of measurement is mercury sphygmomanometer, which is still widely used. The use of polarographic analysis methods for mercury drop electrodes is a national standard method and industry standard in many fields. For example, zinc determination in serum is a method prescribed by the Ministry of Health's inspection protocol, and there are more polar analysis standards in foods. The use of solid electrodes (such as glassy carbon electrode) to measure certain specific elements such as lead is good, but it is impossible to use all of them to solve the detection of all elements, both theoretically and practically. All lack evidence. Those who spend a lot of money to purchase such instruments either have insufficient knowledge or have other reasons. The trace element analysis is low in content, has a small useful signal, and has high technical requirements. Good reproducibility, high sensitivity, stable instrument performance, poor performance, poor repeatability, poor overall instrument infrastructure, and the need to use various means to cope with users and conceal the truth, and users know little about this. The simplest way of judging is to see if the instrument is set up so that it is convenient to perform multiple comparisons of curves and to directly observe the repeatability function, and whether the coefficient of variation can be easily found. After further measurement of zinc in the blood, repeated tests have been performed to see if the repeatability is good or bad. Because the zinc content is low, the performance of the instrument can be evaluated. Before testing, blanks need to be checked to prevent false impressions caused by high reagent blanks.

It is possible to examine other performance indicators on the basis of good repeatability. Objectively speaking, as long as the repeatability is good, other performance indicators should be less problematic. But the kind of instrument that uses one kind of electrode to make all elements, make the difference between blank standard solution and measured sample. That is to say, if you only do a simple standard solution without doing a sample, it may be very good, but when you add a sample, the sample brings a variety of disturbances to make a very large change in repeatability, linearity, and sensitivity. At present, the use of solid glassy carbon electrode for measuring blood lead is more mature. Others should look at the national and industry standards for this area, whether there is any literature in this area, and whether there is an actual sample for the sample. If not, some companies have used this electrode in a very short period of time to come up with a set of analysis methods. Whether it is a superpower or another reason requires interested parties to think for themselves.