Ion Chromatograph (1C) for the Detection of Charged Species in Food
Ion Chromatograph is considered as a derivative of High-Pressure Liquid Chromatography. The use of anion-cation-exchange-pair-exclusion chromatography and detection of charged species is involved here. Because it enables the replacement of several individual wet chemistry methods for common ions with one instrumental technique, IC has been accepted worldwide as a reference method for analyzing anions and cations in water, wastewater and baby foods. Numerous advantages of IC, like good accuracy and precision; numerous detection modes; speed, high selectivity, separation efficiency, a wide range of applications, improved hardware, and low cost of consumables make IC more and more popular in water analysis and baby foods (Michalski, 2017).
The detection advantages of IC are speed, accuracy, specificity, sensitivity, and reproducibility. The conductivity detector of IC provides increased sensitivity, low noise, low drift, a wide range, and swift times to respond. The other advantage of IC is that it enables the determination of a whole group of analytes of interest in the same chromatographic run, without a considerable sample pre-treatment. IC is increasingly used for the quantitative measurement of sodium, potassium, ammonium, iron, calcium, magnesium, nitrite, nitrate, bromide, fluoride, sulfate and phosphate in mineral waters, lactic-citric-malic acids, etc. (Lin et al., 2007) in coffees; citric, ascorbic and acetic acids in other foods and beverages; propylene glycol, chloride, sulfites and nitrate in beers and wines; fluoride in teas; sulfates, phosphates, nitrates and chlorides in sugars and sweeteners; heavy metal limits in milk products; traces of glucose, fructose, and sucrose in alcoholic spirits; amino acids in advanced dietary feeds; calcium, magnesium, sodium, ammonium, and potassium in sugar solutions; carbonate in sparkling drinking water; arsenic in rice; perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) pollution in feed water; phosphoric acid in cola drinks. Rick et al. (2009) showed that the coupling of IC with dialysis was highly effective in the determination of chloride, phosphate, and sulfate in Ultra High Temperature (UHT) and baby milk.
GCMS-QQQ (MS/MS) Gas Chromatograph Triple Quad System for the Analysis of Pesticides in Food Samples
Day by day, the fear and concern over pesticide contamination are increasing and correspondingly the demand for trace-level analysis of residual pollutants in drinks, food and food products is also growing. However, it is difficult to quantify and confirm the presence of target compounds accurately because the extracts from the samples usually contain target residues plus a mixture of organic compounds co-extracted during sample preparation. GC, in combination with MS/ MS (Tandem Mass Spectrometry), uses a triple quadrupole (QqQ) analyzer, which is a robust and quick technique with increased sensitivity and selectivity used for the detection of pesticide residues. The Triple-Quadrupole GC/MS/ MS analyzer, in support of databases for standard references, provides the lowest possible detection and quantitation limits for pesticide residues in complex samples. This technique enables a quick, reliable quantification and identification of low pesticide concentrations for non-polar (semi) volatile compounds belonging to different chemical families. It has also allowed significant improvement in the method's performance in comparison with the traditional GC methods with single-stage quadrupole MS (Hernandez et al., 2013).
2.6.1 GCMS-QQQ (MS/MS) Gas Triple Quad System for Dioxins, PAH and PCB Analysis
Perez et al. (2015) reported the standardization, characterization, validation, and applicability of GC which is coupled to triple quadrupole MS in the tandem operation mode (GC-QqQ(MS/MS)) for the quantification of dioxinlike polychlorinated biphenyls (DL-PCBs) and polychlorinated dibenzo- p-dioxins and furans (PCDD/Fs, dioxins) in the matrices of environment and food. MS/MS parameters were chosen to achieve high selectivity and sensitivity required for the analysis of these types of compounds and samples. They found that the GC-QqQ(MS/MS) sensitivity, lower than that of GC-HRMS, is good enough to detect the normal concentrations of these compounds in food and environmental samples. It should be noted that polychlorodibenzofurans (PCDFs), polychlorodibenzo-p-dioxins (PCDDs), dioxin-like (DL) and non-dioxin-like (NDL) polychlorinated biphenyls (PCBs) are currently regulated under the EU 2017/644-771 system for food and feed. GC-triple quadrupole mass spectrometry operating in tandem mode (GC-QQQMS/MS) and GC-magnetic sector high-resolution mass spectrometry (GC-HRMS) were the confirmatory methods used here for the analysis of checking compliance with maximum levels.
2.6.2 GC-QToF System for Non-target Compounds Analysis in Food
It has already been investigated on the potential use of gas chromatography (GC) combined to HRMS (High-Resolution Mass Spectrometry) with two different ionization sources and analyzers as an advanced analytical strategy applied to the non-target analysis of food packaging contaminants (Cherta et al., 2015). For this, initially, a GC time-of-flight (TOF) MS with electron ionization (El) source was done, which was then permitted to perform an available library search (databases) along with measurements of the mass of specific ions accurately. A second study was then performed using hybrid quadrupole MS (Q-TOF-MS) with a source of atmospheric chemical ionization pressure (APCI) to scan for the molecular ion or the protonated molecule. Thereupon the action of fragmentation was studied. One РР/Al foil/PP film and four multilayer trays of polypropylene/ethylene/vinyl alcohol polypropylene (PP/EVOH/PP) were analyzed using the current method. Each has been subjected to migration assays using food simulants, such as iso-octane and Tenax® to check their ability for migrant substance analysis.
2.6.3 GCMS Single Quad with Electron Capture Detector (ECD) and Flame Ionization Detector (FID) and Nitrogen-Phosphorous Detector (NPD) for Pesticide and Acrylamide Detection in Food
Flame ionization detector (FID) is one of the most widely used detectors and GC-FID (flame ionization detection) is the 'classical' method for determination of fatty acid composition and is also used extensively in the food and beverage industries. The effluent from an analytical column is mixed with hydrogen along with air and is directed into a flame, which later breaks down organic molecules and produces ions. Then a voltage potential is given across the gap that exists between the burner tip and this is followed by placing an electrode above the flame. The resulting current is then measured, which is proportional to the concentration of the components present.
GC can quantify selected organochlorine pesticides coupled with Electron Capture Detector. Here, the sample is checked into the detector through an analytical column that passes over p particles emitted by a 63Ni radioactive source. This causes ionization of the carrier gas and the subsequent release of electrons. As organic molecules containing electronegative functional atoms or groups pass through the detector, some of the electrons are captured and the current measured between the electrodes reduced (Hajslova and Cajka, 2008).
Banerjee et al. (2013) optimized a single quadrupole GC-MS method for multi-residue determination of 47 pesticides in grapes with a limit of quantification of each compound in compliance with the EU-MRL (European Union-Maximum Residue Levels) requirements. Here the sample was prepared by extraction of the sample (10 g) with ethyl acetate (10 ml) and sodium sulfate (10 g) by homogenization at 15,000 rpm followed by centrifugation at 3000 rpm. Dispersive solid-phase extraction was done with primary-secondary amine acidified with 0.1 per cent formic acid to clean the supernatant. Finally, the residues were quantified using the programmable selective ion monitoring mode and temperature vaporizer-large volume (8 pi) injection. All the GC and MS parameters were also thoroughly optimized to achieve satisfactory results and the recovery rate was within 67-120 per cent. This was later applied for the analysis of the real-world samples for incurred residues successfully.
A glass bead containing an alkali metal is electrically heated until electrons are emitted in the nitrogen-phosphorus detector (NPD). These electrons are then captured by stable intermediates to form hydrogen plasma, which later ionizes the compounds present in the column effluent. Here a polarizing field directs these ions to a collector anode, creating a current (Hajslova and Cajka, 2008). Kim et al. (2011) developed an analytical method for the quantification of acrylamide using a GC-nitrogen phosphorus detector (GC-NPD) in food. This technique showed a very reasonable recovery with a good level of sensitivity and accuracy in monitoring levels of acrylamide in food. They suggested that a combination of GC- NPD with LC-tandem mass spectrometry (MS/MS) can be successfully applied to detect and quantitate acrylamide levels accurately and precisely. This contributes to the development of a prescreening tool to analyze the presence of acrylamide in the food industry.