Spectrophotometric Determination of Available Phosphorus in Soil with Bromophenol Blue as an Acid-base Indicator
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摘要:
测定土壤中有效磷的标准方法及通用方法,通常采用酸或碱溶液浸提样品,调节浸提液pH值后用分光光度法测定。该方法过滤操作繁琐、酸碱指示剂二硝基酚颜色易受溶液底色干扰且有毒。对现有方法进行优化创新,提高检测效率,对土壤有效态分析及土壤质量评价具有重要意义。本文比较了不同浸提时间、不同浸提液酸度、不同酸碱指示剂等实验条件对检测结果的影响;采用离心分离代替过滤,使用溴酚蓝作指示剂调节pH。同时对比了溴酚蓝指示剂与标准方法的二硝基酚指示剂的检测结果,吸光度、标准物质准确度、未知样品检测结果均完全一致。研究表明使用溴酚蓝作酸碱指示剂,颜色突变更明显,不易受待测液底色影响,毒性低,测试数据准确。实验条件优化后的方法适用于酸性、中性及石灰性土壤有效磷的快速测定。
Abstract:BACKGROUND Standard and common methods for the determination of available phosphorus in soil are usually spectrophotometry methods. Before measurement, the sample is extracted by an acid or base solution, and the pH of the extracted liquid is regulated. The existing methods include complex operation steps such as filtration, and the acid-base indicator dinitrophenol is highly toxic. Most of all, the color of dinitrophenol is easily altered.
OBJECTIVES To optimize the existing method and improve detection efficiency, and then use the method for soil available state analysis and soil evaluation.
METHODS Different experimental conditions such as extraction time, acidity of the extraction and acid-base indicator type were compared. Centrifugal separation was used instead of filtration, and bromophenol blue was first used as the acid-base indicator. Detection results of bromophenol blue and dinitrophenol were compared.
RESULTS Comparing the detection results of the bromophenol blue indicator and dinitrophenol indicator, the absorbance, accuracy of national standard substance and unknown sample detection results were completely consistent. With bromophenol blue as the acid-base indicator, color mutation was obvious without any interference of bottom color.
CONCLUSIONS Bromophenol blue has low toxicity with accurate detection results. This improved method is appropriate for rapid determination of available phosphorus in acid, neutral and carbonate soils.
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表 1 使用不同pH指示剂测定土壤中有效磷结果对比
Table 1. Comparison of analytical results of available phosphorus in soil extracted by different pH indicator
不同酸碱性土壤 待测液调节pH指示剂 实验样品 吸光度 溶液中有效磷浓度
(μg/50mL)样品中有效磷测定值
(μg/g)有效磷标准值
(μg/g)酸性土壤 二硝基酚 GBW07412 0.245 22.305 22.30 21.2±3.6 未知样A 0.099 8.568 8.57 / 空白溶液 0.009 0.153 / / 溴酚蓝 GBW07412 0.266 23.648 23.65 21.2±3.6 未知样A 0.104 8.458 8.46 / BK 0.006 -0.070 / / 中性或石灰性土壤 二硝基酚 GBW07414a 0.140 14.721 29.44 29±3 未知样B 0.049 6.286 12.57 / 空白溶液 -0.017 0.263 / / 溴酚蓝 GBW07414a 0.116 14.248 28.50 29±3 未知样B 0.024 5.790 11.58 / 空白溶液 -0.020 0.013 / / 表 2 碳酸氢钠浸提液pH对有效磷检测结果的影响
Table 2. Effect of NaHCO3 extraction with different pH on analytical results of available phosphorus
标准物质编号 有效磷测定值(μg/g) 有效磷标准值
(μg/g)未调节pH 调节pH至8.5 GBW07413 14.20 17.49 18.3±2 GBW07414 10.26 12.71 13.8±2.3 表 3 已浸提溶液的存放时间对有效磷检测结果的影响
Table 3. Effect of extracted solution with different storage time on analytical results of available phosphorus
样品 放置不同时间有效磷测定值(μg/g) 有效磷测定值下降比例(%) 0d 3d 5d 3d 5d 未知样品 2.54 2.34 2.30 -7.57 -9.17 GBW07416 17.05 16.98 14.80 -0.43 -13.20 表 4 方法精密度
Table 4. Precision tests of the method
参数 GBW07416 GBW07414 有效磷测定平均值(μg/g) 17.2 12.5 有效磷标准值(μg/g) 14.8±3.1 13.8±2.3 标准偏差(n=7) 0.5907 0.2323 相对标准偏差(%,n=7) 3.44 1.86 -
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