A calibration framework for the determination of accurate collision cross sections of polyanions using polyoxometalate standards

Rationale Polyoxometalates (POMs) are remarkable oxo‐clusters forming compact highly charged anions. We measured their collision cross sections (CCS) in N 2 with drift tube ion mobility spectrometry (DTIMS). These values were then used to calibrate a traveling wave ion mobility spectrometry (TWIMS) device and the accuracy of the calibration was tested. Methods Six POM standards were analyzed by DTIM‐MS (Tofwerk, Thun, Switzerland) at different voltages to determine absolute DT CCS (N 2 ) values. Five POM compounds (Lindqvist TBA 2 Mo 6 O 19; decatungstate TBA 4 W 10 O 32; Keggin TBA 3 PMo 12 O 40 ; TBA 3 PW 12 O 40 and Dawson TBA 6 P 2 W 18 O 62 ) were used for the calibration of the TWIM‐MS instrument (Synapt G2 HDMS, Waters, Manchester, UK) and a sixth Dawson POM, TBA 9 P 2 Nb 3 W 15 O 62 , was used to compare the accuracy of the calibrations with POM or with polyalanine and dextran reference ions. Results We determined 45 DT CCS (N 2 ) values at 30°C or 60°C. Fourteen DT CCS (N 2 ) values at 30°C were used to perform calibration of the TWIMS instrument. Better correlations were observed than when DT CCS values in helium from the literature were used. The accuracy tests on six ions of Dawson POM TBA 9 P 2 Nb 3 W 15 O 62 led to relative errors below 3.1% while relative errors of 3.6% to 10.1% were observed when calibration was performed with polyalanine and dextran reference ions. Conclusions Our novel calibration strategy for determination of CCS values of multiply negatively charged ions on TWIM‐MS devices based on DT CCS (N 2 ) of standard POM structures covered a wider range of CCS and improved the accuracy to 2.1% relative error on average compared with 6.9% using polyalanine and dextran calibration.