diff --git a/chemclipse/plugins/org.eclipse.chemclipse.msd.converter.supplier.amdis/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/io/MSPReader.java b/chemclipse/plugins/org.eclipse.chemclipse.msd.converter.supplier.amdis/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/io/MSPReader.java
index 209e55c964..3492608972 100644
--- a/chemclipse/plugins/org.eclipse.chemclipse.msd.converter.supplier.amdis/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/io/MSPReader.java
+++ b/chemclipse/plugins/org.eclipse.chemclipse.msd.converter.supplier.amdis/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/io/MSPReader.java
@@ -40,6 +40,7 @@
 import org.eclipse.chemclipse.msd.model.core.IIon;
 import org.eclipse.chemclipse.msd.model.core.IMassSpectra;
 import org.eclipse.chemclipse.msd.model.core.IRegularLibraryMassSpectrum;
+import org.eclipse.chemclipse.msd.model.core.Polarity;
 import org.eclipse.chemclipse.msd.model.exceptions.IonLimitExceededException;
 import org.eclipse.chemclipse.msd.model.implementation.Ion;
 import org.eclipse.chemclipse.msd.model.implementation.MassSpectra;
@@ -256,9 +257,9 @@ private void addMassSpectrum(IMassSpectra massSpectra, String massSpectrumData,
 		//
 		String ionMode = extractContentAsString(massSpectrumData, ionModePattern, 2);
 		if(ionMode.equals("POSITIVE")) {
-			massSpectrum.setPolarity("+");
+			massSpectrum.setPolarity(Polarity.POSITIVE);
 		} else if(ionMode.equals("NEGATIVE")) {
-			massSpectrum.setPolarity("-");
+			massSpectrum.setPolarity(Polarity.NEGATIVE);
 		}
 		/*
 		 * MS/MS
diff --git a/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/AbstractRegularLibraryMassSpectrum.java b/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/AbstractRegularLibraryMassSpectrum.java
index f0196c578f..96c2f94302 100644
--- a/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/AbstractRegularLibraryMassSpectrum.java
+++ b/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/AbstractRegularLibraryMassSpectrum.java
@@ -32,7 +32,7 @@ public abstract class AbstractRegularLibraryMassSpectrum extends AbstractRegular
 	//
 	private ILibraryInformation libraryInformation;
 	private String precursorType;
-	private String polarity; // TODO enum?
+	private Polarity polarity;
 	private double neutralMass = 0.0d;
 	private Map<String, String> properties = null; // Initialization on demand
 
@@ -87,7 +87,7 @@ public void setNeutralMass(double neutralMass) {
 	}
 
 	@Override
-	public String getPolarity() {
+	public Polarity getPolarity() {
 
 		if(polarity != null) {
 			return polarity;
@@ -95,17 +95,16 @@ public String getPolarity() {
 		if(properties != null) {
 			String precursorType = getProperty(PROPERTY_PRECURSOR_TYPE);
 			if(precursorType.contains("]+")) {
-				return "+";
+				return Polarity.POSITIVE;
 			} else if(precursorType.contains("]-")) {
-				return "-";
+				return Polarity.NEGATIVE;
 			}
 		}
-		//
-		return "";
+		return Polarity.NONE;
 	}
 
 	@Override
-	public void setPolarity(String polarity) {
+	public void setPolarity(Polarity polarity) {
 
 		this.polarity = polarity;
 	}
diff --git a/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/IRegularLibraryMassSpectrum.java b/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/IRegularLibraryMassSpectrum.java
index 7b777adbc7..5558812011 100644
--- a/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/IRegularLibraryMassSpectrum.java
+++ b/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/IRegularLibraryMassSpectrum.java
@@ -27,19 +27,9 @@ public interface IRegularLibraryMassSpectrum extends IRegularMassSpectrum, ILibr
 
 	void setNeutralMass(double neutralMass);
 
-	/**
-	 * Returns the polarity if set.
-	 * 
-	 * Otherwise returns the polarity (+) or (-)
-	 * if the precursor type is set.
-	 * 
-	 * If none is available "" will be returned.
-	 * 
-	 * @return String
-	 */
-	String getPolarity();
-
-	void setPolarity(String polarity);
+	Polarity getPolarity();
+
+	void setPolarity(Polarity polarity);
 
 	Set<String> getPropertyKeySet();
 
diff --git a/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/Polarity.java b/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/Polarity.java
new file mode 100644
index 0000000000..ee70b71329
--- /dev/null
+++ b/chemclipse/plugins/org.eclipse.chemclipse.msd.model/src/org/eclipse/chemclipse/msd/model/core/Polarity.java
@@ -0,0 +1,39 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Lablicate GmbH.
+ * 
+ * All rights reserved.
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ * 
+ * Contributors:
+ * Matthias Mailänder - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.chemclipse.msd.model.core;
+
+import org.eclipse.chemclipse.support.text.ILabel;
+
+public enum Polarity implements ILabel {
+
+	POSITIVE("+"), //
+	NEGATIVE("-"), //
+	NONE("");
+
+	private String label;
+
+	private Polarity(String label) {
+
+		this.label = label;
+	}
+
+	@Override
+	public String label() {
+
+		return label;
+	}
+
+	public static String[][] getOptions() {
+
+		return ILabel.getOptions(values());
+	}
+}
diff --git a/chemclipse/tests/org.eclipse.chemclipse.msd.converter.supplier.amdis.fragment.test/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/converter/msp/MassBankMS2ImportConverter_ITest.java b/chemclipse/tests/org.eclipse.chemclipse.msd.converter.supplier.amdis.fragment.test/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/converter/msp/MassBankMS2ImportConverter_ITest.java
index dae4c29ce2..9f482bbf54 100644
--- a/chemclipse/tests/org.eclipse.chemclipse.msd.converter.supplier.amdis.fragment.test/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/converter/msp/MassBankMS2ImportConverter_ITest.java
+++ b/chemclipse/tests/org.eclipse.chemclipse.msd.converter.supplier.amdis.fragment.test/src/org/eclipse/chemclipse/msd/converter/supplier/amdis/converter/msp/MassBankMS2ImportConverter_ITest.java
@@ -17,6 +17,7 @@
 import org.eclipse.chemclipse.msd.converter.supplier.amdis.io.ImportConverterMspTestCase;
 import org.eclipse.chemclipse.msd.model.core.IRegularLibraryMassSpectrum;
 import org.eclipse.chemclipse.msd.model.core.IScanMSD;
+import org.eclipse.chemclipse.msd.model.core.Polarity;
 import org.junit.Test;
 
 public class MassBankMS2ImportConverter_ITest extends ImportConverterMspTestCase {
@@ -51,7 +52,7 @@ public void testMassSpectrum() {
 			assertEquals(288.1225d, regularLibraryMassSpectrum.getPrecursorIon());
 			assertEquals(287.11575d, regularLibraryMassSpectrum.getNeutralMass());
 			assertEquals("30(NCE)", regularLibraryMassSpectrum.getProperty(IRegularLibraryMassSpectrum.PROPERTY_COLLISION_ENERGY));
-			assertEquals("+", regularLibraryMassSpectrum.getPolarity());
+			assertEquals(Polarity.POSITIVE, regularLibraryMassSpectrum.getPolarity());
 			assertEquals("[M+H]+", regularLibraryMassSpectrum.getProperty(IRegularLibraryMassSpectrum.PROPERTY_PRECURSOR_TYPE));
 			assertEquals("Q-Exactive Orbitrap Thermo Scientific", regularLibraryMassSpectrum.getProperty(IRegularLibraryMassSpectrum.PROPERTY_INSTRUMENT_NAME));
 		}
diff --git a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_4_Test.java b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_4_Test.java
index 7c7b7e9d87..13796cebe0 100644
--- a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_4_Test.java
+++ b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_4_Test.java
@@ -12,6 +12,7 @@
 package org.eclipse.chemclipse.msd.model.implementation;
 
 import org.eclipse.chemclipse.msd.model.core.IRegularLibraryMassSpectrum;
+import org.eclipse.chemclipse.msd.model.core.Polarity;
 
 import junit.framework.TestCase;
 
@@ -52,7 +53,7 @@ public void test3() {
 
 	public void test4() {
 
-		assertEquals("", massSpectrum.getPolarity());
+		assertEquals(Polarity.NONE, massSpectrum.getPolarity());
 	}
 
 	public void test5() {
diff --git a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_5_Test.java b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_5_Test.java
index 55ba78981f..2a895f2dbb 100644
--- a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_5_Test.java
+++ b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_5_Test.java
@@ -12,6 +12,7 @@
 package org.eclipse.chemclipse.msd.model.implementation;
 
 import org.eclipse.chemclipse.msd.model.core.IRegularLibraryMassSpectrum;
+import org.eclipse.chemclipse.msd.model.core.Polarity;
 
 import junit.framework.TestCase;
 
@@ -55,7 +56,7 @@ public void test3() {
 
 	public void test4() {
 
-		assertEquals("+", massSpectrum.getPolarity());
+		assertEquals(Polarity.POSITIVE, massSpectrum.getPolarity());
 	}
 
 	public void test5() {
diff --git a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_6_Test.java b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_6_Test.java
index 6a21a280d8..7deb9eaed8 100644
--- a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_6_Test.java
+++ b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_6_Test.java
@@ -12,6 +12,7 @@
 package org.eclipse.chemclipse.msd.model.implementation;
 
 import org.eclipse.chemclipse.msd.model.core.IRegularLibraryMassSpectrum;
+import org.eclipse.chemclipse.msd.model.core.Polarity;
 
 import junit.framework.TestCase;
 
@@ -55,7 +56,7 @@ public void test3() {
 
 	public void test4() {
 
-		assertEquals("-", massSpectrum.getPolarity());
+		assertEquals(Polarity.NEGATIVE, massSpectrum.getPolarity());
 	}
 
 	public void test5() {
diff --git a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_7_Test.java b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_7_Test.java
index 7403d9d19e..b422e519b1 100644
--- a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_7_Test.java
+++ b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_7_Test.java
@@ -12,6 +12,7 @@
 package org.eclipse.chemclipse.msd.model.implementation;
 
 import org.eclipse.chemclipse.msd.model.core.IRegularLibraryMassSpectrum;
+import org.eclipse.chemclipse.msd.model.core.Polarity;
 
 import junit.framework.TestCase;
 
@@ -55,7 +56,7 @@ public void test3() {
 
 	public void test4() {
 
-		assertEquals("+", massSpectrum.getPolarity());
+		assertEquals(Polarity.POSITIVE, massSpectrum.getPolarity());
 	}
 
 	public void test5() {
diff --git a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_8_Test.java b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_8_Test.java
index 33ee392843..7f4f2c72b5 100644
--- a/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_8_Test.java
+++ b/chemclipse/tests/org.eclipse.chemclipse.msd.model.fragment.test/src/org/eclipse/chemclipse/msd/model/implementation/RegularLibraryMassSpectrum_8_Test.java
@@ -12,6 +12,7 @@
 package org.eclipse.chemclipse.msd.model.implementation;
 
 import org.eclipse.chemclipse.msd.model.core.IRegularLibraryMassSpectrum;
+import org.eclipse.chemclipse.msd.model.core.Polarity;
 
 import junit.framework.TestCase;
 
@@ -55,7 +56,7 @@ public void test3() {
 
 	public void test4() {
 
-		assertEquals("+", massSpectrum.getPolarity());
+		assertEquals(Polarity.POSITIVE, massSpectrum.getPolarity());
 	}
 
 	public void test5() {