Mental health in patients affected by atopic dermatitis: which effects of treatment with dupilumab?

Atopic dermatitis (AD) is an inflammatory skin disease. Patients with AD are prone to develop anxiety and mood disorders. Aim of this study is to investigate if treatment with dupilumab may improve mental health status of patients affected by AD. A total of 66 patients with severe AD were included: 24 subjects were candidate or have just started (one month) treatment with dupilumab, and 42 have been in treatment for one year. 25.8%, 30.3%, and 45.5% of the total sample showed, respectively, clinically significant anxiety, depression, and symptoms of Internet addiction. Patients with anxiety symptoms resulted to have more severe AD, more sleep problems ( P  = 0.028), less quality of life ( P  = 0.001), more severe depressive symptoms ( P  < 0.001), to be more frequently women ( P  = 0.016), to be less frequently treated with dupilumab for one year ( P  = 0.025). Similarly, patients with clinically significant depressive symptoms resulted to have more severe AD, more sleep problems ( P  = 0.003), less quality of life ( P  < 0.001), more severe anxiety symptoms ( P  < 0.001), to be less frequently treated with dupilumab for one year ( P  = 0.008). Patients with AD treated for one year with dupilumab showed a better mental health profile in terms of less severe anxiety and depression with respect to their counterparts.

Which Factors Are Associated with Persistence of Depressive and Anxiety Symptoms in Patients Affected by Atopic Dermatitis despite 2-Year Treatment with Dupilumab?

Background: Atopic Dermatitis (AD) is a prevalent inflammatory skin disease whose course is often complicated by the presence of concomitant anxiety and depressive disorders. Dupilumab has been demonstrated to be largely effective in AD. The aims of the present study were to (1) to verify the effectiveness of 2-year dupilumab treatment on the depressive and anxiety symptoms of patients affected by AD and (2) to identify predictors of the persistence of psychiatric symptoms despite maintenance treatment with dupilumab. Methods: A total of 331 patients with severe AD were assessed at baseline and at different times over 2 years by a large set of rating scales, including the Eczema Area and Severity Index (EASI), the Hospital Anxiety and Depression Scale (HADS), and the Dermatology Life Quality Index (DLQI). Paired sample t-tests were performed to verify the effectiveness of dupilumab on the severity of AD and mental health items. Two binary logistic regression models were then used to identify the predictors of the persistence of clinically significant depression and anxiety, defined by a score ≥ 8 on each sub-scale of the HADS. Results: After 2 years of treatment with dupilumab, the patients benefited, showing a significant improvement in both the dermatological disease and comorbid depression/anxiety (p < 0.001 for all scales). Overall, 17.5% and 13% of patients, respectively, reported residual depressive and anxiety symptoms after the 2-year treatment with dupilumab. The baseline predictors of the persistence of clinically significant depressive symptoms after the 2-year treatment with dupilumab were found to be a higher body mass index (BMI) (p = 0.012), a lower impact of dermatological disease on quality of life (p = 0.015), and more severe depressive symptoms (p < 0.01), while for anxiety, the only predictor was found to be female gender (p = 0.03). Conclusions: Using a multidisciplinary approach, at baseline, dermatologists should more closely monitor patients who are at a greater risk of maintaining residual psychiatric symptoms despite therapy, such as those with more severe depressive symptoms and those who are overweight.

Does the comorbidity of borderline personality disorder affect the response to treatment in bipolar patients?

Bipolar disorder (BD) is a highly prevalent condition whose response to pharmacological treatment is associated with a number of factors including psychiatric comorbidity. Borderline personality disorder (BPD) shares clinical symptoms and biological vulnerability with BD and the two conditions are frequently comorbid, thus representing a clinical challenge. The purpose of the present review is to summarize the data related to treatment response in bipolar patients with comorbid BPD. According to systematic review process, a literature search was performed on the PubMed, Embase, PsycInfo, Isi Web of Knowledge, Medscape, and Cochrane Library databases. Peer-reviewed articles until December 2022 were eligible for inclusion. Comorbidity with BPD seems to be associated with a more difficult clinical stabilization in bipolar patients, often requiring poly-therapy or a longer duration of hospitalization. However, three studies, assessing the effectiveness of mood stabilizers in bipolar patients, did not demonstrate a prominent influence of BPD comorbidity in achieving clinical response. The most frequently administered pharmacological treatments in the selected studies include mood stabilizers and atypical antipsychotics. The presence of comorbid BPD in bipolar patients may hamper treatment effectiveness. Future studies, comparing different treatments and with larger samples, are needed to confirm the results critically summarized in the present review.

Which Clinical and Demographic Factors are Related to Incarceration in Male Patients With Antisocial Personality Disorder?

Antisocial Personality Disorder (APD) is a condition largely represented in detention centers where can reach a prevalence of 60% in male prisoners. The objective of this study is to identify the clinical and demographic factors that differentiate subjects with APD and hosted in penitentiary with respect to those are treated in outpatient psychiatric clinics. We recruited 65 male patients affected by APD, whose 26 were followed up in community mental health services and 39 were serving their sentence in a detention center located in Monza. Socio-demographic and clinical data were obtained through a review of the clinical charts, and interviews with patients or their relatives (if available). We performed descriptive analyses on the total sample, then we compared the two groups identified by the type of setting (outpatient clinic vs. penitentiary) by independent sample t tests (quantitative variables) or χ2 tests (qualitative ones). For qualitative variables odds ratios (ORs) were also calculated. Outpatients with APD (with respect to those hosted in the detention center) resulted: to be older (p = .02), to be less likely married (p = .01), to have more pre-onset psychiatric comorbidity (p = .05), to have more pre-onset substance poly-misuse (p = .01), to have more previous psychiatric hospitalizations (p < .01), and to be less likely to have received lifetime psychotherapy (p < .01). Globally, the results of this study show how the presence of psychiatric comorbidity or substance abuse (with the probable access to psychiatric services) before the onset of APD prevents imprisonment. This aspect is even more surprising when we consider that the two groups of patients show no differences in the frequency of crimes. Future research will have to confirm if early mental health care can really limit the access to penitentiary of subjects affected by APD.

Which factors are associated with duration of untreated illness in borderline personality disorder?

AIM

Borderline personality disorder (BPD) is a prevalent condition associated with high rates of hospitalizations. The purpose of this manuscript was to detect the factors associated with duration of untreated illness (DUI) in BPD.

METHODS

Through chart review, we identified 152 patients followed up by community psychiatry services in Milan and Monza, Italy. The association between DUI and socioeconomic and clinical variables was examined using Pearson correlation and analyses of variances. The statistically significant variables from univariate analyses were then inserted in regression models.

RESULTS

A longer DUI was associated with several variables (substance misuse after the onset of BPD, older age, earlier age at onset, longer duration of illness), but these results were not maintained in the regression analyses.

CONCLUSIONS

In conclusion, DUI does not seem to be significantly associated with specific clinical aspects of BPD, or significantly modify the course and outcome of the disorder. Studies with larger samples have to confirm these preliminary findings.

Which clinical factors and biochemical parameters are associated with late-life major depression?

INTRODUCTION

Late-life major depression (MD) is a frequent and high-cost psychiatric disorder. Our purpose was to detect clinical and biological factors possibly associated with this condition to better prevent and treat it.

METHODS

We recruited 343 patients, consecutively admitted for a Major Depressive Episode to the inpatient clinic of Policlinico of Milan and ASST Monza, Italy. A large set of clinical and biochemical variables was collected from clinical charts. Univariate analyses were performed both dividing the sample into two groups (age < or ≥65) and considering age as a continuous quantitative variable. Regression analyses were then performed considering as independent variables only those statistically significant at univariate analyses.

RESULTS

Patients aged ≥ 65 resulted in having longer duration of illness, shorter duration of last antidepressant therapy, higher number of antidepressants assumed in the past, higher frequency of treatment-resistant depression, higher frequency of overweight/obesity and diabetes. As for biochemical parameters, patients ≥ 65 showed lower total plasmatic proteins and albumin, higher uric acid and creatinine.

CONCLUSIONS

These preliminary results suggest less effectiveness of antidepressants, more susceptibility to metabolic disorders and poor nutritional status in patients with late-life depression; such aspects may consequently be taken into consideration for a proper therapeutic approach. KEY POINTSDepression in late life seems to be associated with poorer response to antidepressants;Clinicians should prefer compounds with minimal pharmacokinetic interactions and less risk of side effects including metabolic ones;The poor nutritional status and the higher risk of metabolic disorders in older patients points out the importance of proper diet and healthy lifestyle in this group of subjects;Further studies are needed to confirm the results of this research.

Are There Any Differences in Clinical and Biochemical Variables between Bipolar Patients with or without Lifetime Psychotic Symptoms?

INTRODUCTION

Psychotic symptoms occur in more than half of patients affected by Bipolar Disorder (BD) and are associated with an unfavorable course of the disorder. The objective of this study is to identify the differences in the clinical and biochemical parameters between bipolar patients with or without psychotic symptoms.

METHODS

A total of 665 inpatients were recruited. Demographic, clinical, and biochemical data related to the first day of hospitalization were obtained via a screening of the clinical charts and intranet hospital applications. The two groups identified via the lifetime presence of psychotic symptoms were compared using t tests for quantitative variables and χ2 tests for qualitative ones; binary logistic regression models were subsequently performed.

RESULTS

Patients with psychotic BD (compared to non-psychotic ones) showed a longer duration of hospitalization (p < 0.001), higher Young Mania Rating Scale scores (p < 0.001), lower Global Assessment of Functioning scores (p = 0.002), a less frequent history of lifetime suicide attempts (p = 0.019), less achievement of remission during the current hospitalization (p = 0.028), and a higher Neutrophile to Lymphocyte Ratio (NLR) (p = 0.006), but lower total cholesterol (p = 0.018) and triglycerides (p = 0.013).

CONCLUSIONS

Patients with psychotic BD have a different clinical and biochemical profile compared to their counterparts, characterized by more clinical severity, fewer metabolic alterations, and a higher grade of inflammation. Further multi-center studies have to confirm the results of this present study.

Gender differences in clinical and biochemical parameters among patients hospitalized for schizophrenia: towards precision medicine

BACKGROUND

The scientific literature shows some gender differences in the clinical course of schizophrenia. The aim of this study is to identify gender differences in clinical and biochemical parameters in subjects affected by schizophrenia. This would allow for the implementation of individualized treatment strategies.

METHODS

We examined a large set of clinical and biochemical parameters. Data were obtained from clinical charts and blood analyses from a sample of 555 schizophrenia patients consecutively admitted for exacerbation of symptoms to the inpatient clinic of Fondazione IRCCS Policlinico (Milan) or ASST Monza in Italy from 2008 to 2021. Univariate analyses, binary logistic regression, and a final logistic regression model were performed with gender as dependent variable.

RESULTS

The final logistic regression models showed that male patients (compared to females) were more prone to lifetime substance use disorders (p = 0.010). However, they also had higher GAF (global functioning) mean scores (p < 0.001) at the time of hospitalization. Univariate analyses showed that male patients (with respect to females) had an earlier age at onset (p < 0.001), a more frequent family history of multiple psychiatric disorders (p = 0.045), were more often smokers (p < 0.001), had a more frequent comorbidity with at least one psychiatric disorder (p = 0.001), and less often suffered from hypothyroidism (p = 0.011). In addition, men had higher levels of albumin (p < 0.001) and bilirubin (t = 2.139, p = 0.033), but lower levels of total cholesterol (t = 3.755, p < 0.001).

CONCLUSIONS

Our analyses indicate a less severe clinical profile in female patients. This is evident especially in the early years of the disorder, as suggested by less comorbidity with psychiatric disorders or later age at onset; this is consistent with the related literature. In contrast, female patients seem to be more vulnerable to metabolic alterations as demonstrated by more frequent hypercholesterolemia and thyroid dysfunction. Further studies are needed to confirm these results in the framework of precision medicine.

Understanding the Interplay between Air Pollution, Biological Variables, and Major Depressive Disorder: Rationale and Study Protocol of the DeprAir Study

Major depressive disorder (MDD) is a serious and disabling condition, whose etiological mechanisms are not fully understood. The aim of the DeprAir study is to verify the hypothesis that air pollution exposure may exacerbate neuroinflammation with consequent alterations in DNA methylation of genes involved in circadian rhythms and hormonal dysregulation, resulting in the worsening of depressive symptoms. The study population consists of 420 depressed patients accessing the psychiatry unit of the Policlinico Hospital (Milan, Italy), from September 2020 to December 2022. Data collection is still ongoing for about 100 subjects. For each participant demographic and lifestyle information, depression history and characteristics, as well as blood samples, were collected. MDD severity was assessed through five rating scales commonly used in clinical practice to assess the severity of affective symptoms. Exposure to particulate and gaseous air pollutants is assigned to each subject using both air pollution monitoring station measurements and estimates derived from a chemical transport model. DeprAir is the first study investigating in a comprehensive picture whether air pollution exposure could be an important modifiable environmental factor associated with MDD severity and which biological mechanisms mediate the negative effect of air pollution on mental health. Its results will represent an opportunity for preventive strategies, thus entailing a tremendous impact on public health.

Gender differences in clinical and biochemical parameters of patients consecutively hospitalized for unipolar depression

Major Depressive Disorder (MDD) is a medical illness twice as common in women than in men lifetime. Purpose of this study is to identify gender differences in clinical and biochemical parameters in subjects affected by MDD to implement individualized treatment strategies. We recruited 234 patients (112 males and 122 females) consecutively hospitalized for MDD in Milan (Italy). Data were obtained through a screening of the clinical charts and blood analyses. Univariate analyses, binary logistic regressions and a final logistic regression model were performed. The final logistic regression model showed that female patients (compared to males) had lower plasmatic levels of hemoglobin (p = 0.020) and uric acid (p = 0.002), higher levels of cholesterol (p < 0.001), had been treated with a lower number of antidepressants (p = 0.011), presented lower red blood cells (p < 0.001) and showed more frequently comorbidity with hypothyroidism (p = 0.036). Univariate analyses identified also that women had an earlier age at onset (p = 0.043), were less likely to have comorbidity with diabetes (p = 0.002) and were less frequently treated with a psychiatric polytherapy (p < 0.001). Finally, female patients had achieved more frequently remission in the last depressive episode (p = 0.001) and were more likely to have family history for psychiatric disorders (p < 0.001) than males. Female patients globally have a better response to treatments, but they seem to be more vulnerable to specific metabolic abnormalities as showed by more frequent hypercholesterolemia and lower plasma levels of uric acid. These results have to be confirmed by further studies.

Clinical and Biological Factors Are Associated with Treatment-Resistant Depression

Background: Treatment-resistant depression (TRD) is a debilitating condition associated with unmet clinical needs. Few studies have explored clinical characteristics and serum biomarkers associated with TRD. Aims: We investigated whether there were differences in clinical and biochemical variables between patients affected by TRD than those without. Methods: We recruited 343 patients (165 males and 178 females) consecutively hospitalized for MDD to the inpatient clinics affiliated to the Fondazione IRCCS Policlinico, Milan, Italy (n = 234), and ASST Monza, Italy (n = 109). Data were obtained through a screening of the clinical charts and blood analyses conducted during the hospitalization. Results: TRD versus non-TRD patients resulted to be older (p = 0.001), to have a longer duration of illness (p < 0.001), to be more currently treated with a psychiatric poly-therapy (p < 0.001), to have currently more severe depressive symptoms as showed by the Hamilton Depression Rating Scale (HAM-D) scores (p = 0.016), to have lower bilirubin plasma levels (p < 0.001). In addition, more lifetime suicide attempts (p = 0.035), more antidepressant treatments before the current episode (p < 0.001), and a lower neutrophil to lymphocyte ratio at borderline statistically significant level (p = 0.060) were all associated with the TRD group. Conclusion: We identified candidate biomarkers associated with TRD such as bilirubin plasma levels and NLR, to be confirmed by further studies. Moreover, TRD seems to be associated with unfavorable clinical factors such as a predisposition to suicidal behaviors. Future research should replicate these results to provide robust data in support of the identification of new targets of treatment and implementation of prevention strategies for TRD.

The Relation between the Plasma Concentrations of Long-Acting Atypical Antipsychotics and Clinical Effectiveness in Patients Affected by Schizophrenia or Schizoaffective Disorder: A Comprehensive Overview

Atypical antipsychotic depot medications are currently recommended for patients with schizophrenia (SCZ) to prevent relapse and ameliorate the long-term prognosis of these patients. This review critically summarizes the available data about the association between the plasma concentrations of long-acting Second- Generation Antipsychotics (SGAs) and the clinical effectiveness of these compounds in patients affected by SCZ or schizoaffective disorder. Our question is if the measurement of these concentrations can be helpful for clinicians in predicting treatment response and clinical stabilization of patients. Bibliographic research on the main databases was performed, and 13 studies were finally included in this review. Contrasting results were found between plasma concentrations of long-acting injectable (LAI) risperidone and clinical amelioration according to rating scale scores. Data are too scanty to draw conclusions for olanzapine and paliperidone. In contrast, despite small sample sizes, data are quite concordant in showing a relation between long-acting SGA plasma concentrations and D2 receptor occupancy. Despite the preliminary encouraging results, particularly for D2 receptor occupancy, future research with larger samples will have to confirm the clinical usefulness of measuring LAI SGA plasma concentrations to predict the clinical response of patients affected by severe mental conditions such as SCZ.

Short-term air pollution exposure is associated with lower severity and mixed features of manic episodes in hospitalized bipolar patients: A cross-sectional study in Milan, Italy

Bipolar Disorder (BD) alternates depressive, manic or hypomanic phases. A manic episode (ME) is the main psychopathological condition of BD and it often requires hospitalization. Air pollution is thought to play a role in onset and exacerbation of several psychiatric disorders. We aimed to verify the association between exposure to particulate matter ≤10 μm (PM10) and ME severity, assessed through the Young Mania Rating Scale (YMRS). We evaluated clinical records regarding 414 hospital admissions of 186 patients residing in Milan (Italy), hospitalized for ME in the Psychiatry Unit of the Policlinico Hospital from 2007 to 2019. Patients were assigned mean daily PM10 and apparent temperature levels of the Milan municipality. As exposure windows, we considered single days preceding hospitalization (lag0 to 7) and their average estimates (lag0-1 to 0-7). We applied mixed effect models, adjusted for relevant confounders. Short-term PM10 exposure was associated with a reduction in YMRS, both when considering daily lags [β: -0.43 (95% Confidence Interval: -0.83; -0.03) at lag0] and their average [-0.47 (-0.90; -0.04) at lag0-1]. YMRS was higher in psychotic patients (24.8) and lower in ME with mixed components (15.5) if compared to episodes characterized by neither mixed nor psychotic features (17.4, p < 0.001). While PM10 did not influence the risk of psychotic symptoms at admission, it was associated with a higher risk of ME with mixed features, with Odds Ratios ranging from 2.43 (1.02; 5.76) at lag0 to 3.60 (1.22; 10.7) at lag0-2. Our findings show that increasing levels of PM10 move the ME towards the depressive pole of the BD spectrum and augment the probability of hospitalization for ME with mixed components. These results have important clinical implications, as mixed features worsen the course of ME and make the management of bipolar patients challenging.

The Independent Role of Body Mass Index (BMI) and Severity of Depressive Symptoms on Biological Changes of Women Affected by Overweight/Obesity

Background: Both obesity and depression are medical conditions associated with severe disability and biological abnormalities. Our aim was to study associations between Body Mass Index (BMI), depression and biological changes in women affected by overweight or obesity. Methods: Depressive symptoms were evaluated by the Beck Depression Inventory II (BDI-II) questionnaire in 200 women affected by overweight/obesity (mean age of the sample 52.7 ± 12.9 years, BMI 33.8 ± 5.5 kg/m²). A blood sample was obtained for evaluation of biochemical (oxytocin and vitamin D), inflammatory and epigenetic (methylation of clock genes) parameters. Multivariable linear regression models were used to study the association between BMI or severity of depressive symptoms (BDI-II scores) with different biomarkers. Results: BMI was found to be associated with severity of depressive symptoms (p = 0.050). Severity of obesity resulted to be associated with lower plasma levels of oxytocin (p = 0.053), vitamin D deficiency (p = 0.006) and higher plasma levels of IFN-γ (p = 0.004), IL-6 (p = 0.013), IL-7 (p = 0.013), TNF-alpha (p = 0.036) and chemokine ligand 3 (CCL3) (p = 0.013, R² = 0.03). Severity of depression was significantly associated with more methylation of clock genes CRY1 (p = 0.034, R² = 0.16) and CRY2 (p = 0.019, R² = 0.47). More severe depression together with higher levels of IL-8 strongly predicted lower methylation of CLOCK gene (p = 0.009); Conclusions: Different biological abnormalities have been found to be independently associated with BMI and severity of depressive symptoms in women affected by overweight/obesity. The complex interplay between overweight, depression and biological changes will have to be better clarified by future studies.

The Association Between Personality Traits and Dietary Choices: A Systematic Review

Increasing evidence shows how diet may play a role in improving health including mental health. Of note, personality may influence the type of diet and consequently the prognosis of medical and psychiatric conditions. The purpose of the present systematic review is to summarize the available data regarding the influence of personality on dietary habits affecting health outcomes. A search in the main databases was conducted matching the terms "personality," "personality traits" with "food choices," "food preferences," "diet," and "dietary habits." A total of 1856 articles were screened, and 24 articles were finally included. Exclusion criteria consisted of studies on animals or children, studies about eating disorders, types of diet not clearly associated with health outcomes, and studies for marketing reasons. Several studies showed that personality traits can influence both dietary choices and the type of diet, including the preference for healthy or unhealthy food. Unfavorable personality traits such as neuroticism and alexithymia (the inability to identify and describe emotions) were associated with unhealthy diet habits such as low consumption of fruit and vegetables, and the increased consumption of sugar and saturated fats. Personality seems to play a role in food selection and in the propensity to change diet. The interpretation of these results should be weighted by the different cultural contexts in which the studies were conducted and the extreme heterogeneity of tools used to assess personality and food preferences. Future research should clarify how personality can affect diet in specific populations such as patients with severe psychiatric disorders.

Depression and cardiovascular risk-association among Beck Depression Inventory, PCSK9 levels and insulin resistance

BACKGROUND

Depression and cardiovascular disease (CVD) are among the most common causes of disability in high-income countries, depression being associated with a 30% increased risk of future CV events. Depression is twice as common in people with diabetes and is associated with a 60% rise in the incidence of type 2 diabetes, an independent CVD risk factor. Proprotein convertase subtilisin/kexin type 9 (PCSK9), a key regulator of low-density lipoprotein cholesterol, has been related to a large number of CV risk factors, including insulin resistance. Aim of this study was to investigate whether the presence of depression could affect PCSK9 levels in a population of obese subjects susceptible to depressive symptoms and how these changes may mediate a pre-diabetic risk.

RESULTS

In 389 obese individuals, the Beck Depression Inventory (BDI-II) was significantly associated with PCSK9 levels. For every one-unit increment in BDI-II score, PCSK9 rose by 1.85 ng/mL. Depression was associated also with the HOMA-IR (homeostatic model assessment index of insulin resistance), 11% of this effect operating indirectly via PCSK9.

CONCLUSIONS

This study indicates a possible mechanism linking depression and insulin resistance, a well-known CV risk factor, providing evidence for a significant role of PCSK9.

Improved detection limits and sensitivities of potentiometric titrations

Zero-current ion fluxes through polymer membranes of ion-selective electrodes (ISEs) may lead to biased endpoints of potentiometric titrations. The bias is eliminated, and the sensitivity of the end-point detection is improved through reducing transmembrane ion fluxes by an appropriate choice of the inner solution. Surprisingly, ISE membranes that have a significant primary ion flux toward the inner solution show much larger sensitivities than expected by titration theory; however, depending on the experimental conditions, their application may bias the endpoint. With the optimal systems, endpoint detection is now possible with total sample concentrations below 10(-6) M, as demonstrated by the titration of EDTA with a Pb2+ solution.

Potentiometric polymeric membrane electrodes for measurement of environmental samples at trace levels: new requirements for selectivities and measuring protocols, and comparison with ICPMS

It is here established that potentiometric polymeric membrane electrodes based on electrically neutral ionophores are useful analytical tools for heavy metal ion determinations in drinking water at nanomolar total concentrations. This means that they can compete with the most sophisticated techniques of instrumental analysis. With optimized ion-selective membranes based on the lead-selective ionophore 4-tert-butylcalix[4]arenetetrakis(thioacetic acid dimethylamide) as model example, a number of native and spiked drinking water samples are potentiometrically assessed for lead, and the results compared with ICPMS measurements. The goal of this work is to demonstrate that detection limits in real world samples are routinely achieved that are, with 1.5 ppb, at least 10-fold lower than the lead action limit imposed by the U.S. Environmental Protection Agency (15 ppb). In contrast to earlier reports, different conditioning and measuring protocols are followed, and membranes and inner filling solution of optimized composition are used. The sensors are shown to be useful for the speciation analysis of lead in water as well. Typical water samples are acidified to pH 4 to assess total lead rather than free, uncomplexed lead. For lead concentrations above 2 ppb, the values compare very well with ICPMS. Main interferences are found to be H+ and Cu2+, although Cu2+ only shows significant interference at levels around or above its own action limit (1.3 ppm), in which case the water sample would anyway show quality problems. An explicit, simplified flux model targeted to the practical use of these sensors explains the extent of expected interference. Sensors are shown to require a higher selectivity than predicted by models not considering ion fluxes, since in dilute samples, the counterdiffusion flux of lead from the membrane into the sample becomes potential determining. The model and experiments shown here are a foundation for future trace level applications of potentiometric polymeric membrane electrodes.

Direct potentiometric information on total ionic concentrations

Polymeric membrane ion-selective electrodes exhibit an apparently super-Nernstian response at low sample activities if inner solutions are used that induce strong zero-current fluxes of primary ions toward the inner compartment. This is due to the limited ion fluxes in the aqueous boundary layer near the membrane. In the presence of labile complexes, the effective flux rate is increased and the emf depends on the total concentration of the ions. The concept is illustrated experimentally with calcium-selective electrodes based on the ionophore N,N-dicyclohexyl-N',N'-dioctadecyl-3-oxapentanediamide (ETH 5234) that either respond to total or free ion concentrations. Samples can be distinguished that contain varying levels of total calcium but are all buffered with EDTA to the same free calcium concentration of 5 x 10(-8) M.

Continuous monitoring of plant water potential

Plant water potential was monitored continuously with a Wescor HR-33T dewpoint hygrometer in conjunction with a L51 chamber. This commercial instrument was modified by replacing the AC-DC mains power converter with one stabilized by zener diode controlled transistors. The thermocouple sensor and electrical lead needed to be thermally insulated to prevent spurious signals. For rapid response and faithful tracking a low resistance for water vapor movement between leaf and sensor had to be provided. This could be effected by removing the epidermis either by peeling or abrasion with fine carborundum cloth. A variety of rapid plant water potential responses to external stimuli could be followed in a range of crop plants (sunflower (Helianthus annuus L., var. Hysun 30); safflower (Carthamus tinctorious L., var. Gila); soybean (Glycine max L., var. Clark); wheat (Triticum aestivum L., var. Egret). These included light dark changes, leaf excision, applied pressure to or anaerobiosis of the root system. Water uptake by the plant (safflower, soybean) mirrored that for water potential changes including times when plant water status (soybean) was undergoing cyclical changes.