Mass spectrometer

it is because the mass of ion is differentiate by it's speed. For mass spectrometer there are several method to detect the mass charge ratio it not neccesarily by the megnetic sector, for example the (time of fly) method is use the certain distance to let the ion pass through, which all the ion accelarate at once---- the mass is determined by the time of the ion which travel this distance, the lesser mass the shorter time vice verse....
As the invention in progress I think there could be some method need not accelerate the ions..... there also FT-MS method which make the ion run a cyclone path and apply a band of electromagnetic wave which the ion can have resonance.........
I am not really understand this method, maybe you can check it in wilke.....

Why most ions detected are +1?
Not neccessary, the mass spect can be in -1 but the acceleration potential will be the positive charge and the spectrum data bank is completely difference,

Why we mostly use positive charge spectrua?
it is because we always use MS to analysis organic compound and the exitance of ionized organic compound is carbo-cation....

For the second question the answer 001 is right!! Because the time for a molecule be ionized in the ionization chamber is very short, besides, it need much more energy to ionize a compound from ground state to +2 or even +3 more, so it is not so possible to produce +2 or +3 ion if so the quantity of these ion are not enought to make trouble......
as we know MS detect the mass to charge ratio, if there are some +2 +3.... ion they peaks do not place in the original +1 peaks....

The principle of Mass spectrometer is to deflect the charged particle by magnetic field.
The radius of curvature is proportional to its mass, that is, the heavier particle would be deflected less. So. It is a must to make it charged. It also needs to having a particular velocity, it is easy to accelerate a charged particle to a particular speed by using an electric field.

Because of probability, most of the ions formed in the ionization chamber is having a charge of +1.