Chemical Compounds of Wine

Literature Review

1.1 New Zealand Wine Industry

New Zealand is a favourable country to produce wine due to the cool climate which is surrounded by the South Pacific Ocean. The wine industry started from the 19^th century on a small scale but now it is rapidly increasing by different regions. 

	2017	2018	2019
Total wine-producing area	37,129 ha	37,969 ha	38,680 ha
Red grape variety	7,919 ha	7,876 ha	7,758 ha
White grape variety	29,210 ha	30,092 ha	30,921 ha
Amount of vineyards	2005	2031	2019
The regular size of the vineyard	18.5 ha	18.5 ha	19 ha

Table 1: statistics of the New Zealand wine industry adapted from vineyard reports in 2017, 2018 and 2019[1-3]

According to the summary of the wine industry in New Zealand, the growth of wineries has increased from 643 in 2009 to 697 in 2018 and total production has developed up to 301.7 million liters in the year 2018.

Marlborough has become the most producing region by capturing 26,850 ha and Hawke’s Bay has become second by having 4,771 ha for vinery growth in 2019. Then respectively Central Otago(1,884 ha), Waipara Valley( 1,226 ha), Gisborne(1,190 ha), Nelson (1,154 ha), Wairarapa (983 ha) and Auckland (314 ha) have shown their production successively.

Pinot Noir has become second, among top wine-producing verities in New Zealand. In 2019 Pinot Noir producing area has increased up to 5,625 out of total red varieties growing area 7,758 ha. That means 73% captured by Pinot Noir.

Figure 1:  Percentage of producing top red verities in 2019 adapted from Vineyard Register Report 2018-2021[3]

1.2 Pinot Noir

Among plantation of grape varieties in the world Pinot Noir has ranked in no 10^th which has a higher demand than other grapes. It has been found that Pinot Gris, Pinot Blanc, and Pinot Noir grape varieties are identical, other than small mutations of the color [4]. In general, Pinot Noir wine has a deep purple color and lighter taste than others because of the low content of tannin. There are diverse flavours due to the complexity of magical chemical compounds. Primary flavours of Pinot Noir can be differentiated as red fruit ( cherry, strawberry, and raspberry), flower( Hibiscus), spices( cinnamon, peppermint), Herbal( oregano, black olive, and beetroot), mushroom and vanilla [5].

1.3 Compounds responsible for aromas of Pinot Noir wine

There are three types of aromas responsible for increasing market preferences in all over the world.

1.3.1 Primary aromas

Aromas produce during the metabolism of grapes names as Varietal/Primary aroma compounds. These aroma production influenced by the quality of grapes, climate changes, type of soil and maintenance of winemaking practices. They can be present as free volatiles and non-volatiles, bonded by conjugates of cysteine and glycosides.

1.3.1.1 Terpenes

In the present, about sixty terpenes have been discovered through scientific studies. These varieties are responsible for major with fruity and floral aromas. Monoterpenes are the most abundant aroma compound present in wine. Some of them are Geraniol which responsible for rose and geranium odor, Linalool which has floral (rose and lavender) smell, Nerol gives Rose, α-terpineol with floral (lily of the valley) and Citronellal which gives citronella feel[6]. Potentially volatile terpenes (PVT) are more abundant in grapes compared with free volatile terpenes (FVT) which are present largely in grape skins other than flesh or juice [7]. Mostly 90% of them are non-volatile terpenes which can be converted in to free form by hydrolyzation with acids or enzymes during fermentation as well as aging. Rotundone is an example of obscure sesquiterpene which has strong spicy and high black pepper aroma intensity. Eucalyptol / 1,8 – Cineole is a monoterpenoid which bound with medicinal and spicy aroma[8].

                                        

Nerol

Geraniol

Linalool

               

Rotundone

Citronellal

Figure 2: Some terpene structures typically present in Pinot Noir adapted               from Sigma-Aldrich

1.3.1.2 C₆ Compounds

C₆ alcohols and aldehydes form via the lipoxygenase pathway at harvesting, crushing, destemming, during transportation and other forms of mechanical damage during the processing of grapes[9]. Generally, hand-harvested grapes have a low concentration of green compounds when compared with machines[10]. C₆ aldehydes can be seen in grapefruits until harvest after maturation but C₆ alcohols can be seen in high concentration only in an early stage of grape development after that it gradually decreases with the time [11]. These compounds are responsible for cut grass, cucumber and herbaceous odors in wine[12]. GC-FID and GC/MS have been used to do studies on Pinot Noir C6 alcohols and C₆ aldehydes in France[13] and USA[14].

The major two C₆ compounds present in wine at are found to be 1-hexanol and (z)-3-hexanol which are used to be synthesized by polyunsaturated fatty acids (α-linoleic and α-linolenic)[9].

                         

Trans-2-Hexenal

Cis-3-Hexen-1-ol

                                  

1-Hexanol

Hexanal

Figure 3: Some C₆ structures typically present in Pinot Noir adapted from Sigma-Aldrich

1.3.1.3 C₁₃-Norisoprenoids

C₁₃-Norisoprenoids which are consistent with 13 carbon atoms are derived from plant existing pigmented carotenoids (β-carotene, neoxanthin, violaxanthin, lutein)[15]. At the beginning of the winemaking process C₁₃ compounds are in an inactive form, glycosidically bonded with sugars. But during the fermentation process, these bonded precursors convert into aromatic norisoprenoids by the hydrolyzation process.

Some major C₁₃-Norisoprenoids present in wine are can be seen in figure 4

Some studies revealed that by increasing sunlight exposure time towards grapes can produce high norisoprenoid concentration and inspire carotenoid development. β-Damascenone which is the first product during the fermentation process acts as a fruity smell aroma booster while TDN responsible for petrol/kerosene aroma typically can be seen in mature Rieslings. Vitispirane gives floral, fruity, woody and reminiscent of eucalyptus type of smells[16].

                         

β-Damascenone

TDN

Vitispirane

Figure 4: Major C13-Norisoprenoids structures typically present in Pinot Noir adapted from Sigma-Aldrich

 1.3.1.4  Methoxypyrazines

The most important Methoxypyrazine in grapes is Isobutyl-methoxypyrazine (IBMP) which gives green capsicum and herbaceous aroma. The reason for having more vegetative aroma in unripe grapes is a high concentration of IBMP (skin 95%, seeds 4% and pulp 1%). Scientists have found that IBMP generates on its own after flowering happens and it comes to its maximum concentration before version and declines during maturation. Typically IBMP level in a wine is 5-30 ng/L [17]. There are some factors which can impact on the IBMP concentration such as light, temperature, vine water status and various viticulture practices[18]. Due to the presence of Isopropyl-methoxypyrazine (IPMP) grape/wine can be smelled as green bean, Earthy, grassy and bell pepper. Sec-butyl-methoxypyrazine (SBMP) is another type witch responsible for earthy smell [17]. Both of these types present in wine below 10 ng/L. low concentration of these compounds favorable with wine characteristics while high amounts not support.

                                             

IPMP

IBMP

SBMP

 

Figure 5: Three methoxypyrazine structures typically present in Pinot Noir adapted from Sigma-Aldrich

1.3.2 Secondary Aromas

More aroma compounds can be produced by yeast as a result of acidic and enzymatic hydrolysis during the fermentation process and maturation[19].

1.3.2.1  Higher aliphatic fermentation alcohols

This contains alcohols with two or more carbon atoms. These compounds can form from amino acids and sugars. There are some factors which can be an effect on the amount of alcohol compounds production such as type of yeast, the composition of amino acids, sugars and nitrogen, temperature and pH of the system.

Major list of higher alcohols are[20, 21]

• 2-methyl propanol (isobutanol/isobutyl alcohol) which has a nail polish or solvent smell.
• 3-methyl butanol (isoamyl alcohol) gives spicy, smoky and malt olfactory result
• Phenyl-2-ethanol which is very important in pinot noir wines; gives floral like roses, spice, and honey.
• 2-methyl butanol

                                     

2-methyl propanol

3-methyl butanol

2-methyl butanol

Phenyl-2-ethanol

Figure 6: Major higher alcohol structures typically present in Pinot Noir adapted from Sigma-Aldrich

1.3.2.2 Fatty acids

Fatty acids are cytoplasmic saturated unbranched aliphatic compounds or saturated carboxylic acids. They can be dividing into three categories according to the size of the fatty acid chain as short, medium and long. But these sensory descriptors can be changed due to different concentrations. When having a high concentration of C₆-C₁₀ fatty acids they produce various odors like rancid, butter/cheese (below 20 mg/L) and soap[22].

Some examples of fatty acid compounds with their olfactory perception threshold are

• Isobutyric (2.3 mg/L) and Isovaleric/3-Methylbutanoic (33 µg/L) acid with sweat and cheese olfactory perception[23]
• Hexanoic / caproic acid (420 µg/L) with pungent, tobacco, Octanoic acid (500 µg/L) which having soap, cheese
• Decanoic acid (1 mg/L) with rancid or fatty smell[24].

However, the high concentration of these fatty acids makes a negative impact on the flavor of wine[25]. So some studies have done to identify factors responsible for this impact. Zara et al. have found that decanoic acid can be increase and octanoic acid concentration can be decreased with mixed fermentation rather than ferment only with the help of Saccharomyces cerevisiae[26].

Englezos, V et al. have found that by inoculating two types of bacteria ( Saccharomyces cerevisiae, starmerella bacillaris ) can reduce the fatty acid concentration of Cabernet sauvignon from 347 µg/L to 185 µg/L while Merlot from 528 µg/L to 303 µg/L[27].

                                                           

Isovaleric acid

Isobutyric acid

Hexanoic / caproic acid acid

Decanoic acid

Figure 7: Major fatty acid structures typically present in Pinot Noir adapted from Sigma-Aldrich

1.3.2.3 Esters

Esters are positive aroma contributors (floral and in wine which are derived during fermentation by yeast[19]. The two types of esters produced by fermentation are 

Ethyl esters: They can present as alcohol groups with short chains as ethanol or can be medium to long-chain as fatty acids. Ethyl hexanoate is an ester which gives anise, fruity and green apple characteristics; ethyl octanoate gives beer, burned, sweet and fruity sensory perceptions and ethyl decanoate ester is an example for oily, floral and fruity smells[28]. When ethyl decanoate and ethyl octanoate both present in high concentration can result in black cherry aroma and ethyl decanoate can positively influence ethyl octanoate production[29].

Acetate esters: Derives by condensed higher alcohols combining with acetyl-CoA with the use of acetyltransferase enzymes. These kinds of esters production favorable in low temperatures and fermentation with the anaerobic environment and they responsible for fruity odors as banana( isoamyl acetate), strawberry and apple(isobutyl acetate) in wine[30, 31]. Fatty acids with unsaturated bonds as well as dissolved oxygen can lower the production of acetate esters[32].

Ethyl acetate considers as most abundant aroma ester in wine which derived from ethanol and acetic acid formation via spontaneous /enzymatic reaction. Ethyl acetate when present in low concentration it gives fruity aroma contribution to wine while present in high concentration it can be converted in to nail varnish or solvent aroma.  

When all these esters formation water molecules produce as by-products which directly influence on pH of the system and derived more aroma bouquets.  

                                         

2- Phenylethyl acetate

Ethyl acetate

                            

                                                                   

Ethyl butanoate

Ethyl hexanoate

Ethyl octanoate

Figure 8: Major Ester’s structures typically present in Pinot Noir adapted from Sigma-Aldrich

1.4 Sample preparation for analysis

There are some important steps to be followed to obtain better quantitative analyze results. The most major part is the extraction step which has more impact on the final product.

                            Figure 9: Footpath Steps of analysis of the sample

1.5 Sampling techniques and applications

The study of compounds in wine is wonderful learning about a complex of chemicals which are responsible for amazing taste and smell.  To make a good commercial wine it needs to enhance the positive flavors.  For that, it is essential to differentiate and quantify these interesting organic compounds by using a suitable method. But it is a quite challenging task according to some limitations. From the past scientists have been giving an effort to identify and quantify all the complete volatile fraction present in wine, but unfortunately, none of this success to reveal due to some reasons.

• Volatile compounds may be present in very low concentration (ppm, ppb or ppt range) so pre concentration is a requirement before to proceed with the quantification method.
• Non-volatile compounds may create obstacles with interested aroma compounds present in the wine matrix.
• Aroma compounds may easily convert into an oxidized form or destroy by extreme temperature and pH due to instability.
• Different aroma compounds have different polarities, high range of solubility as well as volatility and diverse pH’s

When designing an experimental plan to study the aroma compounds, all these limitations must take into an account and need to be selective and unique to interested aroma compound[33].  Usually, from one extraction method, it is obvious to obtain a complete aroma profile, so we need to combine several sampling methods for a good one.

Through the past decades, there are a lot of sampling techniques that have been tried to make a good aroma profile in wine. They are Liquid-liquid extraction (LLE) which is separate the interested chemical component in to a solution by using a high range of polarity, Solid-phase extraction (SPE) target compound attracts towards to a solid sorbent matrix, solid-phase microextraction (SPME) this use a fiber to separate analytes [34] as well as new techniques like stir bar sportive extraction (SBSE) which use a magnetic stir bar for extraction[35]. But from all of these techniques can liberate interested volatile compounds before analysis and take a lot of time to give results. Because of that latest option is to use dynamic conditions to analyze compounds using purge and trap (P&T) and use SPME in static condition[36]

1.5.1 Liquid-Liquid Extraction (LLE)

The most critical point in this technique is to find a suitable organic compound to separate selected compounds from aqueous immiscible or partially miscible solution. The selected chemical compound is extracted into the organic phase by mixing aqueous solution using a separatory funnel [37]. pH and the polarity are the two main chemical factors that decide the fraction of contribution [38]. A high range of compounds that have different polarities can isolate from this technique other than the solvent-free methods. But some amount of compound can be lost or degrade, time-consuming and may originate emulsions are the drawbacks of this method[39].

                         

Aqueous layer with the analyte

Organic layer

                                 Figure 10:  Concept of the LLE method

To overcome these disadvantages Liquid-liquid micro extraction method has been invented. There are two types

• Single-drop microextraction (SDME) – Use one drop of organic solvent on the tip of a syringe needle and allow it to happen the extraction by immersing in the solution (DI-SDME) or held above the sample space(HS-SDME) and then injected into the GC for analysis[40].

1. The advantages of this method are simple, use only one drop of solvent so solvent consumption is very low and the efficiency of targeted compound extraction is very high[41]. But there are some disadvantages like required treatments to stabilize the micro size organic solvent drop and not suit for solid samples[42]. One of the most famous examples for SDME method is the extraction of chromium(iii) from water[43]

• Dispersive liquid liquid micro extraction (DLLME) – A cloudy/foggy suspension is allowed to form by stirring the solution with minimum volume (µL) of injected solvent. Then centrifuge the solution to make a small droplet with the target analyte in the bottom of the container. Inject into the GC after concentrating the analyte[44].

The pros of this method are fast and simple, cost-effective and sample recovery percentage is high. But if the sample has a complex matrix this method is not suitable and this can be applied only for inorganic samples[45]. This method is very useful to extract Cadmium(Cd), Gold(Au) and lead(Pb)[46].

1.5.2 Solid Phase Extraction (SPE)

Solid Phase Extraction (SPE) is a more advanced technology compared to the LLE method. When the interested analyte is present in different matrices such as blood, urine, drinks like tea, wine or juice and even in the soil can allow to adsorb or partition on to a small column which is consisted of a solid phase [47]. In this method affinity of the analyte should be high for the solid phase rather than the sample matrix[48].

Sample with the interested analyte

Run through the SPE column

 

Bonded analyte with the column + Matrix

 Wash with a solvent to remove the matrix

Bonded analyte with the column

Add a strong solution to elute the analyte from the column

Analyte

                             Figure 11: Basic extraction step by SPE method

There are three types of SPE methods according to the polarity of the adsorbent material fixed with the column.

• Normal Phase Sorbent: These kinds of sorbents (silica, florist, and alumina) can adsorb interested polar analytes and can elute them through non-polar to polar solution gradient. The efficiency of the sorbent matrix can be increased by adding some polar groups. Amino group (NH₂), cyano group (CN) and a group contain C, H, O named diol are some examples for them[49].

• Reverse Phase Sorbent: This act as the opposite of the normal phase sorbent and extract only non-polar analytes. Silica bonded with an octadecyl (C18) and octyl(C8) groups are two main sorbent matrices use for a reverse-phase but silica with cyclohexyl and phenyl groups also use to extract nonpolar compounds. Polar to non-polar gradient solution can be used to elute the interested polar anlyte[48, 50].

• Ion-exchange sorbent: Use ionic interactions through positively charged and negatively charged exchangers to separate the analyte. Negatively charged carboxylic acid and sulfonic acid can use as cation exchange sorbents which have low pKa values near to 1 to 4 and Positively charged primary, secondary, quaternary amines and aliphatic aminopropyl which have high pKa values near to 10 and 12 can use as anion exchange sorbents in SPE extraction technique. Buffers with different ranges can use the elution purpose[49].

SPE method has some advantages when compared with the LLE method such as environmentally friendly because of minimum consumption of organic solvents and low amount of organic disposal, not time-consuming, the efficiency of extraction is considerably higher and no problem with the emulsion formation. But this method is expensive than LLE because of the column, less stability, recovery rate may affect by the solvent flow rate and before starting the extraction process it needs to separate suspended matrices in the solution are some drawbacks of this method[51].

Applications of the SPE method are

     To find the effectiveness of drugs towards living begins, SPE is a good method to separate the targeted compound used in pharmaceutical chemistry. Ex is finding Tramadol drug in blood followed by HPLC [52]

     To extract some compounds present in food and beverages as an example Wang J was able to analyze aroma compounds present in the Australian wine sample by the SPE method followed by GC/MS [53].

1.5.3 Solid-Phase Microextraction (SPME)

This is a technique used to extract volatile compounds, as well as non-volatile compounds using an extracting stationary phase, consist of a small layer of polymer film coated silica fused with fiber [33, 54]. There are two types of methods, direct immersion (DI-SPME) and headspace (HS-SPME) method. This is one of the best analyses techniques to use for aroma quantification under good control of extraction conditions [55]. DI-SPME is better to analyze components present in liquid samples while the HS-SPME method is more sensitive for volatile sample determination[56]. This takes only 10-20 minutes to complete the extraction step within a solvent-free environment[57]. These extraction techniques need to combine with an analyzing instrument (Gas Chromatography, GC mass spectrometry, High-performance liquid chromatography, and LC mass spectrometer) for further steps. Recently aroma compounds in wine have studied using new analytical instruments such as TOFMS which is known as Time-of-flight mass spectrometry and GC×GC known as two-dimensional gas chromatography[55].

                   Figure 12: Two types of SPME method adapted from Nathan.w [58]

The next step is to desorb the extracted analytes through the thermal desorption technique in a hot injection port. It is very fast and takes only time in seconds [59].

From 1990s SPME has used for many analyses such as to detect impurities in pharmaceutical products[60], to quantify organic pesticides mixed with Chinese tea[61], contamination of water samples with environmental pollutants[62] and many. HS-SPME method is very popular with the aroma profiling of wine. If the sample consists of volatile compounds it is better to use thickly coated fiber and for high semi-volatile compounds can analyze using a thin coat. Different types of fibers such as DVB, CAR, and PDMS have used to study the most abundant methoxypyrazine 3-isobutyl-2-methoxypyrazine (IBMP), Earthy smelling 3-sec-butyl-2-methoxypyrazine (SBMP) and green bean or bell pepper smelling 3-isopropyl-2-methoxypyrazine (IPMP) which are present in grape wine or juice[63, 64]. There are two types of aniline derivatives which are responsible for ‘foxy aroma’ in American grapes. They are methyl anthranilate (MA), analyzed by SPME with a PDMS fiber and as 2-Aminoacetophenone (o-AAP) was studied using DVB/AR and PDMS fiber with DI-SPME method[65]. There are different types of commercial fibers which can be chosen according to the target analyte. Fibers can be changed from non-polar to polar and according to the thickness. Polar dimethylsiloxane (PDMS) is an example of non-polar fiber and Carbowax is a polar one[66].  Harrie A. Verhoeven has used silicon fiber to study flower fragrances [67]. Poly(acrylate)(PA) fiber has been used to study components such as alcohols, terpenes, a wide range of aldehydes and esters present in orange juice[68]. High polar compounds present in wine samples such as monoterpenes, CH₃(CH₂)₅OH, and C₈H₁₈O can be analyzed efficiently using CW/DVB fiber[69]. According to Robinson et al (2011) studies, DVB/CAR and PDMS are more suitable fibers for non-targeted compound analysis and has been a success to find out about 350 volatile compounds present in wine[70]. In general, the SPME method is not used to analyze sulfur compounds but developing fiber according to requirements CAR/PDMS/DVB fiber with 50/30 µm width and having about 2 cm length [71].

By adjusting ionic strength and pH, can increase the volatility and decrease the solubility of the interested sample. Agitation using a magnetic stir bar also makes a big influence on extraction efficiency[55].

There are some advantages compared with other extraction methods. It requires a minimum amount of sample volume, solvent-free method, not time-consuming with easy and efficient performance, Accuracy of analyzed data is very high. Some of the disadvantages are only some limited extractions can be performed because of the SPME fiber capacity, cannot use for analyzing sulfur compounds due to low sensitivity, maybe early samples can be contaminated with the extract and fiber is a thin fragile component[68, 72].

1.5.4 Stir Bar Sorptive Extraction (SBSE)

SBSE technique was developed by Baltussen et al. in 1999[73] which has a strong extraction capacity when compared with the SPME method [73-75]. The analyte in the liquid phase efficiently extracts on to better extracting phase with a magnetic bar witch coated with a sorbent [76]. As in figure 5 the magnetic bar allows to rotate in the liquid phase and gives the exact time to absorb interesting compound on to the sorbent. Then desorption process takes place to release the analyte by heat and then analyze through gas chromatography (GC/MS) or release into a solution for analyzing through liquid chromatography (LC/MS). According to the type of sorbent, there are three different magnetic rods. The most typical one is polydimethylsiloxane (PDMS) ; non-polar , polyacrylate (PA) ; polar and ethylene glycol/silicone (EG/silicone); polar[77]. If the extraction process occurs in the headspace of the solution it is called the HSSE technique and if it happens in solution it is called the SBSE immersion sampling technique[78].

Figure 13: Stir bar sorptive extraction; Headspace and immersion adapted from Prieto A. [79]

There are several applications with the SBSE method. When it applies to environmental analysis, it has been very helpful to identify a lot of compounds related to persistent organic pollutants (POPs)[80]. SBSE has been used to analyze the contamination of natural water samples and wastewater samples with polycyclic aromatic hydrocarbons (PAH) by using thermal desorption in GCMS[81]. SBSE is widely used for analyzing food products with impurities and toxins but less with nutrients. Horak et al. studied free fatty acids with medium size chains present in beer with this method[82]. Ha, et al. (2014) has been studied in rice wine to compare dynamic headspace sampling (DHS) and the SBSE method and came with the up conclusion that SBSE is the best method for analyzing volatile organic compounds in rice wine with high accuracy and sensitivity [83]. Aroma compounds present in grapes with glycosidic bonds have been identified by thermal desorption technique with GC[84].  This method is more popular also in pharmaceutical analysis and related medical fields. Anti-tuberculous agent Rifampicin (RIF) drug concentration in plasma was analyzed by stir bar-sorptive extraction and concluded this method is suitable for applications with therapeutic drug analysis[85]. Unceta et al. studied about inhibitor of serotonin reuptake related to plasma, tissues engage in brain and urine samples with the help of the SBSE sampling technique and HPLC[86].

In this new technique there are some advantages such as sample recovery is high, solventless environmental friendly method, due to large extraction surface preconcentration capacity is high, high usage because coated (PDMS) magnetic rod can use particularly, needed less sample volume, different analytical instruments ( GC, capillary electrophoresis, LC and inductive coupled plasma) can be coupled with SBBE extraction method. Some disadvantages of this method are polarity of the sample is real concern in this method and range is very limited, it is necessary to condition the magnetic stir bar prior to every analysis, the extraction process highly depends on the matrix and this method takes lot of time for extraction[84, 87, 88]. 

1.5.5 ICE Concentration Linked with Extractive Stirrer (ICECLES)

Maslamani et al. in 2016 have been developed a new extraction technique which is called ICE Concentration Linked with Extractive Stirrer (ICECLES)[89]. Freeze concentration (FC) is a less popular extraction method which concentrates solutes by decreasing freezing point and allow to analyte frozen in a fraction of liquid [90]. The FC technique widely performs with the food and paper industry[91]. In this method, FC and SBSE combination provides a better extraction system than they are alone. So FC helps to produce a strong concentrated solution to perform SBSE extraction[89]. Figure 6 shows the major steps of ICECLES system. The (a) vial surrounded by a double-layered beaker and allows the circulating cooling system. Vial (b) shows how the aqueous solution gently starts to become ice from bottom to the upside. Vial (c) indicates how magnetic bar contact with the most concentrated sample solution.

Figure 14: Basic steps of ICECLES extraction method adapted from Maslamani et al. in 2016[89].

There are no more applications except one which has performed for analysis pesticides in environmental water samples and got better results than the SBSE method done by Maslamani[89]. The main advantage of this technique is can apply to big polarity range, selectivity and accuracy are very high but it consumes a lot of time[91].

Purge and Trap Extraction (P&T)

This P&T extraction method has used in 1960 to do studies on bodily fluids [92] and later from 1970 it has developed to analyze volatile organic compounds (VOCs) present in drinking water[93]. This technique used for analyzing different food matrices. Dairy products (butter & cheese); Izco, J.M et al in 2000, has succeeded to find 68 volatile flavor compounds in Roncal cheese [94, 95]. Fruits; Hakala, M.A et al, 2002 has found 52 volatile compounds in six different varieties of strawberry [96], Laurentino Rosillo et al in 1999, studied about volatile compounds in seven varieties of grapes [97], soy sauce[98], French fries[99] and wine[100]

In this method closed vial use for the place the sample. Then start to purge by nitrogen or helium gas into an interesting sample constantly to bring out analyte into the headspace and remove immediately towards a packed column trap. Usually optimized gas flow rate and temperature maintain throughout the purging process [101]. Because of this method vapor pressure caused by volatile compounds in the gas phase become negligible and promote movement of all analytes into the headspace and allow absorbing on to column as much as possible. A combination of different sorbet matrices can use for this trap to enhance the absorption of all volatile compounds. Then generate a heating system to desorb the attached volatile compounds and send it to GCMS for analysis.

Figure 15: Basic steps of Purge and Trap Extraction (P&T) extraction method adapted from

The main advantage of this technique is high sensitivity. This method is thousand times sensitive than the headspace extraction method and gives in the ppb range. Compounds with high molecular weight can easily detect by using high temperature throughout the extraction process. But this is not good for light volatile compound detection and they may be lost during the process and time-consuming work[102].

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