This work presents, for the first time, a new sequential injection analysis (SIA) method to simultaneously analyze degree Brix, orthophosphate and pH in raw cane juice. These key parameters relate to price of harvested sugarcane and quality of cane juice for sugar production. The SIA system employed two detectors: the first detector is a diode-array spectrophotometer, equipped with a regular flow cell, for measurements of degree Brix and orthophosphate. Quantitative of degree Brix (°Bx; ca. % (w/w) sucrose) was based on manipulation of the schlieren effect at the interface between plugs of sample and water. Orthophosphate analysis was carried out based on the molybdenum blue method with significant reduction in consumption of the reagents. Compensation of the schlieren effect from sucrose for determination of orthophosphate was achieved by using a dual-wavelength spectrometric detection. Second detector is a pH-sensing device, called ion-selective field-effect transistors (ISFET). The ISFET is based on the current through the ISFET arising according to the H⁺ concentration in solution. Our developed SIA system provides linear calibration graphs fitting for purpose in analysis of sugarcane juice (pH: 0–14, °Bx: 1.0–7.0 and P₂O₅: 20–200 mg L⁻¹). Simultaneous analysis of sugarcane juice for pH, °Bx and P₂O₅ is carried out within 5 min (12 sample per h). Precision of SIA system is acceptable (RSD < 3%). Our SIA system gave quantitative results insignificantly different, as compared with conventional methods for analysis of pH, °Bx and P₂O₅ in sugarcane juice.

In this study, we customized magnetic sorbents by functionalizing silica coated magnetite with octadecyl(C₁₈)silane (Fe₃O₄@SiO₂@C₁₈). This sorbent was intended for the determination of trace orthophosphate (o-PO₄³⁻) in unpolluted freshwater samples. The o-PO₄³⁻ was transformed to phosphomolybdenum blue (PMB), a known polyoxometalate ion. Then the PMB were coupled with cetyl trimethyl ammonium bromide (CTAB), cationic surfactant, in order to hydrophobically bound with the Fe₃O₄@SiO₂@C₁₈ particles through dispersive magnetic solid-phase extraction (d-MSPE) as part of sample preconcentration. The PMB–CTAB–magnetic particles are simply separated from the aqueous solution by the external magnet. The acidified ethanol 0.5 mL was used as PMB-CTAB eluent to produce an intense blue solution, which the absorbance was measured using a UV–Vis spectrophotometer at 800 nm. The proposed method (employing 2 mg of Fe₃O₄@SiO₂@C₁₈) yielded an enhancement factor of 32 with a linear range of 1.0–30.0 µg P L⁻¹. Precision at 6.0 µg P L⁻¹ and 25.0 µg P L⁻¹ were 3.70 and 2.49% (RSD, n = 6) respectively. The lower detection limit of 0.3 µg P L⁻¹ and quantification limit of 1.0 µg P L⁻¹ allowed trace levels analysis of o-PO₄³⁻ in samples. The reliability and accuracy of the proposed method were confirmed by using a certified reference material. Our method offers highly sensitive detection of o-PO₄³⁻ with simple procedures that can be operated at room temperature and short analysis time.

A simple microfluidic thread-based analytical device (mTAD) for determination of phosphorus content in fertilizers based on the formation of phosphomolybdenum blue (PMB) complex was proposed. The proposed mTAD was simply fabricated by stitching the 100 % cotton thread to the polyethylene (PE) mesh canvas. A color developing reagent, which are the mixture of sulfuric acid, ammonium molybdate, potassium antimony tartrate, and ascorbic acid, was firstly loaded into the middle of the thread. A sample solution was subsequently introduced into the same position to form PMB. A digital camera and image processing program were employed for evaluating color intensity of PMB. Variable parameters affecting the mTAD efficiencies were optimized i.e., solution volumes, chemical concentrations, and reaction time. The applicability of the proposed mTAD method was evaluated by analyzing fertilizer samples. The accuracy as expressed by percentages of recovery ranged between 83 and 96 %. The method was highly reproducible with the relative standard deviation (RSD) of 0.84 % (1 mgP/L), 0.92 % (3 mgP/L) and 1.04 % (10 mgP/L) for 10 replicates. The main features of the system are the used of commonly available materials, simple and rapid fabrication, small scale, reduced chemical waste, less sample consumption, and low-cost. HIGHLIGHTS Simple materials such as 100 % cotton thread and PE mesh canvas can be used for fabricating µTAD The proposed µTAD method was fast analysis and good sensitivity (as low as nmol P level within 6 minutes) by using small amount of reagent and sample solutions The method was successfully determining the phosphorus content in fertilizers GRAPHICAL ABSTRACT