影响总氮准确定量的光谱检测因素

Effects of Spectroscopic Uncertainties on Total Nitrogen Quantification

对现行的双波长紫外分光光度法在测定水体总氮中由光学检测本身所产生的影响因素进行了探讨,提出了一种基于三波长的光谱检测总氮量的方法。结果表明,由于仪器信号波动或光散射引起的光谱检测基线上移所造成的误差可以用在NO3-没有吸收的340 nm处的吸光度加以判断,从而用三波长的方法扣除由于光谱基线上移对220 nm和275 nm处吸光度检测的干扰。对2个水样进行同样的光谱检测,以不同的计算公式所得的数据比较可以看出,三波长法明显优于双波长法。三波长法检测重现性相对偏差小于0.2%,其总氮含量的结果要比双波长法高7%～16%。这也解决了人们对总氮含量测定结果总是偏低的困惑。

The paper reports a tri-wavelength spectroscopic method for accurate determination of total nitrogen（TN） in aqueous samples.It is based on the standard dual-wavelength method currently used for TN testing,however a new wavelength,340 nm is introduced.By taking the absorption at 340 nm as a reference,the spectral errors caused by the light scattering or the instability of the spectrophotometer during the sample measurement can be corrected.The results showed that the tri-wavelength method dramatically improves a measurement precision（RSD 0.2%）.The calculated results for TN content from the tri-wavelength method for two given samples are 7% and 16%,respectively,greater than those obtained by the dual-wavelength method,which also solves a long puzzle why TN content is under-estimated in the two-wavelength method.The present method is simple,reliable and accurate.