Direct analysis of plant leaves by EDXRF and LIBS: microsampling strategies and cross-validation

Abstract

Microsampling strategies were evaluated for the direct analysis of dried sugar cane leaves by energy-dispersive X-ray fluorescence spectrometry (EDXRF) and laserinduced breakdown spectroscopy (LIBS). The analysis by EDXRF was carried out by irradiating each leaf fragment in its middle portion with a collimated 5 mm X-ray spot size during 50 s, allowing the determination of P, K, Ca, S, Fe, Mn and Si. EDXRF was also useful to conclude that 15 leaf fragments (37.5 % of the recommended sampling area) were enough for attaining a representative analytical response from the whole diagnostic leaf. Regarding LIBS, that employs a substantial smaller ablation area (i.e., 750 µm laser spot size), sampling strategies were defined by taking into account the microchemical distribution of P, Ca, Mg, Fe, Mn, B and Si in 9 mm x 9 mm leaf fragment area. The proposed sampling protocol relied on the interrogation (rastering) of 3 equally spaced sampling lines in each leaf fragment with 48 accumulated laser pulses per line (Nd:YAG at 1064 nm, 5 ns, 10 Hz, 50 J cm -2 ) perpendicularly to the leaf midrib. This strategy enabled the simultaneous determination of P, K, Ca, Mg, Fe, Cu, Mn, Zn, B and Si by LIBS. Cross-validation between LIBS and EDXRF for P, K, Ca, Fe, Mn and Si predicted mass fractions presented high linear correlation coefficients of up to 0.9778 (selecting 15 leaf fragments per diagnostic leaf from 10 different sugar cane varieties). Results provide insights into a novel and promising strategy for direct and fast plant nutrition diagnosis, fostering further studies for in situ analysis of fresh leaves, strengthening the implementation of Precision Agriculture and Green Chemistry concepts. 3 % (for 15 fragments, 37.5 %diagnostic leaf area). The same trend was also observed for S, as the relative error diminished from 10 % (5 fragments, 12.5 % diagnostic leaf area) to 1.6 % (15 fragments, 37.5 % diagnostic leaf area). For the remaining evaluated elements, sampling 15 leaf fragments was appropriate for this intended purpose.Another alternative to evaluate the sampling representativeness was based on the construction of microchemical maps of P, Ca, Mg, Fe, Mn, B and Si in 9 mm x 9 mm leaf fragment area by LIBS for assessing the spatial distribution of the analytes. The selected number of accumulated laser pulses (i.e., 5 consecutive pulses) was defined as the threshold to perforate the leaf fragment at the experimental conditions set herein (50 J cm -2 , 750 µm spot size and 10 Hz). In addition, the microchemical maps were built

Review: Application Of LIBS To Elemental Analysis And Mapping Of Plant Samples

“…Table 1 provides a list of research conducted on plants using the LIBS technique. 2,16,17,18,47,50,[53][54][55][56][57][58][59][60][61][62][63][64][65][66] Recently, Peng et al carried out a comparative investigation of the 2D mapping of Cr in O. sativa leaf samples using SP-LIBS and DP-LIBS. 67 They found the reheating effect occurring in DP-LIBS allowed the successful imaging of the subcellular location of Cr in the leaves of O. sativa.…”

“…Recently, Guerra et al performed mapping of P, Ca, Mg, Fe, Mn, B, and Si in dried sugar cane leaf fragments by employing the LIBS technology. 56 The authors used both EDXRF and LIBS systems to study the spatial distributions of these mineral elements over the surfaces of the leaf samples.…”

Improving the LIBS analysis of heavy metals in heterogeneous agricultural samples utilizing large laser spotting

“…Typically, agricultural products are analyzed in laboratory conditions by conventional elemental analysis techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), graphite furnace atomic absorption spectrometry (GFAAS), ame atomic absorption spectrometry (FAAS), and X-ray uorescence spectrometry (XRF). [1][2][3][4][5][6][7][8][9][10] At farm or food production line, online control should involve a few hundred analyses per day; thus compact hand-held instruments are required. Nowadays, hand-held instruments based on X-ray uorescence [11][12][13][14] and laser-induced breakdown spectroscopy (LIBS) [15][16][17][18][19] techniques are good candidates for the online control of heavy elements in plant or food materials.…”

Improving Calibration Strategy for LIBS Heavy Metals Analysis in Agriculture Applications

“…Toxic elements and heavy metals in agricultural products can induce intoxication and even diseases, so express multi-elemental analysis techniques are required. Conventional laboratory techniques, such as inductively coupled plasma-atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), graphite furnace atomic absorption spectrometry (GFAAS), flame atomic absorption spectrometry (FAAS), and X-ray fluorescence spectrometry (XRF) have been successfully adopted for food and agricultural products [1][2][3][4][5][6][7]. All the abovementioned techniques require laboratory conditions, are time-consuming, and need sample preparation.…”