13 C sensitivity The 2mm probe can obtain 13 C CPMAS spectra with a sensitivity of about 20 to 30% less than the 3.2mm probe although the sample volume is about 1/3. This probe can be used for a daily use of 13 C measurement and is especially effective for measuring a small amount of sample. Fig.1 Comparison of 13 C sensitivity among various probes. 13 C CPMAS spectra for Hexamethylbenzen (HMB) were obtained using 3.2mm, 2mm, 1mm and 0.75mm HXMAS probes. SNRs were calculated using methyl signals of HMB. Temperature increase caused by MAS In solid state MAS measurement, the sample temperature rises due to the friction between the spinning control gas and the sample tube. Since the 2 mm probe can perform MAS more efficiently than the 3.2 mm probe, the rise in sample temperature can be suppressed. For example, 20kHz MAS raises nearly 40°C in the 3.2mm probe, while it raises only 5°C in the 2mm probe. The 2mm probe is recommended to obtain a 13 C spectrum with less spinning sidebands while suppressing the sample temperature rise. Fig.2 Relation between spinning frequency and temperature increase of samples for 3.2mm and 2mm probes. 1 H indirect detection The sensitivities of nuclei with low gyromagnetic ratios can be dramatically improved by 1 H indirect methods owing to high sensitivity and resolution of 1 H at very fast MAS regime. 40kHz MAS achieved by the 2mm probe provides 1 H high resolution and allows to obtain 1 H indirect spectra. Although the sensitivity with the same sample volume is inferior to that of the 1mm probe, actual sensitivity of the 1 H indirect detection using the 2mm probe is much higher because of much larger sample volume. As an example, natural abundance 1 H/ 15 N CP-based HSQC spectra of cimetidine measured by the 1mm and 2mm probes are shown. Fig.3 Chemical structure of cimetidine Fig.4 1 H/ 15 N CP-based HSQC 2D spectra of cimetidine obtained by 1mm and 2mm HXMAS probes. 1 H sliced spectra at 15 N 163ppm are also shown. MQMAS The 2mm probe is also useful for MQMAS measurement of quadrupole nuclei. The MQMAS is a representative method for observing quadrupolar nuclei with high resolution, and is widely used because it is available with a standard solid state MAS probe. A strong rf magnetic field strength ,B 1 , is essential for the MQMAS method because the excitation efficiency of multi-quantum excitation affects the sensitivity of MQMAS measurements. The 2mm probe can apply a stronger B 1 than the conventional 3.2mm probe, enabling highly sensitive MQMAS measurements. Here, we show the 27 Al 3QMAS spectra of kyanite (Al 2 SiO 5 ) measured with the 3.2mm and the 2mm probes. Fig.5 27 Al 3QMAS spectra of kyanite (Al 2 SiO 5 ) obtained by 3.2mm and 2mm HXMAS probes. The rf field strength B 1 of multi-quantum excitation are 77kHz for 3.2mm and 104kHz for 2mm, respectively.