Mass analyzing apparatus

The present invention relates to a mass analyzing apparatus, comprising a first metal electrode plate, a second metal electrode plate, an RF power supply, a reactant gas and a mass spectrometry. The second metal electrode plate is grounded. There is a gap between the first metal electrode plate and the second metal electrode plate. The RF power supply is electrically connected to the first metal electrode plate. Electric discharge is caused between the first metal electrode plate and the second metal electrode plate, so that the reactant gas becomes dissociation plasma. The dissociation plasma reacts with a gas analyte from a sample and then enters the mass spectrometry for a mass analysis. In addition, since the dissociation plasma is generated under low temperature and atmospheric pressure, the mass analyzing apparatus of the present invention is applicable for biological samples that need to be analyzed at a low temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mass analyzing apparatus. More particularly, the present invention relates to a mass analyzing apparatus capable of generating an ionization source by an RF power, without sample pretreatment at normal temperature and atmospheric pressure.

2. Description of the Related Art

In the conventional art, chemical compositions in samples (such as Chinese medicinal herbs) are analyzed by detection through liquid chromatography/mass spectrometer (LC/MS) or gas chromatography/mass spectrometer (GC/MS). The samples must be pretreated by being extracted with a solvent before being analyzed, so as to get signals.

FIG. 1is a schematic view of an ionization source for a conventional direct analysis in real time (DART) as disclosed in U.S. Pat. No. 7,112,785.

Taking positive ions for example, the operational principle of the ionization source1includes: atoms of an inert gas (e.g., helium gas) that flow around the ionization source1are excited or ionized by a high voltage field at one atmosphere of pressure, as shown in Equation (1); next, the generated helium ions (He+) or the excited-state helium atoms (He*) impact with water molecules (H2O) in the atmosphere, to generate water ions (H2O+) and electrons (e−), as shown in Equation (2); then, water ions (H2O+) react with other water molecules (H2O), to generate hydrated ions (H3O+), as shown in Equation (3); finally, the hydrated ions and molecules (M) of a gas analyte from a sample perform an ion-molecule reaction, so as to generate molecular ions (MH+) of the analyte, as shown in Equation (4). Besides the above ionization process, the molecular ions of the analyte can also be formed by directly impacting the helium ions or excited state helium molecules with gas analyte, as shown in Equation (5).

The ionization source1has a metal needle11therein, and a DC high voltage is applied to the metal needle11. Extremely high electric field intensity is generated due to the very small area of the top end of the metal needle11, and the helium stream flows in through an inlet12behind the metal needle11, to perform the reactions of Equations (1) to (3). As the ion-molecule reaction is merely suitable for gas molecules, the helium stream flows through a heating region13, so that the temperature of the helium gas flowing out from the outlet14of the ionization source1is between 50° C. and 70° C. Once the hot gas stream containing helium gas, helium ions, and excited state helium molecules impacts the surface of the sample (usually, a solid), the chemicals on the surface of the sample are likely to be volatilized, so as to be reacted with the hydrated ions in the atmosphere to form analyte ions, i.e., perform the reactions of Equations (4) and (5). Then, the analyte ions enter a mass spectrometer for a mass analysis.

The ionization source1is characterized by its operation at an atmospheric pressure, so mass signals of the sample can be obtained without any sample treatment, which is very helpful for the object to be analyzed within a very short time or in situ in real time. The ionization source1can be used for analysis in the following situations: the detection of bombs in an airport and the rapid identification of air or water pollutants in environmental analysis. Additionally, the technique can also be used in situ to examine whether medicine is drugs, or to determine whether currency is real or fake by analyzing the ink chemicals.

The ionization source1is disadvantageous in that the operation environment is a high-voltage and high-temperature environment, which is very undesirable when the sample is a biomolecule, since the biomolecule is easily damaged in such an environment. Moreover, as the position where the plasma gas molecules are generated by the ionization source1is far away from the sample and the inlet of the mass spectrometer, after being dissociated, the excited state gas molecules are reduced to a basic state during the flight. Thus, the charge-carrying capacity of the sample molecules is reduced, which leads to poor detection efficiency. Additionally, the ionization source1needs a large gas stream, and therefore the operation cost is high.

Additionally, there is an inductively coupled plasma mass spectrometer (ICP MS), which is applied on ionizing metal atoms. However, in the ICP MS, in order to ionize the metal atoms, it is necessary to consume a large amount of energy, which is generally an AC voltage (1700 V) with an output power of 1200 W and an RF of 13.56 MHz. The temperature of the plasma generated at this condition is approximately between 6000° C. and 8000° C., and the used inert gas is argon gas (Ar), which cannot generate plasma discharge in an environment of high atmospheric pressure in order to generate ionized gas molecules, and thus cannot be applied in detecting biomolecules under an atmospheric pressure.

Therefore, it is necessary to provide a mass analyzing apparatus to solve the above problems.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a mass analyzing apparatus, which includes: a first metal electrode plate, a second metal electrode plate, an RF power supply, a reactant gas, and a mass spectrometer. The first metal electrode plate has a plurality of first through-holes. The second metal electrode plate has a plurality of second through-holes, and the second metal electrode plate is grounded. There is a gap between the second metal electrode plate and the first metal electrode plate. The RF power supply is electrically connected to the first metal electrode plate, so that electric discharge is caused between the first metal electrode plate and the second metal electrode plate. The reactant gas passes through the first metal electrode plate and the second metal electrode plate, and the reactant gas becomes dissociation plasma. The plasma is blown out from the second through-holes of the second metal electrode plate, reacts with the gas analyte from the sample, and enters the mass spectrometer for a mass analysis. Therefore, the plasma is generated in an environment of atmospheric pressure and room temperature, in which the temperature is kept at about 50° C., and the maximum temperature of the gas does not exceed 70° C., and thus, the mass analyzing apparatus of the present invention is suitable for biological samples that should be operated at low temperature. Furthermore, the present invention can be used to perform a mass detection on solid, liquid, or gas samples, and it is not necessary to perform complicated pretreatments on the samples. Moreover, the plasma is immediately blown out from the second through-holes once it is generated and reacts with the gas analyte from the sample, so that the ionization efficiency is much higher than that of the conventional ionization source1does not exceed 70° C., and thus, the mass analyzing apparatus of the present invention is suitable for biological samples that should be operated at low temperature. Furthermore, the present invention can be used to perform a mass detection on solid, liquid, or gas samples, and it is not necessary to perform complicated pretreatments on the samples. Moreover, the plasma is immediately blown out from the second through-holes once it is generated and reacts with the gas analyte from the sample, so that the ionization efficiency is much higher than that of the conventional ionization source1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2shows a schematic view of a mass analyzing apparatus of the present invention.FIG. 3shows a sectional view of an ionization source for the mass analyzing apparatus of the present invention. The mass analyzing apparatus2includes an ionization source3, a mass spectrometer21, a cover22, a heating plate23, and a sample24. The ionization source3includes a first cylinder31, a second cylinder32, an insulation layer33, a first metal electrode plate34, a second metal electrode plate35, an RF power supply36, and a reactant gas supply37.

The first cylinder31is located within the second cylinder32, that is, the inner diameter of the first cylinder31is smaller than that of the second cylinder32. The insulation layer33is located between the outer wall of the first cylinder31and the inner wall of the second cylinder32. In this embodiment, the first cylinder31and the second cylinder32are made of stainless steel. The material of the insulation layer33is a high insulation material, such as Teflon, so as to electrically block the first cylinder31and the second cylinder32.

The first metal electrode plate34has a plurality of first through-holes arranged in an array. The first metal electrode plate34is connected to an open end of the first cylinder31. The second metal electrode plate35has a plurality of second through-holes arranged in an array. The second metal electrode plate35is connected to an open end of the second cylinder32, and the second metal electrode plate35and the first metal electrode plate34are parallel and spaced apart from each other by a gap, so as to form a face discharge room45. The first through-holes communicate with the face discharge room45, and the second through-holes communicate with the face discharge room45. In this embodiment, the second metal electrode plate35and the first metal electrode plate34have a ring-shaped pad40therebetween, so as to make the second metal electrode plate35and the first metal electrode plate34parallel and maintain a gap therebetween. The second metal electrode plate35, the first metal electrode plate34and the ring-shaped pad40define the face discharge room45. In this embodiment, the first metal electrode plate34and the second metal electrode plate35are made of conductive metal, such as stainless steel, aluminum, or copper, and they are disc shaped, and the diameter of the first metal electrode plate34is less than that of the second metal electrode plate35. In this embodiment, the gap between the second metal electrode plate35and the first metal electrode plate34is about 0.5 mm.

In this embodiment, the ionization source3further includes a third cylinder42, a front cover43, and a back cover44. The inner diameter of the third cylinder42is greater than that of the second cylinder32. The third cylinder42, the front cover43, and the back cover44form a back cavity421. The second cylinder32is connected to the front cover43, and the cavity formed by the second cylinder32communicates with the back cavity421. The back cover44has a first opening441and a second opening442. In this embodiment, as the inner diameter of the third cylinder42is greater than that of the second cylinder32, the ionization source3has a step-like appearance. However, it should be understood that the ionization source3can also not have the third cylinder42and the front cover43, that is to say, the second cylinder32can be directly connected to the back cover44so the ionization source3has a single cylinder-shaped appearance.

The RF power supply36is connected to a first opening441of the back cover44through a first connecting pipe38, and electrically connected to the first cylinder31through a wire41, so as to supply an RF AC current to the first metal electrode plate34. The second metal electrode plate35and the second cylinder32are directly grounded. As the distance between the second metal electrode plate35and the first metal electrode plate34is very small, an electric discharge is generated between the first metal electrode plate34and the second metal electrode plate35. In this embodiment, the RF AC current supplied by the RF power supply36has a power of 15 W, and an RF of 13.56 MHz.

The reactant gas supply37is connected to a second opening442of the back cover44through a second connecting pipe39to input a reactant gas to the back cavity421, and further input it to the first cylinder31. The reactant gas can be, for example, helium gas, argon gas, nitrogen gas, or air. In this embodiment, the reactant gas is helium gas at a flow rate of 1-3 L/min. When the helium gas is introduced into the face discharge room45between the second metal electrode plate35and the first metal electrode plate34, dissociation plasma is formed by the impact of the helium molecules on the high-energy electrons generated by the face discharging process occurred in the face discharge room45, and the reaction is as shown in Equation (1). The dissociation plasma is then extruded and blown out by the net gas pressure generated by the continuously introduced helium gas, thereby departing from the second metal electrode plate35.

The cover22is used to carry the sample24therein, and the sample24is located between the second metal electrode plate35of the ionization source3and the mass spectrometer21. The cover22preferably further includes a heating plate23thereunder, for heating the sample24, with the cover22located therebetween. If the sample24is volatile, a gas analyte is generated without being heated; if the sample24is nonvolatile, a gas analyte is generated upon being heated or being irradiated by a laser. Therefore, the present invention preferably further includes a laser generator (not shown) for generating a laser, so as to irradiate the sample24and thus generate a gas analyte.

Additionally, if desired, an opening (not shown) can be made below the cover22, so that the heating plate23can directly carry and heat the sample24.

The mass spectrometer21has a sample receiver211. In this embodiment, the mass spectrometer21is manufactured by Micromass Company, with a model of Quattro LC system. The sample receiver211is located at the top end of a cone with a diameter of about 14 mm. One end (the left end in the figure) of the cover22covers the second cylinder32and the second metal electrode plate35of the dissociation source3; and the other end (the right end in the figure) of the cover22forms a bowl-shaped shrinkage, and has a small hole at the top end for being sleeved on the sample receiver211. In this way, the cover22forms a cavity with the upper part being substantially closed, so as to prevent the ions from being volatilized into the air. In this embodiment, the cover22is made of glass, and has a length of 57 mm.

When the plasma departs from the ionization source3and enters the cover22, as the plasma contains a large amount of excited-state helium atoms (He*) and electrons therein, the plasma can perform a series of ion-molecule reactions and charge exchanges with the moisture in the air and the gas analyte (M) from the sample24, so as to generate protonation molecular ions (MH+) of the analyte, and the reactions are shown by Equations (1)-(5). The molecular ions of the analyte enter the mass spectrometer21through the sample receiver211for a mass analysis.

The present invention is advantageous in that the ionization source3can generate low-temperature plasma at atmospheric pressure, and after being consecutively operated for 60 min., the temperature of the second cylinder32of the ionization source3can still be stably maintained lower than 70° C. Therefore, the ionization source3of the present invention is extremely suitable for biological samples that should be analyzed at a low temperature. Additionally, the concentration of the ionized gas generated by the ionization source3of the present invention will be stably increased along with the input power and gas flow rate of the ionization source3, which indicates that the ionization source3is extremely suitable for being applied as an ionization source for stable mass analysis. Furthermore, the present invention can directly perform mass detection on solid, liquid, or gas samples, and it is not necessary to perform a complicated pretreatment of the samples. Moreover, once generated, the plasma is immediately blown out through the second through-hole of the second metal electrode plate35and reacts with the gas analyte from the sample24, and thus, the ionization efficiency is much higher than that of the conventional ionization source1. Finally, as the ionization source3merely has gas input, the mass spectrometer21does not have the memory effect generated by the conventional ionization source, but performs consecutive analyses of various samples and does not affect the mass analysis signals of the next sample due to the memory effect. Additionally, a laser can be used to heat the samples having higher molecular weights, which is advantageous in focusing on a small area. Therefore, various positions on the sample surface can be detected selectively, and even consecutive detections can be performed, so as to obtain the molecular image of the sample.

The present invention is illustrated in detail through the following examples, but the present invention is not limited to the disclosure of the examples.

FIG. 4shows an ion concentration curve of the ionization source of the present invention at different RF output powers. This example aims at testing the concentration of the plasma ions generated by the ionization source3according to the above embodiment, and the experimental methods are listed as follows: the flow rate of the reactant gas is fixed at 6 L/min, and the output power of the RF power supply36is taken as the manipulating variable, the initial power of the RF power supply36is 6 W, and then is increased by 2 W in one stage. It can be seen in the experimental results shown inFIG. 4that there is an obvious increment in each stage, which indicates that the ionization source3can indeed improve the ion concentration as the power increases stably, and the whole concentration magnitude falls in a range of 108˜1010ions per second, which meets the requirements for the concentration.

FIGS. 5ato5cshow mass spectrums measured by the mass analyzing apparatus of the present invention, in which the sample is chewing gum. In this example, the sample of chewing gum is sliced and then placed into the cover22of the mass analyzing apparatus2for testing.FIG. 5ashows a mass spectrum without the sample of chewing gum being placed therein, from which it can be seen that there is only one background peak signal.

FIG. 5bshows a mass spectrum with the sample of chewing gum being heated 70° C. by the heating plate23, from which it can be seen that many molecular signals have been detected, and the labeled peaks are the spectrums of various saccharides in the chewing gum.FIG. 5cshows a mass spectrum with the sample of chewing gum being heated to 100° C. by the heating plate23, from which it can be seen that more ingredients have been excited and detected.

FIGS. 6ato6cshow mass spectrums measured by the mass analyzing apparatus of the present invention, in which the sample is angelica. In this example, the sample of angelica is sliced and then placed into the cover22of the mass analyzing apparatus2for testing.FIG. 6ashows a mass spectrum without the sample of angelica being placed therein, from which it can be seen that there is only one background peak signal.FIG. 6bshows a mass spectrum with the sample of angelica being heated to 70° C. by the heating plate23, from which it can be seen that liqustilide (with a mass/charge ratio (m/z) of 190.8) and butylidene phthalide (with a mass/charge ratio (m/z) of 189.2) have been detected.FIG. 6cshows a mass spectrum with the sample of angelica being heated to 100° C. by the heating plate23, from which it can be seen that umbelliferone (with a mass/charge ratio (m/z) of 163.1) has been excited and detected.

FIGS. 7ato7cshow mass spectrums measured by the mass analyzing apparatus of the present invention, in which the sample is dried ginger. In this example, the sample of dried ginger is sliced and then placed into the cover22of the mass analyzing apparatus2for testing.FIG. 7ashows a mass spectrum without the sample of dried ginger being placed therein, from which it can be seen that there is only one background peak signal.

FIG. 7bshows a mass spectrum with the sample of dried ginger being heated to 70° C. by the heating plate23.FIG. 7cshows a mass spectrum with the sample of dried ginger being heated to 100° C. by the heating plate23. As shown inFIGS. 7band7c, ion signals of main volatile substances in the dried ginger have been detected.

FIGS. 8ato8cshow mass spectrums measured by the mass analyzing apparatus of the present invention, in which the sample is peach seed. In this example, the sample of peach seed is sliced and then placed into the cover22of the mass analyzing apparatus2for testing.FIG. 8ashows a mass spectrum without the sample of peach seed being placed therein, from which it can be seen that there is only one background peak signal.FIG. 8bshows a mass spectrum with the sample of peach seed being heated to 70° C. by the heating plate23.FIG. 8cshows a mass spectrum with the sample of peach seed being heated to 100° C. by the heating plate23. As shown inFIGS. 8band8c, ion signals of main volatile substances in the peach seed have been detected.

FIGS. 9ato9cshow mass spectrums measured by the mass analyzing apparatus of the present invention, in which the samples are dried ginger and peach seed. In this example, the samples of dried ginger and peach seed are sliced and then placed into the cover22of the mass analyzing apparatus2for testing.FIG. 9ashows a mass spectrum without the samples of dried ginger and peach seed being placed therein, from which it can be seen that there is only one background peak signal.FIG. 9bshows a mass spectrum with the samples of dried ginger and peach seed being heated to 70° C. by the heating plate23.FIG. 9cshows a mass spectrum with the samples of dried ginger and peach seed being heated to 100° C. by the heating plate23. As shown inFIGS. 9band9c, individual signals from the two Chinese medicinal herbs have been detected, wherein ● indicates the signals of dried ginger, ♦ indicates the signals of peach seed, and ▴ indicates the co-signals of dried ginger and peach seed.

FIGS. 10ato10gshow mass spectrums measured at different times when monitoring the epoxidation reaction of chalcone by the mass analyzing apparatus of the present invention, in whichFIG. 10ashows the mass spectrum at 0.722 min.,FIG. 10bshows the mass spectrum at 2.025 min.,FIG. 10cshows the mass spectrum at 3.584 min.,FIG. 10dshows the mass spectrum at 4.134 min.,FIG. 10eshows the mass spectrum at 5.051 min.,FIG. 10fshows the mass spectrum at 5.766 min., andFIG. 10gshows the mass spectrum at 6.372 min. In this example, H2O2and NaOH are added into chalcone to perform the epoxidation reaction, and the reaction equation is shown as follows:

It can be learned fromFIG. 10athat, when the reactant exists by itself, a signal with a mass/charge ratio (i/z) of 209 can be obtained. Next, after adding the catalyst NaOH, no change occurs in the reactant, as shown inFIG. 10b, and still there is merely a signal with a mass/charge ratio (m/z) of209. Then, once H2O2is added, a product is generated, as shown inFIGS. 10cto10g, and signals of the product 1,3-diphenyl-1,2-epoxy-propan-3-one with a mass/charge ratio (m/z) of 225 can be obtained, and signal of 2,3-dihydroxy-1,3-diphenylpropan-1-one with a mass/charge ratio (m/z) of 242 can be obtained, which lacks an OH group compared with the product.

While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope defined in the appended claims.