~ 5 ~ International Journal of Multidisciplinary Trends 2025; 7(10): 05-07 E-ISSN: 2709-9369 P-ISSN: 2709-9350 Impact Factor (RJIF): 6.32 www.multisubjectjournal.com IJMT 2025; 7(10): 05-07 Received: 12-07-2025 Accepted: 18-08-2025 Osime EC Analytical Department, Hydrocarbon Technology & Innovations, LLC, Nigeria Patel M Analytical Department, Hydrocarbon Technology & Innovations, LLC, Nigeria Corresponding Author: Osime EC Analytical Department, Hydrocarbon Technology & Innovations, LLC, Nigeria Comparative evaluation of manual and microwave- assisted acid digestion methods for trace metal analysis in crude oil and its products using nitric and sulfuric acids Osime EC and Patel M Abstract Accurate trace metal analysis in petroleum products is essential for refining efficiency, catalyst protection, and environmental compliance. This study compares manual acid digestion with microwave-assisted digestion (MAD) using the Anton Paar Multiwave 7000 for analyzing trace metals (V, Ni, Fe, Al, Mo) in crude oil total blend (251-20-17 O-3) and unconverted oil fractions (UCO, 390 °C cut). Manual digestion utilized nitric (HNO₃) and sulfuric (H₂SO₄) acids under atmospheri c conditions, while MAD employed HNO₃ alone or a HNO₃-H₂SO₄ mixture in a nitrogen-filled pressurized digestion cavity (PDC). Inductively coupled plasma (ICP) analysis revealed MAD’s superior performance in metal recovery and precision, with higher yields for V (2.56-6.26%), Fe (52.64-53.68%), and Al (3.84-14.95%) compared to manual digestion (V: 0.00%, Fe: 3.01-3.65%). Silicon (Si) recoveries were anomalously high (257.27-379.66%) in MAD due to contamination from borosilicate glass vials, rendering Si data unreliable. Nitrogen in the pressurized digestion cavity (PDC) suppressed boiling, prevented cross-contamination, and enabled higher digestion temperatures, reducing digestion time (115 min vs. 1-2 h) and enhancing safety. Manual digestion was labor- intensive and prone to analyte loss. These findings advocate for MAD with quartz or PTFE-TFM vials to avoid Si contamination, offering laboratories a faster, safer, and more accurate method for trace metal analysis in petroleum matrices. Keywords: Acid digestion, microwave-assisted digestion (MAD), petroleum products, trace metals, Anton Paar Multiwave 7000 Introduction Petroleum products, including UCO, are complex organic matrices containing trace metals from crude oil sources, refining processes, or additives. These metals, such as lead (Pb), nickel (Ni), vanadium (V), and copper (Cu), can impact fuel performance, catalyst poisoning, and environmental emissions (Speight, 2014) [10] . Accurate quantification requires complete mineralization of the organic matrix to release metals into a soluble form, typically achieved through acid digestion. Traditional manual acid digestion using nitric and sulfuric acids has been widely employed due to its simplicity and low equipment cost. Nitric acid acts as a strong oxidant to break down organic components, while sulfuric acid facilitates dehydration and removal of residual organics at elevated temperatures. However, manual methods are labor-intensive, prone to incomplete digestion, and expose operators to hazardous fumes and acids. Microwave-assisted digestion (MAD) addresses these limitations by accelerating the reaction through dielectric heating in closed vessels, enabling higher temperatures and pressures for efficient mineralization. The Anton Paar Multiwave 7000, a semi-automated system with a pressurized digestion cavity (PDC), supports temperatures up to 300 °C and pressures up to 199 bar, accommodating various sample types including petroleum oils. This system uses pressure-sealed quartz or PTFE- TFM vials compatible with nitric and sulfuric acids, minimizing blank values and enabling low-volume digestions that is 2-4 mL (Kingston and Haswell, 1997) [4] . Previous studies have compared manual and microwave digestions for diverse matrices, showing MAD's advantages in speed and completeness for petroleum oils (Nadkarni, 2000) [8] . However, few focus on total blend and UCO using identical acid mixtures. This comparative study evaluates both methods for crude oil and its products digestion, assessing digestion efficiency, metal recovery, time, cost, and safety. The objective is to provide guidance for laboratories transitioning to automated systems.