Single ion counting

Second, it is possible to make use of single ion counting methods to record an actual numerical result (the number of ions) directly at each mass position. Thus, a two-dimensional data matrix is the immediate result. 

Resistive Anode Encoder (RAE). This detector has the advantage that the single-ion events are detected digitally. It therefore it delivers quantitative results, irrespective of local differences in the amplification of the channel plate. One disadvantage is that the count rate is limited to 200000. 

An alternative to the bridge technique was recently reported for thorium analysis in silicate rocks for which both Th and Th are measured on a single lon-counting detector (Rubin 2001). With careful chemistry and mass spectrometry, °Th/ Th ratios of igneous rocks can be measured with this technique with a precision that is similar to the bridge method. The disadvantage of this technique is that °Th ion-count rates are extremely low (around 10 cps) with normal silicate thorium ratios and are therefore subject to perturbations from background variation and low-level isobaric interferences in normal samples. 

Schematic diagram of an electron multiplier showing and (top) electrical connections for analogue and pulse counting and (bottom) how a single ion gives rise to a large...

Methods of counting single ions and compositional analysis... 

The sensitivity of FTMS is also comparable to that of sector instruments. Although sector instrument detectors can be used to count single ions and FTMS detectors cannot, both methods will yield a peak profile for approximately 100 ions. Detecting a single ion in organic or bioanalytical chemistry is of limited utility because its mass cannot be assigned with any certainty. 

Another way of representing the ion concentration differences at equilibrium is by way of single ion interaction coefficients, which count the cations and anions separately ... 

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