Overflow sensor for open port sampling probe
In a sampling interface for mass spectrometry, a method and apparatus are set forth for preventing liquid overflow from a sampling probe into a sample. The apparatus comprises a substrate adapted to retain a droplet of liquid as it forms at an open end of the sampling probe, and a sensor on a surface of the substrate opposite the sample adapted to detect the droplet of liquid and generate a signal for controlling the droplet of liquid before it overflows into the sample.
1 . Apparatus for preventing liquid overflow from a sampling probe into a sample, comprising:
a substrate adapted to retain a droplet of liquid as it forms at an open end of the sampling probe; and
a sensor on a surface of the substrate opposite the sample adapted to detect the retained droplet of liquid and generate a signal to control the droplet of liquid before it overflows into the sample.
2 . The apparatus of claim 1 , wherein the droplet of liquid is controlled by at least one of:
halting a supply of liquid to the sampling probe;
increasing aspiration at the sampling probe to aspirate the droplet of liquid from the substrate;
reducing the supply of liquid to the sampling probe; and,
a combination of increasing aspiration and reducing or halting the supply of liquid to the sampling probe.
3 . The apparatus of claim 1 , wherein the substrate includes an orifice adapted to accumulate and retain the droplet under tension as it grows from a surface of the substrate facing the sample toward the surface of the substrate opposite the sample, whereupon the droplet comes into contact with the sensor for detection thereby.
4 . The apparatus of claim 1 , wherein the sensor is an electrically conductive trace on the surface of the substrate opposite the sample.
5 . The apparatus of claim 1 , wherein the sensor is a conductive wire on the surface of the substrate opposite the sample.
6 . The apparatus of claim 1 , wherein the sensor is a temperature sensor on the surface of the substrate opposite the sample.
7 . The apparatus of claim 6 , wherein the temperature sensor is a thermocouple.
8 . The apparatus of claim 6 , wherein the temperature sensor is a resistance thermometer.
9 . A method for preventing liquid overflow from a sampling probe into a sample, comprising:
retaining a droplet of liquid as it forms at an open end of the sampling probe;
detecting the retained droplet of liquid; and
generating a signal, based on the detecting of the retained droplet of liquid, for controlling the droplet of liquid before it overflows into the sample.
10 . The method of claim 9 , wherein the controlling the droplet of liquid comprises at least one of:
halting a supply of liquid to the sampling probe;
increasing aspiration at the sampling probe to aspirate the droplet of liquid from the substrate;
reducing the supply of liquid to the sampling probe; and,
a combination of increasing aspiration and reducing or halting the supply of liquid to the sampling probe.
11 . The method of claim 9 , wherein the droplet of liquid is detected on a substrate surface opposite the sample.
12 . The method of claim 11 , wherein retaining a droplet of liquid includes accumulating the droplet under tension as it grows from a substrate surface facing the sample toward the substrate surface opposite the sample.
13 . The method of claim 9 , further comprising generating a notification signal indicating an overflow condition.