Validation of a new planar chromatographic method for quantification of the heterocyclic aromatic amines most frequently found in meat

Open-source add-on kit for automation of zone elution in planar chromatography

RATIONALE

High-throughput capacity, maximal efficiency and automation are missing key features for thin-layer chromatography/high-performance thin-layer chromatography-mass spectrometry (TLC/HPTLC-MS) hyphenations. So far, commercial interfaces have been operated without an automated positioning system. Hence, a 3D-printed, fully automated, open-source add-on user interface was built for elution-head-based TLC/HPTLC-MS.

METHODS

Precise plate movement, batch-wise zone elution, and cleaning processes were automated and synchronized with MS data acquisition. The elution head cleaning was made adjustable in intensity and interval, and remaining elution solvent or particles were thoroughly blown out of the MS transfer line. An adjustable short gas beam across the elution zone was integrated to avoid contamination or leakage by released layer particles, or zone distortion by residual eluent flow when lifting the elution head.

RESULTS

By clicking on zones on the chromatogram, these were selected for consecutive automated positioning below the elution head, sealing and elution. Mean spatial deviations of the positioning on 294 target zones were determined to be 160 μm for track-wise and 190 μm for randomized zone positioning order. Reproducibility of the elution of butyl paraben zones (5.4%, 10 ng/band, n = 70) and its quantitative performance (R² = 0.992-0.999, 5-50 ng/band) were proven.

CONCLUSIONS

The stand-alone electronic system design and the compact footprint were achieved by a minimalistic positioning system and internally installed valves. The open-source OC_manager software opened new perspectives in terms of combining MS data evaluation with previous HPTLC results. The successfully demonstrated TLC/HPTLC-MS automation presents a highly efficient, user-independent hyphenation for a broad range of application fields.

Heterocyclic aromatic amines in doner kebab: Quantitation using an efficient microextraction technique coupled with reversed-phase high-performance liquid chromatography

The safety of doner kebab as a traditional Middle East tasty food can threaten via the formation of dangerous compounds such as heterocyclic aromatic amines during heat process. In this regard, the current investigation was devoted to measuring of 4 HAAs (2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)) in doner kebab samples with an innovative microextraction technique combined with high-performance liquid chromatography. The limit of detection was in the range of 4.8 and 5.3 ng/g, while relative standard deviations were between 6.5% and 8.3%, and recoveries were calculated in the range of 89%-97%. The most and the least total mean values of HAA levels were 13.30 ng/g for MeIQx and 5.0 ng/g for IQ. The proposed method showed a high capability to extract trace amount of HAAs from a complex matrix such as doner kebab. Also, this technique is easy, high sensitive, selective, accurate and efficient.

Application of different modes of thin-layer chromatography and mass spectrometry for the separation and detection of large and small biomolecules

Biomolecules are widespread throughout the world. A biomolecule is any organic molecule produced by a living organism, including large polymeric molecules such as proteins, polysaccharides and nucleic acids. Many sample preparation techniques are used in biomolecule analysis; the method selected depends on the complexity of the sample, the nature of the matrix and the analytes, and the analytical technique available. This review covers the current state of knowledge on thin-layer chromatography and mass spectrometry for qualitative analysis of biomolecules. In the first part of the paper the reader will gain useful information to avoid some problems about performing various modes of thin-layer chromatography combined with mass spectrometry experiments and in the second part he will find useful information for application of these techniques for separation, detection, and qualitative investigation of structures and quantitative determination of biomolecules such as proteins, peptides, oligonucleotides, amino acids, DNA, RNA, and lipids.

Quantification of heterocyclic aromatic amines in fried meat by HPTLC/UV-FLD and HPLC/UV-FLD: a comparison of two methods

A recently developed HPTLC/UV-FLD method was compared to the routinely used HPLC/UV-FLD method for the quantification of heterocyclic aromatic amines (HAA) formed at trace levels during the heating process of meat. For formation of these process contaminants under normal cooking conditions, beef patties were fried in a double-contact grill at 230 degrees C for five different frying times and extracted by solid-phase extraction. The HAAs most frequently found, that is, 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5- f]quinoxaline (4,8-DiMeIQx), 9 H-pyrido[3,4- b]indole (norharman), and 1-methyl-9 H-pyrido[3,4- b]indole (harman), were quantified by two chromatographic methods, which were orthogonal to each other (normal versus reversed phase system). Both methods showed a similar performance and good correlation of the results ( R (2) between 0.8875 and 0.9751). The comparison of running costs and run time in routine analysis proved HPTLC/UV-FLD to be more economical (factor of 3) and faster (factor of 4) due to its capability of parallel chromatography. The HAA findings calculated by standard addition increased with the heating time from <1 to 33 microg/kg related to 3-6 min of frying time. The precision (RSD) was between 7 and 49% (HPTLC) and between 5 and 38% (HPLC) at these very low HAA levels formed.

New coupling of planar chromatography with direct analysis in real time mass spectrometry

The coupling of planar chromatography with direct analysis in real time time-of-flight mass spectrometry (DART-TOF-MS) was shown for the first time. Cutting the plate within a track led to substance zones positioned on the plate edge which were directly introduced into the DART gas stream. Mass signals were obtained instantaneously within seconds. Detectability was shown in the very low ng-range per zone on the example of isopropylthioxanthone. The coupling was perfectly suited for identification and qualitative purposes, but it was initially critical for quantification of results. Analytical response (R2 0.8202) and repeatability were strongly dependent from proper manual positioning of the HPTLC plate into the electronic or vibronic excited-state gas stream of the ion source. This drawback was overcome by using stable isotope-labeled standards shown on the example of caffeine. This way, analytical response (R2 0.9892) and repeatability (RSD < +/- 5.4%, n=6) were improved to a high extent. Spatial resolution by an in-house-built plate holder system was shown to be better than 3 mm. The decay of the signal was observed. The efficacy of this new coupling was compared to a plunger-based extraction device for HPTLC/electrospray ionisation-MS. The latter device showed detectability down to the pg-range, e.g. the limit of quantification for isopropylthioxanthone was found to be 100 pg. Repeatability was comparable (RSD +/- 6.7%), however, without the need of internal standard correction. Analytical response was slightly better and showed a determination coefficient R2 of 0.9983. Similar data were obtained for caffeine as well. Spatial resolution was 2 mm or 4 mm depending on the plunger head used. The comparison showed that HPTLC/DART-TOF-MS is a useful coupling method regarding qualitative aspects and it has the potential to cope also with the difficulties of quantification if isotope-labeled standards were used or if a plate holder system is employed as initially shown.

New method for caffeine quantification by planar chromatography coupled with electropray ionization mass spectrometry using stable isotope dilution analysis

A new high-performance thin-layer chromatography/electrospray ionization mass spectrometry (HPTLC/ESI-MS) method for the quantification of caffeine in pharmaceutical and energy drink samples was developed using stable isotope dilution analysis (SIDA). After sample preparation, samples and caffeine standard were applied on silica gel 60 F254 HPTLC plates and over-spotted with caffeine-d3 used for correction of the plunger positioning. After chromatography, densitometric detection was performed by UV absorption at 274 nm. The bands were then eluted by means of a plunger-based extractor into the ESI interface of a single-quadrupole mass spectrometer. For quantification by MS the [M+H]+ ions of caffeine and caffeine-d3 were recorded in the positive ion single ion monitoring (SIM) mode at m/z 195 and 198, respectively. The calibration showed a linear regression with a determination coefficient (R2) of 0.9998. The repeatability (RSD, n=6) in matrix was<or=+/-3.75%. The intermediate precisions (RSD, n=2) for two samples of different brand names were determined three times and ranged between RSD+/-0.68% and+/-2.64% (sample 1) and between+/-3.44% and+/-8.60% (sample 2). The method accuracy was evaluated by comparing the results obtained by HPTLC/SIDA-ESI-MS with those from the validated HPTLC/UV method. The results for pharmaceutical and energy drink samples were (ng/band) 99.82+/-3.75 and 338.09+/-4.87 by HPTLC/SIDA-ESI-MS and 104.74+/-1.51 and 334.86+/-5.63 by HPTLC/UV. According to the F-test (homogeneity of variances) and the t-test (comparison of means) the two methods show no significant difference. The detection and quantification limits were 75 and 250 microg L-1 (0.75 and 2.5 ng/band), respectively, which were a factor of 13 lower than those established for HPTLC/UV. The positioning error (RSD+/-6%) was calculated by comparing HPTLC/SIDA-ESI-MS with HPTLC/ESI-MS. However, using SIDA the positioning error was nullified. HPTLC/SIDA-ESI-MS was demonstrated to be a highly reliable method for the quantification of compounds by planar chromatography coupled online with mass spectrometry.