UJI ADULTERASI EKSTRAK TEMULAWAK DENGAN PEWARNA SINTETIS METANIL YELLOW MENGGUNAKAN SPEKTROFOTOMETRI UV-VIS DENGAN PENDEKATAN KEMOMETRIKA

Handika Eriksa Yumantara, NIM.: 22106030034 (2026) UJI ADULTERASI EKSTRAK TEMULAWAK DENGAN PEWARNA SINTETIS METANIL YELLOW MENGGUNAKAN SPEKTROFOTOMETRI UV-VIS DENGAN PENDEKATAN KEMOMETRIKA. Skripsi thesis, UIN SUNAN KALIJAGA YOGYAKARTA.

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Abstract

This study aimed to evaluate the capability of UV-Vis spectrophotometry combined with chemometric approaches for detecting and quantifying the synthetic dye Metanil Yellow as an adulterant in temulawak (Curcuma xanthorrhiza Roxb.) extract matrices. Spectral characterization revealed that pure temulawak and pure Metanil Yellow exhibited maximum absorption peaks (λmax) in close proximity within the visible region at 424.50 nm and 418.00 nm, respectively (Δλ = 6.50 nm), with a high cosine similarity of 0.980, indicating severe spectral overlap. Component resolution using Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) over the 220–600 nm range successfully decomposed the mixture spectra into two primary components (R2 = 99.99998%; model LOF = 0.04573%), identifying Component 1 as temulawak (cosine similarity = 0.9898; LOF = 14.23%) and Component 2 as Metanil Yellow (cosine similarity = 0.9985; LOF = 5.48%), supported by Hierarchical Cluster Analysis (79.52% similarity). For quantitative modeling, Full-Spectrum Partial Least Squares Regression (PLSR, Factor-4, 220–600 nm) demonstrated the best and most consistent performance with calibration R2 = 0.9981 (RMSEC = 0.0624 mg/L), cross-validation R2 = 0.9625 (RMSECV = 0.3200 mg/L), and exceptional predictive accuracy on an test set (R2 prediction = 0.9941; RMSEP = 0.0384 mg/L; mean recovery = 101.82%; %RSD = 2.36%), with 100% of test samples meeting the AOAC acceptance criteria (80–110%). In contrast, Reduced-Spectrum PLSR (Factor-5) suffered from severe overfitting (R2 prediction = 0.0854; %RSD = 60.30%). Meanwhile, Stepwise Multiple Linear Regression (SMLR) successfully selected two statistically significant wavelengths (415.50 and 424.50 nm, p < 0.05), yielding a parsimonious model with stable predictive performance (R2 validation = 0.986182; RMSEP = 0.2203 mg/L). Consequently, the combination of UV-Vis spectrophotometry and chemometrics (MCR-ALS alongside full-spectrum PLSR / SMLR) proves to be an effective tool for rapid screening and quantitative assay of Metanil Yellow adulteration in herbal temulawak products.

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