JP2009069088A - Method for introducing pulse sample based on laser evaporation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which enables the stable introduction of a sample separated by a gas chromatograph, which is maintained at a high temperature, as an intermittently short pulse, to a mass spectrometer under a condition of a negligible dead volume. <P>SOLUTION: The method includes the steps of reducing the inner diameter of the top end of the vacuum side of a capillary for introducing a sample, cooling the top end of the capillary by adiabatic expansion, and effectively introducing the sample intermittently to the mass spectrometer by vaporizing a coagulated sample instantaneously by pulse laser irradiation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sample introduction method in mass spectrometry.

  Recently, laser ionization mass spectrometry has been widely used. In this method, sample molecules are often ionized instantaneously by a laser pulse and measured by a time-of-flight mass spectrometer. For example, matrix-assisted laser desorption ionization (MALDI) mass spectrometers combined with nitrogen lasers are widely used for protein measurement.

  The sample in the environment generally has a low concentration, and many impurities exist. For this reason, after collecting and concentrating a sample once, the method of measuring a mass spectrum sequentially is used, isolate | separating with a gas chromatograph apparatus.

  The laser ionization method has an advantage that specific molecules can be selectively ionized by appropriately selecting the wavelength of the laser. Therefore, it is advantageous when analyzing a small amount of sample in a large amount of impurities.

  Usually, the sample is continuously introduced into the mass spectrometer. Therefore, when a pulse laser is irradiated, only some sample molecules are ionized, and most samples are wasted. Therefore, although depending on conditions, the sensitivity is reduced by about 10,000 times.

  In view of the above situation, the present invention cools the vacuum side tip of the capillary into which the sample is introduced, and once the sample is adhered thereto, the sample is instantaneously evaporated by irradiation with a pulsed laser, A method and apparatus for intermittently introducing a sample into a mass spectrometer are provided.

In order to solve the above object, the present invention provides
[1] When the sample is introduced into the vacuum vessel through the capillary, the inside diameter of the tip on the vacuum side of the capillary is reduced, and the tip of the capillary is cooled by adiabatic expansion of the diluted gas flowing along with the sample. The sample adhered by the cooling effect is instantly evaporated by pulse laser irradiation, and the sample is intermittently introduced into the vacuum.

  [2] In the method described in [1] above, an apparatus for heating the capillary may be attached so that the temperature at the tip of the capillary can be controlled.

  [3] In the method according to any one of [1] to [2], helium may be used as a dilution gas.

  [4] In the method according to any one of [1] to [3] above, a Yag laser may be used as the pulse laser.

  According to the present invention, the following effects can be achieved.

  (1) When the sample is introduced into the vacuum vessel through the capillary, the capillary tip is cooled by the adiabatic expansion of the dilution gas flowing along with the sample by reducing the inner diameter of the tip on the vacuum side of the capillary. The sample can be intermittently introduced into the vacuum by instantaneously evaporating the sample adhered by the cooling effect by pulse laser irradiation.

  (2) In addition to the above (1), if an apparatus for heating the capillary is attached, the temperature at the tip of the capillary can be controlled, and the amount of adhesion and evaporation of the sample can be optimized.

  (3) In addition to any one of (1) to (2) above, by using helium as the diluent gas, the sample separated by gas chromatography can be directly introduced.

  (4) In addition to any one of (1) to (3) above, by using a Yag laser as a pulse laser, it can operate stably for a long time, and any of the harmonics of 532 nm, 355 nm, 266 nm, and 213 nm By selecting this, the sample can be efficiently evaporated.

  When the sample is introduced into the vacuum vessel through the capillary, the capillary tip is cooled by the adiabatic expansion of the diluted gas flowing along with the sample by reducing the inner diameter of the capillary tip. The sample can be intermittently introduced into the vacuum by instantaneously evaporating the adhered sample by pulse laser irradiation. Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 shows an apparatus for measuring with a time-of-flight mass spectrometer after separating a sample with a gas chromatograph apparatus. When the tip on the vacuum side of the capillary is not processed, the sample is rapidly introduced continuously into the mass spectrometer. On the other hand, as shown in FIG. 2A, when the inner diameter of the capillary tip is reduced, the temperature of the capillary tip is lowered by adiabatic expansion of the dilution gas (carrier gas) flowing together with the sample. For this reason, a sample adheres to a front-end | tip part. Therefore, as shown in FIG. 2B, when the part is irradiated with an evaporating (visible) laser, the sample is instantaneously heated to evaporate. As a result, the sample is localized and ejected as shown in FIG. When an ionizing (ultraviolet) laser is introduced there, a localized (concentrated) sample is obtained, and highly sensitive analysis can be performed.

  FIG. 3 shows the result of determining the relationship between the time interval and the ion signal intensity by changing the time interval (timing) between the evaporation laser and the ionization laser. From this result, it can be seen that the sample is localized in the time width of 10 μs and introduced into the vacuum.

  When a sample is ejected from a nozzle into a vacuum, a pulse nozzle is generally used. However, the upper limit for heating is about 200 ° C., and the pulse width is about 50 μs, which is a practical limit. When the present invention is used, the upper limit for heating is determined by the temperature at which the capillary melts, and can be used at least up to 500 ° C. In addition, since the pulse width can be shortened, the sensitivity can be further improved.

  If the repetition rate of the laser is 10 Hz, the sample evaporates every 100 ms and localizes in a time width of 10 μs. Therefore, in the best case, the sample concentration can be concentrated 10,000 times (100 ms / 10 μs), and the analysis sensitivity can be greatly improved. Further, in the present invention, by adjusting the temperature of the tip portion, low-boiling contaminants can be allowed to flow out without being adhered. Therefore, there is an advantage that the influence of the disturbing component can be reduced.

  FIG. 4 is a chromatogram obtained when the inner diameter of the tip is not reduced and when it is reduced. In the former case, the flow rate of the sample is increased and the time for elution from the chromatograph is slightly shortened. The latter signal intensity increases as the energy of the evaporation laser increases, and finally increases by 4.5 times at the peak value and 18 times at the area value compared to the case where the present invention is not used. Show. The increase rate of the signal is not 10,000 times, which is considered to be due to insufficient sample adhesion or insufficient laser evaporation. To improve this efficiency, the temperature at the tip of the capillary must be lowered sufficiently to completely adhere the sample, while the part where the sample adheres must be localized at the tip as much as possible to increase the efficiency of evaporation. is there.

  FIG. 5 shows a nozzle with a device for heating the capillary. By measuring and controlling the temperature of the capillary holding portion and adjusting the length of the protruding portion of the capillary tip, all the samples can be adhered to the tip and evaporated by laser. In the gas chromatograph, since helium is usually used as a carrier gas, it can be used as it is as a dilution gas. On the other hand, by using a YAG laser as a pulse laser for evaporation, it is possible to operate stably for a long time, and it is possible to efficiently evaporate a sample by selecting one of harmonics of 532 nm, 355 nm, 266 nm, and 213 nm. it can.

  There are harmful dioxin compounds in the environment, and the establishment of a microanalysis method is required. However, the analysis is not easy because the abundance is small and a large amount of impurities coexist. Supersonic molecular jet / laser ionization / mass spectrometry is a powerful method for this purpose, but the sample separated by gas chromatography is kept at high temperature and dead volume is negligible and intermittently short. It is extremely difficult to stably introduce it into a mass spectrometer as a pulse.

  By using the developed sample introduction method, the separated dioxins can be heated to 200 to 400 ° C. to eliminate dead volume and introduced into the mass spectrometer with a pulse width of 10 μs. Therefore, the sensitivity can be improved 10,000 times in the best case. Therefore, it exhibits great power in fields that require analysis of ultra-trace samples such as dioxins in blood and breast milk as well as exhaust gas, fly ash, air, water, and soil.

Gas chromatograph / Laser ionization / Time-of-flight mass spectrometer

Schematic diagram showing sample adhesion, evaporation, and ionization process (A) Adhesion (B) Laser evaporation (C) Laser ionization ○ is a vaporized sample molecule (arrow is the direction of movement), □ is an adhering sample molecule, Those with + in ○ indicate ionized sample molecules. Example of vaporization using visible light (532 nm) and ionization using ultraviolet light (266 nm)

Relationship between delay time of ionization laser pulse and ion signal intensity for evaporation laser pulse

Increase of signal intensity by laser evaporation method Sample is 2,8-dichlorodibenzofuran (A) Conventional method not reducing the inner diameter of the capillary tip (no irradiation with evaporation laser) (B)-(D) Inner diameter of the capillary tip Is reduced and the evaporation laser is irradiated Energy of the evaporation laser: (B) 25 mJ (C) 38 mJ (D) 51 mJ

Nozzle with a device for heating the capillary

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas cylinder 2 Gas chromatograph 3 Sample injection apparatus 4 Heater 5 Capillary 6 Time-of-flight mass spectrometer 7 Ion detector 8 Evaporation laser 9 Mirror 10 Ionization laser 11 Delay circuit 12 Oscilloscope 13 Chromatograph elution sample 14 Capillary 15 Capillary Tip 16 Heating 17 Thermocouple 18 Controller 19 Vacuum chamber (mass spectrometer)

Claims (4)

  When the sample is introduced into the vacuum vessel through the capillary, the inside diameter of the tip on the vacuum side of the capillary is reduced, the tip of the capillary is cooled by adiabatic expansion of the dilution gas flowing along with the sample, A sample introduction method and apparatus characterized in that the sample adhered by the cooling effect is instantaneously evaporated by pulse laser irradiation, and the sample is intermittently introduced into a vacuum. The method and apparatus according to claim 1, comprising an apparatus for heating the capillary. The method according to claim 1, wherein helium is used as the dilution gas. The method according to any one of claims 1 to 3, wherein a yag laser is used as the pulse laser.

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