Mass cytometry apparatus and methods

1. A mass cytometer comprising:

a. a sampler;

b. an ion source which is an inductively coupled plasma (ICP) from an ICP torch, wherein the ICP torch comprises an injector that at the end of the injector proximal to the plasma has an internal diameter of less than 2 mm and more than 250 μm; and

c. a mass spectrometer.

2. The mass cytometer of claim 1 , wherein the sampler is an autosampler.

3. The mass cytometer of claim 1 , wherein the internal diameter of the injector of the ICP plasma torch is between 1.75 mm and 250 μm in diameter.

4. The mass cytometer of claim 1 , further comprising an ion deflector positioned between the ICP torch and the mass spectrometer, operable to control the entry into the mass spectrometer of ions exiting the ICP.

5. The mass cytometer of claim 4 , wherein the ion deflector is activated and deactivated based on ion signals generated by an ion detector.

6. The mass cytometer of claim 1 , further comprising a mass-assignment corrector that compares the peak shape of the signal from one or more mass channels on the MS to an expected shape, and reassigns ions detected in the M±1 channels to the M channel, for each analysed channel.

7. The mass cytometer of claim 1 , further comprising a dead-time corrector that compensates for detector dead-time.

8. A method for performing mass cytometry comprising:

detecting a quantity of a detectable atom using a mass cytometer comprising a sampler, ion source, and mass spectrometer, the mass spectrometer comprising a detector and an analog-digital converter, and recording the digital signal from the analog-digital converter in the mass spectrometer as a first digital output;

(ii) detecting the same quantity of the same detectable atom, and recording the digital signal from the analog-digital converter in the mass spectrometer as a second digital output;

(iii) comparing the first digital output to the second digital output;

(iv) modulating the voltage on the detector of the mass spectrometer based on the difference between the first digital output and the second digital output, so that the analog signal produced by the detector following conversion by the analog-digital converter would result in the same digital signal as the first digital output; and

(v) analysing a sample in the mass cytometer.

9. The method of claim 8 , wherein the detectable atom is (i) xenon or (ii) in a bead introduced into the MS that is doped with the detectable atom.

10. A mass cytometer comprising:

an ion source;

an ion detector;

a mass analyser;

an analog-digital correlator coupled with the ion detector; the analog-digital correlator configured to vary a voltage applied across the detector in response to a detector signal associated with a standard,

wherein the mass cytometer is configured for detecting a quantity of a detectable atom and wherein the analog-digital correlator is configured to calibrate the ion detector by comparing a ratio of an analog ion signal to a pulse-counting signal with an expected ratio, for one or more of the ion masses analyzed by the mass analyzer.

11. The mass cytometer of claim 10 , wherein the analog-digital correlator is configured to compare the detector signal associated with the standard to an expected digital readout.

12. The mass cytometer of claim 11 , wherein the analog-digital correlator varies the voltage applied across the detector such that the detector signal associated with the standard would match the expected digital readout.

13. The mass cytometer of claim 10 , wherein the analog-digital correlator is configured to vary the voltage applied across the detector prior to the introduction of each sample.

14. The mass cytometer of claim 10 , wherein the analog-digital correlator is configured to vary the voltage applied across the detector during a sample run.