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用于土壤中氮钾含量快速测定的非接触电导微流控芯片

  • 洪炎 , 1 ,
  • 王乐 1, 3 ,
  • 王儒敬 , 2, 3 ,
  • 苏静明 1 ,
  • 李浩 1, 3 ,
  • 张家宝 3 ,
  • 郭红燕 2, 3 ,
  • 陈翔宇 , 2, 3
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  • 1. 安徽理工大学 电气与信息工程学院,安徽 淮南 232001,中国
  • 2. 中国科学院合肥物质科学研究院,智能机械研究所,安徽省智慧农业工程实验室,安徽 合肥 230031,中国
  • 3. 中科合肥智慧农业协同创新研究院,农业传感器与智能感知安徽省技术创新中心,安徽 合肥 231131,中国
1. 王儒敬,博士,研究员,研究方向为农业传感器与智能感知。E-mail:;2
陈翔宇,博士,副研究员,研究方向为农业传感器与现场快检装备。E-mail:

洪 炎,研究方向为农业传感器。E-mail:

HONG Yan, E-mail:

收稿日期: 2023-09-18

  网络出版日期: 2024-01-26

Contactless Conductivity Microfluidic Chip for Rapid Determination of Soil Nitrogen and Potassium Content

  • HONG Yan , 1 ,
  • WANG Le 1, 3 ,
  • WANG Rujing , 2, 3 ,
  • SU Jingming 1 ,
  • LI Hao 1, 3 ,
  • ZHANG Jiabao 3 ,
  • GUO Hongyan 2, 3 ,
  • CHEN Xiangyu , 2, 3
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  • 1. School of Electrical and Information Engineering, Anhui University of Science and Technology, Huainan 232001, China
  • 2. Intelligent Agriculture Engineering Laboratory of Anhui Province, Institute of Intelligent Machines, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Anhui Hefei 230031, China
  • 3. Agricultural Sensors and Intelligent Perception Technology Innovation Center of Anhui Province, Zhongke Hefei Institutes of Collaborative Research and Innovation for Intelligent Agriculture, Anhui Hefei 231131, China
1. WANG Rujing, E-mail: ; 2
CHEN Xiangyu, E-mail:

Received date: 2023-09-18

  Online published: 2024-01-26

Supported by

National Key Research and Development Program of China(2021YFD2000204)

National Natural Science Foundation of China(12304236)

Anhui Province Science and Technology Major Project(2020b06050001)

Anhui Provincial Natural Science Foundation(2308085QA19)

Science and Technology Mission Program of Anhui Province(S2022t06010123)

Open Fund for Anhui Digital Agriculture Engineering Technology Research Center(AHSZNYGCZXKF021)

The Dean Foundation of Hefei Institutes of Physical Science, Chinese Academy of Sciences(YZJJ2024QN38)

Copyright

copyright©2024 by the authors

摘要

目的/意义 土壤中氮、钾元素在作物生长和农业生产过程中具有关键作用。快速定量检测土壤中氮、钾含量对指导精确施肥具有重要意义。因此,建立一种快速可靠的土壤氮、钾含量检测方法十分必要。 方法 本研究建立一种基于聚二甲基硅氧烷(Polydimethylsiloxane, PDMS)微流控芯片电泳和电容耦合非接触电导检测(Capacitively Coupled Contactless Conductivity Detection, C4D)方法,快速定量检测土壤中氮、钾养分离子。通过微流控电泳芯片实现对土壤中多种离子快速分离,利用C4D进行电导率变化的精准测量。基于检测器工作频率输出响应特性,激励电压响应特性和电泳电压,确定最佳分离和检测性能。 结果和讨论 该方法对钾离子(K+)、铵根离子(NH4+)和硝酸根离子(NO3)标准溶液的检测限(S/N=3)分别为0.5、0.1和0.4 mg/L。K+、NH4+和NO3在0.5~40.0 mg/L范围内具有良好的线性关系,线性相关系数(R2)分别为0.994、0.997和0.990,表明该方法可以对土壤中氮、钾养分离子进行定量分析。同时,采用峰高、峰面积和出峰时间作为评价指标进行可重复性实验,其相对标准偏差(Relative Standard Deviation, RSD)均小于4.4%,说明该方法具有良好的重复性。此外,对土壤样品进行测试,K+和NH4+可实现完全分离以及同步检测,其检测效率明显提高。通过标准加入法进行回收率实验,回收率保持在81.74%~127.76%。 结论 本研究为土壤氮钾养分离子的快速检测提供了一种简便、高效的方法。

本文引用格式

洪炎 , 王乐 , 王儒敬 , 苏静明 , 李浩 , 张家宝 , 郭红燕 , 陈翔宇 . 用于土壤中氮钾含量快速测定的非接触电导微流控芯片[J]. 智慧农业, 2024 , 6(1) : 18 -27 . DOI: 10.12133/j.smartag.SA202309022

Abstract

Objective The content of nitrogen (N) and potassium (K) in the soil directly affects crop yield, making it a crucial indicator in agricultural production processes. Insufficient levels of the two nutrients can impede crop growth and reduce yield, while excessive levels can result in environmental pollution. Rapidly quantifying the N and K content in soil is of great importance for agricultural production and environmental protection. Methods A rapid and quantitative method was proposed for detecting N and K nutrient ions in soil based on polydimethylsiloxane (PDMS) microfluidic chip electrophoresis and capacitively coupled contactless conductivity detection (C4D). Microfluidic chip electrophoresis enables rapid separation of multiple ions in soil. The electrophoresis microfluidic chips have a cross-shaped channel layout and were fabricated using soft lithography technology. The sample was introduced into the microfluidic chip by applying the appropriate injection voltage at both ends of the injection channel. This simple and efficient procedure ensured an accurate sample introduction. Subsequently, an electrophoretic voltage was applied at both ends of the separation channel, creating a capillary zone electrophoresis that enables the rapid separation of different ions. This process offered high separation efficiency, required a short processing time, and had a small sample volume requirement. This enabled the rapid processing and analysis of many samples. C4D enabled precise measurement of changes in conductivity. The sensing electrodes were separated from the microfluidic chips and printed onto a printed circuit board (PCB) using an immersion gold process. The ions separated under the action of an electric field and sequentially reach the sensing electrodes. The detection circuit, connected to the sensing electrodes, received and regulated the conductivity signal to reflect the variance in conductivity between the sample and the buffer solution. The sensing electrodes were isolated from the sample solution to prevent interference from the high-voltage electric field used for electrophoresis. Results and Discussions The voltage used for electrophoresis, as well as the operating frequency and excitation voltage of the excitation signal in the detection system, had a significant effect on separation and detection performance. Based on the response characteristics of the system output, the optimal operating frequency of 1 000 kHz, excitation voltage of 50 V, and electrophoresis voltage of 1.5 kV were determined. A peak overshoot was observed in the electrophoresis spectrum, which was associated with the operating frequency of the system. The total noise level of the system was approximately 0.091 mV. The detection limit (S/N = 3) for soil nutrient ions was determined by analyzing a series of standard sample solutions with varying concentrations. The detection limited for potassium (K+), ammonium (NH4+), and nitrate (NO3) standard solutions were 0.5, 0.1 and 0.4 mg/L, respectively. For the quantitative determination of soil nutrient ion concentration, the linear relationship between peak area and corresponding concentration was investigated under optimal experimental conditions. K+, NH4+, and NO3 exhibit a strong linear relationship in the range of 0.5~40 mg/L, with linear correlation coefficients (R2) of 0.994, 0.997, and 0.990, respectively, indicating that this method could accurately quantify N and K ions in soil. At the same time, to evaluate the repeatability of the system, peak height, peak area, and peak time were used as evaluation indicators in repeatability experiments. The relative standard deviation (RSD) was less than 4.4%, indicating that the method shows good repeatability. In addition, to assess the ability of the C4D microfluidic system to detect actual soil samples, four collected soil samples were tested using MES/His and PVP/PTAE as running buffers. K+, NH4+,Na+, Chloride (Cl), NO3, and sulfate (SO43‒) were separated sequentially within 1 min. The detection efficiency was significantly improved. To evaluate the accuracy of this method, spiked recovery experiments were performed on four soil samples. The recovery rates ranged from 81.74% to 127.76%, indicating the good accuracy of the method. Conclusions This study provides a simple and effective method for the rapid detection of N and K nutrient ions in soil. The method is highly accurate and reliable, and it can quickly and efficiently detect the contents of N and K nutrient ions in soil. This contactless measurement method reduced costs and improved economic efficiency while extending the service life of the sensing electrodes and reducing the frequency of maintenance and replacement. It provided strong support for long-term, continuous conductivity monitoring.

0 引 言

在目前情况下,农作物必须满足大量且不断增长的人口对粮食供应需求1。为使农作物高产稳产,通常要向土壤施加肥料,其中氮(N)和钾(K)是主要的施肥元素。N是组成蛋白质、叶绿素和酶的主要成分;K可以提高作物的抗逆性,改善农产品品质2, 3。提高作物生产力的关键是维护和改善土壤养分含量4。N、K含量过低会降低农作物预期产量,造成经济损失;而N、K过量时,会削弱作物的生产能力,甚至导致土壤环境污染及水体污染5。因此,监测土壤N、K含量对农业生产和环境保护具有重要意义。
目前,针对土壤N、K的检测方法包括近红外光谱6和原子吸收光谱7等。刘雪梅8利用近红外漫反射光谱测定了150个土壤样品N,并使用其中126个样品建立了N的预测模型,其决定系数大于0.8,表明预测模型效果较好。Barthès等9利用近红外反射光谱测定不同粒径土壤中N的浓度,在粒径小于20 µm时,校准和预测准确,R 2为0.94~0.97,标准误差为12%。Bechlin等10采用原子吸收光谱法测定肥料中的N、磷(P)、K,测定商品肥料的浓度与其他方法保持一致。这些检测方法需要大型检测仪器和专业的操作人员,如原子吸收光谱仪等。大多数技术需要衍生化反应,存在样品前处理复杂、检测周期长、成本高等问题。其中,光谱技术需要依靠建立的预测模型反演出土壤养分信息,对检测环境要求高,且需要获取大量样本数据保证模型的稳定性和准确性11。因此,目前亟需一种快速、简便的土壤N、K养分定量检测方法。
电容耦合非接触式电导检测(Capacitively Coupled Contactless Conductivity Detection, C4D)是一种利用传感电极和被测溶液之间的电容耦合效应进行电导率测量技术。它测量的是被测物质与运行缓冲液之间的电导率差值12, 13。由于其传感电极不与被测溶液直接接触,将用于电泳的高压电场与检测电路隔离,可抑制高压干扰,产生稳定的C4D基线14,具有较好的鲁棒性,已经成功地与毛细管电泳(Capillary Electrophoresis, CE)和微流控芯片电泳(Microfluidic Chip Electrophoresis, MCE)相结合15, 16。微流控芯片电泳分离通过毛细管区带电泳在微流控芯片通道中进行,与高效液相色谱法等相比,其特点是分离效率高、分离时间短、样品量要求小17-20。微流控芯片电泳已迅速成为一种有效的分离分析方法。近年来,MCE与C4D相结合已经应用于各个领域,如医疗诊断21, 22、环境监测23, 24、国防安全25和药物测试26等。Smolka等27开发了一种土壤样品提取物现场分析的移动传感器。Xu等28开发了一种基于电泳的微流控离子营养传感器,用于检测土壤溶液样品中的硝酸根离子(NO3 )含量,检测限约为7.25 µmol/L。微流控芯片制造采用蒸发、沉积、计算机数控(Computer Numerical Control, CNC)和剥离等工艺,需要使用大型专业仪器,制造成本高、耗时,不可批量制作,而且检测效率较低,难以做到N、K养分离子的同步检测。因此,微流控芯片的简便、低成本制作以及N、K离子同步检测对于土壤养分检测应用具有重要意义。
本研究以土壤N、K养分离子态钾离子(K+)、铵根离子(NH4 +)和NO3 为实验对象,采用微流控芯片非接触电导法对土壤浸提液中不同浓度的养分离子进行分离和检测。为达到最佳分离检测性能,对激励信号频率和分离电压进行优化。通过微流控芯片电泳技术实现对土壤养分离子的有效分离;使用C4D测量的信号峰面积实现对土壤N、K离子浓度的定量检测。

1 材料与方法

1.1 仪器与设备

激励端由交流激励信号发生器(郑州飞逸科技有限公司)组成。接收端主要包括自主研制的信号拾取电路15和信号采集模块(杭州赛智科技有限公司)。用于电泳分离的四路高压电源由自主研制而成。真空干燥箱(DZF-6050,上海精宏实验设备有限公司)用于聚二甲基硅氧烷(Polydimethylsiloxane, PDMS)混合物的脱气和固化;等离子清洗机(PC-3S,北京嘉润万丰科技有限公司)实现对PDMS表面的等离子处理;恒温振荡仪(SHZ-92B,上海沙鹰公司)用于土壤养分离子浸提。

1.2 电泳微流控芯片与电极制作

电泳微流控芯片采用十字交叉型通道布局,如图1所示。1和2之间的通道为进样通道,长度10 mm;3和4之间的通道为分离通道,长度87 mm。储液槽1和2距离通道交叉口均5 mm;储液槽3距离通道交叉口6 mm。检测电极放置在分离通道末端7 mm处。微通道的高度为100 µm,宽度为50 µm。微流控芯片由软光刻技术制作而成。首先通过光刻工艺制作出电泳微流控芯片硅基模具。将PDMS和固化剂(Sylgard 184, Dow Corning, USA)以10∶1的质量比充分混合并脱气后浇注到硅基模具上,并在60 oC的环境下烘烤12 h使其固化。固化后将PDMS与模具剥离并打孔。然后将其与PDMS薄膜一同进行表面等离子处理。处理后立即将PDMS与薄膜键合,形成完整的微流控芯片。
图1 微流控芯片与传感电极示意图

注: 1. 样品储液槽; 2.样品废液槽; 3.缓冲液储液槽; 4.缓冲液废液槽。

Fig. 1 Schematic diagram of microfluidic chip and sensing electrodes

图1中黄色所示,传感电极采用分离式,微流控芯片与电极拆卸灵活,具有极大的便利性。为降低两电极间的耦合强度,传感电极采用反平行配置。使用沉金工艺在印刷电路板(Printed Circuit Board, PCB)上制作厚度为2 µm、长度为2 mm、宽度为1 mm、电极间距为0.5 mm的金电极。金具有极高的化学稳定性,在空气中很难被氧化,所以传感电极具有很长的使用寿命。在电极的末端使用射频同轴连接器(SubMiniature Version A, SMA)进行连接,使用射频同轴电缆线用于信号的传输,避免外界的电磁干扰。实验前,将传感电极放置在分离通道末端靠近储液槽处并与分离通道对齐固定。

1.3 缓冲液制备与电泳程序

所有化学品均为试剂级。
1)制备K+和NH4 +缓冲液。称取6.06 g 三(羟基)氨基甲烷(Tris)和0.36 g乙二胺四乙酸(Ethylene Diamine Tetraacetic Acid,EDTA)于100 mL容量瓶中,使用30 mL去离子水完全融化,并定容至100 mL制备成磷酸盐-三羟甲基氨基甲烷-醋酸-乙二胺四乙酸(Phosphate-Trizma-Acetate-EGTA, PTAE)缓冲液。称取0.6 g聚乙烯吡咯烷酮(Polyvinyl Pyrrolidone, PVP)和2 mL PTAE制备100 mL缓冲液。
2)制备NO3 缓冲液。使用100 mL去离子水溶解0.465 g L-组氨酸(L-histidine, His)和0.426 g 2-(N-吗啉基)乙磺酸(2-(N-morpholino)Ethanesulphonic Acid, MES)配制NO3 缓冲液。
实验前,先使用去离子水清洗微通道10 min,避免残留的杂质造成通道堵塞。随后使用缓冲液冲洗微通道10 min以进行平衡。在使用缓冲液清洗时注意避免引入气泡。这会在施加高压时产生电弧,造成通道中产生高温进而导致基线漂移和波动。必要时,可将缓冲液和样品溶液进行超声波处理以去除任何溶解的气体。在使用运行缓冲液冲洗微通道后,吸取4个储液槽中的废液并加入40 µL的运行缓冲液,将高压铂电极浸入储液槽,开启高压电源和采集模块进行基线测试。如果基线稳定,即可进行样品测定。使用相同方法冲洗微通道,避免溶液交叉污染。冲洗后在储液槽2、3、4中加入40 µL运行缓冲液,在储液槽1中加入样品溶液。然后,将高压铂电极浸入储液槽中,依次开启进样电压和电泳电压,得到对应的离子谱图。实验结束后,使用纯水冲洗微通道,防止颗粒堵塞微通道。

1.4 样品采集与处理

本研究的土壤样品采集自安徽省合肥市庐阳区。采用对角线采样法,采样深度为0~20 cm,每个采样点采集土壤样品1 kg,并进行编号和记录采样点的位置信息。将采集的土样及时放在样板上,摊成薄层,然后放在干净整洁的通风区域。自然干燥后,研磨样品,过1 mm孔径筛,装入密封袋保存。
每个土壤样品称取3 g装入样品杯中,加入30 mL去离子水后振荡30 min,然后使用滤纸和注射过滤器对样品进行过滤,得到土壤浸提液。

2 结果与讨论

2.1 检测参数的优化

2.1.1 工作频率的优化

C4D电极和溶液之间可以等效为一个电容器。微流控芯片中的绝缘壁可以被看成是电容器的电介质。整个检测池可以简单等效为两个电容和一个电阻串联模型。检测池中的导纳模量 Y可由公式(1)表示。
Y = 1 Q q 2 + 1 4 π 2 f 2 C 1 C 2 C 1 + C 2 2
式中: Q为两电极间柱状溶液常数; q为溶液电导率,S/m; f为激励信号频率,Hz; C 1 C 2分别为等效的两电容,F。
工作频率显著影响着C4D性能。由上式可知,工作频率直接关系到检测池的导纳。当频率降低时,检测池的导纳模量减小,接收电极上的感应电流减小。当频率升高时,检测池的导纳模量增大,接收电极上的感应电流增大,信号响应得到增强。但是,频率过高同样会使激励电极与接收电极间的导纳模量增大,导致背景噪声水平增加,信噪比降低29。因此,优化工作频率至关重要。
固定激励电压为40 V,考察工作频率在300~1 200 kHz范围内对信号响应和信噪比的影响。采用浓度为10 mg/L的NO3 溶液进行频率扫描实验。实验结果如图2所示。随着工作频率的升高,峰高和信噪比均逐渐增大。在1 000 kHz时,峰高和信噪比达到最大。当工作频率超过 时,峰高和信噪比逐渐减小。因此,选择1 000 kHz作为最优工作频率。
图2 非接触电导检测系统的工作频率对信号响应以及信噪比的影响

Fig. 2 The influence of operating frequency of contactless conductivity detection system on signal response and signal-to-noise ratio

2.1.2 激励电压的优化

激励电压直接影响着C4D的分析响应。采用单变量法优化激励电压以提高信号响应。固定最优工作频率,在20~50 V范围内进行电压扫描,观察激励电压对信号响应的影响。实验结果如图3所示。C4D的信号响应随着激励电压的升高而升高,在50 V达到最大。实验过程中没有观察到基线噪声水平的明显变化,所以峰高代表信噪比。理论上继续增大电压可以进一步提高信号响应,但是考虑到高压放大器带宽和检测器输入限制,选择50 V作为最优激励电压。
图3 非接触电导检测系统的激励电压对C4D信号响应的影响

Fig. 3 The influence of excitation voltage on C4D signal response in contactless conductivity detection system

2.1.3 电泳电压的优化

电泳电压是实现离子分离的关键,因此,考察电泳电压在1.0~3.0 kV范围内对土壤样品分离的影响。在步长为500 V的条件下,钾铵混合标液的峰谱分离度作为研究对象。谱峰分离度计算如公式(2)所示。
R = 2 ( t R 2 - t R 1 ) ( W 1 + W 2 )
式中: t R 1 t R 2分别为相邻两峰前后峰的保留时间,min; W 1 W 2分别为相邻两峰前后峰的峰宽,min。
电泳电压和分离度的关系如图4所示。随着电泳电压的增加,钾铵峰谱分离度逐渐减小。当电泳电压增加到2 kV时,钾铵两峰无法实现完全分离。同时电泳电流增大到7.5 µA时,焦耳热效应增强,基线出现明显漂移,导致基线噪声水平也随之提高。然而,过低的电泳电压会增加离子的电泳迁移时间。当电泳电压减小到1 kV时,离子的迁移时间大幅增加到56 s,且会导致一定程度的峰展宽和拖尾。因此,选择1.5 kV作为最优电泳电压。
图4 微流控芯片电泳中电泳电压对离子分离的影响

Fig. 4 The effect of electrophoresis voltage on ion separation in microfluidic chip electrophoresis

2.2 检测系统性能分析

为分析微流控芯片非接触电导检测系统测定土壤样品中养分离子的性能,采用浓度为5 mg/L的各离子标准溶液进行检测实验。如图5所示,各离子被清晰地检测出,且检测时间均小于1 min。K+、NH4 +和NO3 分别在33、37、40 s时出峰。在电泳过程中,谱图基线存在少量随机噪声。这些噪声主要是热噪声和电子电路噪声的组合。其中热噪声来源于电泳中存在的焦耳热效应;电子电路噪声主要来源于电子器件本身存在的噪声和外界电磁干扰等。通过MES/His缓冲体系进行基线实验,结果如图5(d)所示。系统的基线总噪声水平为0.091 mV左右。在电泳图中观察到一定程度的峰过冲,可能与电容和工作频率有。本实验中造成过冲的主要原因可能是较高的工作频率。在最优实验条件下,通过一系列浓度的标准溶液测得K+、NH4 +、NO3 检测限(S/N=3)分别为0.5、0.1和0.4 mg/L。
图5 养分离子标准样品的电泳谱图及基线噪声水平

Fig. 5 Electrophoretic spectra and baseline noise levels of nutrient ion standard samples

为定量检测土壤养分离子浓度,将各离子标准溶液稀释成一系列浓度梯度,在最优实验条件下,考察峰面积和对应浓度的线性关系。K+各浓度的电泳谱图如图6(a)所示。这是经过基线校正得到的结果。K+、NH4 +和NO3 的线性范围分别为0.5~40、0.1~50和0.4~40 mg/L。在线性范围内,K+、NH4 +和NO3 的线性相关系数(R 2)分别为0.994、0.997和0.990,说明该方法可以定量检测土壤养分离子。
图6 土壤养分离子峰面积和浓度之间的线性响应

Fig. 6 The linear response between the peak area and concentration of soil nutrient ions

为研究该系统的重复性(Relative Standard Deviation, RSD),同一标准样品重复测定4次,将峰高、峰面积和出峰时间作为评价指标,结果如表1所示。K+、NH4 +和NO3 峰高、峰面积、出峰时间的RSD(n=4)均小于4.4%,表明该系统重复性良好。
表1 K+、NH4 +和NO3 的峰高、峰面积和出峰时间%RSD

Table 1 Peak height, peak area, and peak time % RSD of K+, NH4 +, and NO3

离子 峰高/mV 峰面积/mV×min 出峰时间/min
K+ 3.32 1.88 1.82
NH4 + 3.84 1.3 4.34
NO3 2.32 3.29 0.82

2.3 土样测定结果

为验证微流控C4D系统检测实际土壤样品的能力,准备4份土壤样品进行定量检测。图7(a)为土壤养分中钾和铵的电泳图。K+和NH4 +被依次解析,并且在1 min之内被有效分离检测。除检测到目标离子K+和NH4 +外,还检测出Na+。其中Na+的迁移速度较慢,出峰时间为1 min左右。图7(b)为使用MES/His缓冲液得到的土壤养分阴离子电泳图。根据标准加入法确定各离子峰的成分。NO3 峰被解析。除检测到目标离子NO3 外,还检测出Cl和SO4 3‒。其中Cl的迁移速度较快,出峰时间为0.7 min左右;SO4 3‒在NO3 之后出峰,出峰时间为0.9 min左右。计算目标离子峰面积,根据线性方程计算土壤浸提液中离子浓度。土壤样品中的离子浓度 C可通过公式(3)计算得出。
图7 采集的实际土壤样品分析

Fig. 7 Analysis of actual soil samples collected

C = C t × Z × 10 - 3 Y × 10 - 3
式中: C t为土壤浸提液离子浓度,mg/L; Z为浸提时加入的超纯水体积,mL; Y为浸提的土壤质量,g。土壤中N、K养分离子含量如表2所示。
表2 采集的实际土壤样品中K+、NH4 +和NO3 含量
Table 2 K+, NH4 + and NO3 content of the actual soil
samples collected
单位: mg/kg
土样 K+ NH4 + NO3
1 4.5 34.5 13.6
2 9.3 2.0 62.1
3 26.4 17.9 36.0
4 45.1 15.5 126.5
为衡量该方法的准确性,对4份土壤样品进行加标回收率测定实验。在最优实验条件下,取4份土壤样品适量进行加标,测得峰高后根据线性方程计算浓度。回收率测定结果如图8所示。结果显示,土壤N、K养分离子的回收率为81.74%~127.76%,表明该方法准确性良好。
图8 检测系统的实际土壤样品回收率

Fig. 8 The actual soil sample recovery of the detection system

3 结 论

本研究建立了一种基于PDMS微流控芯片电泳和C4D的土壤N、K养分快速定量检测方法。采用沉金工艺在PCB上印刷反平行配置的传感电极,使电极与微流控芯片实现分离,极大地提高了使用灵活性,并延长其使用寿命。首先通过标准溶液优化实验条件,确定了最优工作频率为1 000 kHz,最优激励电压50 V以及最优电泳电压1.5 kV。在最佳实验条件下,对该系统进行性能分析。分别以MES/His和PVP/PTAE为运行缓冲液,在1 min内实现了土壤浸提液中K+和NH4 +的同步分离,显著提升了检测效率。该系统对K+、NH4 +和NO3 的检测限分别为0.5、0.1和0.4 mg/L。由于采用了较高的激励电压,相较于其他平面电极配置检测器7.25 µmol/L的NO3 检测限,实现了更低的检测限。在0.5~40.0 mg/L浓度范围内,线性相关系数R 2分别为0.994、0.997和0.990。采用峰高、峰面积和出峰时间作为评价指标进行重复性实验,其RSD均低于4.4%,表明该方法具有优异的重复性。最后通过该方法对真实土壤样品溶液进行加标回收实验,回收率保持在81.74%~127.76%,验证了该方法检测土壤养分离子的准确性。本研究为土壤氮、钾养分离子的快速检测提供了一种简便、高效的方法,该方法具有较高的准确性和可靠性,能够快速、高效地检测土壤中的氮、钾养分离子含量。这将有效解决农场中土壤养分快检的需求,为农业生产提供科学依据和技术支持。

利益冲突声明

本研究不存在研究者以及与公开研究成果有关的利益冲突。

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