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Experimental determination of the pressure and temperature controls on Ti solubility in quartz provides a calibration of the Ti-in-quartz (TitaniQ) geothermometer applicable to geological conditions up to ~ 20 kbar. We present a new method for determining 48Ti mass fractions in quartz by LA- ICP- MS at the 1 μg g−1 level, relevant to quartz in HP- LT terranes. We suggest that natural quartz such as the low- CL rims of the Bishop Tuff quartz (determined by EPMA; 41 ± 2 μg g−1 Ti, 2 s) is more suitable than NIST reference glasses as a reference material for low Ti mass fractions because matrix effects are limited, Ca isobaric interferences are avoided, and polyatomic interferences at mass 48 are insignificant, thus allowing for the use of 48Ti as a normalising mass. Average titanium mass fraction from thirty-three analyses of low temperature quartz from the Czech Erzgebirge is 0.9 ± 0.2 μg g−1 (2 s) using 48Ti as a normalising mass and Bishop Tuff quartz rims as a reference material. The 2 s average analytical uncertainty for individual analyses of 48Ti is 8% for 50 μm spots and 7% for 100 μm spots, which offers much greater accuracy than the 21-41% uncertainty (2 s) incurred from using 49Ti as an analyte. [ABSTRACT FROM AUTHOR]