Comparison of dynamic range conductivity detector and fixed range conductivity detector

2021-05-08 15:50:58

The naming of the dynamic range conductivity detector is relative to the traditional fixed range conductivity detector, especially the detector based on the analog circuit. The dynamic range conductivity detector is a new type of digital signal conductivity detector. Its main feature is that it does not set the range in advance, but automatically selects and switches the appropriate range according to the change of the conductance signal during the analysis process. The range is not fixed during the sample analysis. Yes, when detecting small signals (low-concentration samples), the high sensitivity range is automatically switched, when detecting large signals (high-concentration samples), the low-sensitivity range is automatically switched, and the conductivity signals detected in different ranges are seamlessly joined by the software to form A complete spectrum of high and low signals coexisting.



As we all know, many instruments (not limited to ion chromatographs) have ranges, and each range limits a maximum detection range. The range is preset before the analysis, and the range remains unchanged during the sample analysis until the end of the sample analysis. If the sample exceeds this range, it cannot be quantified, and the sample needs to be re-injected after switching the range. In this way, when analyzing unfamiliar samples, we cannot accurately determine which range the sample concentration will be in, that is, we cannot determine which range is appropriate to set. There are two solutions in the past. One is to select a higher sensitivity range for test after diluting the sample; the other is to use a low sensitivity range for test without dilution or small multiple dilution. Determine the dilution factor and range according to the test conditions. In this way, the test test cannot be omitted, and when the ion concentration in the sample differs greatly, the sample cannot be injected and analyzed at the same time. In addition to the normal sample analysis process, additional work is required the amount. The dynamic range conductivity detector solves the above problems in a brand-new way.


What is a fixed-range conductivity detector?

Since the conductance signal detected by the detector is linear within a certain range, it will not be linear if it exceeds this range, so the large signal must be attenuated to the detectable range. The range is a tool used to control the signal attenuation multiple, conductance detection Each range of the detector actually specifies the signal amplification factor, such as: 1st gear, 2nd gear, 3rd gear... 10th gear, etc., 1st gear is the most sensitive, 10th gear is the least sensitive and the detection signal range is the most width.

Usually the range has a certain rule, for example, the same ion is detected with different ranges, the peak height of the first detection is 10, then the signal detected by the second detection is a fraction of the first (the regulations of each manufacturer are different) , It is more common that the second gear is 1/2 of the signal of the first gear, that is, the peak height of the second gear is 5, and so on, the third gear is 2.5, the 4th gear is 1.25, the 5th gear is 0.625, the 6th gear is 0.3125, and the 7th gear It is 0.1563, the 8th gear is 0.0781, the 9th gear is 0.0391, and the 10th gear is 0.01953. The signal of the 1st gear is 512 times that of the 10th gear. In other words, the detection limit of the 10th gear is 512 times that of the 1st gear. When we use level 1 to detect low-concentration ions, the high-concentration ions in the sample may exceed the maximum value of this level and flattened peaks appear.

For traditional fixed-range conductivity detectors used for ion chromatography analysis, the range is set before the sample is injected. If the sensitivity is not suitable after the sample is injected, switch the range or dilute the sample once for analysis. Sometimes a sample needs to be injected. It takes several samples to get an accurate result, and its characteristics are as follows:

Control panel: There is an obvious range selection function, such as gear selection (1-10 gears can be selected), or 30μS, 100μS, 1000μS, etc.

Signal unit: mV (millivolt)

Range setting: pre-set before sampling (different manufacturers' products provide different ranges for setting, such as 10 ranges, 8 ranges, and 2 ranges. The common feature is that they need to be pre-set before sampling)

Conductance detection range: The range of small signal and the range of detecting large signals are separated and cannot be detected at the same time, so even if the widest range of the detection range can reach 35000μS, it is meaningless, because low-concentration ions still need to be switched to high sensitivity Re-inject samples in the range (can not analyze high-concentration ions and low-concentration ions in one range at the same time)

Linear range: relatively small. Usually within 100mg/L.

Sensitivity: Poor sensitivity. Usually install 50-100 microliters loop

Standard curve: A standard curve needs to be established for each range. For example, 10 sets of standard curves need to be established for 10 levels. Only by doing this, can the measurement range be accurately quantified, and the sample injection workload is huge.

Sample dilution: the sample needs to be diluted. Since the workload of standard curve for each range is relatively large, it is usually selected to fix a commonly used range and make a set of standard curves. When the concentration of a certain ion in the sample exceeds the range (flat peak or deformed peak), a diluted sample is taken. Reduce the sample concentration to within the measuring range.

Output signal: analog signal, external signal collector is required;

Anti-interference ability: weak

Flat-headed peak: A flat-headed peak appears when the range is exceeded. A more common situation is that a flat peak appears when the signal exceeds 1300mV, and the peak begins to deform when the signal exceeds 800mV.


The new digital circuit-based dynamic range conductivity detector completely solves the problem of the traditional fixed-range conductivity detector range limitation. It can analyze the high and low concentration ions in the sample at the same time with one injection. Its characteristics are as follows:

Control panel: without any range options

Signal unit: μS (micro Siemens)

Range setting: no need to set the range

Conductance detection range: 0-15000μS full coverage

Linear range: 0.001-200mg/L (based on chloride ion, 10μL injection volume);

Sensitivity: high sensitivity;

Standard curve: one set or two sets of standard curves (due to the requirement of quantitative accuracy, it is recommended to make high and low concentrations separately);

Sample dilution: the sample can be injected directly without dilution;

Output signal: digital signal, no external signal collector;

Anti-interference ability: strong

Flat-headed peak: within the capacity of the chromatographic column, there will be no flat-headed peak;





图2. 动态量程电导检测器与固定量程电导检测器谱图叠加对比

















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