Determinations of phosphorus in fertilizers by spark discharge-assisted laser-induced breakdown spectroscopy

Abstract

A spark discharge system was coupled to laser-induced breakdown spectroscopy (SD-LIBS) to improve sensitivity in the determination of P in fertilizers. A LIBS system consisting of a Q-switched Nd:YAG laser operating at 1064 nm and emitting pulses at 50 mJ with a fluence of 70 J cm −2 at the focal point was used. Results of preliminary experiments suggested that the most appropriate wavelength to measure P was the P (I) line at 214.9 nm, which did not show interferences by Fe, Cu and Zn. The electrical discharge was provided by a homemade highvoltage electronic circuit consisting of two cylindrical tungsten electrodes at the optimized output voltage of 4.5 kV, with tips arranged at the optimal distances of 4 mm between them and 2 mm above the sample surface. To minimize the expected matrix effects calibration standards of P 2 O 5 in the range of 4.8 and 33.3% were prepared by mixing various amounts of a phosphate rock reference material (SRM-120c) with a mixture of CaCO 3 , CaSO 4 , (NH 2 ) 2 CO and KCl at a 1:1:1:1 mass ratio. The calibration curves obtained at a 4.5 kV SD-LIBS output voltage showed correlation coefficients ≥0.993, RSD ≤8% and LOQ 5.3% (m/m) P 2 O 5 . Data obtained by analyzing commercial samples by the proposed system were in good agreement, at 95% confidence level, with those obtained by using high-resolution continuum-source flame atomic absorption spectroscopy.

Combining Laser-Induced Breakdown Spectroscopy (LIBS) and Visible Near-Infrared Spectroscopy (Vis-NIRS) for Soil Phosphorus Determination

“…Although no single common variable was selected for all P pools, many similarities in the selected regions were observed, and wavelengths within the region 206–217 nm were selected in all cases ( Figure 2 b, Table S2 ). Earlier LIBS studies and the US National Institute of Standards and Technology (NIST) considered P emission lines at 213.6, 214.9, 215.5, 253.4, 253.6, 255.3 and 255.5 nm relevant [ 28 , 30 , 89 , 90 ]. This agrees well with the iPLS-selected variables between 212.09 and 217.2 nm in our study ( Figure 2 a, Table S2 ).…”

Total Phosphorus Determination in Soils Using Laser-Induced Breakdown Spectroscopy: Evaluating Different Sources of Matrix Effects

“…The reported P(I) emission lines were assigned at 213.6 nm, 214.9 nm, 215.5 nm, 253.4 nm, 253.6 nm, 255.3 nm, and 255.5 nm. 24,25,33–37 We chose to analyze the emission lines at 213.6 nm and 214.9 nm because they were strongly sensitive to soil P content, while the other lines only yielded a very weak P signal. The lack of signal at 253.4 nm, 253.6 nm, 255.3 nm, and 255.5 nm was most probably due to interference with Fe.…”

“…The lack of signal at 253.4 nm, 253.6 nm, 255.3 nm, and 255.5 nm was most probably due to interference with Fe. 25,37 The lack of signal at 215.5 nm could be related to the instrument set up, 20,38,39 where background might have been equal or higher to the signal intensity. The P net emission signal for the two selected emission lines at 213.6 nm and 214.9 nm was determined by subtracting the estimated background.…”

Spark Discharge-LIBS: Evaluation Of One-Point And Multi-Voltage Calibration For P And Al Determination

“…23 For instance, when using the SD method, the signal-to-background (S/B) ratio increased up to 7 times in the analysis of Pb and As in soil, 11 up to 3 times for As, Al, Ba, Ca, Co, Fe, Mg, Pb, Si, Sr, Ti and V in soil, 13 and up to 12 times for P in fertilizer. 18 Furthermore, the detection limit decreased 10 times for Pb, Mg and Sn in soil 15 and improved to 0.028 ppm for Cu in onion leaves. 23 Besides sensitivity, calibration is also considered a main issue in LIBS analysis due to the matrix effects.…”

“…[2][3][4] Among several approaches attempted to achieve LIBS signal enhancement, 2,3,5,6 spark discharge (SD) was found to be simple and relatively low-cost. 7 Since its first proposal in 1962, 7 SD-LIBS has been used to analyze a variety of samples 8 in various sectors of agriculture 9 , such as soil, [10][11][12][13][14][15][16][17] phosphate rock, 10,18 rice, 19 honey, 20 coal 21,22 and onion leaves. 23 For instance, when using the SD method, the signal-to-background (S/B) ratio increased up to 7 times in the analysis of Pb and As in soil, 11 up to 3 times for As, Al, Ba, Ca, Co, Fe, Mg, Pb, Si, Sr, Ti and V in soil, 13 and up to 12 times for P in fertilizer.…”