Thermo Scientifi c Q Exactive GCOrbitrap GC-MS system

A new chapter in GC-MSA new chapter in GC-MSA new chapter in GC-MSA new chapter in GC-MS

The Thermo Scientifi c™ Q Exactive™ GC Orbitrap GC-MS/MS system has fi nally

arrived. For years, scientists have demanded this highly anticipated, high-

resolution, accurate-mass (HRAM) system in fi elds ranging from metabolomics

to food safety, industrial, clinical, and pharmaceutical analysis. These scientists

understand the power that only Thermo Scientifi c™ Orbitrap™ technology can

bring to the detailed characterization of their most challenging samples.

“GC Orbitrap technology signifi cantlyexpands the fi repower of GC-MS, which will spark an acceleration in discovery for small molecule analysis across multiple applications.”

Dr. Alexander MakarovDirector of ResearchLife Science Mass SpectrometryThermo Fisher Scientifi c

Unprecedented Depth in GC-MS Analysis

Until now, GC-MS technology has been limited in its ability to collect comprehensive qualitative and quantitative sample information with high levels of selectivity, sensitivity and confi dence; especially in highly complex samples.

Today, the Q Exactive GC system makes this comprehensive analysis a reality. It is an easy-to-use, dedicated benchtop GC-MS system that provides the highest confi dence in compound discovery, identifi cation, and quantitation for a comprehensive understanding of your samples. This unmatched performance is achieved through the superior resolving power, mass accuracy, and sensitivity that only Orbitrap technology can deliver.

The capabilities of the Q Exactive GC system create a paradigm shift for analysis of GC-amenable compounds and signal the start of an exciting new chapter in GC-MS…

2

“GC Orbitrap technology will bring a new level of performance to high resolution GC-MS.”

Prof. Jana HajšlováUniversity of Chemical TechnologyPrague, Czech RepublicFood Safety and Food Authenticity

“The introduction of the Q Exactive GC system is a game changer in this space.”

Prof. Joshua Coon

Department of Chemistry

University of Wisconsin, USA

Proteomics and Metabolomics

“This is the technology platform I have been waiting for since I started in metabolomics.”

Dr. Karl Burgess

Glasgow Polyomics

University of Glasgow, UK

Metabolomics

“This is clearly a major step forward.”

Dr. Hans MolRIKILT, NetherlandsNatural Toxins and Pesticides

3

The ultimate profi ling toolSuperior compound discovery and identifi cation: the Q Exactive Orbitrap GC-MS/MS system provides you with the

power to discover features within a sample that went unnoticed with previous GC-MS technology. This unrivalled

combination of high-resolution gas chromatography separations and highly sensitive HRAM acquisitions and intelligent

identifi cation software will help unlock answers to questions about the very nature of each sample you inject.

High capacity component detection Part-per-trillion level sensitivity of the Q Exactive GC system in full-scan with a wide dynamic range and HRAM drives high capacity component detection, even in your most complex samples.

This technology will greatly facilitate the identifi cation of unknown compounds.– Joshua Coon

High confi dence confi rmation For further information and/or confi rmations of compounds, positive chemical ionization (PCI) can be used to yield molecular ions. These ions can be measured directly in the Orbitrap or after fragmentation in the HCD for further HRAM investigation into the compound structure.

Full-scan acquisition (60,000 resolution at m/z 200) of a food packaging sample from an extractables and leachables study. A single, unidentifi ed component is visible within the complex matrix background.

EI, PCI, and PCI – MS/MS spectra (60,000 resolution at m/z 200) of terbuthylazine with fragment structure assignment using Thermo Scientifi c™ Mass Frontier™ spectral interpretation software.

EI

CI MS/MS

0.56 ppm

0.58 ppm

0.14 ppm

0.07 ppm

0.18 ppm 0.44 ppm

0.25 ppm

CI

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 0

20

40

60

80

100214.08533

173.04620

141.00049 216.08235

77.03861 170.02699 175.04320 104.00104 132.03233 158.02283

68.02437 145.01498 96.05561 110.04614 83.06037 119.03710 178.10860 160.01980

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 0

20

40

60

80

100

Rel

ativ

e A

bund

ance

138.07743

174.05407

176.05108 214.08528 194.14000 202.08529

216.08239 156.02425

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220

m/z

0

10

20

30

40

50

60

70

80

90

100

172.03835 C 5 H 7 N 5 Cl

138.07741 C 5 H 8 N 5

110.04614 C 3 H 4 N 5

68.02435 C 2 H 2 N 3

145.01495 C 3 H 4 N 5 Cl

136.06178 C 5 H 6 N 5

79.00574 C H 4 N 2 Cl

104.00099 C 2 H 3 N 3 Cl

94.03996 C 4 H 4 N 3

214.08527 C 8 H 13 N 5 Cl

158.02276 C 4 H 5 N 5 Cl

71.06038 C 3 H 7 N 2 61.97932

C H N Cl

N

N

NH2+

N

N

NH

NH

NH2+

+NH2

NN

N

NH

NCl

N

NH

NH

+NH2 NCl

N

NH

N

NH2

+

NCl

N

NH

N

NH2

+

NCl

N

NH

N

+NH2

4

Highly resolved components for chemometric analysis and compound identifi cation In addition to the highest quality raw data, the Q Exactive GC system uses newly developed specialist deconvolution software tools to automatically detect components within your sample and generate clean spectra for further data processing steps.

Co-eluting compounds are deconvoluted to obtain clean mass spectra

High quality deconvolution of spectra from a Scotch whiskey sample during an authenticity study. Automatic identifi cation of unknown peaks was performed using intelligent identifi cation software.

Principle component analysis (PCA) generated using Thermo Scientifi c™ Compound Discoverer™ 2.0 software from a study profi ling single malt whiskies of different age declaration using the Q Exactive GC system.

Analyzing whiskey and pesticide samples, to my surprise, many compounds where automatically identifi ed.– Jana Hajšlová

Powerful software for intelligent identifi cation The Q Exactive GC system uses vast, readily available nominal mass electron ionization (EI) libraries (such as NIST and Wiley) to generate candidate compounds. Hits can be verifi ed automatically using Kovats retention indices and intelligent exact mass interpretation of the fragmented mass spectrum acquired. Customized HRAM libraries can also be used.

The Q Exactive GC brings highly resolved data that allows for advanced deconvolution providing high quality inputs for downstream contextualization software. And the ability to predict elemental formulae of each EI fragment is hugely powerful for metabolite identifi cation.– Karl Burgess

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

180.00957

169.93473

73.01072 115.05767

63.94372142.99848

127.88781

95.91574

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10069.06994

129.03696

135.94709178.0418158.99523 146.0219285.01073 212.00284197.98722116.9828799.02645

153.03693

50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10073.01070

105.99064

180.00956

169.93470

149.04536

115.05767

63.94372142.99847131.05261

78.96710

105.99065

30

20

10

0

PC

2 (1

5.5%

)

-10

-20

-30

-80

2263 2264

12 Year Whisky18 Year Whisky

No Age Statement Whisky

2265

-60 -40 -20PC 1 (62.7%)

0 20 40

5

Confi dent low-level detection and identifi cation for high effi ciency screening workfl ows The Q Exactive GC system offers routine operation, possible at 60k–120k resolution (at m/z 200) with sub-1 ppm mass accuracy and full-scan sensitivity down to part-per-trillion concentrations. This capability drives truly powerful screening methods for food safety, environmental, anti-doping, and many other applications where ultra trace-level detection is required in diffi cult matrices.

Acquisition at 15k yield false negative results based upon identifi cation criteria. Chlorphropham example XIC shows resolution values of 60k and 120k, providing interference-free, confi dent detection with excellent mass accuracy.

The wide dynamic range of the system, along with its high sensitivity, will bolster all quantitative experiments dramatically.– Joshua Coon

Quantitation capability beyond that of other benchtop HRAM GC-MS systems Using full-scan acquisition, the Q Exactive GC system provides the quantitative capability of a GC triple quadrupole instrument operating in selected reaction monitoring (SRM) mode. Sensitivity, quantitative accuracy, precision, and linearity are excellent, even in complex matrices.

Thermo Scientifi c™ TraceFinder™ software uses Q Exactive GC system data and combines compound detection, identifi cation, and quantitation to enable high effi ciency screening. It also allows customizable, automated fl agging for detected peaks along with highly fl exible reporting tools.

For pesticides, I could safely see very low levels.– Jana Hajšlová

30k

60k

120k Chlorpropham Matrix

Mass difference = 18.4 ppm

Mass difference = 0.9 ppm

Mass difference = 0.5 ppm

15k

Mass difference = 0 ppm

127.008 127.010 127.012 127.014 127.016 127.018 127.020 127.022 127.024 127.026 127.028 127.030 127.032 127.034 m/z

0

20

40

60

80

100

Rel

ativ

e A

bund

ance

127.02067

127.008 127.010 127.012 127.014 127.016 127.018 127.020 127.022 127.024 127.026 127.028 127.030 127.032 127.034 m/z

0

20

40

60

80

100

Rel

ativ

e A

bund

ance

127.02164 127.01821

127.008 127.010 127.012 127.014 127.016 127.018 127.020 127.022 127.024 127.026 127.028 127.030 127.032 127.034 m/z

0

20

40

60

80

100

Rel

ativ

e A

bund

ance

127.02117 127.01826

127.008 127.010 127.012 127.014 127.016 127.018 127.020 127.022 127.024 127.026 127.028 127.030 127.032 127.034 m/z

0 20 40 60 80

100 R

elat

ive

Abu

ndan

ce 127.01833

127.02118

127.02261

The ultimate screening toolAnalyzing compounds present at low concentrations, quantitatively, with high selectivity using full-scan acquisition

has been out of reach for GC-MS users for too long. Many leading laboratories in various fi elds require simultaneous

targeted and untargeted sample screening, but that need went unmet until now. Today, the Q Exactive GC system

has the quantitative power of a GC triple quadrupole MS combined with the high precision, full-scan high resolution/

accurate mass capability that only Orbitrap technology can offer. This combination will change your workfl ows, forever.

6

Mass accuracy across n=14 repeat injections of a baby food sample spiked with several pesticides at 5 ng/g.

Effect of resolution (specifi ed @ m/z 200) on mass accuracy for pesticides in leek samples at 10 ng/g.

This technology provides an easier, more effi cient, and more comprehensive way of doing GC-based pesticide residue analysis.– Hans Mol

Wheat matrix calibration curve of chlorpropham (0.5 ppb–50 ppb) including extracted quantifi er and qualifi er ions at 0.5 ppb. Acquired using 60k resolution at m/z 200.

Instrument detection limit (IDL) of 150 pesticides in mixed vegetable matrix using the Q Exactive GC system (full-scan 60k at m/z 200) and Thermo Scientifi c™ TSQ™ 8000 Evo GC-MS/MS system (SRM) with a fast GC separation.

22%

47%

22%

9%

Q ExactiveGC system

TSQ 8000 EvoGC-MS/MS system

16%

49%

33%

2%

<0.5

IDL ng/g

0.5-1.0

1.0-2.0

2.0-4.0

<0.5

IDL ng/g

0.5-1.0

1.0-2.0

2.0-4.0

120k 60k 30k 15k chlorpropham 0.0 0.5 0.9 18.4 Procymidone 0.5 0.0 0.7 8.6 Iprodione 0.2 0.4 3.1 4.9

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

mas

s di

ffere

nce

[ppm

]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

2

3

4

5

6

7

8

9

10

11

12

13

14 Bifenthrin

Chlorpyrifos-ethyl

Chlorthal-dimethyl

Clomazone

2-phenylphenol

Acetochlor

Benalaxyl

BHC, Alpha

Methacrifos

Metribuzin

Nitrothal-isopropyl

Oxadiazon

Pentanochlor

Permethrin

Phosalone

Pirimiphos-ethyl

Propanil

Quinomethionate

Tecnazene

1-14 injection number

7

Bringing GC and Orbitrap technology together

Full-scan spectrum of p,p'-DDT acquired at 120,000 resolution (@ m/z 200).

150 160 170 180 190 200 210 220 230 240 250 260 270m/z

0

10

20

30

40

50

60

70

80

90

100

Rel

ativ

e A

bund

ance

235.00762R=118356C13H9CI2

165.06989R=140457

C13H9

199.03090R=126265

C13H8CI176.06205R=134582

C14H8

212.03871R=119900

C14H9CI

239.00168R=120013C13H9

37CI2

0.2 ppm

0.06 ppm

0 ppm 0 ppm

0.06 ppm

p,p'-DDTC14H9CI5

ORBITRAP MASS ANALYZERMass range between 30–3000 Da with incredible resolving power up to 120,000 FWHM at m/z 200, sub-ppm mass accuracy with a high acquisition rate, driving unrivaled spectral quality.

C-TRAPCurved linear trap for precise ion injection—delivers excellent in-spectrum dynamic range and ensures outstanding HRAM performance across a wide range of concentrations through automatic gain control (AGC).

ADVANCED QUADRUPOLE TECHNOLOGY (AQT)High transmission of selected masses for low-level detection and quantitation of low-abundance compounds in highly complex matrices.

HCD COLLISION CELLHigher-energy collisional dissociation for MS/MS characterization of ions—used in combination with chemical ionization to help elucidate chemical structures.

Fastest route to powerful data With the Q Exactive GC system it is easy to obtain powerful results. The instrument control page provides clear instrument status information, leak check is automated, and mass spectrometer tuning and calibration takes less than a minute.

BENT FLATAPOLEFor lowest possible noise and maximum robustness.

The operation and software handling is very simple.– Jana Hajšlová

8

Bringing GC and Orbitrap technology togetherVariable electron voltage (VeV) technology enables lower electron voltage (eV) settings for Electron Ionization (EI). It is a softer EI technique, which promotes higher mass signals and increases sensitivity for compounds prone to extensive fragmentation.

Key benefi ts:• Increased sensitivity—Compounded by

the unrivalled full-scan sensitivity of Orbitrap

• Increased confi dence in identifi cation—VeV promotes molecular ion and diagnostic high mass signals

• Fully automated for optimum performance—Following the simplicity of Orbitrap GC-MS operation, VeV set-up is easy, with fast, fully automated tuning

Direct probes are used without requiring a break in the vacuum, and they enable the performance of MS and MS/MS experiments on solids and liquids/solutions in real-time while effortlessly switching between electron ionization (EI) and chemical ionization (CI).

Direct Insertion Probe (DIP)—Slower volatilization with heated capillary tube for solid samples. The DIP can be utilized for rapid analysis of solids or trace components in solid matrices such as organic synthesis products, forensic samples, tissue, etc.

Direct Exposure Probe (DEP)—Rapid heating fi lament for liquids or solutions. The DEP is ideal for rapid molecular weight confi rmation of solids dissolved or suspended in a suitable solvent.

Epitestosterone shown with standard EI and VeV EI. Using VeV, the molecular ion signal and high mass fragment abundance are greatly increased, improving sensitivity for quantitative analysis and further MS/MS fragmentation experiments.

Thermo Scientifi c™ ExtractaBrite™ ION SOURCE Robust, rugged electron impact (EI) and chemical ionization (CI) performance—proven in routine applications in the Thermo Scientifi c™ ISQ™ and TSQ series GC-MS systems. Fully removable without breaking vacuum for maintenance or switching to chemical ionization (CI). Also exchangeable for a unique source plug, making GC columns easily exchanged, without venting the MS system.

Direct probes are used without requiring a break in the vacuum, and they enable the performance of MS and MS/MS experimentson solids and liquids/solutions in real-time while effortlessly switching between electron ionization (EI) and chemical ionization (CI).

volatilization with heated capillary tube for solid samples. The DIP can be utilized for rapid analysis of solids or trace components in solid matrices such as organic synthesis

80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440m/z

0

20

40

60

80

100

Rel

ativ

e A

bund

ance

405.26376R=49507C23H41O2Si2

-0.48512 ppm420.28735R=48307

C24H44O2Si2-0.19416 ppm

169.10426R=77407C9H17OSi

-0.32468 ppm

315.21365R=55807C20H31OSi

-0.68228 ppm

73.04680R=116723

C3H9Si-0.06385 ppm

225.16367R=66407

C17H21

-0.49501 ppm

80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440m/z

0

20

40

60

80

100

Rel

ativ

e A

bund

ance

405.26382R=49607C23H41O2Si2

-0.33452 ppm

420.28748R=48007

C24H44O2Si2-0.09628 ppm

169.10440R=77507C9H17OSi

-0.48742 ppm

315.21375R=55807C20H31OSi

-0.39184 ppm91.05423R=104307

C7H7

-0.03214 ppm

73.04680R=116923

C3H9Si

-0.06385 ppm225.16367R=66407

C17H21

-0.49501 ppm

70 eV

12 eV

9

Instant connect injectors

Instant Connect SSLThe Thermo Scientific™ Instant Connect SSL (Split/Splitless) injector features an optimized thermal profile developed to avoid sample discrimination in split and splitless mode, allowing the broadest range of analytes to be accurately injected. Its cool injector head guarantees minimum thermal stress to the septum, therefore reducing bleed and extending septa lifetime. Also available with concurrent backflushing.

Instant Connect-PTVThe Thermo Scientific™ Instant Connect PTV (Programmed Temperature Vaporizing) injector combines the “discrimination-free” performance of a cold injector with the robustness of a vaporizing injector. Merging fast heating and cooling performance with the inertness of the injector chamber and large sample capacity, this injector is the ideal choice for trace analysis in dirty matrices and for thermally labile compounds. Also available with concurrent backflushing.

Instant Connect Helium Saver ModuleA unique solution to a difficult problem, this proprietary split/splitless injector module greatly reduces helium consumption, by using helium only to supply carrier gas flow to the capillary column, while using nitrogen for all other injection processes, including the septum purge, split, and sample vaporization.

Instant connect detectors

Instant Connect-FIDThe Thermo Scientific™ Instant Connect-FID (Flame Ionization Detector) offers the highest sensitivity and a wide dynamic range with rapid acquisition speed, making it ideal for extremely fast GC applications.

Instant Connect-TCDThe newly-designed micro-volume Thermo Scientific™ Instant Connect-TCD (Thermal Conductivity Detector) is used in a wide variety of capillary and packed column applications. Due to its exceptional thermal stability and fast response, this non-destructive detector provides exceptional sensitivity over the widest range of applications.

Instant Connect-ECDThe new Thermo Scientific™ Instant Connect-ECD (Electron Capture Detector) is optimized for trace analysis in challenging samples. Its miniaturized cell, equipped with a purged, removable anode, has been designed to guarantee the utmost sensitivity while maximizing robustness towards the matrix effect.

Instant Connect-NPDBuilt upon the proven sensitivity of the Thermo Scientific™ Nitrogen Phosphorous Detectors (NPD), the new Instant Connect-NPD brings exceptional flexibility to the determination of specific components with the adoption of multiple dedicated ion sources.

Instant Connect-FPD The Thermo Scientific™ Instant Connect-FPD (Flame Photometric Detector) provides excellent sensitivity and response stability for the most demanding sulphur appliations, as well as phosporous or tin determinations. Its extended operating temperature range and dual wavelength capability further expand its applicability.

Transcend the traditionalStep into modern gas chromatography. Tailor the Thermo Scientific™ TRACE™ 1310 Gas Chromatograph to

your needs with its proprietary user-exchangeable Instant Connect injector and detector modules. Swapping

modules is easy to do by removing and replacing three screws, accessible from the top of the GC. The

entire process takes less than five minutes without requiring specialized service assistance. This modularity

enables budget-conscious laboratories to purchase a base-configured GC today, then easily expand their

capabilities to accommodate new applications and throughput demands tomorrow.

10

Fast oven temperature cycling and excellent retention time performance mean that high-precision, high-productivity data sets can be realized. This type of data is especially important to facilitate statistics in larger batches, e.g., in “-omics”-type studies with many biological or technical replicates.

The TRACE 1300 Series GC system quickly reaches near ambient temperatures.

Warm-up Times. From OFF Conditions to Readiness (minutes)

Oven at 50 °C

Injector and Detectors at 250 °C

TRACE 1300 Series GC system

Standard GC system

3.5 10.2

A step ahead in automated samplingA perfect match for the Exactive GC system, the Thermo Scientifi c™ TriPlus™ RSH autosampler utilizes robotic sample handling to expand automated capabilities beyond liquid, headspace, and solid-phase microextraction (SPME) injections to advanced sample handling cycles. Your results benefi t from improved precision and reproducibility, while your laboratory gains unique advantages from the system’s unattended operations and sample handling fl exibility.

• Automate basic sample and standards preparation procedures such as dilution, internal standard addition, and derivatization.

• High precision injection from low volumes to maximize your analysis opportunities with your most precious samples.

• Automated toll exchange to switch between different syringes and techniques “on-the-fl y”.

Exceptional retention time stability Outstanding retention time stability is achieved, even in the most complex GC and GC-MS applications, through the use of innovative and unique IEC (integrated electronic control) modules. This stability guarantees industry-leading 0.001 psi control through the entire working range. These miniaturized gas controls, integrated within every injector or detector module for compact, self-suffi cient, fully-featured devices, deliver strictly controlled pressure or fl ow to columns and detectors. Setting constant or ramped pressures and fl ows is easy through the software or the local user interface, while the electronic control maintains the stability during every run for exceptional retention time, accuracy, and precision. To further enhance analytical performance, the IEC module also supports the automated leak check of the injector and column installed and column evaluation procedures.

Retention time stability on 10 consecutive runs of hydrocarbon mix. Retention time standard deviation is always ≤1/1000 minute.

The TriPlus RSH autosampler provides excellent repeatability with microsamples, down to 5 µL in a vial. This feature is particularly interesting for trace analysis, radioactive samples, or samples requiring expensive internal standards.

Hydrocarbon Mean RT Min. Std. Dev. Min. Hydrocarbon Mean RT Min. Std. Dev. Min.

C12 4.6200 0.0003 C28 12.4725 0.0005

C14 6.0192 0.0004 C30 13.1348 0.0006

C16 7.2268 0.0005 C32 13.7557 0.0006

C18 8.3051 0.0005 C34 14.3395 0.0007

C20 9.2825 0.0006 C36 14.8908 0.0005

C22 10.1767 0.0006 C38 15.4118 0.0007

C24 10.9997 0.0004 C40 15.9063 0.0006

C26 11.7629 0.0005

1 µL splitless injection 40 ppm C20 in toluene

Volume in vial (μL) Peak area

50 81244277

40 80268993

30 82088809

20 82095395

10 84436788

5 84312030

RSD% 2.0

11

Find out more at thermofisher.com/QExactiveGC

©2017 Thermo Fisher Scientific Inc. All rights reserved. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries. This information is presented as an example of the capabilities of Thermo Fisher Scientific products. It is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others. Specifications, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details. BR10445-EN 0517M

Thermo Scientific chromatography columns and consumablesGet the most out of the Exactive GC system by pairing it with advanced, high-performance Thermo Scientific products. Our wide range of consumables and accessories offer customers applications-focused solutions in the environmental, food safety, toxicology, clinical, petrochemical, pharmaceutical, and general analytical industries.

• Thermo Scientific™ TraceGOLD™ columns – low bleed, high reproducibility

• Consumables tested and certified on the Thermo Scientific™ TRACE™ 1300 Series GC systems

• Vials guaranteed for Thermo Scientific autosampler systems

• Thermo Scientific™ GFM Pro Gas Flowmeter and Thermo Scientific™ GLD Pro Gas Leak Detector for system installation and maintenance

• Derivatization reagents and derivatization-grade solvents

Learn more: thermofisher.com/chromexpert