Basics of LC/MS

A Primer

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Interfacing LC and MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Atmospheric Pressure Ionization . . . . . . . . . . . . . . . . . . . . . . . . . 4

API-Electrospray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Atmospheric Pressure Chemical Ionization (APCI) . . . . . . . . . . 6

Scan and SIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Collision-Induced Dissociation . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Adapting LC Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Molecular Weight Determination . . . . . . . . . . . . . . . . . . . . . . . . . 10

Combinatorial Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Pharmaceutical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Biochemical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Clinical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Food Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Environmental Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2

Sample Types

LC/MS systems facilitate the analysis of samples that traditionally have beendifficult to analyze. Despite the power andusefulness of gas chromatography/massspectrometry (GC/MS), many compoundsare impossible to analyze with GC/MS.

LC/MS significantly expands the effectiveanalytical use of mass spectrometry to amuch larger number of organic compounds.Gas chromatography and GC/MS can beused to analyze a small percentage of the 9 million registered compounds. Because

Introduction

Liquid Chromatography/Mass Spectrometry (LC/MS) is fast becoming the preferred

tool of liquid chromatographers. It is a powerful analytical technique that combines

the resolving power of liquid chromatography with the detection specificity of mass

spectrometry. Liquid chromatography (LC) separates the sample components and

then introduces them to the mass spectrometer (MS). The MS creates and detects

charged ions. The LC/MS data may be used to provide information about the molecu-

lar weight, structure, identity and quantity of specific sample components.

they impart little or no heat to the analytemolecules, LC and LC/MS-based methodscan be applied to most organic compounds.Sample types range from small pharma-ceutical compounds to large proteins.

Because it is a much more widelyapplicable method than GC/MS, LC/MS is suitable for the analysis of large, polar,ionic, thermally unstable and involatilecompounds. Some of these compounds can be made amenable to GC/MS byderivatization, but LC/MS eliminates the need for time-consuming chemicalmodifications. This permits MS analysis of

non-volatile, thermallylabile, or chargedmolecules.

Mol

ecul

ar W

eigh

t

Analyte Polarity

API-Electrospray

GC/MSParticleBeam

APCI1000

100,000

10,000

nonpolar very polar

FABThermospray

Figure 1. Applications of various LC/MS techniques

3

Selectivity and Sensitivity

A mass spectrometer combined with a liquidchromatograph can detect masses charac-teristic of a compound or of a class ofcompounds. The system can selectivelydetect compounds of interest in a complexmatrix, thus making it easy to find andidentify suspected impurities at trace levels.

When configured to simultaneously detect a range of masses (and depending on thecompound) LC/MS sensitivity can be com-parable to that provided by a diode-arraydetector (DAD). Far greater sensitivity ispossible when the LC/MS is configured todetect only those masses characteristic ofthe compounds being monitored.

Complementary Information

Using MS in combination with other LCdetectors gives richer information. Forexample, a DAD acquires data on selectedultraviolet (UV) and visible (Vis) wave-lengths and spectra. This information isuseful for identifying unknown peaks and

for determining peak purity or for both. An MS acquires mass information bydetecting ions; it offers molecular-weightand structural information. The LC/MS can be used with analytes that do not have chromophores. The two orthogonalsets of data can be used to confidentlyidentify, confirm, and quantitatecompounds. In addition, an LC/MS can be used as a highly selective andsensitive tunable detector. An MSchromatogram for a single mass oftenproduces an interference-free signal thatoffers high precision and low minimumdetection limits.

Using both a UV detector and a massselective detector is more effective than using either one alone. There arecompounds (such as metabolites ordegradents) for which the UV-Vis spectra of two analytes will be very similar and it may be difficult to detect an impuritybased on UV spectra alone. It is alsopossible to have impurities that have thesame mass, especially

at lower molecularweights. It is rare,however, for twocomponents to haveidentical UV-Vis spectra and mass.Figure 2 shows theability to separatepolymer componentsfrom an unresolvedpeak using theinformation availablein a mass spectrum.This separation would not be possibleusing a conventionalUV detector.

Figure 2. Separation of isomers in a chromatographically unresolved peak

400000

800000

1200000

MS TIC

2000

4000m/z 648

min.5 10 15 20 25 30 35 40

100

200

300

m/z 1325

4000

8000

12000

m/z 376

4

Interfacing LC and MS

There has been a major focus on improvingthe interface between the LC and the MS.Liquid chromatography uses high pressureto separate a liquid phase and produces ahigh gas load. Mass spectrometry requiresa vacuum and a limited gas load. Forexample, common flow from an LC is 1 ml/min of liquid which, when convertedto the gas phase, is 1 l/min. However, atypical mass spectrometer can accept onlyabout 1 ml/min of gas. Furthermore, an LC operates at near ambient temperaturewhere as an MS requires an elevatedtemperature. There is no mass rangelimitation for samples analyzed by the LC but there are limitations for an MSanalyzer. Finally, LC can use inorganicbuffers and MS prefers volatile buffers.

Recent developments in atmosphericpressure ionization sources have expandedthe molecular weight, sample polarity, and flow-rate limitation of older LC/MStechniques. In many cases, analysts areable to use unmodified high-pressure LC methods.

Instrumentation

LC/MS systems have improved dramatically over the last 20 years. Instruments have

been transformed from complex, high-cost, highly advanced research tools to low-cost,

robust, easy-to-use routine detectors. And, as the instruments have been refined, more

applications have been developed.

Atmospheric Pressure

Ionization

Atmospheric pressure ionization (API)techniques are soft ionization processeswell suited for the analysis of large and small, polar and nonpolar, labilecompounds. These techniques can be used to rapidly confirm the identity of a wide range of volatile and nonvolatilecompounds by providing sensitive and accurate molecular-weight andfragmentation information. API techniquescan be used in metabolite confirmation analysis of most pharmaceuticalcompounds, and other applications.

5

API-Electrospray

Application

API-electrospray (API-ES) is useful inanalyzing samples that become multiplycharged such as proteins, peptides, andoligonucleotides, as well as in analyzingsamples that are singly charged, such asbenzodiazepines and sulfated conjugates.

API-ES can be used to measure themolecular weights of most polymers,peptides, proteins, and oligonucleotides up to 150,000 Daltons quickly and withhigh mass accuracy. In biopharmaceuticalapplications, chemists use API-ES to speedprotein characterization, to accuratelyidentify and characterize post-translationalmodifications, and to quickly confirm themolecular weight of synthetic peptides.

Process

API-ES is a process of ionization followedby evaporation. It occurs in three basicsteps: (1) nebulization and charging; (2) desolvation and; (3) ion evaporation.

Nebulization

The HPLC effluent is pumped through anebulizing needle whichis at ground potential.The spray goes througha semi-cylindricalelectrode which is at a high potential. Thepotential differencebetween the needle andthe electrode produces a strong electrical field.This field charges the

surface of the liquid and forms a spray of charged droplets. There is a concentricflow of gas which assists in the nebuli-zation process.

Desolvation

The charged droplets are attracted towardthe capillary sampling orifice. There is acounterflow of heated nitrogen drying gaswhich shrinks the droplets and carriesaway the uncharged material.

Ionization

As the droplets shrink, they approach apoint where the electrostatic (coulombic)forces exceed the cohesive forces. Thisprocess continues until the analyte ionsare ultimately desorbed into the gas phase.These gas-phase ions pass through thecapillary sampling orifice into the low-pressure region of the ion source and themass analyzer, see Figure 3.

EvaporationRayleigh

limitreached

Coulombexplosion

Analyte ionEvaporation

+++

+ + +++

+++

-- -- -- +++++++

++++-- -

- --+++++++

++++-- -

- --

+++++++++

++-- -

- --+++

++

+ ----

+++ +++ ----

+

+++

++ --

--

+++

++

+ ----+

+++

++ --

--

+

++

++

+ ----

+

+++

+ + +++

+++

-- -- -- +++++++

++++-- -

- -- +++++++++++

-- -- --

+++

++

+ ----

++

++

+++

+ + + + + + + + + + + + +

+

+

Heated nitrogen drying gas

Dielectric capillary entrance

Nebulizer gas

Solvent spray

Electrospray ions

-5,000 V

Figure 3. API-electrospray ionization

6

Atmospheric Pressure ChemicalIonization

Application

Atmospheric pressure chemical ionization(APCI) is an ionization technique that isapplicable to a wide range of polar andnonpolar analytes that have moderatemolecular weights.

Process

APCI, a process of evaporation followed byionization, is complementary to API-ES.

Nebulization and Desolvation

APCI nebulization is similar to that in API-ES. However, APCI nebulizationoccurs in a hot (typically 250°C–400°C)vaporizer chamber. The heat rapidlyevaporates the spray droplets, resulting in gas-phase HPLC solvent and analytemolecules, see Figure 4.

Ionization

The gas-phase solvent molecules areionized by the discharge from a coronaneedle. In APCI there is a charge transferfrom the ionized solvent reagent ions tothe analyte molecules in a way that issimilar to chemical ionization in GC/MS.These analyte ions then are transportedthrough the ion optics to the filter anddetector.

Dielectric capillary

High wattageheater

HPLC inlet

Corona discharge needle

Vaporizer

Nebulizer gas

+

+

+

++

++

+

+

+

+

+

+

+

++

++

+

++

+

+

[Solv + H]+ + ASolv + [A + H]+

Figure 4. Atmospheric Pressure Chemical Ionization (APCI)

7

Scan and SIM

Mass spectrometers can be operated ineither a scan mode or a selected ionmonitoring (SIM) mode (Figure 5).

Scan Mode

In the scan mode, the instrument detectssignals over a mass range (e.g. from 50–2000 m/z) during a short period of time(e.g. 2 sec). During this scan period, the MS electronics sequentially read the signals detected within narrower massintervals until the full mass range iscovered. The spectra that are storedrepresent the detected signal for the full mass range. Since full mass spectra are recorded, this mode of operation istypically selected for qualitative analysis,or for quantitation when all analyte massesare not known in advance.

Samples may be introduced into a massspectrometer by infusion or through anHPLC. In the latter, it is important to matchthe peak width and the scan range. The

narrower the peaks, the shorter the totalscan time must be in order to get properpeak definition. In order to get a short totalscan time, it may be necessary to reducethe scan range.

SIM Mode

Mass spectrometers can also operate in the selected ion monitoring (SIM) mode.Rather than scanning continuously, theycan be set to only monitor a few mass-to-charge ratios (m/z). As a result thequadrupole is able to spend significantlymore time sampling each of the m/z values,with a concomitant and large increase insensitivity. Moreover, because the cycle-time between data points is often shorterthan it is in scan mode, quantitativeprecision and accuracy are improvedthrough optimal peak-shape profiling.

Since the m/z values to be sampled mustbe set in advance, SIM is most often usedfor target compound analysis. For analysesconsisting of multiple target compounds,SIM ion sampling choices can be time-

programmed tomatch compoundelution timewindows. No data is collected at m/zvalues other thanthose specificallysampled, so SIM is rarely used inqualitative analysis.

Figure 5. Scan and SIM data acquisition

m/z

time m/z

abun

danc

e

m/z

abun

danc

e

m/z

time

1 Scan

1 Scan

Mass Range

Discrete Masses

Scan

SIM

8

Collision-Induced Dissociation

MS/MS is accomplished by a process called collision-induced dissociation (CID)in which ions break apart as a result of collisions with other molecules.Electrospray ionization can also be used to produce CID spectra even with a singlequadrupole system. In many instances, asingle quadrupole system can be used forwork that has traditionally required triplequadrupoles or ion traps.

Electrospray is a soft ionization techniquethat produces a large number of molecularadduct ions. Adduct ions are typicallyprotonated parent ions [M+H]+. These ions are guided into the vacuum region byapplied voltages on lenses. By changing thevoltage, various degrees of fragmentationmay be achieved. With a low voltage, thereis little fragmentation; with higher voltages,

Figure 6. CID with single quadrupole and triple quadrupole mass spectrometers

the parent ion is fragmented to a largerdegree. Electrospray CID has theadvantage of more efficient transfer thanin a triple quadrupole.

There are some limitations to using CID in a single quadrupole mass spectrometer.In a triple quadrupole or ion trap, a singleion can be selected and fragmented. In CID with a single quadrupole instrument,there will be multiple ions in the sourcethat are fragmented. These other ions may interfere with the analyte of interestby generating additional fragments. Inmany cases, this problem can be solved by improving the chromatography toisolate the analyte (Figure 6).

LC/MS/MS

LC/MS

Q1CIDm/z

abun

danc

e

Q1 Q2 (CID) Q3m/z

abun

danc

e

9

Adapting LC Methods

Compared to previous LC/MS interfaces,the API-ES and APCI interfaces arerelatively rugged. In many cases, existingmethods may be used with little or noadaptation. Some instruments allow flowrates of 1 to 2 ml/min without splitting.

One of the most critical factors in adaptingLC methods is the choice of buffer.Involatile buffers interfere with good MS performance. For the best long-termperfomance, it is highly recommended that the method be modified to use avolatile buffer.

Modern mass spec-trometer designsincorporate a number of features to increasetheir tolerance forinvolatile buffers. In the first-generationsystems, the spray fromthe LC was directed into the lens axis forquadrupole systems. In newer designs, theflow is directed

orthogonal to the lens axis and ions arefocused into the mass filter (Figure 7). The extraneous material is pumped away.

Figure 8 shows a source that had beensubjected to 600 injections with a complexinvolatile salt solution (approximately 9 g/l). Even after this abuse, theperformance was only slightly degraded.This ruggedness makes this techniqueattractive for laboratories in which thereare many users of the system and in whichlarge varieties of sample are commonlyhandled. The instrument does not need tobe finely adjusted for every sample.

Capillary

Fragmentation zone (CID)

Skimmers Octopole

Lenses Quadrupole

HPLC inlet

Nebulizer

++ ++

+++ + + + + ++

+

HED detector

Figure 8. Salt deposits on an

HP 1100 Series LC/MSD System

API interface

Figure 7.

Orthogonal

spray of API-

electrospray

source

10

Molecular Weight Determination

One of the key applications of API-electrospray and APCI LC/MS systems is in determining molecular weights.

Differentiation of Similar Octapeptides

Figure 9 shows the spectra of two peptideswhose mass-to-charge ratio differ by only 1 amu. The only difference in the sequence

is at the C-terminus where one peptide has threonine and the other has threonineamide. The smaller fragements areidentical in the two spectra, indicating that large portions of the two peptides are similar. The larger fragments containthe differentiating peptides.

0

20

40

60

80

100 8

58.5

739

.3

880

.3

444

.2

576

.3

498

.2

841

.3

343

.1

397

.2

m/z400 600 800

0

20

40

60

80

100 857

.5 8

79.5

739

.3

840

.3

576

.3

444

.2

379

.1

Ala-Ser-Thr-Thr-Thr-Asn-Tyr-Thr

Ala-Ser-Thr-Thr-Thr-Asn-Tyr-Thr amide

Applications

Figure 9. Octapeptides with 1 amu difference

LC/MS is suitable for many applications, from pharmaceutical development to envi-

ronmental analysis. The ability to detect a wide range of compounds has made API

techniques popular with scientists in a variety of fields.

11

spectrometer measures the mass-to-chargeratio, the molecular weight of a largemolecule such as GFP can be determinedif it is multiply charged.

The upper part of the display in Figure 10shows the mass spectrum of the chromato-graphic peak. There is a regular pattern to the spectral peaks, each one of whichrepresents the molecule with a differentnumber of charges. The lower display is a deconvoluted spectrum generated by the data system for the singly charged molecule.

Determining the Molecular Weight of

Green Fluorescent Protein

API-electrospray LC/MS can be used to rapidly determine the molecular weight of a protein. Although pure proteins can be done by infusion, this recombinantprotein required chromatography. Greenflourescent protein (GFP) is a 27,000Dalton polymer with 238 amino acids. Itemits a green light when excited by UV.

Even though GFP is a very large molecule,a mass spectrometer with a smaller massrange can be used to determine itsmolecular weight. Since the mass

1000 1500

100000

120000

20000

40000

60000

80000

726

.25

746

.15

767

.55

789

.95

839

.45

866

.45

895

.45

926

.15

959

.15

994

.85

103

2.95

107

4.15

111

8.85

116

7.55

122

0.45

127

8.75

134

2.65

141

3.25

157

9.65

26700 26800 26900 27000

200000

400000

600000

800000

1000000

Deconvoluted spectrumMW = 26828.84

Figure 10. Molecular weight

determination of

Green Fluorescent Protein

by API-electrospray

12

Combinatorial Chemistry

Combinatorial chemistry has transformedthe drug discovery process. Rather thancreating compounds through manualmanipulations, robotics is applied togenerate whole classes of compounds fromsets of reagents. Reactions are typicallydone using 96-well capacity (or greater)plates. These plates are loaded into anautosampler that injects samples into theLC/MS. The instrument acquires the dataand produces a report showing whetherthe compounds detected are of theexpected molecular weight.

Recent advances in software allow manychemists to use the high sample capacityof automated LC/MS systems. Trays areloaded on the autosampler; the method isspecified; the instrument analyzes eachwell in the plate; and the data systemprints a report. Figure 11 shows a typicaldisplay of a sample tray. Green dots showthe locations where the reaction product is of the expected molecular weight. Reddots show where the reaction product didnot have the expected molecular weight. A more detailed display and report of eachposition is possible.

Figure 11. Display for

combinatorial chemistry

on the HP 1100 Series

LC/MS System

13

a series of benzodiazepines was run usingboth UV and MS detectors. The UV tracecould not be used for quantitation, but theextracted ion chromatograms for the MScould be used.

The mass spectral information providesadditional confirmation of the identity.Chlorine has a characteristic pattern

because of the relativeabundance of the two most commonisotopes. In Figure 12,the triazolam spectrumshows that the moleculehas two chlorines, and the diazepamspectrum shows that it has only one.

Detection of

Degradation Products

for Salbutamol

Detecting degradationproducts can often bedifficult because theycan be structurally verysimilar to the originalproduct. If the chromo-phoric region is intact,the two compoundscannot be distinguishedwith a UV detector.

The UV spectra for thesalbutamol and itsdegradation productsare very similar. Theunique mass spectralfragments can be usedto identify the com-pounds. Figure 13 shows the extracted ion chromatograms for various masses.

Pharmaceutical Applications

Rapid Chromatography

of Benzodiazepines

The information available in a massspectrum allows some compounds to beseparated even though they are chroma-tographically unresolved. In this example,

Figure 12. Benzodiazepines by API-ES

min1 2 3 4

0

50

100

150

200

250

300

350

oxazepam Diazepam

Lorazepam

Estrazolam

Alprazolam

Diazepam

Clobazam

Triazolam

343.1

345.1

250 300 350

285.2

287.2

Triazolam

Diazepam

2 Cl

1 Cl

min1 2 3 4

mAU

0

0.5

1

1.5

2

MS

UV

Figure 13. Salbutamol degradation products

min5 10 15 20 25 30

0

20

40

60

80

100

120

nm200 250 300 350

Norm.

40

80

120

160

min2 4 6 8 10 12 14 16

mAU

0

5

10

15

20

* * ***

*

m/z 346

MS TICm/z 224m/z 282

Rapid chromatography and isotopic information

UV Signal and spectra MS TIC and EICs

14

Biochemical Applications

Detection of Glycosylation in a Tryptic

Map of a 60 kD Protein

Proteins are sometimes chemically orenzymatically digested to identify thecomponents. The digestion mixture is thenchromatographed to produce a peptidemap. Figure 14 shows two chromatogramsfor a 60,000 Dalton glycoprotein from amass spectrometer and a UV detector.

Although the chromatographic patternswith the two detectors are very similar, the mass spectrometer can provideadditional data. Glycosylation is thecovalent modification of certain amino

acids which result in the attachment ofcomplex carbohydrates. The sugars can be fragmented from the peptide fragmentsusing in-source collision-induceddissociation (CID). The code at the right in Figure 15 is used to designate variousmarkers. Since glactose and mannose havethe same molecular weight, they cannot bedistinguished from each other. Therefore,they are designated simply as Hex.

Figure 16 shows the extracted ionchromatogram (EIC) for three of theglycosylation markers. The fragments withthe glycosylation markers can be easilyidentified.

MS TIC36 pmol

500000

1000000

1500000

2000000

UV @ 214nm

min15 20 25 30 35 40 45

mAU

0

5

10

15

20

Abundance

Figure 14. Tryptic map of a 60 kD protein

15

Fucose Mass: 146Residue Marker Ion: 147

Sialic Acid Mass: 291Residue Marker Ion: 292

HexNAc Mass: 203Residue Marker Ion: 204

Galactose Mass: 162Residue Marker Ion: 163

Mannose Mass: 162Residue Marker Ion: 163

Fragmentor @ 300 V

min15 20 25 30 35 40 45 50 55

10000000

20000000

50000

150000

40000

80000

50000

150000

Total Ion Current

m/z 204: HexNAc

m/z 292: Sialic Acid

m/z 366: HexNAc + Hex

Figure 16. Detection of glycosylation

Figure 15. Typical glycosylation markers

16

Clinical Applications

High Sensitivity Detection of

Trimipramine and Thioridazine

For some compounds, MS provides moresensitive detection. Trimipramine is atricyclic antidepressant with sedativeproperties. Thioridazine is a tranquilizer.Figure 17 shows these compounds in aurine extract at a level that could not bedetected by UV. To get the maximumsensitivity, the analysis was done byselected ion monitoring.

Food Applications

Aflatoxins are toxic metabolites producedby certain fungi in foods. Figure 18 shows the total ion chromatogram for four aflatoxins; each could be uniquelyidentified by their mass spectra (Figure 19).

mAU

0

200

0

80000

0

40000

0

20000

min1 2 3 4 5 60

8000

Trimipramine

Thioridazine

UV280 nm

EICm/z 295

EICm/z 100

EICm/z 126

EICm/z 371

Trimipramine

Thioridazine

Figure 17. Trimipramine and thioridazine in urine extract

17

Scan of 2 ng

6.00 8.00 10.00 12.00 14.00 16.00 18.00

40000

80000

120000

160000

200000

1 23

4

1) Aflatoxin G2

2) Aflatoxin G1

3) Aflatoxin B2

4) Aflatoxin B1

TIC

120 160 200 240 280 320

50

90

285

Aflatoxin B1

335[M+Na]+

313[M+H]+

O

OCH3OO

O

O

120 160 200 240 280 320 360

50

90 Aflatoxin G2

353[M+Na]+

331 [M+H]+

313[M-OH]+

OO

O O

O O

OCH3

120 160 200 240 280 320 360

50

90

329[M+H]

243 283

Aflatoxin G1

351[M+Na]+

311[M-OH]+

+

OO

O O

O O

OCH3

120 160 200 240 280 320

50

90

287

Aflatoxin B2O

OCH3OO

O

O

315[M+H]+

337[M+Na]+

Figure 18. Afltoxins by API-ES

Figure 19. Mass spectra of aflatoxins

18

Environmental Applications

Carbamates by APCI-LC/MS

Carbamates are a class of pesticidesusually analyzed by post-column

derivativation and fluorescence detection.The chromatogram in Figure 20 is that of a tomato extract that has been spiked with 11 carbamates. Using APCI, these compounds are detected withoutderivitization. The extracted ion chromato-

gram displays the peaksfor the individualcompounds.

Detection of

Phenylurea

Herbicides

Many of the phenylureaherbicides are verysimilar and difficult todistinguish with a UVdetector (Figure 21).Monuron and diuronhave one ring and differby a single chlorine.Chloroxuron has twochlorines and a secondbenzene ring attached to the first by anoxygen. The UV-Visspectra are similar fordiuron and monuron,but different forchloroxuron. Each of these compounds has a distinct mass spectrum. The standardswere run with an API-electrospray LC/MSsystem.

41.5 pg/component

min

20

40

150

300

20

40

2.5 5 7.5 10 12.5 15 17.5

20

40

200

400 MS TIC

m/z 132

m/z 226

m/z 202

m/z 222

Aldicarb Sulfoxide

Carbofuran

Carbaryl

Promecarb

nm

Norm.

200 250 300 350

0

100

200

300

400

500

min5 10 15 20 25

mAU

0

20

40

60

80

100

**

*

233.1

199.2

100 200 300 400 500

291.2

Chloroxuron

Diuron

Monuron

UV shows class; MS identifies species

41.5 pg/component

Figure 20. Carbamates by APCI

Figure 21. Phenylurea herbicides by API-ES

19

Notes

20

21

Information, descriptions andspecifications in this publication aresubject to change without notice.

Copyright © 1998Hewlett-Packard Company

All Rights Reserved.Reproduction, adaption or translationwithout prior written permission isprohibited, except as allowed underthe copyright laws.

Printed in the USA 10/98(23) 5968-2543E

The HP LC/MSD system hasbeen designed andmanufactured under aquality system that has been registered to ISO 9001. Certificate No: FS25109

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OF CERTIFICATIONBODIES