Singer Pressman Melissa A, Aldstadt Iii Joseph H
Department of Chemistry & Biochemistry, University of Wisconsin-Milwaukee, 53211, USA.
J Environ Monit. 2005 Aug;7(8):809-13. doi: 10.1039/b503754a. Epub 2005 Jun 30.
We describe the design, optimization, and application of a small, lightweight, deployable monitoring instrument for accurately measuring parts-per-billion levels of hexavalent Cr in surface waters at hourly intervals. The monitor quantifies Cr(vi) using a standard molecular absorbance spectroscopic method, i.e. by formation of a complex with 1,5-diphenylcarbazide (DPC). The continuous flow analysis (CFA) design uses narrow conduits (0.90 mm) that are hot-forged onto poly(methyl methacrylate) ('Plexiglas') plates based on the method of Jannasch et al.(Anal. Chem., 1994, 66, 3352). The sample stream is drawn through the manifold at 25 microl min(-1) using a mini-peristaltic pump; osmotic pumps (10 microl h(-1)) are used to continuously inject reagent (2.0 mM DPC, 0.60 M HNO(3), 5.0% w/v acetone, and 0.10% w/v Brij-35) and to periodically introduce quality control standards and a cleaning solution (0.50 M HNO(3)). The 'Z-type' optical cell uses a liquid-core waveguide (10 mm) to collimate the light-emitting diode source beam (lambda(max) 574 nm) to a broadband photodiode detector. Figures of merit are: 7 min cycle time, response within 28 min and clear-down within 31 min, low waste generation (<40 ml d(-1)), detection limit (3sigma) of 48.4 microg l(-1) as Cr(vi) or 0.411 microM as chromic acid, 1.54% relative standard deviation at 100 microg l(-1), and selectivity for dissolved Cr(vi) in authentic surface water samples containing moderate levels (>0.21% w/v) of total particulate matter. Using a test chamber containing Milwaukee Harbor water that was periodically fortified with Cr(vi) standards, continuous testing over a 15 day period (354 h) yielded results that were in excellent agreement (<5% variation) with measurements made using an ICP-MS reference method. Drift in the calibration model over the test period was 1.23% and the variation in a 0.50 mg l(-1) Cr(vi) standard was 3.8%(n= 11). Known interferences to the DPC chemistry (Mo, V, and Hg at >5 mg l(-1)) were undetected in the harbor water by ICP-MS.
我们描述了一种小型、轻便、可部署的监测仪器的设计、优化及应用，该仪器用于每小时准确测量地表水中十亿分之一水平的六价铬。该监测仪采用标准分子吸收光谱法对六价铬进行定量，即通过与1,5 - 二苯基卡巴肼（DPC）形成络合物来实现。连续流动分析（CFA）设计使用了窄导管（0.90毫米），这些导管基于扬纳斯克等人（《分析化学》，1994年，66卷，3352页）的方法热锻在聚甲基丙烯酸甲酯（“有机玻璃”）板上。样品流通过微型蠕动泵以25微升/分钟的流速通过歧管抽取；渗透泵（10微升/小时）用于连续注入试剂（2.0毫摩尔/升DPC、0.60摩尔/升硝酸、5.0%重量/体积丙酮和0.10%重量/体积Brij - 35），并定期引入质量控制标准溶液和清洗液（0.50摩尔/升硝酸）。“Z型”光学池使用液芯波导（10毫米）将发光二极管源光束（最大波长574纳米）准直到宽带光电二极管探测器。性能指标如下：周期时间7分钟，响应时间在28分钟内，清除时间在31分钟内，低废物产生量（<40毫升/天），六价铬的检测限（3σ）为48.4微克/升或铬酸为0.411微摩尔/升，在100微克/升时相对标准偏差为1.54%，对含有中等水平（>0.21%重量/体积）总颗粒物的真实地表水样品中的溶解六价铬具有选择性。使用一个装有密尔沃基港水的测试室，该测试室定期添加六价铬标准溶液，在15天（354小时）内进行连续测试，所得结果与使用电感耦合等离子体质谱（ICP - MS）参考方法进行的测量结果高度吻合（变化<5%）。测试期间校准模型的漂移为1.23%，0.50毫克/升六价铬标准溶液的变化为3.8%（n = 11）。通过ICP - MS在港水中未检测到已知对DPC化学方法有干扰的物质（钼、钒和汞，浓度>5毫克/升）。
