Spectrophotometric flow system using vanadomolybdophosphate detection chemistry and a liquid waveguide capillary cell for the determination of phosphate with improved sensitivity in surface and ground water samples

Abstract

Orthophosphate reacts with molybdate in acidic medium to yield 12-molybdophosphoric heteropolyacid; subsequently, detection is undertaken either on the molybdophosphate reduction product (molybdenum blue method) or on the yellow vanadomolybdate complex [2,5,6]. The molybdenum blue method became broadly used due to its higher sensitivity and lower susceptibility to interferences [4,7,8], than the vanadophosphomolybdate method. Nevertheless, the low concentration levels imposed by legislation are difficult to achieve. Therefore, the development of new methodologies capable of monitoring trace phosphate levels in environmental samples with adequate precision, has gained importance [9]. Flow injection analysis (FIA) is a widespread and well established approach to determine phosphorus. In fact, the first publication on FIA is dedicated to phosphate determination [10] and discusses both the yellow vanadomolybdate and the molybdenum blue method. Compared to the blue molybdenum method, the yellow vanadomolybdate analytical procedure can present some advantages that make it more suitable for flow systems: (i) the use of a single reagent mixture with extended stability makes the method suitable for field portable applications and for unattended operation in water monitoring [11,12] and (ii) the formation of a fine precipitate, accompanying the development of the blue colour, does not occur. However, maybe because of its limited sensitiv

An Automated Multi-Pumping Pulsed Flow System with Spectrophotometric Detection for the Determination of Phosphate in Natural Waters

“…These typically involve the reaction between phosphate and molybdate in acidic conditions in order to form a heteropolyacid. Detection is generally undertaken either on molybdophosphate reduction product (molybdenum blue method) (Ruzicka and Hansen 1975;Mirabó et al 2009;Gentle et al 2010;Mesquita et al 2011) or on the yellow vanadomolybdate complex (vanadomolybdate method) Silva et al 1998;Bowden et al 2002;Neves et al 2008). Other alternatives employing mostly SIA and based on the formation of ionic pairs of either molybdophosphate or vanadomolybdophosphate with basic dye compounds such as Rhodamine 6 G (Frank et al 2006a(Frank et al , 2006b, Malachite Green , Cristal Violet (Burns, Chimpalee, and Ittipornkul 1991) or Methylene Blue (Matsuo, Shida, and Kurihara 1977) have also been proposed.…”

Energy‐Dispersive X‐Ray Fluorescence Spectrometric Determination of Phosphate in Water Samples via a 12‐Molybdophosphate–Crystal Violet Complex

“…There have been a number of methods for determining orthophosphates in water samples including inductively coupled plasma-optical emission spectrometry (ICP-OES) [2], inductively coupled plasma-mass spectrometry [3], chemiluminescence [4,5], fluorimetry [6,7], capillary electrophoresis [8], voltammetry [9,10], potentiometry [11], and amperometry [12]. However, spectrophotometric methods for phosphate determination are the most widely used [13][14][15][16][17][18][19], often in conjunction with flow injection analysis [20,21] or cyclic injection analysis [22,23]. Most of the methods are indirect and involve determining an element or a molecule associated (in a stoichiometric ratio) with phosphorus in a readily isolated compound.…”

Synthesis of Cellulose Functionalized with Polyallylamine and Its Application to On-line Collection/Concentration and Determination of Phosphate by ICP/AES

“…1 Phosphorus present as phosphate in natural, waste and industrial water samples has been determined by a variety of techniques. As sensitive methods, flow injection analysis, 2 HPLC, 3,4 ion chromatography (IC) [5][6][7][8] or column preconcent ration, [9][10][11] are widely used; such methods are well-established approaches to determine phosphorus. Guo et al 5 determined phosphate in water by IC-inductively coupled plasma-mass spectrometry (ICP/MS), reporting a limit of detection (LOD) of 0.7 μg P l -1 .…”

“…Yokoyama et al 3 recently published a technique for phosphate determination in environmental waters by ion-pair liquid chromatography; a LOD of 3 μg l -1 as PO4 was achieved. Neves et al 6 determined phosphate in ground water using a flow injection procedure based on vanadomolybdate method and reported a LOD of 8 μg P l -1 . The anion-exchange IC-ICP/MS method with aqueous 11 mM ammonium carbonate (pH 11.2) as eluent could detect phosphate in the presence of common anions; this LOD was a little higher, 36 μg l -1 .…”