REAL-TIME SOIL RESPIRATION DETERMINATION:

MICRO-RESPIROMETER (MICRORES®)*

(US Patent 7,141,430,B2 , 2006)

Based on the simple principle of acid-base titration at a steady-state of CO2 absorption/evolution, MicroRes® is a highly sensitive and rapid determination of respiration rates, key to monitoring soil microbial activity.
— Yuch-Ping Hsieh and Yun-Hwa P. Hsieh. 2000

The Microrespirometer (MR) method is non-instrumental, inexpensive and can be operated by a non-technical person.  It is sensitive (detection limit in sub-µL CO2/hour), rapid (≤ 60 minutes), accurate, rarely false negative and cost-effective. It was developed based on the patented “Microrespirometer and Associated Methods” (US Patent 7,141,430,B2, 2006) principle to do sensitive and accurate real-time CO2 respiration rate measurement in a solid or liquid or mixed sample.

Currently, there are two versions of the MR technology available for applications: the original and the “one-shot” versions.

The original MR version requires pre-assay shaking followed by exchange of the reagent and a timed observation period when the reagent changes color. The original version is rigorous in principle and can detect the respiration rate far below the detection limit of any other existing respirometer in the market with a high level of confidence.  

For a soil respiration rate determination, which usually is much greater than the sub-µL CO2/hour level, the “one-shot” version of the MR technology eliminates the requirements of the 10-minute pre-assay shaking, the exchange of reagent after the pre-assay shaking and the reagent color change observation period. The “one-shot” version requires a finite one hour time to determine the respiration rate. Its procedure is simple although it is an approximation of the original version. Repeated experiments showed that the “one-shot” version has an estimated ±5% deviation of the results from those of the original method.  


WHAT IS UNIQUE ABOUT THIS MR DEVICE?

  • The method is sensitive (detect limit in sub-µL CO2/hour), rapid (in 1 hour), accurate, rarely false negative and cost-effective.
  • Directly determines the CO2 respiration rate without monitoring the CO2 concentration in the headspace of the device.
  • Eliminates the trouble of determining CO2, volume, temperature and pressure changes of the headspace of a respirometer.
  • Fundamentally different from other CO2 absorption methods, which can’t be real-time, because the CO2 in a headspace can never be truly and exhaustively absorbed by an alkaline solution on a real-time basis.

HOW DOES THE MR METHOD WORK?

  • The method first establishes a steady-state status in the device after a short pre-assay shaking (10 minutes*).
  • During this pre-assay shaking, the CO2 absorption rate of the reagent in a MR is forced to adjust itself to be equal to the CO2 respiration rate of the sample (the patented MR principle).
  • After the pre-assay shaking, one can determine the respiration rate of a sample by determining the CO2 absorption rate of the reagent.

*The minimum time required for the pre-assay shaking was first determined by a simulation model (Hsieh and Hsieh, 2000) and later verified by repeated laboratory experiments.

“ORIGINAL” VERSION OF THE MR METHOD:

  • Determined the CO2 respiration rate measurement in a solid or liquid or mixed sample; i.e. food safety, microbial activity of paints, agrichemicals and other products.
  • Requires pre-assay shaking followed by exchange of the reagent and the observation of the time when the reagent changes color.
  • It is rigorous in principle and can detect respiration rate far below the detection limit of any other existing respirometer in the market with confidence. 

“ONE SHOT” VERSION OF MR METHOD:

  • Designed for determining the soil respiration rate which is greater than a few µL CO2/hour level.
  • Simple approximation of the “Original Version”.
  • Eliminates the requirements of the 10-minute pre-assay shaking, the exchange of reagent after the pre-assay shaking and the need of timing the duration before the reagent changes color.
  • Requires a finite one (1) hour to determine the respiration rate.
  • Estimated ±7 % deviation of the results from those of the “Original”. 

 

References:

  1. Hsieh, Y.P., and Y.-H. P. Hsieh, 2000. Determination of Carbon Dioxide Evolution Rates using a novel non- instrumental microrespirometer. J. AOAC Int. 83(2): 277-281.
  2. Li, X., and Y.-H. P. Hsieh, 2003. Comparison of the real-time microrespirometer and aerobic plate countmethods for determination of microbial quality in ground beef. J. Food Sci. 68:2758-2763.
  3. Ren, Z., and Y.-H. P. Hsieh, 2005. Real-time determination of microbial activity of pasteurized fluid milk using a novel microrespirometer method. J. AOAC International 88:1756-1761.
  4. US Patent 7,141,430,B2(2006)

Above information is courtesy of MicroDetect LLC