# Nitrite: From Application to Detection and Development
## 2 Traditional Detection Methods  
Nitrite is widely present in human body, food and environment, and its detection methods are being improved with the continuous advancement of research. Its detection methods include ion chromatography, electrochemical methods, optical detection methods, biosensor methods, and so on. The classification of relevant methods is presented in Figure 1.  
Figure 1: Classification and characteristics of nitrite detection methods. Firstly, ion chromatography, as a representative of the traditional methods, is mainly introduced. Traditional methods have a great degree of accuracy and reliability, while there are limitations such as cumbersome operation, a long analysis period and high requirements for equipment. However, these traditional detection methods are constantly being improved to achieve better detection purposes. Ion chromatography, as a traditional detection method, is used in many fields of detection, including food, medicine, environment and others. In the medical field, ion chromatography has been usually used in the detection of nitrite in drugs and human blood. For example, researchers have used ion chromatography to determine DMA(N,N-Dimethylacetamide) and nitrite in five medicines, including metformin, losartan, ranitidine, Nytol, and Benadyrl, as well as two drug substances, losartan potassium and metformin hydrochloride [13], along with the determination of nitrite ions in rifampicin and rifampicin capsules by solid phase extraction ion chromatography [14]. The nitrite content in homogeneous meat samples of infant food was detected by ion chromatography and conductivity [15]. A simple ion chromatographic method [16] can be used for the analysis of nitrite in processed foods. The detection of nitrite in freshwater can be performed by one-dimensional ion chromatography [17]. The steps of ion chromatography are mainly divided into the following steps: The first step is to pre-treat the sample, then adjust the chromatographic conditions, including the adjustment of the chromatographic conditions of the column, eluent, flow rate, column temperature, suppressor, detector, and injection volume. Next, draw a standard curve, and finally the specimen determination and qualitative determination. Looking at the general steps of the determination, we can learn that the steps for determining nitrite content are complicated. Therefore, more and more researchers have been targeting the improvement in each part of the above steps. Based on further improving the detection efficiency, researchers firstly improved the strategy from the pretreatment of raw materials, using a simple ultrafiltration method for sample preparation, which can shorten the time of pretreatment of samples and improve the detection efficiency. Ultrasonic extraction followed by static separation is also a good pretreatment method [18]. Solid phase extraction (SPE) technology [14] simplifies the pretreatment process and also improves the efficiency of pretreatment. Choosing the right column temperature is an essential part of achieving better detection results because a stable column temperature is conducive to maintaining good column performance. Generally speaking, a column temperature of 30 \({}^{\circ}\)C and a detector temperature of 35 \({}^{\circ}\)C have been commonly used for the detection of nitrite [19]. Additionally, the selection of separation column, eluent and detector are very important. Taking the determination of nitrite in valsartan and other satrans as an example, the sensitivity and accuracy of the detection were improved by optimizing the relevant chromatographic conditions. A KOH (potassium hydroxide) solution generated by an in-line eluent generator (EG) was used as the 2D mobile phase for gradient elution at a rate of 1 mL/min. Water and acetonitrile were used as 1D mobile phases for gradient elution at 0.5 mL/min. All of these mentioned parameters are the better parameter conditions derived by the experimenter through continuous trying.