An Automatic Respirometer for use with Small Invertebrates

1. An automatic respirometer is described which has been developed to measure the rate of oxygen consumption by small arthropods in closed chambers. 2. The instrument removes 0.5 \mul subsamples of air from the head space of specially designed sample chambers using a precision sampling valve and a motorized syringe. The prototype can monitor up to 10 sample chambers automatically over periods of several hours, using an electronic sequence switch to control the operation. 3. Oxygen concentration is measured using a coulometric fuel cell which produces an output signal directly proportional to the mass of oxygen passing over it and requires no calibration. The results are recorded on an integrator of the type commonly used with gas chromatographs. 4. The sensitivity of the respirometer is better than 1 \mul h-1 when small chambers (1-2 ml) are monitored over 3-4 h. 5. The instrument is also capable of measuring the volume of the sample chambers to an accuracy of c. 2% allowing the volume of oxygen consumed by the sample to be calculated. 6. The instrument may be modified to measure the oxygen concentration in the head space of almost any container and would operate on a low-voltage DC supply for field operation