We studied the analysis of trace amounts of neonicotinoid insecticides by liquid chromatography coupled with a thermal lens spectrometric detector (TLS). This multi-residue analysis method is based ...on the reversed phase separation on C^sub 18^ column, isocratic elution and collinear dual beam TLS detection. The insecticides thiamethoxam, imidacloprid, acetamiprid and thiacloprid were detected with retention times of 4.4, 5.7, 6.5 and 8.5 min and limits of quantifications of 50, 89, 10, and 25 μg/L, respectively. The retention times agreed well with those obtained by the same chromatographic method but using a diode-array detector (DAD). The limits of quantifications for imidacloprid were identical in both techniques. However, the limits of quantifications for thiamethoxam, acetamiprid and thiacloprid were up to 8.5 times lower using the TLS detector compared to the diode-array detector. The applicability of the developed procedure was tested on spiked river water and potato samples.PUBLICATION ABSTRACT
The fact that β-carotene might be the protective factor against various cancers, suggests the need for a rapid reliable assay for this potential marker. We have proposed the method for selective, ...precise and simple profiling of carotenoids as well as for simultaneous ultrasensitive assaying of
trans-β-carotene (TBC) and
cis-β-carotene(s) (CBC) in five vegetable oils. The oil samples diluted 20 or 100 times were directly injected and analysed by means of the isocratic non-aqueous reversed-phase high-performance liquid chromatography (HPLC) combined with ultrasensitive thermal lens detection (TLS).
Elution of TBC was followed by CBC; both were identified and determined in olive, safflower, sesame, wheat germ and linseed oil by standard addition method. The presence of lutein/zeaxanthin, some xanthophyll and/or early eluting carotene may be also presumed in the aforementioned oils. The examined oils showed different and characteristic carotenoid/carotene profiles and characteristic TBC-to-CBC ratios. Both analytes were selectively detected in the presence of palmitic, oleic, linoleic, linolenic and stearic acid, β-sitosterol and
dl-α-tocopherol. This extends applicability of the method to other vegetable oils as well.
Favourable analytical performances (high sensitivity, low limits of detection (LODs) and wide linearity span) enabled the direct analyses of highly diluted oils. This resulted in several major benefits of the proposed method, among which (i) reduced risk of stationary phase deterioration, (ii) avoiding the risk of carotenoids transformations and (iii) substantial labour and time savings. The TBC and CBC in diluted vegetable oils were reliably measured at ultratrace level (1–26
ng
ml
−1) with the
S/
N ratio ranging from 4 to 140 and precisely determined (imprecision 0.4–8.3%). The concentrations of TBC+CBC estimated in the original oils were as follows: 90.5+51.2
ng
ml
−1 in sesame oil, 146.0+164
ng
ml
−1in safflower oil, 464.6+206.1
ng
ml
−1in linseed oil, 453.7+143.3
ng
ml
−1 in olive oil and 2.31+2.63
μg
ml
−1 in wheat germ oil. The characteristic and variable portion of TBC within total β-carotene may serve as a reliable indicator of both, quality and authenticity of the vegetable oil. The HPLC–TLS assay proposed may therefore be successfully applied in nutritional, agricultural and epidemiological studies.
The performance of various analytical methods is compared in terms of their potentiality to quantify the concentration of carotenoids in some foods accurately and rapidly. High performance liquid ...chromatography (HPLC) and spectrophotometry (SP), two absolute reference techniques, were used in parallel experiments. The emphasis is on the application of the new methods to significantly reduce the long analysis time (due to a laborious and costly extraction) characteristic for both HPLC and spectrophotometry. Among such direct quantification methods are colorimetry and a variety of novel photoacoustic (PA) and photothermal (PT) detection schemes that obviate the extraction step. The outcome of numerous studies shows a number of important advantages provided by these methods. Furthermore, the promising results suggest that the availability of practical, versatile, compact and affordable quality control instruments that offer a low-cost solution to routine analysis of specific carotenoids in some foods is within reach.
This research study demonstrates that thermal lens spectrometry (TLS) combined with efficient isocratic HPLC separation provides an excellent analytical means to profile and quantify carotenes in ...fish body oils and possibly also in vegetable oils. In particular, a highly sensitive, selective, simple and rapid method for the determination of ultratraces of β-carotene in fish oil-based supplementary drugs has been proposed. The analyte could be determined reliably and precisely in the presence of a complex matrix including other fat-soluble vitamins (A, D and E), polyunsaturated fatty acids, sterols and other pigments by matrix-matched calibration in cod liver oil. The suitability of the method is also evidenced by favourable analytical figures of merit for β-carotene such as a linearity range of 1–120 ng ml
−1, LOD of 0.58 ng ml
−1, recovery of 101.4±3.3% and measurement repeatability of 4.1%.
