A recently introduced microtiter-plate multienzyme-inhibition assay using rabbit liver esterase (RLE),
(BS2) esterase, and cutinase from
Fusarium solani pizi
has been successfully transferred to high-performance thin-layer chromatography. Paraoxon, malaoxon, and carbofuran as esterase inhibitors with high, medium, and low inhibitory activity, respectively, were used to optimize method performance with regard to enzyme concentration, incubation time, and time of immersion in α-naphthyl acetate-fast blue salt B substrate. For paraoxon as strongest inhibitor, limits of detection (LOD) of 1.3, 1.2, and 540 pg per band were determined using RLE, BS2, and cutinase, respectively. Respective LODs were 7.9, 7.4, and 760 ng per band for malaoxon, and 33, 54, and 1420 ng per band for carbofuran. With regard to the LODs of strong, medium, and weak inhibitors, the detectability range is favorably reduced for the low-sensitivity cutinase (0.54–1420 ng per band) whereas it was approximately 3 × 10
and 5 × 10
for RLE and BS2, respectively.
Flexible packaging films, lids of glass jars, elastic toys, or medical commodities made of poly(vinyl chloride) contain different plasticizers, which tend to migrate out of the respective product. To test compliance to regulations, the content of plasticizers and their migration properties have to be determined analytically. With a rapid high-performance thin-layer chromatography (HPTLC) method it was able to quantify phthalic acid esters, diisononyl cyclohexane-1,2-dicarboxylate, sebacates, citrates, adipates, and epoxidized soybean oil (ESBO) simultaneously. Chromatography was performed on HPTLC silica gel glass plates, and detection was enabled by dipping the plate into primuline solution. ESBO could be quantified after a newly introduced lipase treatment and chromatography of the epoxidized fatty acids. Validation was performed by analyzing self-made plastisols, showing good recoveries and standard deviations. Limits of detection and quantification generally were approximately 10–20 and 30–60 ng per zone, respectively, but the detection of ESBO required 70 ng per zone. Thus, plasticizers in PVC samples could be quantified even if they were present as contamination at low concentrations.
Food generally enjoys public confidence; food analysis, however, is a growing and challenging sector. Analytical methods must keep pace with the continuously changing attitudes and preferences of consumers to ensure product quality. Planar chromatography, a very flexible technique for rapidly changing issues, can assist food analysts. But few users of planar chromatography (approx. 10%) use high-performance thin-layer chromatography (HPTLC). Use of appropriate instrumentation will improve the precision of the method. There is therefore, much potential to increase the efficacy and attraction of planar chromatographic applications in food analysis. Validated HPTLC methods fulfill the requirements for reliable food analysis in many fields. Planar chromatography can support food analysis by simultaneous determination of analytes with different detection principles, for example point of care analysis by digital imaging and effect-directed assays via bioactivity-based detection. Parallel analyses under identical conditions or the targeted use of mass spectrometry contributes to its cost-effectiveness. Planar chromatography is an optimum tool for national and international standards
to keep analysis inexpensive
— especially nowadays.