纳氏试剂

熔点：120-127℃，溶于水，溶于乙醇、醚和丙酮。

奈氏试剂(Nessler's reagent），即K2HgI4的碱性溶液。

用作铵离子的定性检定和比以测定试剂。

通常配法为：称取碘化钾(KI)5克，溶于5毫升水（无氨）中，分次少量加入二氯化汞溶液[2.5克HgCl2溶于10毫升热的水（无氨）中]，不断搅拌至微有沉淀为止，冷却后，加入氢氧化钾溶液[15克KOH溶于30毫升水（无氨）中]，再以水（无氨）稀释至100毫升，并加入0.5毫升HgCl2溶液，放置过夜，取其清液即得。

贮存于棕色瓶中，低温保存，有效期为1个月。

一、IAA：
1、72 h old Culture supernatant of the bac-terial isolates grown in the respective medium supplemented withL-tryptophan (200 g ml−1) and 2% NaCl at 27 ± 2◦C was mixedwithSalkowski reagent (50 ml, 35% of perchloric acid, 1 ml 0.5 MFeCl3solution) in the ratio of 1:1. Development of pink colorindicates production of IAA【促生菌筛选】
The indole acetic acid (IAA) production was determined asreported by Loper and Scroth (1986). Bacterial cultureswere grown for 72 h in YEM broth (5 mL) containing Ltryptophan(100 μgmL−1) and incubated at 28±2°C. Fullygrown cultures were centrifuged at 5,600 g for 5 min. Thesupernatant (2 mL) was mixed with two drops oforthophosphoric acid and 4 mL of the Salkowski reagent(50 mL, 35% of perchloric acid, 1 mL 0.5 M FeCl3solution). The mixture was incubated at room temperaturefor 25 min, and the absorbance of pink color developed wasread at 530 nm by the spectrophotometer UV-1601,Shimadzu.【促生3】
二、Ammonia production
Bacterial isolates were grown in peptone water broth for fiveday s at 27 ± 2◦C.0.2 ml culture supernatant was mixed with 1 mlNessler’s reagent and volume of this mixture was made up to 8.5 mlby addition of ammonia free distilled water. Development of brownto yellow color is the indication of ammonia produced, and itsoptical density was measured at 450 nm using spectrophotome-ter (Cappucino and Sherman 1992). The concentration of ammoniawas estimated using the standard curve of ammonium sulphateinthe range of 0.1–1 mol ml−1【促生菌筛选】
三、. Qualitative screening of HCN and chitinase production
For the qualitative estimation of HCN production, Picrate assaydescribed by Castric (1974) was used. Bacterial isolates werestreaked on nutrient broth supplemented with 4.4 gm% glycine. AWhatman filter paper No. 1 (soaked in solution of 2% Na2CO3in0.5% picric acid) was placed in-between base and lid of the culture-plate. Plates were sealed with parafilm and incubated at 27 ± 2◦Cfor 96 h. Production of HCN was indicated by color change of filterpaper from yellow to orange-brown. For qualitative estimation ofchitinase, chitin agar plate amended with 2% phenol red was pre-pared and isolates were spot inoculated and incubated for 120 hat 27 ± 2◦C. Clear zone around the spot inoculants indicates thepresence of chitinase (Wang et al. 2008).【促生菌筛选】。