A flame photometric detector with a silicon photodiode assembly for sulfur detection

A Miniaturized and Highly Sensitive "Windmill" Three-Channel Fluorescence Detector for Simultaneous Detection of Various Mycotoxins

A novel "windmill" three-channel light-emitting diode induced fluorescence detector (LED-IF) was proposed to maximize the excitation efficiency and fluorescence collection efficiency. Compared with the typical collinear arrangement, the fluorescence intensity of the three channels was increased by 7.85, 3.88, and 2.94 times, respectively. The compact shaping optical path was designed to obtain higher excitation efficiency and a lower background stray light effect caused by high divergence angle high-power ultraviolet (UV)-LEDs simultaneously, which increased the sensitivity of three channels by 4.6 to 5.7 times. It was found that using a photodiode (PD) with a flat window and a larger photosensitive surface can collect the Lambertian emission fluorescence in the flow cell more efficiently, increasing the signal-to-noise ratio of each channel 1.3 to 1.8 times. The limits of detection (LODs, 3 times peak-peak noise) of aflatoxin B2 (AFB2), ochratoxin (OTA), and zearalenone (ZEN) were 0.33, 1.80, and 28.2 ng/L, respectively. Finally, six mycotoxins were analyzed simultaneously by the detector coupling with HPLC. The results showed that the sensitivity of the detector was at the best level to date, which was better than that of the top commercial fluorescence detectors (FLDs). The developed detector has the advantages of having small volume, low cost, and long lifetime and being robust, which has wide application and market prospects.

A 96-well plate UV fluorometer based on micro fluorescence detector array and dynamic zero correction algorithm

A 96-well plate UV fluorometer was developed and evaluated. Eight micro fluorescence detectors close to each other were used as detector array for 8 channels. Each detector employed an UV light emitting diode (LED) as light source and a photodiode (PD) with an amplifier circuit as optoelectronic detector. The optical paths of the detectors were designed by ray tracing method to avoid crosstalk between wells. Simultaneously scanning and detecting of 8 channels saves scanning time and improves detection efficiency. The scanning time of the 96-well plate was about 80 s. A dynamic zero correction algorithm was proposed to solve the problem of measurement accuracy reduction caused by the background fluorescence differences between plates and wells under irradiation of UV light. The measurement repeatability (RSD) for 1 μg/L 7-Diethylamino-4-methylcoumarin sample was 2.25%. Compared with the fixed zero correction method, the limit of detection (LOD), measurement repeatability, and average relative error were improved by 3.3, 2.7, and 4.5 times, respectively. The proposed method is robust and can be applied to different analysis systems. The developed fluorometer has great potential in high-throughput rapid detection of food safety and life sciences.

Enhancement of Chemiluminescence Intensity of S2* in Non-premixed Hydrogen Microjet Flame in the Photometric Detector for Sulfur Detection

A transparent quartz rod (q) placed vertically on top of a non-premixed hydrogen microjet flame in a flame photometric detector (qFPD) was developed and evaluated for sulfur detection. The microjet flame burned around the quartz rod because of Coanda effect, forming an extended downstream flame zone with a relatively low temperature between 550 and 650 °C, which is favorable to the formation of S₂*. The emission intensity of S₂* and the signal-to-noise ratio (SNR) of sulfur response were enhanced 2.6- and 2.1-fold, respectively. It was found that the quartz rod of diameter 4 mm with a tip shape of semicircle placed 6 mm above the nozzle yielded the highest SNR. The limits of detection (LOD) for seven kinds of tested sulfur-containing compounds of qFPD were 0.3-0.5 pg S s^-1, which is 5-7 times better than that of commercially available FPD detectors (LOD: 1.6-2.8 pg S s^-1). The selectivity of sulfur over carbon was 10⁵ on qFPD when the SNR for the mass flow rate of S and C atoms was ∼3 times. It was the first time that a quartz rod was used vertically on top of a microjet hydrogen-rich flame in FPD to enhance the chemiluminescence of S₂* and improve the LOD down to 0.3-0.5 pg S s^-1.