Guidelines for Quality Management in Soil and Plant Laboratories. (FAO Soils Bulletin - 74)













Table of Contents


Compiled by
L.P. van Reeuwijk
Associate Professor
Head of Laboratory
International Soil Reference and Information Centre (ISRIC)
Wageningen, the Netherlands

with a contribution by
V.J.G. Houba
Associate Professor, Director of Wageningen Evaluating
Programmes for Analytical Laboratories (WEPAL)
Department of Soil Science and Plant Nutrition
Wageningen Agricultural University
Wageningen, the Netherlands

INTERNATIONAL SOIL REFERENCE AND INFORMATION CENTRE

Food and Agriculture Organization of the United Nations

Rome, 1998

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations or the International Soil Reference and Information Centre concerning the legal status of any country, territory, city or area or of its autorities, or concerning the delimitation of its frontiers or boundaries.

M-90
ISBN 92-5-104065-6

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Information Division, Food and Agriculture Organization of the United Nations, Viale delle Terme di Caracalla, 00100 Rome, Italy.

© FAO and ISRIC 1998

This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.


Table of Contents


FOREWORD

PREFACE

1 INTRODUCTION

1.1 What is Quality?
1.2 Quality Management
1.3 Quality Assurance
1.4 Quality Control
1.5 Good Laboratory Practice (GLP)

2 STANDARD OPERATING PROCEDURES

2.1 Definition
2.2 Initiating a SOP
2.3 Preparation of SOPs
2.4 Administration, Distribution, Implementation
2.5 Laboratory notebook
2.6 Relativization as encouragement
SOPs

F 002 - Administration of Standard Operating Procedures
PROT 005 - The Use of Laboratory Notebooks
Model page of Laboratory Notebook

3 ORGANIZATION AND PERSONNEL

3.1 Function and aims of the institute
3.2 Scope of the laboratory
3.3 Organigram
3.4 Description of processes
3.5 Job descriptions, personnel records, job allocation, replacement of staff

3.5.1 Job descriptions
3.5.2 Personnel records
3.5.3 Substitution of staff

3.6 Education and training of staff
3.7 Introduction of new staff
SOPs

ORG 001 - Organigram
PERS 011 - Job Description Form
PERS 012 - Qualifications and skills of laboratory staff
PERS 013 - List of laboratory staff
PERS 014 - Proficiency list of laboratory staff
PERS 015 - Job allocation laboratory staff

4 FACILITIES AND SAFETY

4.1 Housing facilities

4.1.1 The scientific block
4.1.2 The storage block
4.1.3 Climate

4.2 Safety

4.2.1 Equipment
4.2.2 Chemicals, reagents, and gases
4.2.3 Waste disposal
4.2.4 General rules to observe
4.2.5 First Aid
4.2.6 Fire fighting

4.3 Admittance to the laboratory
SOPs

PROT 051 - The replacement of a gas cylinder
SAF 011 - Safety Logbook (Laboratory)
RF 031 - Stock record of chemicals

5 MATERIALS: APPARATUS, REAGENTS, SAMPLES

5.1 Introduction
5.2 Apparatus

5.2.1 Registration

5.2.1.1 Instrument Identification List
5.2.1.2 Instrument Maintenance List. Instrument Calibration List

5.2.2 Operation

5.2.2.1 Operation Instruction Manual
5.2 2.2 Instrument Maintenance Logbook
5.2 2.3 User Logbook
5.2.2.4 SOPs for use of equipment

5.3 Reagents

5.3.1 Reagent chemicals
5.3.2 Standard and Reagent solutions

5.4 Samples
SOPs

APP 003 - Instrument Identification List
APP 004 - Instrument Maintenance/Calibration List
APP 041 - Logbook of AAS
APP 051 - User Logbook of AAS
F 011 - Standard Instructions for drafting apparatus SOPs
APP 061 - Operation of Eppendorf Varipette 4810
APP 062 - Operations of electronic balance Sartorius
APP 071 - Operation of pH meter Metrohm E 632
RF 032 - Page of Reagents Book
PROT 011 - Protocol for custody chain of samples
RF 011 - Protocol for accepting delivery of samples
RF 021 - Form for accepting order for analysis

6 BASIC STATISTICAL TOOLS

6.1 Introduction
6.2 Definitions

6.2.1 Error
6.2.2 Accuracy
6.2.3 Precision
6.2.4 Bias

6.3 Basic Statistics

6.3.1 Mean
6.3.2 Standard deviation
6.3.3 Relative standard deviation. Coefficient of variation
6.3.4 Confidence limits of a measurement
6.3.5 Propagation of errors

6.3.5.1. Propagation of random errors
6.3.5.2 Propagation of systematic errors

6.4 Statistical tests

6.4.1 Two-sided vs. one-sided test
6.4.2 F-test for precision
6.4.3 t-Tests for bias

6.4.3.1. Student's t-test
6.4.3.2 Cochran's t-test
6.4.3.3 t-Test for large data sets (n³ 30)
6.4.3.4 Paired t-test

6.4.4 Linear correlation and regression

6.4.4.1 Construction of calibration graph
6.4.4.2 Comparing two sets of data using many samples at different analyte levels

6.4.5 Analysis of variance (ANOVA)

7 QUALITY OF ANALYTICAL PROCEDURES

7.1 Introduction
7.2 Calibration graphs

7.2.1 Principle
7.2.2 Construction and use
7.2.3 Error due to the regression line
7.2.4 Independent standards
7.2.5 Measuring a batch

7.3 Blanks and Detection limit

7.3.1 Blanks
7.3.2 Detection limit

7.4 Types of sample material

7.4.1 Certified reference material (CRM)
7.4.2 Reference material (RM)
7.4.3 Control sample
7.4.4 Test sample
7.4.5 Spiked sample
7.4.6 Blind sample
7.4.7 Sequence-control sample

7.5 Validation of own procedures

7.5.1 Trueness (accuracy), bias
7.5.2 Precision

7.5.2.1 Reproducibility
7.5.2.2 Repeatability
7.5.2.3 Within-laboratory reproducibility

7.5.3 Sensitivity
7.5.4 Working range
7.5.5 Selectivity and specificity
7.5.6 Recovery
7.5.7 Ruggedness, robustness
7.5.8 Interferences
7.5.9 Practicability
7.5.10 Validation report

7.6 Drafting an analytical procedure
7.7 Research plan
SOPs

VAL 09-2 - Validation of CEC determination with NH4OAc
METH 006 - Determination of nitrogen in soil with micro-Kjeldahl

8 INTERNAL QUALITY CONTROL OF DATA

8.1 Introduction
8.2 Rounding and Significant figures

8.2.1 Rounding
8.2.2 Significant figures

8.2.2.1 Rounding of test results
8.2.2.2 Rounding of means and standard deviations

8.3 Control charts

8.3.1 Introduction
8.3.2 Control Chart of the Mean (Mean Chart)

8.3.2.1 Principle
8.3.2.2 Starting with Mean Charts
8.3.2.3 Using a Mean Chart

8.3.3 Control Chart of the Range of Duplicates (Range Chart)

8.3.3.1 Principle
8.3.3.2 Range chart of Control Sample
8.3.3.3 Starting the first chart
8.3.3.4 R-chart of Test Samples

8.3.4 Automatic preparation of control charts

8.4 Preparation of a Control Sample

8.4.1 Collection and treatment of soil material
8.4.2 Collection and treatment of plant material
8.4.3 Stability
8.4.4 Homogeneity

8.5 Complaints
8.6 Trouble-shooting
8.7 LIMS

8.7.1 Introduction
8.7.2 What is a LIMS?
8.7.3 How to select a LIMS

SOPs

Model: Mean Chart
Model: Range Chart
Model: Combined Mean Chart and Range Chart

9 EXTERNAL QUALITY CONTROL OF DATA

9.1 Introduction
9.2 Check-analyses by another laboratory

9.2.1 Single value - single value check
9.2.2 Replicate data - single value check
9.2.3 Replicate data - replicate data check

9.2.3.1 Comparison of replicate results on one sample
9.2.3.2 Comparison of replicate results on multiple samples

9.3 Interlaboratory sample and data exchange programmes

9.3.1 Types of interlaboratory programmes
9.3.2 Proficiency testing
9.3.3 Examples: ISE and IPE

9.3.3.1 Data processing
9.3.3.2 Rating with t-value
9.3.3.3 Proficiency control chart
9.3.3.4 Rating with Z-score

9.4 Trouble-shooting
9.5 Organization of interlaboratory test programmes
9.6 Quality audit

APPENDIX 1. Critical values of t

APPENDIX 2. Flow diagram for t-tests for comparison of two sets of data (see section 6.4.3).

APPENDIX 3. Flow diagram for t-tests for comparison of two sets of data

APPENDIX 4. Code of reference materials (COMAR).

ACKNOWLEDGEMENTS

LITERATURE