Abstract
A highly sensitive analytical procedure for photometric determination of molybdenum in plant materials was developed and validated. This procedure is based on the reaction of Mo(V) with thiocyanate ions (SCN−) in acidic medium to form a compound that can be monitored at 474 nm and was implemented employing a multicommuted flow analysis setup. Photometric detection was performed using an LED-based photometer coupled to a flow cell with a long optical path length (200 mm) to achieve high sensitivity, allowing Mo(V) determination at a level of μg L−1 without the use of an organic solvent extraction step. After optimization of operational conditions, samples of digested plant materials were analyzed employing the proposed procedure. The accuracy was assessed by comparing the obtained results with those of a reference method, with an agreement observed at 95% confidence level. In addition, a detection limit of 9.1 μg L−1, a linear response (r = 0.9969) over the concentration range of 50–500 μg L−1, generation of only 3.75 mL of waste per determination, and a sampling rate of 51 determinations per hour were achieved.
Highlights
Molybdenum is an essential micronutrient for plant growth, being a part of plant enzymes [1, 2]
The detection procedure was based on the reaction of Mo(V) with thiocyanate; the analyte is present as Mo(VI) in the sample solution
Sn(II) chloride has been used as a reducing reagent to convert Mo(VI) to Mo(V), which reacts with thiocyanate to form a colored complex that can be monitored at 470 nm [7, 28, 29]
Summary
Molybdenum is an essential micronutrient for plant growth, being a part of plant enzymes [1, 2]. The molybdenum in plants has been determined using UV-vis spectrophotometry [7, 8], inductively coupled plasma mass spectrometry (ICP-MS) [9], flame atomic absorption spectrometry (FAAS) [10], and high-resolution continuum source flame atomic absorption spectrometry (HR-CS AAS) [11] All these methods, except ICP-MS, require a preconcentration step to improve sensitivity, which has been implemented using solvent extraction. Experimental results show that Bouger-Beer-Lambert’s law is obeyed up to a flow cell length of 200 mm for LEDs emitting a radiation beam with a narrow opening angle [17] This resource is exploited in the current study to develop a highly sensitive photometric procedure for the determination of Mo in plant materials, without the use of a solvent extraction step. The analytical procedure was implemented using a multicommuted flow analysis process [23, 24], employing a flow system module with a syringe pump as the fluid propelling device
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