Applications of Hadamard Transform-Gas Chromatography/ Mass Spectrometry (HT-GC/MS) to the Detection of Pesticides in Rice

, 1995; . , 2007; al . 2004 In this work, we developed a novel method by combining an on-line sample SFE collection system and the Hadamard transform GC/MS (HT-GC/MS) method for the extraction/detection of pesticide in rice (Fan et al ., 2010; Johansen . , 1994; Fuoco al . , 1997; Aguilera al . , 2005 Gmuer ., 1987). The methodology of HT-GC/MS and the design of an on-line SFE sample collection system are demonstrated. Details of the experimental conditions for the determination of pesticides in rice are also reported herein. The book offers a professional look on the recent achievements and emerging trends in pesticides analysis, including pesticides identification and characterization. The 20 chapters are organized in three sections. The first book section addresses issues associated with pesticides classification, pesticides properties and environmental risks, and pesticides safe management, and provides a general overview on the advanced chromatographic and sensors- and biosensors-based methods for pesticides determination. The second book section is specially devoted to the chromatographic pesticides quantification, including sample preparation. The basic principles of the modern extraction techniques, such as: accelerated solvent extraction, supercritical fluid extraction, microwave assisted extraction, solid phase extraction, solid phase microextraction, matrix solid phase dispersion extraction, cloud point extraction, and QuEChERS are comprehensively described and critically evaluated. The third book section describes some alternative analytical approaches to the conventional methods of pesticides determination. These include voltammetric techniques making use of electrochemical sensors and biosensors, and solid-phase spectrometry combined with flow-injection analysis applying flow-based optosensors.


Hadamard transform (HT)
The Hadamard transform (HT) technique has been applied in a variety of fields, including time-of-flight mass spectrometry (Brock et al., 1998;Fernández et al., 2002;Trapp et al., 2004;Fernández et al., 2001), Raman spectrometry (Treado et al., 1990;DeVerse et al., 2000;DeVerse et al., 1999), fluorescence imaging (Chen et al., 1995;Mei et al., 1996;Tang et al., 2002;Hassler et al., 2005) ion mobility spectrometry (Clowers et al., 2006;Szumlas et al., 2006), and NMR (Kubo et al., 1996;Feliz et al., 2006). In addition, the application of the cross correlation technique to chromatographic separation was first proposed by Izawa and coworkers. A Hadamard matrix on the order of n, H n , is an n × n of +1's and -1's with the property of the scalar product of any two distinct rows being 0. Thus, H n must satisfy the following equation, H n H n T = H n T H n = nI n (1) where H n T is the transpose of H n and I n is the unit matrix on the order of n. A fundamental equation of the Hadamard transformation is given by where η is a series of data, i.e., the observed chromatogram, encoded by a cyclic S-matrix, S, which is the (n-1) × (n-1) matrix consisting of "zero" and "one" elements, and C is a series of data representing a chromatogram. A cyclic S-matrix on the order of (n-1) is obtained by omitting the first row and column of H n and then changing +1's to 0's and -1's to 1's. To encode the chromatogram, C, a sample and eluent are introduced into a column according to the PRBS (pseudorandom binary sequence) derived from the cyclic S-matrix. When the elements of the PRBS are "one" and "zero," sample and eluent plugs are introduced into the column, respectively. As a result, the encoded chromatogram, η, is obtained. The encoded chromatogram is decoded to the chromatogram, C, by multiplying an inverse matrix of S, S -1 , as follows. [ Applications of Hadamard Transform-Gas Chromatography/Mass Spectrometry (HT-GC/MS) to the Detection of Pesticides in Rice

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Consequently, the decoded chromatogram shows improvement in the S/N ratio (Fellgett advantage). In both correlation and HT methods, the key technology, based on multiple input techniques according to PRBS, is the injection device, which permits the continuous introduction of a sample. Multiple injection devices for GC have also been developed for correlation GC, in which the solenoid valve (Smit, 1970;Annino and Bullock, 1973), cylindrical slide valve (Kaljurand and Küllik, 1979), and fluidic logic gate (Annino et al., 1979) were used. Conversely, in correlation LC, the input signals modulated by PRBS were generated by valve systems (Lub et al., 1978;Smit et al., 1980;Laeven et al., 1983;Mars and Smit, 1990;Kaljurand et al., 1992) and by an electrochemical concentration modulator (Engelsma et al., 1990).

Hadamard-injector
A schematic drawing is shown in Figure 1. The developed Hadamard-injector permits a pressurized gas or pressurized liquid to be injected into a separation column according to a pseudorandom binary sequence (PRBS), i.e. a Hadamard code. In fact, it was made by

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Pesticides in the Modern World -Trends in Pesticides Analysis 416 modifying a regular pulse nozzle (Lin and Imasaka, 1993). Instead of a pinhole, which is used in general pulse nozzles, a piece of a capillary was used for the introduction of the pressurized sample solution (I.D., 50 μm; 8 cm in length). The body of the Hadamard-injector was made of brass; the plunger had a diameter of 9.5 mm and a length of 34 mm. A 24 V electromagnetic coil and the spring were removed from a solenoid valve (SMC model VX2110: 0~1.5 MPa, Japan), respectively, and used directly. A septa-BTO (Item No. 298735) was inserted into a brass holder, which was used to firmly attach the capillary and prevent gas or liquid leaks, and was sealed with a brass stopper. The Hadamard-injector can be heated and directly inserted into the GC inlet; the injection volume of the sample solution can be adjusted by changing the background pressure (nitrogen gas), the inner diameter of the capillary, the capillary length and the injection time to achieve a micro-controlled injection. During the sample injection process, a personal computer was used to rapidly turn the Hadamard-injector on and off through the PCI 6221 device, according to a series of Hadamard codes, leading to the introduction of the pressurized sample solution through the capillary into the GC column. The injection volume of the pressurized sample solution can be adjusted by changing the background pressure (nitrogen gas), the inner diameter of the capillary, capillary length, and injection time. Figure 2 shows the relationship between the injected volume and injection time based on various background pressures (A, for pressurized gas: 1.3~ 1.8Kg/cm 2 ; B, for pressurized liquid: 1.5 ~ 3 Kg/cm 2 , respectively). Herein, the injected volume was recognized by means of a gas drainage method ( Figure 2A) and by weighing the collected liquid ( Figure 2B), respectively. As can be seen in Figure 2A (for pressurized gas), when the injection time was adjusted in the range of 1 ~3 s, the injection volume can be controlled from 0.3 to 4.2 μL; in Figure 2B (for a pressurized liquid), when the injection time was adjusted in the range of 0.1 ~1 s, the injection volume can be controlled from 0.04 to 0.3 μL. It should be noted that both show very good linear relationships. The RSD (related standard deviation) values of within-day and betweenday were determined to 0.24 ~ 0.38% and 0.27%, respectively, indicating the stability and reproducibility of the procedure. Furthermore, the sample injection time, volume and split-ratio were investigated in detail during GC separation experiments. Figure 3 shows a schematic diagram of the on-line SFE/HT-GC/MS system. This system consists of a commercial SFE instrument, a commercial GC/MS, a holding tank and the Hadamard-injector. A 2.0 g sample of rice, obtained from a local supermarket, was spiked with three different pesticides (diazinon, chlorpyrifos and parathion-methyl, 30 µg each). The rice sample had first been subjected to a typical GC/MS method to confirm the absence of pesticide contaminants. The extraction liquid was 1.5 mL of acetonitrile. A 0.8 g quantity of glass beads was also placed in the holding tank to suppress bubbling. The CO 2 pressure was set at 20.3 MPa so as to extract the pesticides at a flow rate at 1 mL/min (oven temperature, 50 °C). After adding 15 mL of supercritical CO 2 fluid, the liquid was slowly passed through the spiked rice sample at a constant rate, the extracts were passed through a filter (0.45 µm) and then directly injected into the GC column by a personal computer, which turned the Hadamard-injector on and off, quickly, based on the Hadamard codes. The optimized conditions were a background pressure of 3 Kg/cm 2 and an injection time of 0.2 s. The injection volume was estimated to be ~ 66 nL for a single injection.

Results and discussion
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Figure 4 shows typical GC/MS chromatograms for parathion-methyl standard by means of single injection (frame A) and
Hadamard injection (frame B). The concentration level was 20 µg/1 mL acetonitrile. In the case of single injection, injection volume was 66 nL (absolute amount, 1.3 ng). The findings show that the S/N ratio of the chromatogram was relatively poor in frame A. However, under the same experimental conditions, when the Hadamard injection was performed (as shown in frame B; matrix order, n = 255), and each injection volume was still 66 nL, the S/N ratio was dramatically improved. The inset in frame B shows the details of raw data before the inverse Hadamard transformation (chromatogram a, whole chromatogram; chromatogram b, portion chromatogram of n = 127 ~ 238) and the Hadamard code (chromatogram c, n = 127 ~ 238). As can be seen, chromatograms b and c are quite matched, and for this reason, the S/N ratio improved as excepted.
www.intechopen.com  When analyzing a mixture of different pesticides, the use of Hadamard transform is also helpful to improve the S/N ratio. In this case, three types of pesticides (diazinon, parathionmethyl and chlorpyrifos) were spiked in the sample rice. Figure 5 shows typical HT-GC/MS chromatograms of the on-line SFE extracts from the spiked rice sample. Herein, the SIM mode was used (ion peaks at m/z = 125, 137 and 199 were selected for monitoring). Chromatograms a and b show the results obtained for a single injection and a Hadamard injection (matrix order, n = 255), respectively. As can be seen, the S/N ratio is again substantially improved. The detected peaks are also completely consistent with the theoretical prediction. Table 1 shows the relationship between the enhancement in S/N ratios and mass conditions for analysis based on on-line supercritical fluid extraction/HT-GC/MS methods (SIM mode was used; m/z = 125, 137, 199 for diazinon, chlorpyrifos and parathion-methyl, respectively). The results indicate that the on-line SFE/Hadamardinjector described herein also permits precise multiple injections and that it can be used for the determination of actual samples. Fig. 4. Typical GC/MS chromatograms for parathion-methyl standard; concentration level, 20 µg/1 mL acetonitrile. In frame A, chromatogram was obtained by single injection (injected volume, 66 nL; absolute amount, 1.3 ng). In frame B, chromatogram was obtained by Hadamard injection (Hadamard matrix, n = 255; each injection volume, 66 nL; total injection volume, 16.8 µL). The inset in frame B shows the details of raw data before the inverse Hadamard transformation (chromatogram a, whole chromatogram; chromatogram b, portion chromatogram of n = 127 ~ 238) and the Hadamard code (chromatogram c, n = 127 ~ 238). The enhancement of the S/N ratio was calculated as the ratio of S/N values obtained in the chromatograms, measured by HT-GC/MS and a single injection method. Table 1. Relationship between the enhancement in S/N ratios and mass conditions for analysis based on on-line supercritical fluid extraction/HT-GC/MS methods (SIM mode was used; m/z = 125, 137, 199 for diazinon, chlorpyrifos and parathion-methyl, respectively).

Conclusion
In this study, we developed novel Hadamard-injectors coupled with sample collection systems. The SFE system was successfully interfaced with the Hadamard-injector and the extracts were successfully collected. The utility of the method was demonstrated using some representative pesticides as model compounds. The device permitted continuous and precise sample injections in HT-GC/MS, resulting in a substantial improvement in S/N ratios through the application of the Hadamard transformation. The enhancement factors for the S/N ratios were matched with the theoretical values. Thus, this method has a variety of applications and could potentially be used in practical trace analysis.  The book offers a professional look on the recent achievements and emerging trends in pesticides analysis, including pesticides identification and characterization. The 20 chapters are organized in three sections. The first book section addresses issues associated with pesticides classification, pesticides properties and environmental risks, and pesticides safe management, and provides a general overview on the advanced chromatographic and sensors-and biosensors-based methods for pesticides determination. The second book section is specially devoted to the chromatographic pesticides quantification, including sample preparation. The basic principles of the modern extraction techniques, such as: accelerated solvent extraction, supercritical fluid extraction, microwave assisted extraction, solid phase extraction, solid phase microextraction, matrix solid phase dispersion extraction, cloud point extraction, and QuEChERS are comprehensively described and critically evaluated. The third book section describes some alternative analytical approaches to the conventional methods of pesticides determination. These include voltammetric techniques making use of electrochemical sensors and biosensors, and solid-phase spectrometry combined with flow-injection analysis applying flow-based optosensors.