Anhydrous methanol (99.9%) and sulfuric acid (97.3%) were supplied by Productos Químicos Monterrey. The gas chromatography reference standard for fatty acid methyl esters was obtained from Supelco; and methyl heptadecanoate supplied by Sigma Aldrich (puriss. p.a., standard for GC, ⩾99.7%) was used for quantifying methyl esters.
The sea sand for this study was collected from Puerto Telchac at 21°20′26″N/89°15′47″ W. The sand was taken directly from the upper surface. It is worth mentioning that Puerto Telchac is in the State of Yucatan, México. Generally speaking, the sea sand and soil from that region have been reported to have a high content of calcium carbonate [19].