CN106124606B - A kind of 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating method - Google Patents
A kind of 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating method Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
- G01N27/626—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using heat to ionise a gas
- G01N27/628—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using heat to ionise a gas and a beam of energy, e.g. laser enhanced ionisation
Abstract
The invention discloses a kind of 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating methods, being first introduced directly into the standard solution sample that concentration is 1ppb is made to level four bars icp ms by optimizing instrument parameter205The response intensity of Tl is greater than 200000cps/ppb, and relative standard deviation is 1%~2%, and double charge is less than 1.5%, and oxide yield is less than 1%；It recycles the mode of laser ablation to introduce 610 solid etalon sample of man-made glass NIST to level four bars icp ms, matches the carrier gas of laser and the carrier gas of level four bars icp ms, make238The counting of U reaches highest；The mode of laser ablation is recycled to introduce monazite standard sample 44069 to level four bars icp ms, the laser energy density used is 3J/cm2, pulse frequency 4Hz, with the 10 μm small laser beam spot measurement monazite U-Th-Pb age.Present invention greatly enhances the spatial resolutions of monazite LA-Q-ICP-MS U-Th-Pb age dating, meet monazite testing requirement.
Description
Technical field
The invention belongs to geological test technical field more particularly to beam spot LA-Q-ICP-MS U- 10 μm of a kind of monazite small
Th-Pb age dating method.
Background technique
Monazite ((LREE, Th) PO4) be lree enrichment mineral, be widely present in sedimentary rock, metamorphic rock and middle acid
Property igneous rock in, while being also relatively conventional hydrothermal solution accessory mineral.Monazite Th, U content usually with higher, low is common
Pb content and higher Pb closure temperature (~750 DEG C) are a kind of common geological epoch meters.Especially interestingly, solely
It is more sensitive to the change of environment in geologic process to occupy stone, easily record hydrothermal activity information, ingredient domain not only records
The generation epoch of different geologic events, and can clearly reflect geologic process and hydrothermal activity history, U-Th-
Pb the study of isotope chronology has important geological Significance.
But just because of to the movable sensibility of fluid, monazite is subject to hydrothermal alteration, forms complicated ingredient point
Area.In carrying out micro-zone in situ analysis test process, it is desirable that analysis beam spot is the smaller the better.Electron probe chemical method is common one
Kind monazite micro-zone in situ U-Th-Pb dating methods, analysis beam spot diameter, are 1 μm or so, have very high spatial resolution,
But the detection limit for height of electron probe, it is generally difficult to measure young or in the lower monazite sample of U, Th content Pb and contains
Amount, can not provide the U-Th-Pb age.Laser ablation level four bars inductively coupled plasma mass spectrometry also belongs to micro-zone in situ point
Analysis, and detection limit is low, for monazite LA-Q-ICP-MS U-Th-Pb determine the common laser ablation beam spot diameter, in year for 32 μm or
24 μm, guarantee the high sensitivity of Q-ICP-MS with enough sample volumes, and then obtains stationary signal to measure the U- of monazite
The Th-Pb age.But monazite particle is usually smaller (~50 μm), and has complicated ingredient subregion, 32 μm or 24 μm of larger beam
Spot can only generally obtain the U-Th-Pb age of mixing, and not only data are difficult to explain, but also have no geological Significance, or even cause mistake
Geologic interpretation accidentally.When laser ablation beam spot diameter, is reduced into 10 μm, it is able to satisfy in test process to laser beam spot size
Demand, but it is inadequate to will lead to measurement sensitivity, and detection signal stabilization is deteriorated, meanwhile, under the conditions of small beam spot, with erosion pit
Intensification, detection signal can sharply decline, cause element fractionating degree increase severely, it is difficult to the Accurate Determining monazite U-Th-Pb age.
Summary of the invention
The purpose of the present invention is to provide a kind of 10 μm of the monazite small age dating sides beam spot LA-Q-ICP-MS U-Th-Pb
Method, it is intended to it is usually smaller and have complicated ingredient subregion to solve monazite particle, current 32 μm can only be obtained compared with large beam spot it is mixed
At the U-Th-Pb age of conjunction, data are inaccurate and have no geological Significance, or even cause mistake geologic interpretation, and 10 μm of small beam spots
It is inadequate to will lead to measurement sensitivity, detection signal stabilization is deteriorated, meanwhile, with the intensification of erosion pit, detecting signal can be sharply
Decline causes element fractionating degree to increase severely, it is difficult to the problem of the Accurate Determining monazite U-Th-Pb age.
The invention is realized in this way a kind of 10 μm of monazite small age dating side beam spot LA-Q-ICP-MS U-Th-Pb
Method, the 10 μm small beam spot LA-Q-ICP-MS U-Th-Pb age dating method of the monazite first introduce 1ppb standard solution sample
To level four bars icp ms, optimizes mass spectrometer parameters, make205The response intensity of Tl is greater than 200000cps/
Ppm, relative standard deviation are 1%~2%, and double charge is less than 1.5%, and oxide yield is less than 1%；It is re-introduced into man-made glass
610 solid etalon sample of NIST matches level four bars inductive coupling to laser ablation level four bars icp ms
The carrier gas Ar gas of plasma mass spectrograph and the carrier gas He gas of laser；It is to degrade object with monazite standard sample 44069, uses
Laser ablation energy density 3J/cm2, laser pulse frequency 4Hz, with 10 μm small beam spot measurement monazite the U-Th-Pb age.
Further, the 10 μm small beam spot LA-Q-ICP-MS U-Th-Pb age dating method of the monazite includes following step
It is rapid:
Step 1, optimization level four bars icp ms parameter.Due to temperature in instrument local environment, wet
The variation of degree, under causing identical tuner parameters to be arranged, the indexs such as element response intensity, double charge and oxide yield difference is very
Greatly, it needs by adjusting quarter bend position, sampling depth, extraction lens voltage, Omega lens voltage, RF power, carrier gas flux etc.
Parameter makes in 1ppb concentration standard solution205The response intensity (i.e. sensitivity) of Tl is greater than 200000cps, relative standard deviation
It (RSD) is 1%~2%, double charge (70/140) is less than 1.5%, and oxide yield (156/140) is less than 1%.Specific tuning is each
The step of item parameter, is as follows: preparing 1ppb standard solution, and is introduced into level four bars icp ms, monitors205The counting of Tl and RSD, and156CeO+/140Ce and70Ce++/140Ce+Ratio tunes each instrument parameter item by item, repeatedly；Usually
Sampling depth is smaller,205The counting of Tl is higher, and RSD is smaller, but double charge and oxide yield can also increase；With carrier gas flux
Raising,205The counting of Tl can be increased first to be declined again；Collision cell exit potential on oxide yield substantially without influence, but to double electricity
Lotus yield impact is very big；The influence of Omega lens voltage centering mass number is very big, right205The counting of Tl slightly influences；Omega is inclined
The inverse change of light weight mass number can be caused by turning voltage；Plate Bias voltage is affected to sensitivity；There are also some parameters
Variation can cause the irregular variation of sensitivity, double charge and oxide yield, can only adjust repeatedly to reach level four bars electricity
Feel the optimal detection state of couple plasma mass spectrometer.
Step 2, the carrier gas (Ar gas) for matching laser carrier gas (He gas) and level four bars icp ms, make
610 standard sample of man-made glass NIST degrades parameter in fixed laser and (degrades 24 μm of beam spot, energy density 6J/cm2, pulse frequency
Rate 7Hz) under,238U, which is counted, is greater than 450000cps, and relative standard deviation (RSD) is less than 3%.Specific matching process is as follows: with people
Making 610 standard sample of glass NIST is test object, utilizes laser ablation sample introduction to level four bars inductivity coupled plasma mass spectrometry
Instrument, fixed laser degrade parameter (24 μm, 6J/cm2, 7Hz), guarantee that sample volume is the same, level four bars inductively coupled plasma constitution
He flow is separately fixed at 700,750,800 and 850mL/ referring to the parameter after optimization in step 1 by the parameter setting of spectrometer
Under the magnitude of min, change Ar flow (variation range: 0.65~0.95L/min), record238U is counted and RSD is obtained by comparing
It is flux matched to optimal He gas and Ar air-flow.
Step 3, the parameter for optimizing laser.Degraded beam spot (10 μm) by fixed laser, transformation laser energy density and
The mode of pulse frequency explores the laser ablation for being suitble to the 10 μm small beam spot LA-Q-ICP-MS U-Th-Pb age dating of monazite
Parameter makes monazite238The sensitivity of U instantaneous signal is greater than 300000cps, and206Pb-238The element fractionation index of U is less than
3%.Specific Optimization Steps are as follows: being test object with monazite standard sample 44069, utilize laser ablation sample introduction to level four bars
The parameter setting of icp ms, level four bars icp ms optimizes referring in step 1
Carrier gas (Ar gas) flow set reference of parameter afterwards, laser carrier gas (He gas) and level four bars icp ms
Optimum Matching in step 2 first fixes beam spot diameter, (10 μm) and laser ablation energy density (2J/cm2), conversion pulse frequency (1
~7Hz), in such a way that single-point degrades, the signal of monazite standard sample 44069 under the conditions of recording every group；Then it fixes
Beam spot diameter, (10 μm) and laser ablation energy (3J/cm2), conversion pulse frequency (1~7Hz), in such a way that single-point degrades,
The signal of monazite standard sample 44069 under the conditions of recording every group；Finally the signal recorded is handled, is sifted out solitary
Stone238The maximum sensitivity of U instantaneous signal calculates monazite under the conditions of each group206Pb-238U element fractionation index and206Pb
/238The RSD of U value compares to obtain the optimal laser stripping for determining year suitable for beam spot LA-Q-ICP-MS U-Th-Pb 10 μm of monazite small
Lose parameter.
Under step 4, level four bars icp ms and laser ablation parameter after optimization, 10 μm are utilized
Small beam spot measures the monazite U-Th-Pb age, makes208Pb-232Th and206Pb-238U element fractionation index less than 3%,208Pb
/232Th and206Pb/238The single-spot testing precision of U isotopic ratio is respectively less than 3%,206Pb-238U and208Pb-232Th weighted average
Age is consistent in error range, and within the scope of recommendation.Specific step is as follows: being to survey with monazite standard sample 44069
Object is tried, laser ablation sample introduction to level four bars icp ms, level four bars inductively coupled plasma body are utilized
Mass spectrometric parameter setting is referring to the parameter after optimization in step 1, laser carrier gas (He gas) and level four bars inductively coupled plasma
The mass spectrometric carrier gas of body (Ar gas) flow set is referring to Optimum Matching in step 2, and the parameter setting of laser is referring to excellent in step 3
Laser ablation parameter after change, test process are all made of single-point and degrade mode, and each measuring point bulk analysis time is 60s, wherein carrying on the back
Scape signal 10s, sample signal 40s purge signal 10s.Data acquisition, which uses, jumps peak mode,204Pb、206Pb、207Pb、208Pb、238The detection residence time of U is 20ms,232The residence time of Th is 10ms.5 unknown sample points of every measurement, alternately measurement 2
Secondary standard sample.The school of U-Th-Pb isotopic fractionation and instrumental shift is carried out as external standard using monazite standard specimen 44069
Positive calculating, correction, which calculates, uses software Glitter 4.0, does not carry out any common lead correction to data, and data throw use of desiring to make money or profit
Isoplot 3.7 is completed, the final monazite that obtains208Pb-232Th and206Pb-238U weighted average age.
Further comprise: preparing 1ppb7Li,59Co,89Y,140Ce,205Tl standard solution is optimized using the solution example
Level four bars icp ms parameter.
Further, the summation of He flow and Ar flow is between 1.55~1.65L/Min.
Another object of the present invention is to provide one kind to be applied to 10 μm of monazite small beam spot U-Th-Pb age dating method
Laser ablation level four bars icp ms.
Further, the laser ablation level four bars icp ms are to degrade object with monazite, are adopted
With laser ablation energy density 3J/cm2, laser pulse frequency 4Hz, with 10 μm small beam spot measurement monazite the U-Th-Pb age.
Technical effect of the invention is as follows:
1, under conditions of solution sample introduction, the element response intensity of raising level four bars icp ms,
Calibrating quality axis, guarantee mass resolution, the balanced consistent element response of acquisition, reduction are double in entirely monitoring mass range
Charge and the interference of oxide etc. guarantee the optimal detection state of level four bars icp ms
2, carrier gas (He) and level four bars inductively coupled plasma body during laser ablation sample introduction, by laser ablation system
Mass spectrometric carrier gas (Ar), is transferred to mass spectrometric detection system for solid sample particle jointly.The matching of the two flow is direct
Efficiency of transmission is influenced, sensitivity is influenced very big.Only optimal Ar gas and He air-flow is flux matched, could utilize LA-Q-
When ICP-MS measures the monazite U-Th-Pb age, there is high sensitivity.
3, excessively high energy density and pulse frequency, may puncture mineral, and too low energy density and pulse frequency,
It may cause sample volume deficiency, it is difficult to detect, therefore need for monazite, it is fixed that acquisition is appropriate for beam spot U-Th-Pb 10 μm small
The laser ablation parameter in year, guarantees sufficiently high sensitivity, and low element fractionating degree.
4, solitary suitable for small beam spot in the Q-ICP-MS parameter of optimization, matching two-way carrier gas flux (Ar and He), acquisition
On the basis of stone U-Th-Pb determines the laser ablation parameter in year, the U-Th-Pb age of monazite standard sample 44069 is measured, is established
A kind of 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating method.
In short, 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating method provided by the invention, greatly
Ground improves the spatial resolution of monazite U-Th-Pb age dating, is allowed to meet the testing requirement of most of monazite；It utilizes
Laser ablation level four bars icp ms instrument, under the conditions of instrument parameter after optimization, with 10 μm of tuftlets
Spot measures the U-Th-Pb age of monazite standard specimen 44069, the applicability of inspection institute's method for building up.
Detailed description of the invention
Fig. 1 is 10 μm of monazite provided in an embodiment of the present invention small beam spot U-Th-Pb age dating method flow diagrams.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to embodiments, to the present invention
It is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, it is not used to
Limit the present invention.
Application principle of the invention is explained in detail with reference to the accompanying drawing.
As shown in Figure 1, the age dating side the monazite of embodiment of the present invention beam spot LA-Q-ICP-MS U-Th-Pb 10 μm small
Method the following steps are included:
S101: solution sample introduction optimizes Q-ICP-MS parameter, makes it have high sensitivity, and RSD is small；
S102: solid sampling (man-made glass standard specimen NIST610) matches the load of carrier gas (the Ar gas) and laser of Q-ICP-MS
Gas (He gas), make it is online after LA-Q-ICP-MS there is high sensitivity, and RSD is small；
S103: first group of laser ablation condition experiment of design (being to degrade object with monazite standard specimen 44069), it is preliminary to obtain
The laser ablation parameter area in year is determined suitable for the small beam spot of monazite；
S104: second group of laser ablation condition experiment of design (being to degrade object with monazite standard specimen 44069) is applicable in
In the laser ablation parameter for carrying out monazite U-Th-Pb age dating under the conditions of 10 μm of beam spots；
S105: utilizing LA-Q-ICP-MS, under the conditions of instrument parameter after optimization, measures monazite with 10 μm small beam spot
The U-Th-Pb age of standard specimen 44069, the applicability of inspection institute's method for building up.
Application principle of the invention is further described combined with specific embodiments below.
Embodiment 1
10 μm of monazite small beam spot U-Th-Pb age dating methods of the embodiment of the present invention the following steps are included:
Step 1, preparation 1ppb tuning liquid (7Li,59Co,89Y,140Ce,205Tl), the solution example is then introduced into four
Grade bar icp ms are aided with manual tuning on the basis of automatic tuning, the level four bars electricity optimized
Sense couple plasma mass spectrometer parameter specifically includes that quarter bend position, sampling depth, extracts lens voltage, Omega lens electricity
Pressure, RF power, carrier gas flux etc., target be improve the response intensity of element to be measured, calibrating quality axis, guarantee mass resolution,
Balanced consistent element response is obtained in entirely monitoring mass range, reduces double charge and the interference of oxide etc., wherein
,205The response intensity (i.e. sensitivity) of Tl is greater than 200000cps/ppm, and relative standard deviation (RSD) is 1%~2%, double charge
(70/140) less than 1.5%, oxide yield (156/140) is less than 1%.Introducing solution example is excellent to plasma mass spectrograph
Change plasma mass spectrograph parameter, makes plasma mass spectrograph that there is high sensitivity, and relative standard deviation is small；
Step 2 carries out the online of laser and level four bars icp ms, it may be assumed that by laser beam focus in
610 surface man-made glass standard specimen NIST is allowed to corrode gasification, is sent sample particle (aerosol) to level four bars by carrier gas (He gas)
In icp ms, quantitative analysis is carried out.During laser ablation sample introduction, by the carrier gas of laser ablation system
(He) and the carrier gas of plasma mass spectrograph (Ar) solid sample particle, is transferred to mass spectrometric detection system jointly.The two
The matching of flow directly influences efficiency of transmission, influences on sensitivity very big.Parameter, which is degraded, in fixed laser (degrades 24 μ of beam spot
M, energy density 6J/cm2, pulse frequency 7Hz), that is, in the case where guaranteeing that sample volume is the same, when the summation of He flow and Ar flow
When between 1.55~1.65L/Min,238U counting is higher, and wherein He flow and Ar flow are respectively 800ml/Min, 0.8L/
When Min,238U is counted as 460000cps, and relative standard deviation (RSD) is 3% or so.Man-made glass standard specimen NIST610 is introduced to arrive
Laser plasma Mass Spectrometry instrument, the carrier gas He gas of the mass spectrometric carrier gas Ar gas of match plasma and laser, make it is online after swash
Light plasma mass spectrograph has high sensitivity, and relative standard deviation is small；
Step 3, according to common zircon laser ablation parameter, under larger beam spot diameter, (32,24 μm), desk study
It is suitble to the laser ablation energy density and pulse frequency of monazite.Specific operation process is as follows: fixed laser beam spot diameter, first
(32 μm) are respectively 2,4,6,8J/cm in energy density2Under conditions of, conversion pulse frequency (5,7,10Hz)；Then fixed to swash
Light beam spot diameter (24 μm) is respectively 2,4,6,8J/cm in energy density2Under conditions of, conversion pulse frequency (5,7,10Hz),
Comprehensive Correlation206Pb、208Pb、238U、232The element fractionating degree of the sensitivity of Th instantaneous signal and RSD and Pb, Th, U
(with208Pb-232Th and206Pb-238U is calculated).
The result shows that monazite206Pb、208Pb、238U、232The sensitivity of Th instantaneous signal is higher, and RSD is small.Phase
Than in zircon laser parameter (24 μm, 6J/cm2, 7Hz) under206Pb-238The element of U is fractionated index (12%), monazite
's208Pb-232Th and206Pb-238The element fractionation index of U is lower, respectively 0.2%~6.1%, 0.1%~17.0%.Separately
Outside, the (>=6J/cm when energy density is excessively high2), even if being also easy using small pulse frequency (5Hz) by sample breakdown.Explanation
Monazite is easier to degrade compared with zircon, and the laser ablation condition (energy density, pulse frequency) of initial setting is all higher, needs again
One group of experiment is set.
First group of laser ablation condition experiment is designed, is to degrade object with monazite standard specimen 44069, is tentatively suitable for
The small beam spot of monazite determines the laser ablation parameter area in year；
Step 4, according to monazite elementary laser condition experiment as a result, the present invention has carried out one group of orthogonal test, beam spot again
Diameter is 10 μm；Energy density is 2,3J/cm2；Pulse frequency is 1~7Hz.Since laser energy density is 1J/cm2When, it is insufficient
To degrade monazite, even if pulse frequency is raised to 7Hz, after degrading lasting 10s, sample signal just can be detected obviously, therefore real
Testing process not being related to laser energy density is 1J/cm2Correlated condition.Experimentation is as follows: fixed beam spot diameter, (10 μm),
Laser ablation energy density is respectively 2,3J/cm2Under conditions of, conversion pulse frequency (1~7Hz), Comprehensive Correlation206Pb、208Pb、238U、232The sensitivity of Th instantaneous signal and RSD, Pb, Th, U element fractionating degree (with208Pb-232Th and206Pb-238U
Calculate) and208Pb/232Th value and206Pb/238The RSD of U value explores under the conditions of small beam spot the measurement monazite U-Th-Pb age most
Excellent laser ablation parameter.
Experiment shows under the conditions of small beam spot, monazite206Pb、208Pb、238U、232The sensitivity of Th instantaneous signal according to
It is so higher, and RSD is small.When beam spot diameter, is 10 μm, in 3J/cm2, under the conditions of 4Hz,208Pb-232Th and206Pb-238The element of U
Being fractionated index is respectively 1.5%, 2.7%,208Pb/232Th and206Pb/238The RSD difference 9.6%, 11.4% of U value, it is smaller,
Optimum Matching in this group of condition experiment.
Second group of laser ablation condition experiment is designed, is to degrade object with monazite standard specimen 44069, obtains and be suitable for 10
The laser ablation parameter of monazite U-Th-Pb age dating is carried out under the conditions of μm beam spot；
Step 5 is measured under 10 μm of beam spot diameter,s solely using laser ablation level four bars inductively coupled plasma mass spectrometry
Occupy the U-Th-Pb age of stone standard specimen 44069.Under 10 μm of beam spot diameter,s, the laser energy density used is 3J/cm2, pulse frequency
Rate is 4Hz, and monazite standard specimen 44069 can achieve the sensitivity of enough measurements,208Pb-232Th and206Pb-238The element of U is fractionated
Index less than 3%,208Pb/232Th and206Pb/238The RSD of U isotopic ratio less than 12%,208Pb/232Th and206Pb/238U is same
The single-spot testing precision of the plain ratio in position is respectively less than 3%.It is surveyed207Pb/235U-206Pb/238The U age is harmonious,206Pb-238U weighting is flat
The equal age is 425.7 ± 7.2Ma,208Pb-232Th weighted average age is 426.6 ± 6.1Ma.
Utilize SHRIMP method measurement monazite 44069206Pb-238U weighted average age is 426 ± 3Ma, utilizes TIMS
Method measures monazite 44069207Pb/235U-206Pb/238U concordant age is 424.9 ± 0.4Ma, with the surveyed monazite of the present invention
44069 LA-ICP-MS method206Pb-238U and208Pb-232Th weighted average age is consistent.Show to utilize laser ablation level four bars
It is feasible that inductively coupled plasma mass spectrometry measures the method at monazite U-Th-Pb age under 10 μm of beam spot diameter,s.
Using laser ablation level four bars icp ms instrument, instrument parameter condition after optimization
Under, with the U-Th-Pb age of 10 μm small beam spot measurement monazite standard specimen 44069, the applicability of inspection institute's method for building up.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all in essence of the invention
Made any modifications, equivalent replacements, and improvements etc., should all be included in the protection scope of the present invention within mind and principle.
Claims (3)
1. a kind of 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating method, which is characterized in that described solitary
10 μm of stone small beam spot LA-Q-ICP-MS U-Th-Pb age dating method is first introduced directly into the standard solution sample that concentration is 1ppb
Made to level four bars icp ms by optimizing instrument parameter205The response intensity of Tl is greater than
200000cps/ppb, relative standard deviation are 1%~2%, and double charge is less than 1.5%, and oxygenation efficiency is less than 1%；Recycle laser
The mode degraded introduces man-made glass NIST610 solid etalon sample to level four bars icp ms, matching
The carrier gas He gas of laser and the carrier gas Ar gas of level four bars icp ms, make238The counting of U reaches highest；
It recycles the mode of laser ablation to introduce monazite standard sample 44069 to level four bars icp ms, adopts
Laser energy density is 3J/cm2, pulse frequency 4Hz, with the 10 μm small beam spot measurement monazite U-Th-Pb age；
The small beam spot LA-Q-ICP-MS U-Th-Pb age dating method of described 10 μm of monazite the following steps are included:
Step 1, optimize level four bars icp ms parameter；By adjusting quarter bend position, sampling depth, extraction
Lens voltage, Omega lens voltage, RF power, carrier gas flux make in 1ppb concentration standard solution205The response intensity of Tl is greater than
200000cps, relative standard deviation are 1%~2%, and double charge is less than 1.5%, and oxide yield is less than 1%；
The step of specific tuning parameters, is as follows: preparing 1ppb standard solution, and is introduced into level four bars inductively coupled plasma
Constitution spectrometer, monitoring205The counting of Tl and RSD, and156CeO+/140Ce and70Ce++/140Ce+ ratio tunes each item by item, repeatedly
Instrument parameter；
Step 2, the carrier gas Ar gas for matching laser carrier gas He gas and level four bars icp ms, make man-made glass
NIST610 standard sample in the case where fixed laser degrades parameter,238U, which is counted, is greater than 450000cps, and relative standard deviation is less than 3%；
Specific matching process is as follows: using 610 standard sample of man-made glass NIST as test object, being arrived using laser ablation sample introduction
Level four bars icp ms, fixed laser degrade parameter, guarantee that sample volume is the same, level four bars inductive coupling etc.
He flow is separately fixed at 700,750,800 and referring to the parameter after optimization in step 1 by the mass spectrometric parameter setting of gas ions
Under the magnitude of 850mL/min, change Ar flow, record238U is counted and RSD obtains optimal He gas and Ar air-flow by comparing
It is flux matched；
Step 3, the parameter for optimizing laser；Beam spot is degraded by fixed laser, converts laser energy density and pulse frequency
Mode is explored the laser ablation parameter for being suitble to the 10 μm small beam spot LA-Q-ICP-MS U-Th-Pb age dating of monazite, is made solitary
Stone238The sensitivity of U instantaneous signal is greater than 300000cps, and206Pb-238The element fractionation index of U is less than 3%；
Specific Optimization Steps are as follows: being test object with monazite standard sample 44069, utilize laser ablation sample introduction to level four bars
The parameter setting of icp ms, level four bars icp ms optimizes referring in step 1
The carrier gas Ar throughput setting of parameter afterwards, laser carrier gas He gas and level four bars icp ms is referring to step
Laser beam spot diameter is first fixed as 24 μm by Optimum Matching in 2, is respectively 2J/cm in energy density2, 4J/cm2, 6J/cm2,
8J/cm2Under conditions of, conversion pulse frequency, preliminary obtain is suitable for the laser ablation parameter model that monazite U-Th-Pb determines year
It encloses；Beam spot diameter, and laser ablation energy density are separately fixed at 10 μm and 2J/cm again2, conversion pulse frequency from 1Hz to
7Hz, in such a way that single-point degrades, the signal of monazite standard sample 44069 under the conditions of recording every group；Then beam spot is straight
Diameter and laser ablation energy are separately fixed at 10 μm and 3J/cm2, conversion pulse frequency degraded from 1Hz to 7Hz using single-point
Mode, the signal of monazite standard sample 44069 under the conditions of recording every group；Finally the signal recorded is handled, is sieved
Monazite under the conditions of each group out238The maximum sensitivity of U instantaneous signal calculates monazite under the conditions of each group206Pb-238The member of U
Element fractionation index and206Pb/238The RSD of U value compares to obtain suitable for beam spot LA-Q-ICP-MS U-Th-Pb 10 μm of monazite small
Determine the optimal laser ablation parameter in year；
Under step 4, level four bars icp ms and laser ablation parameter after optimization, 10 μm of tuftlets are utilized
Spot measures the monazite U-Th-Pb age, makes208Pb-232Th and206Pb-238U element fractionation index less than 3%,208Pb/232Th
With206Pb/238The single-spot testing precision of U isotopic ratio is respectively less than 3%,206Pb-238U and208Pb-232Th weighted average age exists
It is consistent in error range, and within the scope of recommendation；
Specific step is as follows: being test object with monazite standard sample 44069, utilizes laser ablation sample introduction to level four bars inductance
Couple plasma mass spectrometer, after the parameter setting of level four bars icp ms in step 1 referring to optimizing
The carrier gas Ar throughput setting of parameter, laser carrier gas He gas and level four bars icp ms is referring in step 2
Optimum Matching, for the parameter setting of laser referring to the laser ablation parameter after optimization in step 3, test process is all made of single-point stripping
Erosion mode, each measuring point bulk analysis time are 60s, and wherein background signal 10s, sample signal 40s, purge signal 10s；Data are adopted
Collection, which uses, jumps peak mode,204Pb、206Pb、207Pb、208Pb、238The detection residence time of U is 20ms,232The residence time of Th is
10ms；5 unknown sample points of every measurement alternately measure 2 standard samples；It is carried out using monazite standard specimen 44069 as external standard
The correction of U-Th-Pb isotopic fractionation and instrumental shift calculates, and correction, which calculates, uses software Glitter 4.0, non-logarithm
According to any common lead correction is carried out, data throwing, which is desired to make money or profit with Isoplot3.7, to be completed, final acquisition monazite208Pb-232Th
With206Pb-238U weighted average age.
2. 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating method as described in claim 1, feature
It is, further comprises: prepares 1ppb7Li,59Co,89Y,140Ce,205Tl standard solution optimizes level Four using the solution example
Bar icp ms parameter.
3. 10 μm of monazite small beam spot LA-Q-ICP-MS U-Th-Pb age dating method as described in claim 1, feature
Be, the summation of laser carrier gas He flow and level four bars inductivity coupled plasma mass spectrometry carrier gas Ar flow between 1.55~
1.65L/Min。
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