主题：氮谱请教，大家帮帮忙呀

N-15的谱是比较难做，因为丰度低，而且弛豫时间长。所以得用高浓度的样品，弛豫延迟最好长一些（如3秒），脉冲角度不要太大（如45度）。累加时间可能会较长。关于化学位移标尺，在蛋白质里是以液氨为0ppm,所以酰胺N在120ppm附近。而在小分子里好象用CH3NO2为0ppm更普遍，这时FORMAMIDE为-267。8ppm。以下是从一片文献里（Monatshefte fur Chemie 131, 437±449 (2000)）拷来的作为参考：
Experimental
The 15N NMR spectra were measured using a GE 300MHz NMR spectrometer with an observation frequency of 30.45MHz for 15N. The non-decoupled 15N NMR spectra were calibrated against external formamide (ˇ267.8 ppm) and are referenced to the delta () scale with nitromethane set to zero [13,14]. Previous standardizations used liquid ammonia (ˇ381.9 ppm) [14]. Following the general practice, chemical shift values that are more shielded than the reference are given negative
signs and those less shelded will have a positive sign. This means that most 15N values are negative.Sample tube diameter: 10 mm; temperature: ambient; spinning condition: 15 Hz; RF pulse length:
10 ms (45). The addition of the paramagnetic reagent ferric chloride hexahydrate (FeCl3
6H2O,20 mg) helped to shorten the acquisition times for several compounds because it decreased the
Nuclear Overhauser Effect (NOE) [6].
Most tetraalkylammonium salts used in this work [1,7,9,12] were readily soluble in water.Aqueous solutions of 3.0M and above for the tetra-n-alkylammonium halide salts were not uncommon. Solution preparation in aqueous and methanolic reagents yielded similar results for obtained chemical shift data of these salts. The acquisition times of these solutions were about 1 h. N-Alkyl substituents on the nitrogen atom exerted the most important effect on the chemical shift of amines and ammonium salts. Other factors showed were of less inØuence on either the acquisition times and/or on the chemical shift values.

你的样品浓度可能太稀了. 氮谱检测需要的时间比碳谱长得多.
建议: 用液体含氮化合物 (例如三乙胺) 检测看看, 可以初步感觉浓度的问题.

谢谢了，我昨天打了很多电话，向别人询问做氮谱的问题，都说比较难，但是还是能做出来，都说至少要5-6个小时，或者要过夜，次数大概1万次。我昨天采了一个谱，次数为4000次，迟豫时间为3秒，但是一点峰都没出来，我的样品是NH4NO3,不过是做的固体CP/MAS，今天我又在做固体，到现在还是没做出来，以前也没做出来过，不知道下午能不能做出来。

我也查了一些文献，formimade的化学位移相对于NH4=0为112.6ppm，相对于NO3=0则为-268.1ppm，谢谢上面的两位，不知道信号刚刚出来时采样次数大概为多少呢，我是600兆的。你们定的谱宽是多少？