Vapour generation inductively coupled plasma optical emission spectrometry in determination of total iodine in milk

Abstract

Vapour generation inductively coupled plasma optical emission spectrometry (VG-ICP-OES) was used for the determination of the iodine content in milk samples. Modified alkaline ashing of the milk sample was employed for the total digestion of organic matrix constituents. A mixture of potassium hydroxide (2 mL, 2 mol L À1 in ethanol) and calcium nitrate (2 mL, 0.4 mol L À1 in ethanol) was used in the digestion step as an ashing aid for 2 ml of milk sample (or 200 mg of milk powder). Sample ash was then treated with hydrochloric acid (1.5 mL, 5 mol L À1 ) and sodium sulfite (1.25 mL, 1 mol L À1 ) for the elimination of carbonates, which would otherwise cause spectral interference. The vapour of elemental iodine was generated by means of oxidation of iodide by hydrogen peroxide (1 mol L À1 ) in sulfuric acid (5 mol L À1 ). Using a gas phase separator, matrix elements were completely eliminated; thus the spectral interference of phosphorus (178.222 nm) was removed and the most intense analytical line of iodine (178.218 nm) could be used for determination. The accuracy of the method was verified by analysis of CRM Non-Fat Milk Powder 1549 from NIST, as well as by the comparative study of VG-ICP-OES and ICP-MS results after alkaline solubilization (TMAH 2.5 mL, 10%). The limit of detection for the VG-ICP-OES method is 20 mg L À1 for original milk samples (based on 3s of blank value). The concentration of iodine in real milk samples was found in the range 0.2-0.8 mg L À1 with a precision of determination from 0.5 to 3.5% (3 replicates).

Ultra-trace determination of iodine in sediments and biological material using UV photochemical generation-inductively coupled plasma mass spectrometry

“…Losses of iodine were experienced for both standards and spiked samples, amounting to 15% for standards and 20-40% for spiked samples. Such losses likely arise as a result of formation of volatile species such as HI or I 2 [15]. Similar problems have been reported by others and, consequently, quartz vessels are most frequently recommended for this purpose [25].…”

“…Similar results were reported by Vieira et al [38] who noted that the efficiency of the UV generation process for Hg is also influenced by the opacity of the sample solution, since penetration of UV into the aqueous solution is more efficient for clear and colorless samples than for colored solubilized samples. According to Niedobova et al [15], elemental iodine is a strong oxidizing agent effectively reacting with many organic compounds, especially those with double bonds and these interactions may account for the observed interference.…”

“…The need for reliable determination of iodine at ultra-trace levels is thus significant. Several analytical methodologies have been applied for this purpose, including ion chromatography (IC) [1][2][3], gas chromatography-mass spectrometry (GC-MS) [4,5], radiochemical neutron activation analysis (RNAA) [6][7][8], accelerator mass spectrometry AMS [9][10][11] inductively coupled plasma optical emission spectrometry (ICP-OES) [12][13][14][15] and, most recently, inductively coupled plasma mass spectrometry (ICP-MS) [16][17][18][19].…”

Determination of iodine and molybdenum in milk by quadrupole ICP-MS

“…For iodine determination alone, an alternative approach is to deliberately convert iodine in the sample to elemental iodine vapour for analysis, and total iodine has been determined in milk by vapour generation ICP-optical emission spectrometry [17], though an alkaline digestion was still required to destroy the organic matrix prior to generating the iodine vapour. Iodine has been determined directly in milk powder by electrothermal vaporization-ICP, but again interference from the organic matrix was a problem, necessitating the use of pre-reduced Pd as a chemical modifier and internal standard [18].…”

A Review of Spectrophotometric and Chromatographic Methods and Sample Preparation Procedures for Determination of Iodine in Miscellaneous Matrices

“…For any given purpose, one of the first factors taken into account is whether the method's detection limit is adequately low. Several methods of iodine determination have been proposed, including catalytic methods (with LOD=0.1 μg/ l) (Kamavisdar & Patel, 2002), chromatography in various modes (eg., IC with LOD = 0.1-0.8 μg/l (Hu et al, 1999;Bichsel & Von-Gunten, 1999), (chromatographic methods are especially useful for iodine speciation when coupled with ICP-MS or elecrochemical detection), GC-EC: gas chromatography with electron capture detection (0.11μg/l) (Maros et al, 1989), GC-MS: gas chromatography-mass spectrometry(0.010 μg/l) (Das et al, 2004), FAAS: flame atomic absorption spectrometry (2.75 μg/l) (Yebra & Bollaín, 2010), NAA (0.1-0.2 μg/l) (Hou et al, 1999), ETAAS: electrothermal atomic absorption spectrometry (1.2 -3.7 μg/l) (Bermejo-Barrera et al, 1999), inductively coupled plasma mass spectrometry ICP-MS (1.0-9.0 μg/l) (Fernandez-Sanchez & Szpunar 1999), ICP-AES (40.0-470.0 μg/l) (Anderson & Markowski, 2000), inductively coupled plasma optical emission spectrometry (ICP-OES) (2 µg/l) (Naozuka et al, 2003), ion selective electrodes (1.96 μg/l) (Kandhro et al, 2009), X-rayfluorescence (XRF) (180 μg/L) (Varga, 2007), VG-ICP-OES: vapour generation inductively coupled plasma optical emission spektrometry (20 μg/l) (Niedobová at al., 2005). The iodine content can also be measured by the use of titrimetric methods usually combined with potentiometric measurements.…”