MALDI-TOF MS

MALDI-TOF MS:
-consist of 3 components: (i) a specimen ionization chamber, within which the laser-based vaporization of the specimen takes place;
(ii) a time of flight mass analyzer; and
(iii) a particle detector

- sample is spotted onto a target
plate, along with a chemical matrix (5).
The matrix is selected for certain prop-
erties, including easy sublimation, e.g. α-cyano-4-hydroxycinnamic acid

-sample-matrix
mixture is pulsed with a laser, Ultra-
violet nitrogen lasers (337 nm)

- Laser irradi-
ation results in vibrational excitation of
the matrix and the ejection (desorption)
of analyte molecules surrounded by
clusters of matrix molecules, water, and
ions. Once desorbed, the matrix mole-
cules transfer protons to the analyte,
resulting in positively charged analyte
cations in the gas phase.

-accelerated
across an electric field within the ion-
ization chamber to a velocity that
depends on the mass-to-charge (m/z)
ratio of the analyte.

New Role in TB testing

Quantiferon-TB assay (QFT):

Collect blood-->simulate cells with purified protein derivative (PPD)-->detect IFN-gamma by enzyme immunoassay (EIA), which serve as an indirect indicator of exposure to TB

QFT Gold (QFT-G):
-replaced the PPD antigen with early secreoty antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10)
-phytohemagglutinin (PHA) as a +ve control, a mitogen to ensure cells are responding to antigens
-+ve control must show a production of IFN-gamma >=0.5IU/ml
-positive immune response to TB if IFN-gamma >=0.35IU/mi after substracting the value of the Nil control
-IFN-gamma <0.35IU/ml and IFN-gamma of +ve control >=0.5IU/ml ==> unlikely to have TB infection



The manufacturer’s package insert states that a positive QFT result does not “necessarily indicate the presence or absence of active tuberculosis disease.” Other diagnostic procedures, such as mycobacterial culture and radiologic examination, should be used when there is clinical suspicion of TB disease.