Simultaneous optimization of the resolution and analysis time of flavonoids in reverse phase liquid chromatography using Derringer's desirability function

Development and Validation of HPLC-DAD Method for Simultaneous Determination of Seven Food Additives and Caffeine in Powdered Drinks

The usage of food additives must respect the general legislation in force in the country and requires a reliable analytical method for surveillance. This research aimed to develop a high-performance liquid chromatography with diode array detection (HPLC-DAD) method for the simultaneous determination of seven food additives and caffeine in powdered drinks. Three factors likely to affect the chromatographic separation, namely, mobile phase composition at the beginning (x₁, 0–10% of the amount of methanol in the phosphate buffer) and the end (x₂, 60–100% of the amount of methanol in the phosphate buffer) of the gradient program and pH (x₃, 3–7), were evaluated with the aid of a Box–Behnken Design (BBD). Subsequently, multi-response optimizations for chromatographic resolutions (Rs) and analysis time were performed using the response surface methodology (RSM) in conjunction with the desirability function (DF). Complete separation (Rs > 1.5) of seven food additives and caffeine was achieved in less than 16 min by applying 8.5% methanol in the phosphate buffer at the beginning and 90% at the end of the gradient program, in pH 6.7. The developed method was validated with low limits of detection (ranging from 1.16 mg kg⁻¹ (sodium saccharin) to 3.00 mg kg⁻¹ (acesulfame potassium)), low limits of quantification (ranging from 3.86 mg kg⁻¹ (sodium saccharin) to 10.02 mg kg⁻¹ (acesulfame potassium)), high precision (CV < 4%), and high accuracy (recoveries from 95 to 101% at 80, 100, and 120% of the target concentration). The method was successfully used to assess the seven food additives and caffeine in commercially available powdered drinks.

Parallel gradients in comprehensive multidimensional liquid chromatography enhance utilization of the separation space and the degree of orthogonality when the separation mechanisms are correlated

Comprehensive two-dimensional liquid chromatography (LC×LC) offers increased peak capacity, resolution and selectivity compared to one-dimensional liquid chromatography. It is commonly accepted that the technique produces the best results when the separation mechanisms in the two dimensions are completely orthogonal, which necessitates the use of gradient elution for each second-dimension fraction. Recently, the use of similar separation mechanisms in both dimensions has been gaining popularity, but full or shifted gradients are still used for each second dimension fraction. Herein, we argue that when the separation mechanisms are correlated in the two dimensions, the best results can be obtained with the use of parallel gradients in the second dimension, which makes the technique nearly as user-friendly as comprehensive two-dimensional gas chromatography. This has been illustrated through the separation of a mixture of 39 pharmaceutical compounds using reversed phase in both dimensions. Different selectivity in the second dimension was obtained through the use of different stationary phase chemistries and/or mobile phase organic modifiers. The best coverage of the separation space was obtained when parallel gradients were applied in both dimensions, and the same was true for practical peak capacity.

Fast Determination of Phenolic Compounds in Rice Grains by Ultraperformance Liquid Chromatography Coupled to Photodiode Array Detection: Method Development and Validation

There are several phenolic compounds in rice grains providing benefits for human health. The concentration of phenolic compounds in rice is strongly affected by the polishing steps during rice production. A new sensitive ultraperformance liquid chromatography-ultraviolet-visible spectroscopy method with a photodiode array detection protocol has been developed and validated for the quantitation of phenolic compounds in rice grains. Several working variables and two different columns were evaluated. Finally, a less than 3 min analysis time was developed to achieve enough resolution for the simultaneous determination of the 20 most common phenolic compounds in rice. The analytical properties for the separation method produced an adequate sensitivity for all phenolic compounds in the regular range for phenolics in rice, 0.5-100 mg L^-1 ( R² > 0.997), with high precisions for both repeatability and intermediate precisions (coefficients of variation less than 0.4 and 2.5% for the retention time and area of the peaks, respectively).